Stainless Steel for Water Handling

7/31/2019 Stainless Steel for Water Handling

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H A N D B OOK

D E S I G N E R

STA I N LES SSTEEL IN

W AT ER

H A N D L I N G

& D E L I V E RY

S Y S TEM S

StainlessSteel

TheValueOption


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The material presented in this booklet has beenprepared for the general information of the reader.

The Specialty Steel Industry of North America(SSINA) and the individual companies it representshave made every effort to ensure that the informa-tion presented is technically correct. However, nei-ther the SSINA nor its member companies war-rants the accuracy of the information contained inthis handbook or its suitability for any general andspecific use. The SSINA assumes no liability orresponsibility of any kind in connection with theuse of this information. The reader is advised thatthe material contained herein should not be usedor relied on for any specific or general applicationwithout first securing competent advice withrespect to its suitability.

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TABLE OF CONTENTS

INTRODUCTION .......................................................................................................... 1

BACKGROUND ............................................................................................................ 2

ALLOYS .............................................................................................................................. 3

CORROSION RESISTANCE .............................................................................. 3

WELDING .......................................................................................................................... 4

OTHER JOINING METHODS ............................................................................ 4

ADVANTAGES TO STAINLESS STEEL ................................................ 4

SPECIFICATIONS ...................................................................................................... 5

ASTM SPECIFICATIONS ...................................................................................... 6

PRODUCTS ...................................................................................................................... 6

SUGGESTIONS ON FABRICATIONOF PIPING SYSTEMS ............................................................................................ 7

TESTING AND MAINTENANCE .................................................................... 7

ACKNOWLEDGMENTS ........................................................................................ 7

REFERENCES .............................................................................................................. 7

LISTING OF STAINLESS STEELPIPE AND TUBE MANUFACTURERS ...................................................... 8


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INTRODUCTIONStainless steel is not a single alloy, butrather the name applies to a group ofiron based alloys containing a minimum10.5% chromium. Other elements areadded and the chromium contentincreased to improve the corrosionresistance, improve heat resisting prop-erties, enhance mechanical properties,and/or to improve fabricating character-istics. There are over 50 stainless steelgrades that were originally recognizedby the American Iron and Steel Institute(AISI). Three general c lassifications areused to identify stainless steel. They are:1. Metallurgical structure. 2. The AISInumbering system (200, 300 and 400series numbers). 3. The Unified Num-bering System, which was developed bythe American Society for Testing Materi-als (ASTM) and the Society of Automo-tive Engineers (SAE) to apply to all com-mercial metals and alloys.

The various types of stainless steelare detailed in a designer handbook,Design Guideline for the Selection andUse of Stainless Steel, available fromthe Specialty Steel Industry of NorthAmerica (SSINA). Several other publica-tions are also available, including:Stainless Steel Fabrication, StainlessSteel Fasteners, Stainless Steel Fin-ishes, Stainless Steel Specifications,to mention a few. To order these freepublications, or a list of all SSINAliterature, call our toll-free number:1-800-928-0355

Historically, stainless steels haveestablished themselves as excellentcorrosion resistant materials exhibitingsuperior performance in a variety ofwater-related applications in the food,drug, brewing and biotechnologyindustries.

Stainless steel has been extensivelyused for potable water service since themid-1960s in domestic plumbing instal-lations in the U.S., U.K., Germany andJapan; in desalination plants for han-dling product water; in potable watertreatment plants for gravity filtration andpiping; in Japan for small diameterhousehold connectors; and in New YorkCity for large diameter risers and otherpiping systems.

This handbook is intended to updatethe variety of water handling/deliveryapplications that are, or, should beutilizing stainless steel; particularly in

view of the recent NSF Internationalacceptance of stainless steel in potable water applications . Stainless steel is anaccepted material as listed inAppendix C of ANSI/NSF Standard #61Drinking Water System Components -Health Effects. Copies of ANSI/NSF 61are available from NSF International(1-800-NSF-MARK).


