DESIGN GUIDELINES FOR STAINLESS STEEL IN PIPING SYSTEMS

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DESIGN GUIDELINES FOR STAINLESS STEEL IN PIPING SYSTEMS

Introduction

Contents This publication presents information on the design,

fabrication, installation and economy of stainless steel in piping systems. The guidelines presented contain important information for piping specialists and design engineers that will save money, time and effort in the several diverse industries utilizing piping systems.

Stainless steels are defined as iron-base alloys con-taining 10 percent or more chromium. They are en-gineering materials selected primarily for their excellent resistance to corrosion, their outstanding mechanical properties at either ambient, high, or low temperature, and their economy.

Of the 57 stainless steels recognized as standard by the American Iron and Steel Institute (AISI), those most commonly used in piping systems are the austenitic alloys represented by AISI Types 304, 304L, 316 and 316L. The austenitic Types 309 and 310, containing considerably more chromium and nickel than Types 304 and 316, are also widely used, but for piping exposed to elevated temperatures. The stabilized Types 321 and 347 are also used, as are some commercially available proprietary grades. Appendix A shows chemical compositions and typical properties. (Table 1 lists all 57 AISI numbered stainless steels.)

Introduction ............................................................ 3 The Selection of a Piping System ........................... 6 Stainless Steel in Piping Systems ........................... 6 Advantages ......................................................... 6 Limitations .......................................................... 13 The Economics of Stainless Steel in Piping Systems .................................................. 17 Design Costs ...................................................... 18 Material Costs ..................................................... 18 Fabrication Costs ................................................ 19 Erection Costs .................................................... 19 Applicable Standards ............................................. 19 The Design, Fabrication, and Erection of Plant Piping Systems ......................................... 20 Construction Phase.............................................. 21 Bibliography ........................................................... 22 Appendices ............................................................ 23

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Table 1 RELATIVE CORROSION RESISTANCE OF AISI STAINLESS STEELS

Mild Atmospheric Atmospheric Chemical

AISI TYPE Number

UNS Number

and Fresh Water

Industrial Marine Salt Water

Mild Oxidizing Reducing

201 (S20100) X X X X X 202 (S20200) X X X X X 205 (S20500) X X X X X 301 (S30100) X X X X X 302 (S30200) X X X X X 302B (S30215) X X X X X 303 (S30300) X X X 303 Se (S30323) X X X 304 (S30400) X X X X X 304L (S30403) X X X X X (S30430) X X X X X 304N (S30451) X X X X X 305 (S30500) X X X X X 308 (S30800) X X X X X 309 (S30900) X X X X X 309S (S30908) X X X X X 310 (S31000) X X X X X 310S (S31008) X X X X X 314 (S31400) X X X X X 316 (S31600) X X X X X X X 316F (S31620) X X X X X X X 316L (S31603) X X X X X X X 316N (S31651) X X X X X X X 317 (S31700) X X X X X X X 317L (S31703) X X X X X X 321 (S32100) X X X X X 329 (S32900) X X X X X X X 330 (N08330) X X X X X X X 347 (S34700) X X X X X 348 (S34800) X X X X X 384 (S38400) X X X X X 403 (S40300) X X 405 (S40500) X X 409 (S40900) X X 410 (S41000) X X 414 (S41400) X X 416 (S41600) X 416 Se (S41623) X 420 (S42000) X 420F (S42020) X 422 (S42200) X 429 (S42900) X X X X 430 (S43000) X X X X 430F (S43020) X X X 430F Se (S43023) X X X 431 (S43100) X X X X 434 (S43400) X X X X X 436 (S43600) X X X X X 440A (S44002) X X 440B (S44003) X 440C (S44004) X 442 (S44200) X X X X 446 (S44600) X X X X X (S13800) X X X X (S15500) X X X X X (S17400) X X X X X (S17700) X X X X X The "X" notations indicate that a specific stainless steel type may be considered as resistant to the corrosive environment categories.

This list is suggested as a guideline only and does not suggest or imply a warranty on the part of the American Iron and Steel Institute, the Committee of Stainless Steel Producers, or any of the member companies represented on the Committee. When selecting a stainless steel for any corrosive environment, it is always best to consult with a corrosion engineer and, if possible, conduct tests in the environment involved under actual operating conditions.

Source: STEEL PRODUCTS MANUAL, STAINLESS AND HEAT RE-SISTING STEELS, DECEMBER 1974, American Iron and Steel Institute, Washington, D. C.

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º

Source: STAINLESS STEEL AND THE CHEMICAL INDUSTRY, Climax Molybdenum Company, Greenwich, Connecticut, 1966.

Table 2WHERE DIFFERENT GRADES ARE USED

Environment Grades Environment Grades

Acids Hydrocloric acid

Stainless generally is not recommended except when solutions are very dilute and at room temperature.

"Mixed acids" There is usually no appreciable attack on Type 304 or 316 as long as sufficient nitric acid is present.

Nitric acid Type 304L or 430 is used.

Phosphoric acid Type 304 is satisfactory for storing cold phosphoric acid up to 85% and for handling concentrations up to 5% in some unit processes of manufacture. Type 316 is more resistant and is generally used for storing and manufacture if the fluorine content is not too high. Type 317 is somewhat more resistant than Type 316. At concentrations up-to 85%, the metal temperature should not exceed 212ºF (100ºC) with Type 316 and slightly higher with Type 317. Oxidizing ions inhibit attack and other inhibitors such as arsenic may be added.

Sulfuric acid Type 304 can be used at room temperature for concentrations over 80%. Type 316 can be used in contact with sulfuric acid up to 10% at termperatures up to 120ºF (50ºC) if the solutions are aerated; the attack is greater in airfree solutions. Type 317 may be used at temperatures as high as 150ºF (65ºC) with up to 5% concentration. The presence of other materials may markedly change the corrosion rate. As little as 500 to 2000 ppm of cupric ions make it possible to use Type 304 in hot solutions of moderate concentration. Other additives may have the opposite effect.

Sulfurous acid Type 304 may be subject to pitting, particularly if some sulfuric acid is present. Type 316 is usable at moderate concentrations and temperatures.

Bases Ammonium hydroxide, sodium hydroxide, caustic solutions

Steels in the 300 series generally have good corrosion resistance at virtually all concentrations and temperatures in weak bases, such as ammonium hydroxide. In stronger bases, such as sodium hydroxide, there may be some attack, cracking or etch- ing in more concentrated solutions and at higher termperatures. Commercial purity caustic solutions may contain chlorides, which will accentuate any attack and may cause pitting of Type 316 as well as Type 304.

Organics Acetic acid

Acetic acid is seldom pure in chemical plants but generally includes numerous and varied minor constituents. Type 304 is used for a wide variety of equipment including stills, base heaters, holding tanks, heat exchangers, pipelines, valves and pumps for concentrations up to 99% at temperatures up to about 120ºF (50ºC). Type 304 is also satisfactory for contact with 100% acetic acid vapors, and–if small amounts of turbidity or color pickup can be tolerated–for room temperature storage of glacial acetic acid. Types 316 and 317 have the broadest range of usefulness, especially if formic acid is also present or if solutions are unaerated. Type 316 is used for fractionating equipment, for 30 to 99% concentrations where Type 304 cannot be used, for storage vessels, pumps and process equipment handling glacial acetic acid, which would be discolored by Type 304. Type 316 is likewise applicable for parts having temperatures above 120ºF (50ºC), for dilute vapors and high pressures. Type 317 has somewhat greater corrosion resistance than Type 316 under severely corrosive conditions. None of the stainless steels has adequate corrosion resistance to glacial acetic acid at the boiling temperature or at superheated vapor temperatures.

Aldehydes Type 304 is generally satisfactory.

Amines Type 316 is usually preferred to Type 304.

Cellulose acetate

Type 304 is satisfactory for low temperatures, but Type 316 or Type 317 is needed for high temperatures.

Citric, formic and tartaric acids

Type 304 is generally acceptable at moderate temperatures, but Type 316 is resistant to all concentrations at temperatures up to boiling.

Esters From the corrosion standpoint, esters are comparable with organic acids.

Fatty acids Up to about 300ºF (150ºC), Type 304 is resistant to fats and fatty acids, but Type 316 is needed at 300 to 500ºF (150 to 260ºC) and Type 317 at higher temperatures.

Paint vehicles Type 316 may be needed if exact color and lack of contamination are important.

Phthalic anhydride

Type 316 is usually used for reactors, fractionating columns, traps, baffles, caps and piping.

Soaps Type 304 is used for parts such as spray towers, but Type 316 may be preferred for spray nozzles and flake-drying belts to minimize offcolor product.

Synthetic detergents

Type 316 is used for preheat, piping, pumps and reactors in catalytic hydrogenation of fatty acids to give salts of sulfonated high molecular alcohols.

Tall oil (pulp and paper industry)

Type 304 has only limited usage in tall-oil distillation service. High-rosin-acid streams can be handled by Type 316L with a minimum molybdenum content of 2.75%. Type 316 can also be used in the more corrosive high-fatty-acid streams at temperatures up to 475ºF (245ºC), but Type 317 will probably be required at higher temperatures.

Tar Tar distillation equipment is almost all Type 316 because coal tar has a high chloride content. Type 304 does not have adequate resistance to pitting.

Urea Type 316L is generally required.

Pharmaceuticals Type 316 is usually selected for all parts in contact with the product because of its inherent corrosion resistance and greater assurance of product purity.

Elevated Temperatures

Generally speaking increased chromium content increases oxidation resistance. Those alloys containing 16 to 20% chromium such as Types 304 and 316 are generally useful in air to temperatures of 1600 to 1700ºF (870 to 925ºC). Alloys such as Types 309 and 310 with higher chromium and nickel contents may extend this temperature range to 1800 or 1900ºF (180 to 1035ºC). Exposure to fluctuating temperatures or even mild environments such as carbon dioxide or water vapor may result in significant increases in corrosion rates at these temperatures.

Cryogenic Temperatures

Austenitic stainless steels exhibit good ductility and toughness at the most severe of cryogenic temperatures - minus 423ºF (- 253ºC). Impact tests show that Type 304 is very stable over long periods of exposure and does not exhibit any marked degradation of toughness. Properly made welds also have excellent low-temperature properties. Austenitic grades cold worked to high strength levels are also suitable for low-temperature service. Type 310 can be cold worked as much as 85% and still exhibit a good notched-to-unnotched tensile ratio down to - 423ºF (- 253ºC).

