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PRESSURE VESSELS

DESIGN PROCEDURES

Engr. Butch G. Bataller ChE 192 Process Equipment Design

September 20, 2011

Pressure Vessels

Closed vessel having an internal pressure between 15 psig to 3000 psig

ASME Boiler and Pressure Vessel Code contains rules for the design, fabrication and inspection of boilers and pressure vessels

May include reflux drum, storage tanks, heat exchangers, chemical reactors, distillation columns, absorption tower, stripping columns, etc.

PV Design: Shell Thickness

In general, the minimum wall thickness of welded metal plates subject to pressure, excluding corrosion allowances, should not be less than 2.4 mm

a function of the ultimate tensile strength of the metal at operating temperature, operating pressure, vessel diameter and welding joint efficiency

PV Design: Shell Thickness

For a cylinder based on Inside diameter

0.6pPRt C

SE P

wheretp = shell thickness required (inch) [m]P = Internal design gauge pressure (psig) [kN/m2]R = Inside Radius (inch) [m]S = Allowable stress (psi) [kN/m2]E = Joint efficiency factor (Table 6-2)C = Corrosion allowance (inch) [m]

PV Design: Shell Thickness

For a cylinder based on Inside diameter

0.6pPRt C

SE P

Provided that

• tp less than or equal to or

• Pressure is less than or equal to 0.385 SE (Jawad and Farr, 1988)

2R

PV Design: Shell Thickness

For a cylinder based on Outside diameter

wheretp = shell thickness required (inch) [m]P = Internal gauge pressure (psig) [kN/m2]R = outside Radius (inch) [m]S = Allowable stress (psi) [kN/m2]E = Joint efficiency factor (Table 6-2)C = Corrosion allowance (inch) [m]

0.4pPRt C

SE P

PV Design: Shell Thickness

Allowance for Vertical PV

For 10>( L/Di)2/ Pd>1.34:

tv = tp[0.75 + 0.22E( L/Di)2/Pd]

If (L/Di)2/Pd < 1.34, tv=tp

PV Design: Shell Thickness

Corrosion Allowance 1/8 inch for noncorrosive conditions

¼ for corrosive environments.

ts = tV + tc

PV Design: Shell Thickness

For Vacuum Vessels2

0.5

2.6

0.45

em

oc

e e

o o

T ED

PT TD D

where

Pc = Collapsing pressure (psi)Te = Thickness to withstand external pressure (inch)Do = Outside diameter (inch)Em = Material’s modulus of elasticity [Table 6-4]

** Te must be high enough so that Pc is five times greater than the difference between atmospheric pressure and design vacuum pressure

PV Design: Shell Thickness

For Vacuum Vessels (alternate)tE=1.3(PdL/EmDo)4

tEC=L(0.18Di-2.2 )x 10 -5- 0.19tV = tE + tEC

wherePd = internal design gauge pressure (psi)Te = Thickness to withstand external pressure (inch)Do = Outside diameter (inch)Em = Material’s modulus of elasticity

PV Design: Shell Thickness

Spherical Vessels

p

p

t2.0RSEt

P

whereP = internal design gauge pressure (psig)R = Inside Radius (inch)tp = Minimum required thickness (inch)E = Lowest joint efficiencyS = Max allowable stress (psi)

J

i

SEPorrt

665.0356.0

Design Temperature

design temperature may be equal to operating temperatue plus 50oF

Design Pressure

Operating Pressure ,Po (psig)

Design Pressure ,Pd (psig)

0 -5 1010 – 1,000 P= exp{0.60608 + 0.91615[ln Po]

+ 0.0015655 [ ln Po ]2 }1,000 + 1.1Po

Material of Construction

Carbon Steel >>> Non-corrosive environment, T= (-20 to 650 OF)

Low Alloy Steel >>> Non-corrosive environment, T= (650 to 900 OF)

Stainless Steel 300 Series >>> can be used up to 1,500 OF

Modulus of Elasticity Values

Temperature (ºF)