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BACKGROUNDStainless steel owes its stainless charac-teristics to an adherent, durablechromium oxide layer only a fewangstroms thick. This passive film ofchromium oxide forms almost instantly inair or water and is self replenishingwhen scratched or damaged. Stainlesssteels are easy to fabricate and join,employing compression, capillary orweld fittings, although the techniquesare somewhat different than thoseemployed for carbon steel or copper.

An extensive use of stainless steelpiping for potable water has been forproduct water from desalination plantsin the U.S., the Caribbean, and theMiddle East. Types 304L and 316Lare used for collection troughs in theplant and for piping in the blendingplant where the high purity productwater is blended with locally availablegroundwaters.

Subsequent to a decade of testing,the Tokyo Water Bureau has pioneeredthe use of stainless steel for the connec-tor piping from the submain in the streetto the meter at the dwelling, p rimarily toreduce leakage rates. By 1997, alldwellings in the city of Tokyo are sched-uled to be served by stainless steel pipeconnectors. Tokyo has also initiated theuse of stainless steel piping on bridgesas a means to circumvent troublesomepipelines originally installed under riverswhere needed repairs are extremely dif-ficult to complete.

Based upon a 15-year evaluation ofcandidate materials, New York City initi-ated substantial use of stainless steel(304L) in municipal water distributionsystems for the large diameter risers inwater tunnel 3, stage 1, which went intoservice in 1993. Even more extensiveuse of stainless steel piping is underway in stage 2. Stainless steel piping isbeing used selectively for sectionsthat are difficult to replace and in whichmaximum durability is desired.

Stainless steel was introduced foruse in the large central-control gravityfilters in water treatment plants in 1965and has since been used in more than75 plants.

Stainless steel piping has beenemployed instead of ductile iron in morethan 30 potable water treatment plants,largely because of cost savingsachieved. As an example, the savingsattributed to the use of stainless overductile iron were estimated at $50,000for the Taunton, MA, potable watertreatment plants.

Extensive testing over a 10-yearperiod in Tokyo soils convinced Japan-ese utility personnel that T316L pipingcould be buried without external protec-tion. This study confirmed earlier testsconducted in the U.S. by the NationalBureau of Standards under auspicesof the American Iron & Steel Institute.Other tests and experience indicatethat stainless steels perform well in

well-drained soils with clean backfill,but in poorly drained soils or backfill;the practices designed for carbon steel(wrap or cathodic protection) shouldbe employed for buried stainlesssteel piping.


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The following grades of stainless steel are used in water handling applications: The thin chromium oxide film to whichstainless steel owes its corrosion resis-tance forms almost instantly in air, water,or other media containing oxygen. Dis-solved oxygen is the principal con-stituent of water that affects the corro-sion behavior of stainless steel and the

effect is highly beneficial. The agitation,turbulence, and high velocity of waterthat are so troublesome to carbon steel,cast and ductile iron, are highly benefi-cial to the durability and performance ofstainless steel. There is no known limit tothe durability of clean stainless in clean,aerated, low chloride waters.

Conversely, under crevice corrosionconditions the important factors arecleanliness and chloride concentration.Sediment-laden water and crevices canlead to localized pitting-type attack ifchlorides are present in sufficient con-

centrations. Below 200 mg/l chlorides,crevice corrosion of T304 stainless steelis rare in natural waters, and crevicecorrosion of T316 stainless is equallyrare below 1000mg/l chlorides. Nonethe less, crevice corrosion can andsometimes does occur in waters oflower chloride content if sediment, otherdeposits, or manmade crevices are ableto occlude and concentrate chloridesfrom the water.

The 2-3% molybdenum addition inboth the wrought and cast versionsgreatly improves their resistance tolocalized corrosion. When corrosion ofstainless does occur, it consists of oneor more small pits in a very localizedregion. In natural water, stainless steeldoes not suffer general metal loss asdoes carbon steels. The thin, but tough,durable chromium oxide film that pro-tects stainless steel from corrosionoccasionally contains defects, and maycorrode when environmental conditionsbecome aggressive enough to takeadvantage of weaknesses in the film.Except for the rusting of iron particlesembedded in the surface during fabrica-tion and handling, corrosion is rare inatmospheric exposures but does occa-sionally occur in water or soil exposure