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THE SELECTION OF A PIPING SYSTEM

The most commonly used material for metal piping systems is carbon steel. Where carbon steel pipe is satisfactory, it generally results in the most economical system. The justification for the selection of a more expensive material, however, is usually either a longer life because of reduced corrosion, or an improvement in product quality as a result of reduced contamination (corrosion). The selection of a more expensive material may also be dictated by piping code material restriction, such as in those cases where operating conditions are above or below the range of working temperatures approved for carbon steel.

A variety of materials, both metallic and nonmetallic, are available to fill the varied piping needs of industry. Each of these materials has its own particular attributes that justify its use in certain applications and they each have limitations. A check-list has been developed (Ap-pendix B) listing some of the factors which should be weighed in making a decision on the relative merits of alternative pipe materials. These include, among other important considerations, pressure and temperature limitations, supporting structure requirements, chemical resistance, protection from exposure to fire, thermal expansion, piping code restrictions, safeguarding re-quirements, tracing, vacuum collapse and insulation.

STAINLESS STEEL IN PIPING SYSTEMS

The role of stainless steel in piping systems can be defined by outlining its advantages and disadvantages as a piping material.

Advantages

ries of corrosive environments. Table 2 details more specific environments in which various grades are used, and a list of useful references to aid in the selection of stainless steels is included on page 22.

When dealing with corrosive environments, the pip-ing system designer and specifier should take careful note of the fact that there are significant differences in corrosion resistance and strength among the various stainless alloys. If Type 304 is not suitable for a particu-lar environment there is no reason to rule out other stainless steels. There are stainless steels with higher chromium and nickel contents or with other alloying elements that provide better resistance to corrosion than Type 304. For instance, the AISI-numbered stain-less steels are not recognized as being outstanding materials for use in seawater environments. There are, however, commercially available proprietary stainless steels that have exhibited excellent resistance in sea-water environments.

STRENGTH CHARACTERISTICS

A very important consideration in evaluating various pipe system materials is strength. The mechanical properties of stainless steels yield a number of important advantages over nonmetallic pipe systems.

High-Temperature Characteristics. The austenitic stainless steels are unique in that they combine high-temperature strength and oxidation resistance. Appli-cations at 1000ºF are common and some applications utilizing stainless steels operate at temperatures ap-proaching 1900ºF.

Figure 1 gives a broad concept of the hot strength advantages of the austenitic stainless steels in com-parison with other materials. The stress values for Type 304 seamless pipe compared with a low-alloy chrome molybdenum steel pipe shown in Table 3 illustrate an important reason why austenitic stainless steels are preferred over other alloys for steam service at temper-atures over 1050ºF. (Many companies use Type 316 for high-temperature steam service.)

The most common criteria currently used in the United States for the design of hot piping are found in ANSI B31.3.* This code prescribes minimum require-ments for piping systems subject to pressure or vacuum, over a range of temperatures up to 1500ºF.

The basic allowable stress for a particular material at a particular temperature is based on several criteria, any of which may govern. In accordance with the Code, this basic allowable stress shall not exceed the lowest of the following:

CORROSION RESISTANCE

Stainless steels possess broad resistance to a wide variety of corrosives from fresh water to strong nitric acid. This corrosion resistance generally allows the use of light-weight construction with Schedule 5S or 10S piping.

While full discussion of corrosion resistance in spe-cific media is beyond the scope of this publication, Table 1 lists the relative corrosion resistance of the 57 AISI-numbered stainless steels in seven broad catego-

1. One third of the material's minimum tensile strength at room temperature.

2. One third of the material's minimum tensile strength at design temperature.

3. Two thirds of the material's minimum yield strength at room temperature.

4. Two thirds of the material's minimum yield strength at the design temperature.

*ANSI B 31.3. American National Standards Institute Code for Chem-ical Plant and Petroleum Refinery Piping, published by the American Society of Mechanical Engineers, 1976.

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Table 3 ALLOWABLE STRESS AT MAXIMUM METAL TEMPERATURE

ºF 900 950 1000 1050 1100 1150 1200 ºC 482 510 538 566 593 621 649 Type ksi MPa ksi MPa ksi MPa ksi MPa ksi MPa ksi MPa ksi MPa

304 2¼Cr-1 Mo

10.0 13.1

68.9 90.3

9.8 11.0

67.2 75.8

9.5 7.8

65.2 53.8

9.0 5.8

62.1 40.0

8.3 4.2

56.9 29.0

6.9 3.0

47.6 20.7

5.5 2.0

37.9 13.8

Source: Stainless Steel Industry Data

5. The average stress for a creep rate of 0.01 percent per 1,000 hours.

6. 67 percent of the average stress for rupture at the end of 100,000 hours.

7. 80 percent of the minimum stress for rupture at the end of 100,000 hours.

An exception to the fourth criterion above is that for austenitic stainless steels (generally the 300 series) and for some of the nickel alloys, when used at temper-atures below 1100ºF, the limit may be as high as 90 percent of the minimum yield strength at the design temperature. However, this high allowable stress is not recommended for flanged, gasketed joints or other ap-plications where a slight deformation could cause leak-age.

An excellent discussion of this subject is in an article by J.D. Dawson, "Designing High-Temperature Piping." (CHEMICAL ENGINEERING, April 9, 1979.)

Low-Temperature Characteristics. At the other ex-treme, austenitic stainless steels are among the few materials that retain their toughness and ductility at the

most severe of cryogenic temperatures. Table 4 shows mechanical properties of some of these materials at cryogenic temperatures.

In contrast, thermoplastics, fiberglass reinforced plastic (FRP), and plastic-lined carbon steel have a much narrower range of temperatures at which their performance is acceptable. According to ANSI B31.3 the suggested temperature limits for thermoplastic pipe is from -30ºF to 210ºF, depending upon the specific material. The temperature limits for reinforced ther-mosetting resins are from -20ºF to 300ºF. For thermoplastics used as linings, the range is from 0ºF to 500ºF, again depending upon the specific material.

Design Considerations. Because of excellent strength characteristics, stainless steel piping can withstand higher pressures, or a full vacuum, over a wide temperature range–which, in turn, means a greater degree of safety. For example, austenitic stainless steels provide satisfactory service from low cryogenic temperatures to temperatures of 1800ºF and above. Strength and toughness are especially impor-tant for pipe systems handling hot acid solutions, other

Table 4 TYPICAL MECHANICAL PROPERTIES OF STAINLESS STEELS AT

CRYOGENIC TEMPERATURES

AISI Type

Test Temperature

Yield Strength

0.2% Offset

Tensile Strength

Elongation in 2"

Izod Impact

ºF ºC ksi MPa ksi MPa % ft. lbs. J 304 - 40 - 40 34 234 155 1,069 47 110 149 - 80 - 62 34 234 170 1,172 39 110 149 -320 -196 39 269 221 1,524 40 110 149 -423 -252 50 344 243 1,675 40 110 149 310 - 40 - 40 39 269 95 655 57 110 149 - 80 - 62 40 276 100 689 55 110 149 -320 -196 74 510 152 1,048 54 85 115 -423 -252 108 745 176 1,213 56 316 - 40 - 40 41 283 104 717 59 110 149 - 80 - 62 44 303 118 814 57 110 149 -320 -196 75 517 185 1,276 59 -423 -252 84 579 210 1,448 52 347 - 40 - 40 44 303 117 807 63 110 149 - 80 - 62 45 310 130 896 57 110 149 -320 -196 47 324 200 1,379 43 95 129 -423 -252 55 379 228 1,572 39 60 81 410 - 40 - 40 90 621 122 841 23 25 34 - 80 - 62 94 648 128 883 22 25 34 -320 -196 148 1,020 158 1,089 10 5 7 430 - 40 - 40 41 283 76 524 36 10 14 - 80 - 62 44 303 81 558 36 8 11 -320 -196 87 607 92 634 2 2 3 Source: Stainless Steel Industry Data

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hazardous liquids, or compressed gases (which in large systems contain a substantial concentration of potential energy). Flanged joints in nonmetallic sys-tems are more susceptible to gasketing and leakage problems due to their low modulus of elasticity. In lined pipe, vacuum service often leads to liner buckling. (Table 5 shows the thickness for stainless steel pipe designed to withstand a full vacuum of 30 inches of mercury.)

Because of their excellent high-temperature charac-teristics, stainless steel piping systems are readily steam jacketed, and they have a greater tolerance for steam tracing than the nonmetallic or lined systems. Steam tracing of lined pipe may lead to buckling of the liner. (Care should be exercised in steam tracing any metallic pipe system to prevent hot spots, which could cause accelerated corrosion.)

Also relative to the use of pipe systems at high or low temperatures, are the thermal expansion characteris-tics of the materials. The coefficient of thermal expan-

Figure 1 HOT STRENGTH CHARACTERISTICS

General comparison of the hot-strength characteristics of austenitic, martensitic and ferritic stainless steels with those of low-carbon unal-loyed steel and semi-austenitic precipitation and transformation-hardening steels.

Table 5 THICKNESS FOR STAINLESS STEEL PIPE DESIGNED

TO WITHSTAND FULL 30 in. H.G. VACUUM

Where vibration exists, the thickness should be increased and/or reinforcing rings added.

Note: Standard rolled angle face rings may be used for reinforcing rings. (Dimensions are given in inches)

Source: SUGGESTED STANDARDS FOR STAINLESS STEEL PIP-ING FOR THE PULP AND PAPER INDUSTRY, Tappi En-gineering Conference, November 1968, Houston, Texas

sion of stainless steels is much closer to that of carbon steel than that of plastic materials. Lined metallic piping systems have been known to fail because of the differ-ence in expansion between the pipe and its lining.

In contrast to the excellent performance characteris-tics of stainless steel pipe systems exposed to elevated temperature (either internally or externally), special provisions are required to protect nonmetallic pipe sys-tems. These provisions are frequently in the form of thermal insulation, shields or process controls to protect against excessive heat or thermal shock, and/or armor guards or barricades for protection against mechanical abuse.

In the event of a fire, a stainless steel piping system is more resistant than a plastic system, as it is neither flammable nor readily melted. Also, heat can seriously affect nonmetallic systems.