Psi x 106

Carbon Steel Low-alloy Steel

-20 30.2 30.2200 29.5 29.5400 28.3 28.6650 26.0 27.0700 - 26.6800 - 25.7900 - 24.5

Recommended Stress Values Joint efficiencies Recommended stress values

Metal Temp., ºC S, kPaFor double-welded butt joints If fully radiographed = 1.0 If spot-examined = 0.85 If not radiographed = 0.70

In general, for spot examined If electric resistance weld = 0.85 If lap-welded = 0.80 If single-butt-welded = 0.60

Carbon steel(SA-285, Gr. C)

Low-alloy steelfor resistance toH2 and H2S(SA-387, Gr. 12C1.1)High-tensile steelfor heavy-wallvessels(SA-302, Gr.B)

High-alloy steelfor cladding andcorrosion resistanceStainless 304(SA-240)

Stainless 316(SA-240)

Nonferrous metals Copper (SB-11) Aluminum(SB-209, 1100-0)

-29 to 343399454

-29 to 427510565649

-29 to 399454510538

-29343427538

-29345427538

3820438

204

94,50082,70057,20094,50075,80034,5006,900

137,900115,80069,00042,750

128,90077,20072,40066,900

128,90079,30075,80073,100

46,20020,70015,9006,900

Sample Problem

Determine the thickness of a 5 meter inside diameter spherical tank for handling a corrosive liquid at a design pressure and temperature of 300KPa and 27F, respectively. The material of construction is made of carbon steel.

Sample Problem

If the height of the tank is 35m, what is the thickness of the tank incorporating earthquake and wind load?

What if the given pressure is an operating pressure?

Types of Welded JointsButt jointCorner jointEdge jointLap jointT joint

Square Butt Joints

Used to butt weld light sheet metal1/16 to 3/16 thick metal.

Beveled Butt Joints

Used to butt weld heavier pieces of metal together

3/8 to ½ inch metal can welded using a single V or U joint

½ Inch metal and up can be welded using a double V or U joint

Beveled Cont.

Corner JointsUsed to join to pieces of metal that are

approximately right angles to each other

Closed corner joint is used on light sheet metal were strength is not required at the joint

Half open corner joint is used on heavier metal when welding can only be done on one side. Used when load is not severe.

Corner Cont.

Open corner joint is used on heavy material. It is the strongest of the corner joints

Corner joints on heavy material are welded on both sides The outside first then reinforced on the inside

Corners Cont.

Edge Joints

Used to join two parallel or nearly parallel pieces of metal (0.25 in thick or less). Not very strong.

Used mainly to join edges of sheet metal, reinforce flanges of I beams, and mufflers.

Lap Joints

Used to join two overlapping pieces of metal

Single lap joint welded from one sideSingle lap joint welded from two sides

develops full strengthOff set lap joint is used when two pieces of

metal need to be joined in the same plain.

Lap Joints Cont.

A- single lap joint, one weld.

B- single lap joint, two welds.

C- offset lap joint.

Tee Joints

Used to join two pieces of metal that are approximately 90 degrees to each other, but the surface of one piece of metal is not in the same plain as the other metal.

Tee Joints Cont.

A- plain teeB- single beveledC- double beveledD- single JE- double J

Types of Welds

Fillet weld- basic weld used. Used when joining two pieces of metal without preparing the surface of the metal first.

Groove weld- basic weld, used when preparing the metal before welding it into place.