All of the above exhibit an austeniticmetallurgical structure and are non-magnetic. T304 is referred to as the

basic 18-8 alloy and is the most readilyavailable, often specified for all purposeapplications, and exhibits excellent cor-rosion resistance with unusually goodformability. T316 is basically a 304grade enhanced by the addition of 2-3%molybdenum for greater corrosion resis-tance. It is selected for long term servicein aggressive industrial, chemical andseacoast atmospheres. The low carbonversion of these grades is designatedwith an L after the alloy number and iscommonly referenced in conjunctionwith the standard grade. These are

referred to as dual certified grade; i.e.,(T304/304L) and are preferred wherewelding is the joining method. Thelower carbon improves corrosion resis-tance at the weld site. Dual certificationprovides for meeting the .03% carbonmaximum while meeting the highermechanical properties of the standardgrade.

ALLOYS CORROSIONRESISTAN CE

Grade UNS C Max Chromium Nickel Molybdenum Y.S. T.S. E(ksi) (ksi) (%)

304 S30400 .08 18.0-20.0 8.0-11.0 30 75 35

304L S30403 .03 18.0-20.0 8.0-13.0 25 70 35

316 S31600 .08 16.0-18.0 11.0-14.0 2.0-3.0 30 75 35

316L S31603 .03 16.0-18.0 11.0-15.0 2.0-3.0 25 70 35

Cast

CF3 J92500 .03 17.0-21.0 8.0-12.0 30 70 35

CF8 J92600 .08 18.0-21.0 8.0-11.0 30 70 35

CF3M J92800 .03 17.0-21.0 9.0-13.0 2.0-3.0 30 70 30

CF8M J92900 .08 18.5-21.0 9.0-12.0 2.0-3.0 30 70 30


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under unusual conditions. The benefi-cial effect of molybdenum in enhancingthe resistance to localized corrosion inthose environments where localized cor-rosion of T304/304L occurs should beconsidered.

As discussed previously, corrosion,when it occurs, is usually localized increvice areas. Crevices can be of twotypes: manmade, originating from

design or construction; or natural, occur-ring at sites formed by sediments ordeposits. Typical manmade crevicesmight occur as the result of incompletefusion welds, flange faces, undergas-kets, or any metal to metal junctions.Attention should be directed to eliminat-ing manmade crevices through designand during construction. Naturallyoccurring crevices from sediment canbe reduced by high flow rates or, whendesign or operating conditions are suchthat sediment deposits may occur, apractice of periodic flushing with a highpressure water stream should beemployed and prior design should pro-vide for the necessary flushing ports.

Another natural occurring crevice isthe underdeposit crevice formed byblack Fe-Mn deposits in some high Mn-Fe raw water lines when an oxidant suchas chloride or potassium permanganateis employed. This deposit is normallybenign to T304L stainless steel, but hasresulted in serious underdeposit crevicecorrosion near welds in the presence offree chloride and where heat tint oxidescale from welding has not beenremoved. The removal or prevention ofheat tint scale will minimize this type ofunder deposit corrosion. Heat tint maybe prevented by employing very tightfit-ups and using an internal inert gaspurging equipment that excludes essen-tially all oxygen.

Stainless steel performs best in c lean,flowing water, i.e., flow rates greaterthan 1.5 to 2 ft/s. The minimum designflow rate in raw water is 3ft/s to reducesediment deposition.

W ELD I N G

The low (L .03 max) carbon versionsof T304 and T316 in both wrought andcast compositions are used for weldedapplications such as piping or antici-pated repair/rebuild at some future time.Utilization of the low carbon g radesensures that the heat of welding will notsensitize the heat affected zone (HAZ)

of the weld to intergranular corrosion.Sensitization is the term used todescribe the reduction in corrosionresistance that occurs in the conven-tional (.08 max C) grade stainless steelin some environments because of theprecipitation of carbides during weldingin the HAZ adjacent to welds.

The precipitated carbides are com-bined with Chromium thereby depletingthe adjacent areas of this vital elementwhich provides for the durable, toughpassive film. Sensitization is unlikely tolead to intergranular corrosion in most

atmospheric and fresh water exposures,but it can lead to attack in aggressive(high sediment, high chloride) environ-ments where the depleted regions actas point defects disrupting the continu-ous passive film.