High strength means fewer and less complicated supporting structures. Generally speaking, in a metallic piping system a minimum of two supports is used for each length of pipe for practical handling during instal-lation and removal, and valves are usually supported by the pipe system itself. In contrast, nonmetallic sys-tems use more supports, plus additional supports for each valve. For outside pipe runs, the supporting struc-tures for nonmetallic systems are more substantial and more expensive.

EASE OF FABRICATION

The excellent ductility of the austenitic stainless steels enables extensive forming operations. Forming

Size Gauge U.S. Standard Thickness 1 14 0.078

1½ 14 0.078 2 14 0.078 3 14 0.078 4 14 0.078 6 14 0.078 8 14 0.078

10 12 0.109 12 12 0.109 14 11 0.125 16 11 0.125 18 11 0.125 20 3/16 0.1875 22 3/16 0.1875 24 3/16 0.1875 26 3/16 0.1875 28 3/16 0.1875 30 ¼ 0.250 32 ¼ 0.250 34 ¼ 0.250 36 ¼ 0.250

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of Van Stone flanges and pipe bending, for example, offer economies that are unavailable with other less-ductile materials.

Table 6 REPRESENTATIVE PRESSURE RATING FOR VAN STONE FLANGED TYPES 304L and 316L

Van Stone Flanging

Van Stone flanging involves roll flaring of the pipe end to form a lap perpendicular to the pipe axis. Using a lap joint back-up flange, or a slip-on flange with the inner corner between the flange face and bore slightly cham-fered, offers one of the best methods of providing a flanged connection. The advantages, compared to a weld-neck flange, are readily apparent:

Reliability–This is a machine operation with precise tooling. Each lap is virtually identical. Speed–Always faster than welding. Ease of Installation–Since the back-up flange is free to rotate, there is never a problem of bolt-hole align-ment with the mating flange. No Need for Expensive Flange–Back-up flanges have a mechanical function, which does not require corrosion resistance. A forged steel or ductile iron back-up flange may be used with stainless steel pipe. Cost–Fast fabrication, elimination of welds, fast in-stallation, and inexpensive flanges add up to sub-stantial cost savings. Stainless steel welded and full-finished pipe man-

ufactured in accordance with standard specification ASTM A312 is preferred for flanging Type 304 or 316 (plus low-carbon grades) in ½ to 12-inch diameters in Schedules 5S, 10S, and 40S. Table 6 shows represen-tative pressure rating data for Van Stone flanged Types 304 and 316, while Table 7 shows typical Van Stone lap geometries. Figures 2 and 3 show typical examples.

Pipe Bending

The piping designer can achieve significant cost sav-ings by specifying close-radius bending of stainless steel wherever possible in the piping system. Important

Temp. ºF Schedule 10S Schedule 40S

100 275 psi 300 psi 200 240 psi 300 psi 300 210 psi 300 psi 400 180 psi 300 psi 500 150 psi 300 psi 600 130 psi 300 psi 650 120 psi 300 psi

Ratings are based on the following: 1. Stresses used are not more than ½ allowed by ASME code. 2. Use of standard slip-on flanges per ASA B16.5. 3. Where lightweight back-up flanges are used, the bolt circle bolt size

and bore diameter should be per ASA B16.5. In this case the rating of stub and back-up assembly is limited by the capabilities of the back-up flange.

4. These ratings allow for normally encountered bending moments due to thermal cycling. Where such conditions are severe and a piping flexibility analysis is made, stresses due to bending moment should be limited to a stress range of 20,000 psi (±10,000) in the wall adjacent to the lap.

Source: PIPE FABRICATION, SGL Piping Systems, a division of SGL Industries, Inc., Newport, Delaware

is the fact that close-radius bends match standard forged steel long-radius elbows per USAS B16.9; 4-inch iron pipe size (IPS), for example, is bent on a 6-inch radius while 2-inch IPS pipe is bent on a 3-inch radius. Close-radius bending may be used interchangeably with forged elbows in any piping system with no revision in layout.

Bends of 1 to 180 degrees are possible. Table 8 provides guidelines for maximizing the use of bending, and Figures 4 and 5 show typical applications. Bending is used generally for sizes up to 4 inches in diameter. Bending of larger sizes is possible with special equip-ment. For example, in some shops fabricating piping systems for nuclear power plants, 34-inch diameter pipe with a 4-inch wall thickness is being successfully bent utilizing induction heating of the bend area. This type of bending results in lower welding and fitting

Table 7 VAN STONE LAP GEOMETRIES

Flange Type IPS

(in inches) LAP OD

(in inches) Schedules

5S/10S Schedules 40S/80S

Serrated Face

½ 13/8 SO LJ A ¾ 111/16 SO LJ A

1 2 SO LJ A 1¼ 2½ SO LJ A 1½ 27/8 SO LJ A 2 35/8 SO LJ A 2½ 41/8 SO LJ A 3 5 SO LJ A 4 63/16 SO LJ A 6 8½ SO LJ A 8 105/8 SO LJ A

10 12¾ SO LJ NA 12 15 SO LJ NA

SO–Slip-On; LJ–Lap Joint; A-Available; NA–Not Available Back-up flanges may be forged steel or ductile iron, flat face or raised face.

Source: PIPE FABRICATION, SGL Piping Systems, a division of SGL Industries, Inc., Newport, Delaware

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Figure 2 Typical example of a Van Stone flange. The flange, which can be of a noncorrosion resistant material, is slipped over the end of the pipe and then the end is flared by an operation that resembles spinning.

Figure 3 The flared end of the pipe or tube can be smooth, or it can be flared with a serrated face, as shown here. The serrations are formed by the flaring tool and are "rolled" in, not machined.

Table 8 CLOSE RADIUS BENDING TABLES

Min. Center-to-Center and Center-to-Face Dimensions to allow adequate clamping. (Dimensions in inches)

90°Bends 45°Bends Pipe Size

Radius R A B C D E F

½ 1½ 5½ 7½ 7 45/8 65/8 5¼ ¾ 11/8 51/8 7½ 6¼ 49/16 6¾ 5

1 1½ 5½ 8 7 45/8 73/8 5¼ 1½ 2¼ 8 9 10¼ 611/16 77/8 7¼ 2 3 11 9 14 9¼ 73/8 10½ 3 41/8 13½ 12 18 107/8 9½ 12¾ 3½ 5¼ 14¼ 13 19½ 11¾ 10 133/8 4 6 16¾ 14 22¾ 13¼ 10½ 15¾

A or D–Plain or Beveled End B or E–Flanged End C or F–Center to Center Source: PIPE FABRICATION, SGL Piping Systems, a division of SGL Industries, Inc., Newport, Delaware

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Figure 4 This is a "pancake" heating coil of 1½inch Type 304 stainless steel pipe, 40 feet in diameter. The detail (inset) shows how 180 degree bends were made to the centerline spacing. By bending, the fabricator eliminated one weld per return, significantly reducing the cost as compared to conventional U-bend fittings.

AVAILABILITY

Stainless steel pipe and tubing are available as either welded or seamless products.

Welded pipe is ordinarily preferred to seamless pipe for chemical plant piping because it is more eco-nomical. The greater uniformity of wall is beneficial in performing the fabricating operations of short radius

Figure 5 CONVENTIONAL CONSTRUCTION

Requires seven welds and four purchased fittings. FLARED LAPS AND BENT CONSTRUCTION Requires

one weld and no purchased fittings. (Branch is made with a saddle weld.)

costs. In any piping system, the need for fewer welds translates into a significant reduction of in-service in-spections and nondestructive examination require-ments.

The repair or replacement of a stainless steel section can be easily and quickly accomplished while other materials often require involved repair procedures with significant downtime. For example, special fixtures are required with lined pipe to form the liner over a flange face.

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Table 9 PIPE SIZES AND WEIGHTS-304, 304L, 309, 310, 316 and 316L

Nominal Nominal Schedule 5S Schedule 10S Schedule 40S Schedule 80S

IPS inches

OD inches

Wall inches

Weight pounds/foot

Wall inches

Weight pound/foot

Wall inches

Weight pounds/foot

Wall inches

Weight pounds/foot

1/8 0.405 0.049 0.1880 0.068 0.2470 0.095 0.3175 ¼ 0.540 0.065 0.3328 0.088 0.4287 0.119 0.5401

3/8 0.675 0.065 0.4274 0.091 0.5729 0.126 0.7457

½ 0.840 0.065 0.5430 0.083 0.6773 0.109 0.8589 0.147 1.098 ¾ 1.050 0.065 0.6902 0.083 0.8652 0.113 1.141 0.154 1.487

1 1.315 0.065 0.8759 0.109 1.417 0.133 1.695 0.179 2.192

1¼ 1.600 0.065 1.117 0.109 1.822 0.140 2.294 0.191 3.025 1½ 1.900 0.065 1.286 0.109 2.104 0.145 2.743 0.200 3.665 2 2.375 0.065 1.619 0.109 2.662 0.154 3.687 0.218 5.069

2½ 2.875 0.083 2.498 0.120 3.564 0.203 5.847 0.276 7.733 3 3.500 0.083 3.057 0.120 4.372 0.216 7.647 0.300 10.35 3½ 4.000 0.083 3.505 0.120 5.019 0.226 9.194 0.318 12.62

4 4.500 0.083 3.952 0.120 5.666 0.237 10.89 0.337 15.12 5 5.563 0.109 6.409 0.134 7.842 0.258 14.75 0.375 20.97 6 6.625 0.109 7.856 0.134 9.376 0.280 19.15 0.432 28.84

8 8.625 0.109 10.01 0.148 13.52 0.322 28.82 0.500 43.79 10 10.750 0.134 15.34 0.165 18.83 0.365 40.86 0.500 55.25 12 12.750 0.156 21.18 0.180 24.39 0.375 50.03 0.500 66.03

14 14.000 0.156 23.28 0.188 27.99 16 16.000 0.165 28.17 0.188 32.05 18 18.000 0.165 31.72 0.188 36.10

20 20.000 0.188 40.15 0.218 45.49 22 22.000 0.188 44.21 0.218 51.19 24 24.000 0.218 55.89 0.250 64.01 30 30.000 0.250 80.18 0.312 99.85

Source: Stainless Steel Industry Data

bending and forming flared laps. On the other hand, seamless pipe is accorded a

higher allowable hoop stress without special examina-tion than is welded pipe, and heavier wall thicknesses are more readily available in seamless pipe, which would be required for some high-pressure applica-tions.