Fillet Welds

Groove Welds

Weld/Joint Efficiency

Welding – heats the metal surrounding the welding area

- results in warping, shrinking of the welded area

Stress Relieving - required to release locked up localized stress

- annealing or hammering

Radiographing - locate weld defects and other structural trouble- welded joints are exposed to x-ray to detect excessive porosity, defective fusion and other defects in the welding process

Weld/Joint Efficiency

For carbon steels (t ≤ 1.25 in) requires only 10% x-ray check E = 85%

For thicker walls requires 100% x-ray check E = 100%

Weld/Joint Efficiency

Longitudinal joints should be butt- weldedVessels in lethal application should be

butt-welded and fully radiographedAll vessels fabricated on carbon or alloy

steel requires post-heat treatment

All welded joints of cryogenic tanks must be butt welded, postweld heat treated and X- ray examined

For double butt joint, the following are the corresponding efficiencies

Full radiography 100%Spot radiography 85%No radiography 70 %

** when welded joint efficiency is not known, assume a no spot radiography

Welded Joints Categories

Category A – Longitudinal welded joints within main parts (shells, heads, cones, flat plates, nozzles, and the attachment weld of a hemispherical head to a shell)

Welded Joints Categories

Catefory B – Circumferential welded joints within the main parts (shell, cone, nozzles and the attachment joint between formed heads (elliptical and torispherical) and shell).

Welded Joints Categories

Category C – welded joints connecting flanges, tubesheets, flat heads to main shell, formed heads, transition in diameter, nozzles, or any welded joint connecting one side plate to another side plate of a flat-sided vessel

Category C – welded joints connecting flanges, tubesheets, flat heads to main shell, to formed heads, to transition in diameter, to nozzles, or any welded joint connecting one side plate to another side plate of a flat-sided vessel

Welded Joints Categories

Category D – welded joints connecting nozzles to main shells, spheres, formed heads, flat heads, flat-sided vessels.

Category C – welded joints connecting flanges, tubesheets, flat heads to main shell, to formed heads, to transition in diameter, to nozzles, or any welded joint connecting one side plate to another side plate of a flat-sided vessel

Maximum Allowable Joint Efficiencies for Arc and Gas Welded Joints

Type No.

Joint Description Limitations Joint Category

Degree of Radiographic Examination

a b cFull Spot None

(1)Butt joints as attained by double-welding or by other means which will obtain the same quality of deposited weld metal on the inside and outside weld surfaces to agree with the requirements of UW-35; welds using metal backing strips which remain in place are excluded.

None A, B, C & D

1.0 0.85 0.70

(2)Single welded butt joint with backing strip other than those included in (1)

(a) None except as shown in (b) below

A, B, C & D

0,90 0.80 0.65

(b) Circumferential butt joints with one plate offset, see UW-13(c) and Fig. UW-13.1 (k).

A, B & C

0.90 0.80 0.65

Type No.

Joint Description Limitations Joint Category

Degree of Radiographic Examination

a b c

Full Spot None

(3) Single-welded butt joint without use of backing strip

Circumferential butt joints only. Not over 5/8in. thick and not over 24in outside diameter

A, B & C

NA NA 0.60

(4)Double full fillet lap joint Double full fillet lap joint

longitudinal joints not over 3/8in. thick

A NA NA 0.55

circumferential joints not over 5/8in. thick

B & C NA NA 0.55

Type No.

Joint Description Limitations Joint Category

Degree of Radiographic Examination

a b cFull Spot None

(5) Single full fillet lap joints with plug welds confirming to UW-17

Single full fillet lap joints with plug welds confirming to UW-17

(a) Circumferential joints2 for attachment of heads not over 24in. outside diameter to shells not over 1/2in. thick.

B NA NA 0.50(b) Circumferential joint for the attachment to shells of jackets not over 5/8in. in nominal thickness where the distance from the center of the plug weld to the edge of the plate is not less than 1-1/2 times the diameter of the hole for the plug.

C NA NA 0.50

(6) Single full fillet lap joints without plug welds

(a) For the attachment of heads convex to pressure to shells not over 5/8in. required thickness. only with use of fillet weld on

inside of shells, or(b) For attachment of heads having pressure on either side. To shells not over 24in. inside diameter and not over 1/4in. required thickness with fillet weld on outside of head flange only.

A & B NA NA 0.50