If heat tint is not prevented from form-ing, it should be removed by pickling,grinding with an abrasive tool such as arotating silicon carbide impregnatedfiberbrush or electropolishing. Rathercomplex pipe sections of stainless steelpiping are routinely cleaned in the fieldvia grinding, pickling or electropolishing.

OTHER JOIN IN GM ET H OD S

The bulk of the aforementioned tech-nical information presented hasassumed welding to be employed for

joining and therefore addressed poten-tial problems associated with pipegreater than 2 NPS or section sizesexceeding .062.

When extending water handling and

delivery systems further downstream at2 NPS or less, additional joining sys-tems become available, specificallycompression and capillary fittings whichemploy non-metallic O-Rings and sol-dering respectively.

Standard O.D. pipe sizes through 2 at.049 wall are available with associatedcompression fittings. This systemrequires no flame as with welding orsoldering; no cutting oils, chips or prepa-ration times as with threading or flanging.The system simply consists of cuttingpipe to a predetermined length, insertioninto a coupling/fitting followed by press-ing the coupling with a pneumatic tool as

provided by the manufacturer.Stainless steel tubing is also available

in O.D.s equivalent to copper water tubethrough 2 at wall thickness representinga 50% reduction in thickness when com-pared to type L copper water tube. Join-ing is accomplished via soldering byemploying copper fittings, manufacturedto ANSI standards, lead free solderssuch as 95-5 ( Tin - Antimony) andfluxes bases upon phosphoric acid orwater soluble chloride based fluxeswhich mandate internal flux removal byflushing subsequent to joint completion.

ADVAN TAGES TOSTAIN LESS S TEEL

Stainless steel does not require a cor-rosion allowance as is needed for ductilecast iron and carbon steel and therebypermits the selection of minimum thick-ness solely based on structural strengthand pressure requirements. An addedadvantage is the reduction in weight oftube and pipe and their ability to be

transported and installed manually in lieuof expensive machinery such as back-hoes or cranes for trench site operations.

The ANSI/NSF standard confirms thatstainless steels are highly resistant toleaching of any species that might cont-aminate potable water. The excellentperformance offered by stainless steeldepends on factors different from thosethat influence the performance of ductilecast iron, galvinized or coated steel, orcopper alloys in potable waters. Thisguide has been developed to assistdesign engineers and operators in

avoiding problems that have occurredwith stainless steel so that the excellentperformance of stainless steel can berealized.


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Table 2 MECHANICAL DEVICES

Acceptable Materials

Material Specific Standard Surface Area-to- CompositionDesignation (Product) Volume Ratio

ReferenceGray Cast Class B ASTM A 126 473 cm2 /L Percent Composition1:Iron (73 in2 /L) Carbon (3.20-3.55), Sil icon (1.60-2.20),

Phosphorus (0.40 max.), Sulphur (0.15 max.Manganese (0.40-0.80), Chrome (0.05-0.40)Aluminum (0.005 max.), Lead (0.005 max.)Tin (0.10 max.), Iron Balance

Stainless UNS S30400 ASTM A 312 3,484 cm2 /L Percent Composition:Steel (Type 304) ASTM A 269 (540 in2/L) Carbon (0.08 max.), Manganese (2.00 m

Phosphorus (0.040 max.), Sulfur (0.030 max.Silicon (0.75 max.), Nickel (8.00-11.0),Chromium (18.0-20.0)

Stainless UNS S30403 ASTM A 312 3,484 cm2 /L Percent Composition:Steel (Type 304L) ASTM A 269 (540 in2 /L) Carbon (0.035 max.), Manganese (2.00 max

Phosphorus (0.040 max.), Sulfur (0.030 max.Silicon (0.75 max.), Nickel (8.00-13.0),Chromium (18.0-20.0)

Stainless UNS S31600 ASTM A 312 3,484 cm2 /L Percent Composition:Steel (Type 316) ASTM A 269 (540 in2 /L) Carbon (0.08 max.), Manganese (2.00 max.)