The code for chemical plant and petroleum piping, ANSI B31.3, permits use of the same stresses for welded pipe as those used for seamless pipe, provided the longitudinal seam weld has passed the requisite 100 percent radiographic examination.

Both pipe and the necessary fittings of stainless steel conforming to ASTM and ANSI standards are readily available from a number of sources. Table 9 shows pipe sizes, wall thicknesses and weights of Types 304, 304L, 309, 310, 316, and 316L stainless steels.

of different methods. If the application involves a sterile environment, they are readily sterilized.

ABRASION RESISTANCE

Stainless steels possess good abrasion resistance for handling slurries.

HEAT TRANSFER

A metallic piping system has distinct advantages over nonmetallic systems if heat transfer is important. Table 10 provides data on the conductivity and overall heat transfer coefficients of various metals.

PROTECTIVE COATINGS

Protective coatings are usually not required due to the inherent corrosion resistance of stainless steel. However, sometimes coatings are applied to the exterior of pipe for color coding or for protection against chloride attack from wet insulation.

EASE OF CLEANING Stainless steels can be readily cleaned by a number

ECONOMY

When all costs are considered, stainless steel piping systems often win out over other materials. This is es-pecially true if advantage is taken of the mechanical properties and corrosion resistance of stainless steel which allow light-weight construction. For instance, Schedule 5S, Type 304 stainless steel approaches Schedule 40 carbon steel in installed cost, and it is certainly more economical than Schedule 80 carbon steel.

13

Limitations CORROSIVE ENVIRONMENTS

No piping material is resistant to all corrosive media. Stainless steels have a few limitations (or precautions) which must be considered in the design of a piping system. For instance, unsatisfactory service may result from use of stainless steels in strongly reducing envi-ronments, depending on concentration and tempera-ture. Likewise, problems may be encountered with stainless steels exposed to high-chloride environ-ments. Precautions must also be taken to avoid corro-sive attack on the exterior of the pipe by chlorides leached from pipe insulation. Chlorides may cause pit-ting, crevice corrosion or stress-corrosion cracking. Materials engineers familiar with these types of corro-sive attack can avoid problems with stainless steels by selecting the proper grade and by taking proper pre-ventive measures, such as avoiding environments known to corrode stainless steels, by eliminating cre-vices, by providing for regular cleaning to remove de-posits or by using silicate inhibited insulation.

The types of corrosive attack which are more likely to be of concern in utilizing stainless steels are: pitting, crevice attack, stress-corrosion cracking, and inter-granular corrosion.

Pitting occurs when the protective oxide film on stain-less steel breaks down in small isolated spots. Halide ions are most often responsible for this type of attack. Once started, the attack may propogate because of differences in electric potential between the large area of passive surface vs. the small active pitted area.

Pitting is avoided in many environments by using Type 316 or 317 or other stainless steels containing higher levels of chromium and molybdenum.

Crevice corrosion results from local differences in oxygen concentration associated with deposits on the metal surface, gaskets, lap joints, or crevices under bolt or rivet heads where small amounts of liquid can

collect and become stagnant. The material being utilized in the formation of a cre-

vice need not be metallic. Scale, wood, plastics, rub-ber, glass, concrete, asbestos, wax, and living or-ganisms have all been reported to cause crevice corro-sion. Once attack begins within the crevice, its prog-ress may be very rapid. The stainless steels containing molybdenum are more resistant to this type of attack and are often used to minimize the problem. Not-withstanding, the best solution to crevice corrosion is a design that eliminates as many crevices as possible.

Stress-corrosion cracking is caused by the com-bined effects of tensile stress and corrosion. Many alloy systems have been known to experience stress-corrosion cracking–for example, brass in ammonia, carbon steel in nitrate solutions, titanium in methanol, aluminum in sea water, and gold in acetic acid. Some stainless steels (i.e. the austenitic grades) are suscep-tible to stress-corrosion cracking in chloride and caustic environments.

It is necessary for tensile stress, chlorides in solution and elevated temperature all to be present for stress-corrosion cracking to occur in stainless steel. Wet-dry or heat transfer conditions, which promote the concen-tration of chlorides, are particularly aggressive with respect to initiating stress-corrosion cracking. A typical problem area is under pipe insulation. If the insulation becomes wet, chlorides in the insulation can leach out and concentrate on the metal surface as a result of alternate wetting and drying. The problem with insula-tion can be prevented by using a silicate-inhibited insu-lation.

While the mechanism of. stress-corrosion cracking is not fully understood, laboratory tests and service expe-rience have resulted in methods to minimize the prob-lem. For instance, Type 329 (an austenitic-ferritic stain-less containing 25-30 percent chromium, 3-6 percent nickel, and 1-2 percent molybdenum) exhibits superior resistance to chloride stress-corrosion cracking; plus it has a general corrosion and pitting resistance similar to Type 316. Recent studies indicate that Type 317 with 3.5 percent (minimum) molybdenum has excellent re-

Table 10 EFFECT OF METAL CONDUCTIVITY ON "U" VALVES

Application Material

Film Coefficients Btu/hr/ft2/F (W/m2•K)

Thermal Conductivity of Metal Btu/hr/ft2/F/in.

(W/m•K)

"U" Value Btu/hr/ft2/F

(W/m2 •K)

ho hi

Heating Copper 300 (1704) 1000 (5678) 2680 (387) 299 (1300) water with Aluminum 300 (1704) 1000 (5678) 1570 (226) 228 (1295) saturated Carbon Steel 300 (1704) 1000 (5678) 460 (66) 223 (1266)

steam Stainless Steel 300 (1704) 1000 (5678) 105 (15) 198 (1124) Heating Copper 5 (28) 1000 (5678) 2680 (387) 4.98 (28) air with Aluminum 5 (28) 1000 (5678) 570 (226) 4.97 (28)

saturated Carbon Steel 5 (28) 1000 (5678) 460 (66) 4.97 (28) steam Stainless Steel 5 (28) 1000 (5678) 105 (15) 4.96 (28)

Where ho = outside fluid film heat-transfer coefficient

hi = inside fluid film heat-transfer coefficient

Stainless steel is 300 Series Type

Source: Tranter Mfg. Inc.

14

sistance. Several proprietary austenitic stainless steels with higher nickel content also have shown resistance to stress cracking in hot chloride environments.

The ferritic stainless steels, which are very resistant to stress-corrosion cracking, should also be considered when the potential exists for this type of corrosion.

Intergranular corrosion. When austenitic stainless steels are heated or cooled through the temperature range of about 800-1650ºF, the chromium along grain boundaries tends to combine with carbon to form chromium carbides. The carbide precipitation causes a depletion of chromium and the lowering of corrosion resistance in areas adjacent to the grain boundary. This phenomenon, known as sensitization, is time and tem-perature dependent.

Sensitization may result from slow cooling from an-nealing temperatures, stress-relieving in the sensitiza-tion range, or welding. Due to the longer time at tem-perature of annealing or stress-relieving, it is possible that the entire piece of material will be sensitized. Weld-ing, on the other hand, may cause sensitization of a narrow band adjacent to but slightly removed from the weld in the region known as the heat-affected-zone (HAZ).

Intergranular corrosion depends upon the mag-nitude of the sensitization and the aggressiveness of the environment to which the sensitized material is ex-posed. Many environments do not cause intergranular corrosion in sensitized austenitic stainless steels. For example, glacial acetic acid at room temperature or fresh clean water do not; strong nitric acids do. (High purity water, however, such as used in primary circuits of nuclear reactors can be aggressive to sensitized stainless steels.)

Carbide precipitation and subsequent intergranular corrosion in austenitic stainless steels have been thor-oughly investigated; the causes are understood and methods of prevention have been devised. These methods include:

Columbium stabilization is preferred because its carbides are more readily retained in welds and it is easier to add in the steelmaking process. However, the use of columbium stabilized steel requires additional care in welding.

A low-carbon grade is usually specified for welding fabrication, while a stabilized grade is usually specified when the component is to be used at elevated tempera-ture.

HIGH-TEMPERATURE ENVIRONMENTS

Stainless steels are generally selected, first, on the basis of their resistance to corrosion and, second, on the basis of their mechanical properties. As the tem-peratures of operating environments increase, however, elevated temperature properties quickly become the primary concern. The stainless steels are most ver-satile in their ability to meet the requirements of high-temperature service.

There are three primary design factors that engineers consider when choosing materials for service at elevated temperature. These design factors are:

1. Service life (corrosion resistance and mechanical properties)

2. Allowable deformation 3. Environment.

Service life–For a given type of steel at a specific thickness, the expected service life depends on the maximum temperature to which it is exposed plus the maximum stresses to which it is subjected; also whether service is at a constant temperature or intermit-tent high temperature, plus corrosion resistance.

For a prolonged anticipated service life, such as 20 years, plain carbon steels are usually limited to a maxi-mum operating temperature of 750ºF; the ½ percent molybdenum alloy steels to approximately 850ºF; and the stainless steels to considerably higher tempera-tures depending upon the type used and the nature of the environment. It is important to recognize that for high-temperature service, strength at temperature is related to time at temperature.

Allowable deformation–Another factor to consider in designing for high-temperature service is the amount of deformation that can be permitted during the antici-pated service life. This factor determines which of two high-temperature strength properties should be given priority; creep or creep-rupture (sometimes called stress-rupture). If the component is small and/or the tolerances very close (such as in turbine blades) creep is regarded as the overriding factor. But if the compo-nent is large and capable of accommodating greater deformation, such as shell-and-tube heat exchangers, the creep rupture strength is the usual basis for selec-tion. Where considerable deformation is permitted, it is well to know the anticipated time to rupture, so parts can be scheduled for replacement before failure oc-curs.

It is also useful to know whether or not service at elevated temperature is cyclic or continuous. Cyclic operation may lead to failure by fatigue or loss of metal due to flaking of the oxide scale prior to the expected creep-rupture time.