Phosphorus (0.040 max.), Sulfur (0.030 max.Silicon (0.75 max.), Nickel (11.00-14.0),Chromium (16.0-18.0), Molybdenum (2.0-3

Stainless UNS S31603 ASTM A 312 3,484 cm2 /L Percent Composition:Steel (Type 316L) ASTM A 269 (540 in2 /L) Carbon (0.035 max.), Manganese (2.00 max

Phosphorus (0.040 max.), Sulfur (0.030 maxSilicon (0.75 max.), Nickel (10.0-15.0),Chromium (16.0-18.0), Molybdenum (2.0-3

1 Chemical content will vary from those shown, depending upon wall thickness and othr characteristics of castingpoured from melt, to ensure desired physical properties of the iron in the castings.

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SP ECIFICATION S

Pipe is usually specified to AWWAC220 which allows the use of eitherASTM A312 or A778 or A269 (see Table 1) . Fittings are usually specifiedto ASTM A403 or A774.

ANSI/NSF 61As previously mentioned, stainless

steel is listed as an accepted material tothis standard (see Table 2) . That meansin all applications involving potablewater stainless steel may be used with-out the need to obtain app roval of thematerial from NSF.

AWWA C220Pipe is usually specified to AWWA

C220 which allows the use of eitherASTM A312 or A778 (see Table 1) .Fittings are usually specified to ASTMA403 or A774. Only T304L and T316Lare permitted in pipes 4 and larger;

surface scale and/or heat tint removalare required.

Table 1 SPECIFICATION REQUIREMENTS

Specifications

Pipe/Tube A312 Welded A778 AWWA C220(1) A-269 A-778 A-26Form & Seamless Welded T034L & T316L 304/304L Dimensions

Welded & Seamless Welded T304/304LWelded

Size NPS 1/4-30 3-48O.D. 4 & Greater NPS 3/4, 1 5/8, 7/8, 1-1/4, 1-1/2, 2 1-3/8, 1-5/8, 2

Wall Schedule .062-0.5 (1) .049 .020, .0225, .Thickness 5S-80S .0275, .030, .03

Solution Required As welded (1) Required As weldedAnneal

Mechanical Tensile & Tensile & (1) Hardness HardnessTest Face Bend welded Flange Flange

guided Reverse Reversebend Flatten Flatten

Hydrostatic Required Optional (1) Required RequiredTest

Filler Autogenous/ Matching (1) Autogenous AutogenousMetal Matching

Scale Required Optional Must specify Required Optional

RemovalAssociated ASTM A403 ASTM ASTM A403 Compression Copper CapFitting A774 ASTM A774 self-contained FittingsSpec O-Ring grade ANSI B 16.18

E Vi c- Press ANSI B 16.22

(1) AWWA C220: Allows use of either ASTM A312 or A778.


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ASTMSP ECIFICATION S

The American Society for TestingMaterials covers stainless steel in itsspecifications. The most common arelisted below:

Pipes

ASTM A312Standard specification for seamless

and welded austenitic stainless steelpipes.

This spec ification covers seamlessand straight-seam welded austeniticstainless steel pipe intended for high-temperature and general corrosiveservice.

Pipe FittingsASTM A403

Standard specification for wroughtaustenitic stainless steel pipe fittings.

This specification covers two generalclasses, WP and CR, of wroughtaustenitic stainless steel fittings ofseamless and welded construction cov-ered by the latest revision of ANSIB16.9, ANSI B16.11, ANSI B16.28, MSSStandard Practice SP-79, MSS StandardPractice SP-43 and MSS SP-95.

ASTM A774

Standard specification for as-weldedwrought austenitic stainless steel fittingfor general corrosion service at low ormoderate temperature.

This specification covers five gradesof as-welded wrought austenitic stain-less steel fittings for low-pressure pipingand intended for low and moderate tem-peratures and general corrosive service.

Tubular ProductsASTM A778

Standard specification for welded,unannealed austenitic stainless steeltubular products.

This specification covers straightseam and spiral butt seam weldedunannealed austenitic stainless steeltubular products intended for low andmoderate temperatures and corrosiveservice where heat treatment is not nec-essary for corrosion resistance.

ASTM A269

Standard specification for seamlessand welded austenitic stainless steeltubing for general service.

This specification covers grades ofnominal-wall-thickness, stainless steeltubing for general corrosion-resistanceand low- or high-temperature service.

Joints and FittingsCompression Fittings: Self-Contained

O-RingCapillary Fittings: Copper Fittings;

ANSI B 16.18 & B 16.22Welding: ASME Section IX AWS B2.1

PRODUCTS

Pipe & Tube:These products are enclosed sections

used to transport or carry liquids andgases. Pipe was the first type of productmade for these purposes and has looserdimensional tolerances. Outside diame-ter and wall thickness can vary more inpipe than in tube. Tubing is more refinedwith tighter tolerances on the diameterand wall thickness. Pipe is usually apressure or mechanical type product.Tubing can be pressure, mechanical,structural, ornamental, etc.

Stainless steel pipe and tube are pro-duced by several companies in varioussize ranges (see Table 3) .

Pumps, Valves, Flanges,Castings:

The transfer or delivery of liquids, par-ticularly water, requires equipment for

moving and controlling, in addition to theuse of pipes and tubes for transmission.There are many d ifferent types of theseproducts and many of them are manu-factured out of stainless steel. Onceagain, if stainless steel is used in con-

junction with drinking water, the materialin the specific component is alreadyaccepted by the ANSI/NSF 61 standard.

The American Water Works Associa-tion (AWWA - 6666 W. Quincy Ave.,Denver, CO 80235 Tel: 303-794-7711)has a product directory that lists manu-facturers and suppliers.

Applications Commercial Building Water

Supply Systems Household Plumbing Systems Municipal Potable Water

Treatment Plants Wastewater Treatment Plants Hydroelectric Plants Dams, Locks, Gates Pipes for River Crossings


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SU GGESTION S ONFABRICATION OFP I P I N G S Y S TEM S

Quality work in the fabricating shopand during erection and particularly fieldwelding is essential for a quality job.Whenever possible compression fittingor capillary fitting should be used. Ifwelding is required, utilize reputableorganizations with experience with stain-less steel. Minimum fabrication require-ments should include the following: Proof of acceptable welding procedure

specifications for the work to be per-formed and verified welder perfor-mance qualifications. The engineerand/or customer should review andverify both. Suggested guides areASME Section IX and AWS B2.1

Require full penetration welds, free ofcracks, overlaps and c old laps.

Limit weld reinforcement and concaveroot (1/16 in. (1.6 mm) or as agreed).

Limit on undercut 1/32 in. (0.8 mm) or10% on base metal thickness, whichever is less.

Require prevention or removal of heattint on all water side surfaces.

Provide for secure end c losure afterwelding to remain in place until finalassembly.

TESTIN G AN DM A IN TEN A N C E

Provide for prompt and completedrainage of the piping system afterhydrostatic testing.

Establish a schedule to flush out sedi-ment and debris on the horizontal runsof raw water piping.

During downtimes, drain completelyand dry or, alternatively, circulatewater for one hour every two days.

Check for manganese/iron deposits inraw water lines going to green sand fil-ters and flush or hydroblast to clean asneeded.

Provide proper ventilation to avoidhigh chlorine vapor areas.

The Specialty Steel Industry of NorthAmerica would like to thank the follow-ing organizations for their contributionto this handbook:Nickel Development Institute (NiDI)214 King Street West, Suite 510Toronto, Ontario Canada M5H 3S6416-591-7999Consultants to the NickelDevelopment Institute:R.E. AveryS. LambA.H. Tuthill(Note: NiDI has workshops and othertechnical publications on water andwater handling applications)

Steel Service Center InstituteKey Center - Suite 2400127 Public Square,Cleveland, OH 44114-1216216-694-3940(Note: Steel service centers stockstainless steel pipe and tube products)

REFEREN CES

ANSI/NSF 61NSF International3475 Plymouth RoadP.O. Box 130140Ann Arbor, MI 48113-0140

800-NSF-MARK

ASTM Specifications Volume 01.01American Society for TestingMaterials

1916 Race StreetPhiladelphia, PA 19103-1187

ACKN OW LEDGM EN TS

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Stainless Steel for Water Handling