Environment–The effect of exposure of a material to media can be a very complex subject. Elevated tem-peratures tend to increase corrosive action, heat trans-fer may affect corrosivity, thermal cycling can increase metal wastage through spalling of protective scale on the metal surface, and metal temperature probably will not be the same as the environment to which it is ex-posed. Generally, if oxidation or other forms of scaling are expected to be severe, a greater cross-sectional area–beyond that indicated by mechanical-property requirements–is usually specified. Problems like this

1. Use of welded stainless steel pipe in the annealed condition (post-weld annealing).

2. Selection of the low-carbon (0.030 percent maxi-mum) stainless steels when welding is involved. Low-carbon grades are Types 304L, 316L, and 317L. The less carbon available to combine with the chromium, the less likely is carbide precipita-tion to occur. However, the low-carbon grades may become sensitized at extremely long expo-sures to temperatures in the sensitization range.

3. Selection of a stabilized grade, such as Type 321 (titanium stabilized) or Type 347 (columbium stabilized). The stabilization provided by titanium and columbium is based upon the greater affinity that they have for carbon than does chromium.

15

cannot be solved by laboratory analysis. They require observation of test specimens in actual operating envi-ronments in pilot plants or full-size units.

A brief discussion of the corrosion behavior of stain-less steels in various high-temperature environments follows:

Oxidation

In noncyclic-temperature service, the oxidation re-sistance (or scaling resistance) of stainless steels de-pends on chromium content. Stainless steels with less than 18 percent chromium (ferritic grades primarily) are limited to temperatures below 1500ºF. Those containing 18 to 20 percent chromium are useful to temperatures of 1800ºF, while adequate resistance to scaling at tem-peratures up to 2000ºF requires a chromium content of at least 25 percent, such as Types 309, 310, or 446.

Carburization

Carburization is the diffusion of carbon into a metal. It can be carried to such a degree as to form high-carbon alloys with low ductility and impact strength at ambient temperature. The chromium carbides thus formed are prone to rapid oxidation under oxidizing conditions. The virtual disappearance of the metal carbides leaves deep holes. Such an extension of carburization, which is relatively uncommon, is known as metal dusting.

Carburization can be caused by continuous over-heating of a metal in the presence of hydrocarbon gases, carbon monoxide, coke, or molten metals con-taining dissolved carbon.

Laboratory and field experience indicate that the rate of carburization is affected by chromium content.

Sulfidation

Sulfur attack is second only to air oxidation in fre-quency of occurrence in many industries, and it is of even greater consequence because deterioration is likely to be more severe. Like oxidation, sulfidation pro-ceeds by converting metal to scale, which may be protective except that metal sulfides melt at lower tem-peratures than comparable oxides, and diffusion through a molten corrosion product is much faster than through a solid corrosion product. Also, sulfides are less likely to form tenacious, continuous protective films. Fusion and lack of adherence can result in accelerated corrosion.

As with oxidation, resistance to sulfidation relates to chromium content. Unalloyed iron will be converted rather rapidly to iron sulfide scale, but when alloyed with chromium, sulfidation resistance is enhanced. Silicon also affords some protection against sulfidation.

In addition to the usual factors of time, temperature, and concentration, sulfidation depends upon the form in which the sulfur exists. Of particular interest is the effect of sulfur vapor, sulfur dioxide, hydrogen sulfide, and flue gases.

For example, it is extremely difficult to generalize about corrosion rates in flue and processes gases, since gas composition and temperature may vary con-siderably within the same process unit. Combustion gases normally contain sulfur compounds; sulfur dioxide is present as an oxidizing gas along with carbon dioxide, nitrogen, carbon monoxide, and excess oxygen. Protective oxides are generally formed, and depending on exact conditions, the corrosion rate may be approximately the same as in air or slightly greater. The resistance of stainless steels to normal combustion gases is improved by increasing chromium content.

Reducing flue gases contain varying amounts of hyd-rogen sulfide, hydrogen, carbon monoxide, carbon dioxide and nitrogen. The corrosion rates encountered in these environments are sensitive to hydrogen sulfide content and temperature, and satisfactory material selection often necessitates service tests.

Hydrogen Attack

Atomic hydrogen, which results from a corrosion reaction or the dissociation of molecular hydrogen, can diffuse rapidly through the steel lattice to voids, imper-fections, or low-angle grain boundaries. The diffusing atoms accumulate and combine to form molecular hyd-rogen or, at high temperature, react with carbon to form methane. The larger hydrogen or methane molecules are trapped, and the subsequent pressure buildup re-sults in blisters or laminations (hydrogen damage) and/or degradation of ductility (hydrogen embrittle-ment). Eventually the steel cracks and may become unsuitable for continued use.

In low-temperature environments, carbon or low-alloy steels are usually suitable, but for temperatures above 800ºF and at high pressures (about 10,000 psi) the austenitic stainless steels have sufficient chromium to impart good resistance to hydrogen attack.

Ammonia and Nitrogen

Most metals and alloys are inert towards molecular nitrogen at elevated temperature. However, atomic ni-trogen will react with and penetrate many steels, pro-ducing hard, brittle nitride surface layers.

The behavior of stainless steels in ammonia depends on temperature, pressure, gas concentration, and chromium and nickel contents. Results from service tests have demonstrated that corrosion rates for straight-chromium stainless steels are greater than those for the chromium-nickel grades. (See publication "Stainless Steels for Ammonia Production" by the Committee of Stainless Steel Producers.)

Halogens

Austenitic stainless steels are severely attacked by halogen gases at elevated temperatures. Fluorine is more corrosive than chlorine, and the upper tempera-ture limits for dry gases are approximately 480ºF and 600ºF, respectively, for the high chromium-nickel grades. Wet chlorine gas containing 0.4 percent water is more corrosive than dry chlorine up to about 700ºF.

16

Liquid Metals Liquid-metal corrosion differs from aqueous and

gaseous corrosion since it depends primarily on the solubility of the solid metal in the liquid metal instead of on electro-chemical forces. Although chemical reactions may play an important role in liquid-metal corrosion, mass transfer mechanisms are the most significant.

The resistance of austenitic stainless steels to vari-ous liquid metals cannot be generalized, so some of the low-melting metals and alloys are discussed separately:

Sodium and sodium-potassium alloys–The austeni-tic stainless steels have been used extensively to contain sodium and sodium-potassium alloys (NaK). They are not susceptible to mass transfer up to 1000ºF, and the rate of transfer remains within moderate levels up to 1600ºF.

Molten sodium may cause severe carburization of stainless steels if it becomes contaminated by car-bonaceous material. For example, carburization has occurred from the storage of the liquid metal under kerosene.

Lead–Mass transfer will be experienced to varying degrees with any of the common engineering alloys exposed to molten lead under dynamic conditions. In addition, lead is an active corrodent in static systems. Lead has a comparatively high solubility for a number of metals, and therefore simple solution attack may result in serious deterioration even in the absence of mass transfer. Further, lead absorbs oxygen readily and may cause rapid oxidation of susceptible alloys, particularly at the interface in an open pot where oxygen contami-nation is high. In some instances when the lead bath has been maintained in a reduced state by the introduc-tion of a hydrocarbon, carburization of stainless steel containers has resulted.

Other low-melting metals–Molten metals and alloys such as aluminum, zinc, antimony, bismuth, cadmium, tin, lead-bismuth, and lead-bismuth-tin are generally corrosive to stainless steels.

Molten salts–Molten salts may corrode metals ac-cording to the reaction processes described for liquid-metal corrosion, namely, simple solution, temperature and concentration gradient mass transfer, and impurity reactions. Corrosion may also occur by direct chemical reaction, or a combination of corrosion and the reaction processes. Most information available concerns the corrosive nature of heat treating salts or salt mixtures.

Stainless steels high in nickel and low in chromium, such as Type 330, are usually selected for chloride salt containments.

For low-temperature heat treating (300 to 1100ºF) mixtures of potassium nitrate and sodium nitrate are fre-quently used. While cast iron or steel are serviceable for temperatures below 800ºF, the austenitic stainless steels show excellent resistance at the upper service temperatures.

Molten cyanide salt baths are used widely to surface-harden mild or low-alloy steels by the formation of a carburized, nitrided, or carbonitrided layer on the surface. Since a chemical reaction is an essential part of the process, these salts are more corrosive than the salts used purely as heat transfer media. As discussed earlier, chromium inhibits carburization but promotes nitriding. Nickel, however, inhibits both reactions, therefore, stainless steels with low chromium and high nickel–Type 330 for example–are used in this service.

COEFFICIENT OF THERMAL EXPANSION The coefficient of thermal expansion of austenitic

Table 11 PHYSICAL PROPERTIES OF TYPICAL PIPING STAINLESS STEELS (ANNEALED)

Type 304 Type 316 Type 309 Type 310

Modulus of Elasticity in Tension psi x 106 (GPa) 28.0 (193) 28 (193) 29 (200) 30 (207)

Modulus of Elasticity in Torsion psi x 106 (GPa) 12.5 (86.2)

Density, Ibs/in3(kg/m3) 0.29 (8060) 0.29 (8060) 0.29 (8060) 0.29 (8060) Specific Heat, Btu/Ib/F

(J/kg•K) 32-212ºF (0-100ºC) 0.12 (503) 0.12 (503) 0.12 (503) 0.12 (503) Thermal Conductivity, Btu/hr/ft/ft/F

(Jkg•K) 212ºF (100ºC) 9.4 (0.113) 9.4 (0.113) 8.0 (0.096) 8.0 (0.096) 932ºF (500ºC) 12.4 (0.149)

Mean Coefficient of Thermal Expansion x10-6/ºF (x1 0-6/ºC) 32-212ºF (0-100ºC) 9.6 (17.3) 8.9 (16.0) 8.3 (15.0) 8.8 (15.9) 32-600ºF (0-315ºC) 9.9 (17.9) 9.0 (16.2) 9.3 (16.6) 9.0 (16.2) 32-1000ºF (0-538ºC) 10.2 (18.4) 9.7 (17.5) 9.6 (17.2) 9.4 (17.0) 32-1200ºF (0-648ºC) 10.4 (18.8) 10.3 (18.6) 10.0 (18.0) 9.7 (17.5) 32-1500ºF (0-815ºC) - - 11.1 (20.0) 32-1800ºF (0-982ºC) - - - - 11.5 (20.6) 10.6 (19.1)

Melting Point Range ºF 2550 to 2650 2550 2650 2650 (ºC) (1398 to 1454) (1398) (1454) (1454) Source: Stainless Steel Industry Data

17

stainless steels is approximately 1½ times that of carbon steel. The design of a stainless steel pipe system must allow for this by providing more flexibility. Coefficients of thermal expansion and other characteristic physical properties are given in Table 11.

PROPER IDENTIFICATION

Although stainless pipe is shipped from the mill with proper identification, this identification is sometimes damaged during fabrication and handling. Carelessness in maintaining alloy identification can lead to the installation and use of the wrong alloy, which in turn often results in unexpected and premature pipe failure. If the material has lost its identification, qualitative tests can and should be made. Unfortunately, field tests cannot distinguish among some grades of stainless steel, so when in doubt, consult a stainless steel supplier.

THE ECONOMIES OF STAINLESS STEEL IN PIPING SYSTEMS For any proposed piping installation, the design en-gineer will quickly narrow down a long list of available piping materials to one or more that satisfy chemical, temperature, and pressure requirements. More often than not, stainless steels emerge as the obvious and uncontested choice, in which case design efforts are then directed toward achieving maximum economies. This includes "fine tuning" the piping layout to reduce its complexity as much as possible, choosing the proper stainless steel composition to avoid ''over specifying," and selecting efficient and economical fabrication and installation methods, such as shop fab-rication utilizing Van Stone flanging and close-radius bending.

Occasionally, situations arise when two or more pipe materials appear suitable from an engineering stand-point, so the designer wants to base his final selection on an economic study. In large companies with well staffed engineering and construction departments, such studies are often programmed for computer analysis with much of the cost data available from previous projects. For small companies or applications for which there is no previous experience, a new study is con-ducted. This can be a complex problem, because the costs of systems of different materials depend on many factors, such as system complexity, pipe sizes, availa-bility of building steel for support, capability of available pipe fabricating facilities, etc.

Piping system designers should avoid the inclination to base selection on general comparisons which have been published in the literature. While many of these comparisons appear complete with a large amount of data, they are often based on one specific installation. Furthermore, the installation on which the study is based is usually tailored to take advantage of one par-ticular material, and the data are often not valid for other specific installations.

For example, it has been the experience of many companies in the chemical and pulp and paper indus-tries that the two materials most often vying for a particu-lar piping installation are FRP and stainless steel. An economic study conducted by one manufacturer of nonmetallic piping (J. Yamartino, Dow Chemical Com-pany, "Installed Cost of Corrosion-Resistant Piping–1978," CHEMICAL ENGINEERING, November 20, 1978) gives the advantage to FRP.

In order for FRP and stainless steel to be considered for the same installation, the service has to be corrosive enough to warrant going to stainless steel; and the temperature and pressure requirements must be low enough to be within the range of FRP pipe. Fur-thermore, there have been many other studies of other installations in which the installed cost gives the advan-tage to stainless steel. To illustrate, consider the follow-ing study, which was made in 1972.

STAINLESS STEEL VERSUS REINFORCED PLASTIC

A cost comparison between stainless steel and two types of reinforced plastic for a scrubber water piping system at Copper Cliff, Ontario, was made by an inde-pendent engineering firm. The study indicates that stainless steel, in normal wall thickness of Schedules 10S and 40S, was competitive with the best reinforced epoxy and polyester piping systems on an installed-cost basis. The cost comparison is given in Table 12. Dollar figures are Canadian and equivalent to .98 U.S. dollars.

Most of the stainless steel considered in the study was more expensive than Type 304; 53.8 percent of the total length of piping was Type 316L, 27.4 percent was Type 304L and 9.3 percent was Type 316 and only the remaining 9.5 percent was Type 304.

Machine-made, reinforced epoxy pipe was not made in Canada and had to be imported from the U.S. Therefore, the material cost for this system included a 17½ percent duty plus a small brokerage charge amounting to a total of $7,890. The hand-layed-up polyester system was made in Canada and no duty was included in the estimate.

Several grades of machine-made, reinforced epoxy piping systems were available. This estimate was based upon one of the better grades with the best chemical resistance and a rating of 150-350 psig. (depending on size) and a temperature rating of 250-300ºF.

The system consisted of a total of 2,747 feet of piping and 565 fittings which varied in size from one-inch to 14-inch as shown in Table 13.

18

Screwed fittings (150 lb) were specified for the stain-less steel 1½ inch and under, and butt-welded fittings were specified for the larger sizes. Where welding was required the low-carbon grade was utilized.

On the basis of this cost comparison, the stainless steel system was chosen because it was more eco-nomical than either a machine-made epoxy system or a hand-layed-up polyester system. There would have been an even greater cost differential if an all-lightweight stainless steel system could have been used. If the installation were to be installed in the United States, the epoxy system would have been more com-petitive but still higher priced ($128,650 vs $128,100 for the installed stainless steel).

It should be stressed that every installation has to be considered separately, and there are a number of con-siderations to take into account. A quick check of piping costs alone is likely to indicate a definite cost advan-tage for reinforced plastic. There are, however, factors favoring lightweight, thin-wall stainless steel piping that should be considered. For example, the cost figures for stainless steel cited in this example could be consid-erably less if Van Stone lapped joints were used and if bending were substituted for many of the elbows in the smaller diameter pipe.

It soon becomes apparent that each system must be estimated in considerable detail to reach a trustworthy cost comparison.

A comparative estimate should reflect a comparison of costs for each of the following elements (their in-dividual significance is reviewed in the following text):

Design Costs Models Piping Arrangement Drawings Detail Sketching Pipe Support Design

Material Costs Pipe Fittings Valves Supporting Structures Miscellaneous Material

Fabrication Costs Field Fabrication Shop Fabrication Purchase of Fabricated Pipe

Erection Costs Pipe Supports Pipe Erection Testing Incidental Work

Design Costs Either models or piping arrangement drawings are

required on any major scope of piping work. They serve the same purpose, namely to route pipe runs between the pieces of equipment they are connecting. The re-quirements will be the same for all the piping materials being compared; i.e. stainless steel, FRP, or plastic-lined carbon steel.

Pipe support design and detail sketching are interre-lated. They will be dependent on the kind of piping installed. For example, FRP piping requires the most support, including separate supports at each valve and other special considerations covered in the manufac-turers design manuals. (Note: Thermoplastic pipe sys-tems would require more support than FRP.) The pre-ferred routing of the three systems being compared may differ somewhat to take advantage of the most economical layout to suit fabrication or the use of standard pieces. Plastic lined steel pipe can generally follow the route of stainless steel pipe although the cost and availability of standard or special fittings may be-come a problem. It should also be noted that the smaller sizes of pipe valves and fittings are not avail-able for FRP or plastic-lined steel systems.

Material CostsIt is common practice to purchase FRP and plastic-

lined steel pipe prefabricated. Stainless steel pipe and fittings can be purchased and shop fabricated into a piping system locally at the construction site. For small projects it may be more economical to purchase the pipe prefabricated. These alternatives are discussed under Shop Fabrication.

Table 12 COST COMPARISON FOR GLASS-REINFORCED PLASTIC PIPING

SYSTEMS VS STAINLESS STEEL IN CANADIAN CHEMICAL PLANTa

(a) Estimates by independent engineering firm. (b) Canadian dollar floating at time of estimate–exchange rate,

$1.00 U.S. equal to $.98 Canadian.

(c) System has to be imported into Canada from U.S. and is subject to duty of 17½% plus brokerage charge. This comes to $7,890; therefore, cost in U.S. would be $45,200 for material, $128,650 for total, times .98.)

Estimated Cost, Canadian Dollarsb System Material Labor Total

Machine-made, glass reinforced epoxy (high quality) $53,090c $83,450 $136,540

HLU Glass reinforced polyester made in accordance

with Canadian Government Specifications Board Standard 41-GP-22 (for 125 psig, 0 - 100ºF) $58,422 $83,450 $141,872

Types 304, 304L, 316 and 316L Stainless steel–

Schedule 40S for 1½ in. piping and below, Schedule 10S for 2 in. piping and over $56,930 $71,170 $128,100

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Table 13 PIPING BREAKDOWN FOR ESTIMATE

AISI Type Schedule

Size (inches)

Quantity (feet)

Number of Fittings

304 40S 1½ 115 18 304 40S 1 145 73 304L 10S 8 300 30 304L 10S 6 98 32 304L 10S 4 40 4 304L 10S 3 195 70 304L 10S 2 120 33 316 40S 1 255 79 316L 10S 14 70 7 316L 10S 12 60 6 316L 10S 10 65 16 316L 10S 8 227 45 316L 10S 6 382 66 316L 10S 4 245 42 316L 10S 3 155 24 316L 10S 2½ 15 2 316L 10S 2 160 18

suit the fabricating methods available. As an example, savings can be effected in a combination by routing the pipe so that there is space for machine access to pro-vide for the bending and lapping operations.

For small piping projects that must be carried out with a minimum of shop facilities, purchase of prefabricated pipe should be evaluated. Custom fabricating shops are available with the capability of short radius bending and flare-lapping stainless steel pipe.

Stainless steel pipe has an advantage over competi-tive materials since last minute field modifications can utilize conventional fittings and welding methods, whereas FRP or plastic-lined pipe generally require special fittings as well as special techniques and tool-ing. In the case of plastic-lined steel pipe, this means liner flaring tooling for the various sizes. In the case of an FRP system, it may mean tooling suited to forming the proprietary joint arrangement of the particular pipe manufacturer.

Fittings are generally high-cost items in FRP systems. They are frequently an even greater cost item in plastic-lined steel systems. The material cost for these systems increases much more rapidly with increasing complexity than does the cost of a stainless steel sys-tem. FRP and plastic-lined valves are likewise much more expensive than stainless steel valves. The mate-rial requirements for supporting structures will usually be somewhat greater for FRP and plastic-lined steel than for a stainless steel system.

The requirements for miscellaneous materials, such as paint, will vary according to the system. FRP may require an ultra-violet resistant paint coat, while plastic-lined steel pipe and flanges will require painting. The steel backup flanges on the stainless steel system will require corrosion protection by painting (an alternative is galvanizing). Also, the supports should be painted, while bolting is sometimes galvanized.

Generally, FRP does not require insulation because the plastic is, in itself, a good insulator. However, some insulation may be required for ambient heat or fire pro-tection of the FRP pipe.

Fabrication Costs

Erection Costs Somewhat higher erection costs might be expected

with FRP due to more frequent support than that re-quired for stainless steel pipe. In the case of plastic-lined steel pipe, there are usually more erection joint flanges to be bolted up, resulting in a direct cost in-crease.

Testing is required for all piping systems. Some FRP manufacturers advocate the practice of test-pressure application and release for 5 to 10 pressure cycles in order to assure integrity of the system. This recommen-dation represents an added cost consideration com-pared to stainless steel or plastic-lined steel where a one-cycle test is usually adequate.

Incidental erection labor is, of course, required for painting, insulation, etc., already discussed under mis-cellaneous materials.

In conclusion, it is obvious that comparing the costs of corrosion-resistant systems of various materials is a complex problem. Very few overall conclusions can be reached. There is no known shortcut solution. The as-sumptions used for a general comparison may or may not be valid for a particular system. A detailed analysis of the specific installation is the only reliable cost guide.

Field fabrication of pipe at the point of installation is extremely inefficient. Estimates of labor for field fabrica-tion are often 50 percent higher than for the identical work done under shop conditions. The concentration of work in a shop may also increase the shop work load sufficiently to justify improved shop facilities. For example, the addition of equipment to make flared Van Stone laps may reduce fabricating labor 15 percent and eliminate the cost of stub ends. The addition of modern short-radius bending facilities may reduce fabricating labor another 20 percent in addition to eliminating the purchase of elbows. In both cases, savings in labor results from the elimination of the welds at the fittings, two in the case of the elbow and one in the case of the stub end.

Economies can often be effected by detailing pipe to

APPLICABLE STANDARDS AISI

The American Iron and Steel Institute recognizes 57 stainless steels as standard, and indicates their chemi-cal composition limits. A table of the AISI stainless steel grades most commonly used for piping and their corre-sponding UNS numbers, typical properties and appli-cable ASTM specifications are included in Appendix A.

20

ASTM The American Society for Testing and Materials covers AISI grades and proprietary grades of stainless steel in their specifications. They also add a number of other requirements, such as dimensional tolerances, heat treatment, mechanical property requirements, etc. and in this way are more definitive and restrictive.

ASME Piping may be considered to fall under the fired or unfired pressure vessel codes of the American Society of Mechanical Engineers. These codes are used for design. Allowable design stresses for code piping are defined in the codes.

ANSI The American National Standards Institute has prepared codes for pressure piping. These fall under the several sections of B31 listed in Appendix C. ANSI B31.3 was written specifically for chemical plants and petroleum refineries.

SPECIFICATION SUMMARY

The characteristics of distinct piping systems may be recapped by pipe codes for reference and possible use for piping fluids not yet identified. See Appendix E.

THE PROCESS PIPING DIAGRAM This is a type of flow diagram. All significant pipe lines complete with valves and equipment are assigned line numbers and shown. Sizes are based on flow require-ments. Information on piping system specifications, in-sulation, tracing, etc. is added as it is developed. See Appendix F.

SELECTION OF MATERIALS OF CONSTRUCTION

Usually this step occurs simultaneously with the preparation of the index of fluids and gases, although it may be delayed until a cost analysis can be made. Cost comparisons, reliability predictions, corrosion allow-ances and product contamination must be given con-sideration.

THE DESIGN, FABRICATION AND ERECTION OF PLANT PIPING SYSTEMS

DEVELOPMENT OF PIPING SYSTEM SPECIFICATIONS

Utilizing the size requirements from the process pip-ing diagram (Appendix F) the wall thickness, and hence the pipe schedule, is calculated from temperature, pressure and corrosion allowances. Gasket materials, fittings, joints, fabrication techniques, valves, weld testing, and cleaning requirements are then de-termined. Allowable stresses are available in the appli-cable ANSI B31 Codes (Appendix C).

The following sequence indicates the natural devel-opment of the selection and design of a piping system. The discussion is provided by Addison Hempstead. The sequence is similar to that in use by some of the major chemical companies.

INDEX OF FLUIDS AND GASES

It is appropriate to begin with an alphabetical list of the products and services that will require piping sys-tems (Appendix D is a hypothetical listing which serves as a basis for discussion in this section). The piping material, maximum operating pressures and tempera-tures and other pertinent information are tabulated for each item. If sizes or operating conditions cover a broad range for a given service, it may be desirable to assign two or more pipe codes to most effectively satisfy the requirements (Example: Items 1 and 8, Ap-pendix D). When a line carrying any one of these ser-vices is added to a piping diagram, the proper pipe code can be selected from this list. This procedure provides for an orderly assignment of piping specifi-cations, and it may be maintained as a standard for reuse on future installations having the same service. This will save design time otherwise required to rede-velop the pipe code requirements.

THE PROCESS MODEL

A scale model of the proposed installation is fre-quently made, which is useful for many purposes such as:

1. Visualizing equipment arrangement to assure space for operating access and maintenance.

2. Planning installation of the facilities. 3. Avoiding interferences. 4. Pipe sketching and takeoff of construction mate-

rials. 5. Operator training. The detail of the model depends on its complexity

and the specific design. Models usually include all significant pipelines with their valves and flanged joint locations.

Final models are usually scaled ¾ inch equals one foot, although a preliminary study model is sometimes made at a scale of 3/8 inch equals one foot.

PIPING FLEXIBILITY ANALYSIS

ANSI B31.3, The Code for Chemical Plant and Petro-leum Refinery Piping, requires that piping systems shall have sufficient flexibility to prevent thermal expansion or contraction or movements of pipe supports and ter-minals from causing: Failure of piping or supports from

21

overstress or fatigue, leakage at joints, or detrimental stresses or distortions in piping or in connected pumps, turbines, valves, etc.

A formal analysis of piping flexibility is not always required to meet code requirements. For details the reader is referred to the ANSI B31 Codes.

ESTIMATING At this point in the development of design informa-

tion, it is usually possible for an experienced estimator to develop an estimate to any degree of detail required.

Organizations with highly developed estimating data often can calculate average costs based on a typical pipe line run, which is then multiplied by a simple count of the number of pipelines. This provides an estimate on a broad scope. However, in order to accurately compare costs of alternate pipeline materials, it may be necessary to calculate the costs of individual elements, such as pipe, fittings, valves, hangers, etc., which may then be built up into a detail estimate of a single pipe line.

PRELIMINARY COMMENTS AND APPROVALS

It is appropriate at this point to review the model, the index of fluids and gases, the specifications for the piping systems, corrosion data, system safety under emergency conditions, maintainability of the piping, experience with the operation of similar facilities etc., among the interested parties. This is the "last chance" to make changes without incurring major cost penal-ties.

PIPING SKETCHES

Isometric pipe sketches are prepared from a combi-nation of the model and equipment arrangement data that provide precise connection locations. These sketches and the requisite material takeoff may be drawn manually or computer generated. Computer generated sketches are generally more accurate. Computer programs are available that also generate shop (traveller) cards providing exact cut lengths for each piece of pipe as well as shop routing for any bending or end preparation (laps, flanges, bevels or threading).

Construction PhaseFABRICATION

General considerations–Craft labor is more effi-cient working in a shop than at the pipe installation site. For economy, productivity and quality, any large vol-ume of pipe, as a general rule, should be shop fabri-cated. The shop, to be efficient, should have suitable modern equipment and it must have some effective production control system. Material should not be re-leased to the shop for fabrication until all the material required for a line or other unit has been assembled. Since labor is usually more than half the cost of a piping system, it must be used efficiently. When a pipe line

goes from the shop to the field for erection, it should be sent complete with all of the valves, bolts, nuts, hangers and gaskets.

If possible, steam tracing and insulation should be applied before the piping leaves the shop. The im-provements in productivity and quality come both from the better facilities that can be made available at a shop and from the conveniences in material availability and better working conditions. Pipe should follow a rudi-mentary production line thru the shop.

It should be noted that stainless steels are generally more easily fabricated (for repair or replacement) in the field as compared with other piping materials.

Welding–There are four principal processes for fu-sion welding stainless steels. They are:

1. Shielded Metal Arc Welding (SMAW), using coated electrodes.

2. Gas Tungsten Arc Welding (GTAW or TIG), using an inert gas (such as argon) to protect the weld zone from the atmosphere.

3. Gas Metal Arc Welding (GMAW or MIG), also an inert gas shielded process.

4. Submerged Arc Welding (SAW), which is seldom used on piping except for heavy sections.

In the submerged arc process shielding is provided by a granulated flux covering the weld area and welding electrode. Automated or semi-automated welding equipment is available. Table 14 shows time study data for GTAW welding of eight sizes of stainless steel pipe.

Bending–Modern "push" bending equipment is available that will accomplish bends at conventional Long Radius (bend radius = 1½ x nominal pipe diam-eter) radii with wall thinning of 20 percent or less. This operation eliminates the cost of the purchased elbow and the two welds required for its installation, with sav-ings up to approximately 35 percent realized in some sizes. Flared (Van Stone) laps–The ANSI B31 Series of pipe codes permits the use of laps formed by flaring the end of the pipe in most applications. (ANSI B31.3-76 paragraph 306.4.2). Flared laps can be formed with either a smooth or modified spiral finish depending on the type of roller used for flaring. This technique elimi-nates the cost of a purchased stub end and the weld required for its installation.

ERECTION

To maintain the pattern of labor effectiveness, pipe erection in the field should follow a production se-quence. When a line has been received complete in the field, it can be erected most efficiently by first installing the hangers, followed by sequential erection of the pipe and bolting up the flanges. Efficient tools, such as rachet wrenches, are a labor-saving investment. Spe-cialized crews may be utilized for the various opera-tions where the scope of the job warrants, such as a crew for hangers, one for pipe erection, one for testing, etc.

TESTING

Testing requirements are usually prescribed by the specifications. Shop testing of individual fabricated sections followed by testing the erected pipe may

22

prove economical. It is generally permissible to make a preliminary air test at not more than 25 psig prior to making a final hydrostatic test. This preliminary air test is useful in locating major leaks before the system is filled with a fluid that must be drained before the leak can be corrected.

An excellent presentation of a method for establish-ing nondestructive examination (NDE) levels for fluid services in chemical plants and refineries is in an arti-cle, ''A Quantitative Method for Determining NDE Levels" by R. Getz. (HEATING/PIPING/AIR CONDI-TIONING, August 1979.)

Table 14 TIME STUDY DATA FOR WELDING THREE SIZES OF STAINLESS STEEL PIPEa

Time, hrb,c

Pipe size, in. 1 1¼ & 1½ 2 2½ 3 4 6 8 Time required to make one butt weld

Schedule 5S 0.067 0.083 0.083 0.1 0.1 0.112 0.166 0.333 Schedule 10S 0.1 0.1 0.133 0.166 0.2 0.232 0.333 0.5 Schedule 40S 0.25 0.3 0.333 0.415 0.415 0.5 0.75 1.166

Time required to align, tack, and weld one 90 deg elbow


Time required to align, tack, and weld one 45 deg elbow


Time required to align, tack and weld one tee


Time required to align, tack and weld one slip-on flange


Time required to align, tack and weld one butt-weld flange


a All values are based on gas tungsten-arc welding of austenitic stainless steel, using 3/32 and 1/8 in. diam filler metals, where required.

b Add 10 minutes to each fabrication (tee, elbow, pipe joint, etc.) for purging, if a purge is required.

c These times do not include cutting and beveling.

Source: H. A. Sosnin, "The Joining of Light-Wall Stainless Steel Piping," WELDING JOURNAL, October 1967.

BIBLIOGRAPHY 1. "Design Guidelines for the Selection and Use of

Stainless Steel," April 1977, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

2. "High Temperature Characteristics of Stainless Steels," April 1979, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

3. "Welding of Stainless Steels and Other Joining Methods," April 1979, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

4. "The Role of Stainless Steels in Petroleum Refining," April 1977, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

5. "Effective Use of Stainless Steels in FGD Scrubber Systems," April 1978, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

6. "Stainless Steels for Pumps, Valves and Fittings,"

April 1978, Committee of Stainless Steel Produc-ers, American Iron and Steel Institute, Washington, D.C.

7. "The Role of Stainless Steels in Desalination," April 1974, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

8. "Stainless Steels: Effective Corrosion Control in Water and Waste-Water Treatment Plants," March 1974, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

9. "Stainless Steels in Ammonia Production," November 1978, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

10."Stainless Steels for Acetic Acid Service," April 1977, Committee of Stainless Steel Producers, American Iron and Steel Institute, Washington, D.C.

11.''Joining of Light Wall Stainless Steel Piping," WELDING JOURNAL, October 1967

23

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24

APPENDIX B

Useful Guides In Making A Selection Of Material For A Piping System

I. General Considerations

A. Consider the safety inherent in stainless steel compared to alternative materials by virtue of its properties, methods of joining and history of ser-vice, reliability.

1. Does the fluid have hazardous properties that need special consideration?

2. What quantity of fluid could be released by a piping failure?

3. What would be the effect on the environ-ment?

4. What potential exists for personnel expo-sure?

B. Would special provisions be required to protect plastic or reinforced thermo-setting resin pipe against possible failures such as: thermal insula-tion, shields or process controls to protect from excessive heat or thermal shock; armor, guards, barricades or other protection from mechanical abuse?

C. Is a metallic system preferred tofacilitate ground-ing static charges?

D. How important is continuity of service? 1. What are the relative reliabilities of the pipe,

fittings, and joints of the alternative system materials under consideration?

E. Is insulation an adequate precaution to protect piping against failure under fire exposure?

F. Are the thread sealant, packing, gasket material, etc., compatable with the fluid being handled?

II. Metallic Pipe A. Ability of stainless steel pipe to withstand higher

and lower temperatures than plastic, reinforced thermo-setting resin, or plastic-lined carbon steel pipe.

B. Ability to withstand full vacuum over a wide tem-perature range.

C. Greater tolerance for steam tracing than non-metallic or lined systems.

D. Readily steam jacketed. E. Minimum of flanged joints required.

1. Reduces cost of piping. 2. Reduces leakage potential and maintenance

cost.

F. Branches and taps can be provided without spe-cial fittings at a minimum cost.

G. Requires fewer supports. 1. Requires less support for runs. A minimum of

two supports are often provided for each length of pipe for practical handling in instal-lation and removal.

2. Valves are generally supported by the piping in a metallic pipe system. Special valve support is usually required in most non-metallic piping systems.

H. Thermal expansion of stainless steel is greater than that of carbon steel but considerably less than that of most nonmetallic piping materials. Lined metallic piping systems sometimes fail be-cause of the difference in the expansion of the pipe and liner.

I. A metallic system offers greater safety for com-pressed air or gas service applications. This is especially true for larger systems with a substan-tial amount of potential energy stored in the com-pressed gas.

J. Carbon and low-alloy steels are generally more susceptible to corrosion than stainless steels, leading to reduced life and potential contamination of the product.

K. The maximum and minimum temperatures for carbon and low-alloy steel and nonmetallic piping systems are limited compared to stainless steels. See the B31. Piping Codes for limitations.

L. Is the pipe material compatible with the fluid being handled?

1. Consider the possibility of embrittlement when handling strong caustic fluids in carbon or low-alloy steel.

2. Consider the increased possibility of hyd-rogen damage under some conditions when carbon or low-alloy steel piping material is exposed to hydrogen or aqueous acid solution. The austenitic stainless steels re-sist hydrogen effects.

M. Stainless steel pipe has excellent resistance to most atmospheric corrosion. Does not require painting or other protection from sunlight, oxygen or ultraviolet exposure, as is the case with some nonmetallic materials.

25

* Addenda are issued at intervals between publication of complete editions. Information on the latest issues can be obtained from the American Society of Mechanical Engineers, New York, NY

III. Nonmetallic Pipe A. Principal Classes

1. Thermo-plastic 2. Reinforced thermo-setting resin 3. Special materials, (ceramic, asbestos-

cement, glass, impregnated graphite) gen-erally are limited to very specialized appli-cations.

B. The applications of thermo-plastic pipe are se-verely limited by service temperature consid-erations.

C. Thermo-plastics are excluded from use in flamm-able liquid service above ground by the B31.3 Code.

D. Nonmetallic pipe is not susceptible to electrolytic corrosion.

E. Nonmetallic pipe may be permeable by toxic materials.

1. Internal to external permeation. 2. External to internal (buried lines in contami-

nated soil). F. Nonmetallics are very resistant to corrosion in

some classes of fluids such as non-oxidizing acids and chlorides.

G. Nonmetallic pipe may require insulation or other provisions for protection from any potential fire exposure.

H. Flanged joints of nonmetallic materials are sus-ceptible to gasketing and leakage problems due to the low modulus of elasticity of the flanges.

I. Nonmetallic lines generally require more closely spaced supports and guiding than metallic pip-ing. This may necessitate supplementary inter-mediate steel structures.

J. Valves generally require independent support.

IV. Lined Metallic Pipe A. Linings are available of materials resistant to

most chemical environments. B. Fittings are required for all branches and taps.

All pipe joints are flanged. C. Less support is required than for nonmetallic

pipe, particularly in smaller sizes. Valves gen-erally do not require independent support.

D. Steam tracing or vacuum service may result in liner buckling.

E. Thermal cycling may cause liner to crack at flanges.

F. Lined flanged fittings are required at all branches, taps and changes in direction. These added flange joints increase both the cost and potential for leakage.

G. Field or shop fabrication requires special fixtures for forming the liner over the flange face.

APPENDIX C Status of ANSI B31 Code for Pressure Piping

Standard Number and Designation Scope and Application Remarks B31.1.0 Power Piping For all piping in steam generating stations. * B31.2 Fuel Gas Piping For fuel gas for steam generating stations

and industrial buildings. *

B31.3 Chemical Plant and

Petroleum Refinery Piping

For all piping within the property limits of facilities engaged in the processing or handling of chemical, petroleum, or related products unless specifically excluded by the code.

*

B31.4 Oil Transportation

Piping For liquid crude or refined products in cross-country pipe lines.

*

B31.5 Refrigeration Piping For refrigeration piping in packaged units

and commercial or public buildings. *

B31.7 Nuclear Power Piping For fluids whose loss from system could

cause radiation hazard to plant personnel or general public.

Withdrawn; see Section 3, ASME Boiler & PV Code

B31.8 Gas Transmission

and Distribution Systems

For gases in cross-country pipe lines as well as for city distribution lines.

*

26

APPENDIX D Index of Fluids and Gases

Product

Max. Operating Condition Test

Pipe

or Degrees Press. Basic Code Item Service PSIG ºF ºC PSIG Material Number Remarks

1 Air, Plant 150 375 190 Copper P14 ¾" and smaller 150 300 148 Steel P13 On-Off valve-B120 for Galv. ½"–2"; G92JH for 3"

2 Oil, Lubrication 150 300 148 304 SST P10 Tubing

3 Process Piping 175 350 176 304 SST P16A

4 Steam Tracers, 1000 600 315 304 SST P10 Tubing Acid Exposure

5 Steam, 50 PSIG & 50 300 148 Steel P18

Lower

6 Water, 120 220 104 Steel P11 Use X11A Aboveground, Ball Valve

7 Water, 50 300 148 Steel P19

Condensate

8 Water, 150 376 190 304 SST P16 Demineralized 1400 200 93 304 SST P17

9 Water, Process 150 500 260 Steel P12

A.G. 3" & Larger 220 150 65 Steel P12A

10 Water, Process, 150 375 190 304 SST P16 Hot

11 Water, Process 150 150 65 Cast Iron P15

Underground Cement Lined

APPENDIX E Pipe Code Summary

Max. Operating Condition Pipe

Code Degrees Basic

Number PSIG ºF ºC Material Remarks P10 1000 600 316 304 SST Tubing P11 125 220 104 Steel P12 150 500 260 Steel P12A 220 150 65 Steel P13 175 330 148 Steel-Galvanized P14 150 375 190 Copper P15 150 150 65 Cast Iron Cement Lined P16 150 375 190 304 SST P16A 175 350 176 304 SST P17 1500 250 120 304 SST P18 75 350 176 Steel P19 100 340 171 Steel

27

APPENDIX F Typical Process Piping Diagram

Line Numbers (a) Numbers allotted 1-99(b) Last number used 7 (c) Numbers canceled 1

(a) Record Numbers allotted to this diagram in this block. (b) Record last number used in this block. (c) Record canceled numbers of those allotted in this block.

Valve

Line Number and Direction of Flow

Documents

DESIGN GUIDELINES FOR STAINLESS STEEL IN PIPING SYSTEMS