PRESSURE VESSEL

DESIGN of

Disusun oleh : Agus Suwarno

PUSPETINDO - GRESIK

• Pressure vessels are used in many industries (e.g., hydrocarbon processing, chemical, power, pharmaceutical, food and beverage).

• The mechanical design of most pressure vessels is done in accordance with the requirements contained in the ASME Boiler and Pressure Vessel Code, Section VIII.

Main Pressure Vessel Components

- Shell- Head- Nozzle- Support

SHELL

• The shell is the primary component that contains the pressure. Pressure vessel shells are welded together to form a structure that has a common rotational axis. Most pressure vessel shells are either cylindrical, spherical, or conical in shape.

HEAD

• Head is part/component to close at both end of shell.

• Heads are typically curved rather than flat.• Curved configurations are stronger and

allow the heads to be thinner, lighter, and less expensive than flat heads. Heads can also be used inside a vessel.

NOZZLES

• A nozzle is a cylindrical component that penetrates the shell or heads of a pressure vessel. The nozzle ends are usually flanged to allow for the necessary connections and to permit easy disassembly for maintenance or access.

• Nozzles are used for the following applications:– Attach piping for flow into or out of the vessel.– Attach instrument connections, (e.g., level

gauges, thermowells,or pressure gauges)– Provide access to the vessel interior at

manways.– Provide for direct attachment of other

equipment items, (e.g., aheat exchanger or mixer).

SUPPORT

• The type of support that is used depends primarily on the size and orientation of the pressure vessel. In all cases, the pressure vessel support must be adequate for the applied weight, wind, and earthquake loads.

• The design pressure of the vessel is not a consideration in the design of the support since the support is not pressurized.

• Temperature may be a consideration in support design from the standpoint of material selection and provision for differential thermal expansion.

Material Selection Factors

• The main factors that influence material selection are:

• Strength• Corrosion Resistance• Resistance to Hydrogen Attack• Fracture Toughness• Fabricability

Strength

• Strength is a material's ability to withstand an imposed force or stress. Strength is a significant factor in the material selection for a particular application.

• Strength determines how thick a component must be to withstand the imposed loads

Corrosion Resistance

• Corrosion is the deterioration of metals by chemical action. A material's resistance to corrosion is probably the most important factor that influences its selection for a specific application.

• The most common method that is used to address corrosion in pressure vessels is to specify a corrosion allowance. A corrosion allowance is supplemental metal thickness that is added to the minimum thickness that is required to resist the applied loads.

Resistance to Hydrogen Attack

• If this hydrogen diffusion continues, pressure can build to high levels within the steel, and the steel can crack.

• At elevated temperatures, over approximately 600°F (315,5C), monatomic hydrogen not only causes cracks to form but also attacks the steel. Hydrogen attack differs from corrosion in that damage occurs throughout the thickness of the component, rather than just at its surface, and occurs without any metal loss.

• In addition, once hydrogen attack has occurred, the metal cannot be repaired and must be replaced.

• Instead, materials are selected such that they are resistant to hydrogen attack at the specified design conditions.

Fracture Toughness

• Fracture toughness refers to the ability of a material to withstand conditions that could cause a brittle fracture. The fracture toughness of a material can be determined by the magnitude of the impact energy that is required to fracture a specimen using Charpy V-notch test.

• Generally , the fracture toughness of a material decreases as the temperature decreases. The fracture toughness at a given temperature varies with different steels and with different manufacturing and fabrication processes.

Fabricability

• Fabricability refers to the ease of construction and to any special fabrication practices that are required to use the material.

• Pressure vessels commonly use welded construction. The materials used must be weldable so that individual components can be assembled into the completed vessel.

• Design Conditions and Loadings• All pressure vessels must be designed for the

most severe conditions of coincident pressure and temperature that are expected during normal service. Normal service includes conditions that are associated with:– Start up.– Normal operation.– Deviations from normal operation that can be

anticipated (e.g., catalyst regeneration or process upsets).

– Shutdown.

DESIGN

DESIGN PRESSURE• Generally, design pressure is the maximum internal

pressure, that is used in the mechanical design of a pressure vessel.

• For full or partial vacuum conditions, the design pressure is applied externally and is the maximum pressure difference that can occur between the atmosphere and the inside of the pressure vessel.

• Some pressure vessels may experience both internal and external pressure conditions at different times during their operation.

• The mechanical design of the pressure vessel in this case is based on which of these is the more severe design condition. (see UG-21)

Operating Pressure

• Operating pressure is is the pressure to be used in operating condition.

• The operating pressure must be set based on the maximum internal or external pressure that the pressure vessel may encounter.

• The following factors must be considered:– Ambient temperature effects.– Normal operational variations.– Pressure variations due to changes in the

vapor pressure of the contained fluid.– Pump or compressor shut-off pressure.– Static head due to the liquid level in the

vessel.– System pressure drop.– Normal pre-startup activities or other

operating conditions that may occur (e.g., vacuum), that should be considered in the design.

Design Temperature

• The design temperature of a pressure vessel is the maximum fluid temperature that occurs under normal operating conditions, plus an allowance for variations that occur during operation.

• The maximum temperature used in design shall be not less than the mean metal temperature (through the thickness) expected under operating conditions for the part considered (see 3-2).

• The minimum metal temperature used in design shall be the lowest expected in service.

Operating Temperature

• The Operating temperature is fluid temperature that occurs under normal operating conditions.

• The operating temperature must be set based on the maximum and minimum metal temperatures that the pressure vessel may encounter.

Other Loadings

• The loadings that must be considered to determine the minimum required thicknesses for the various vessel components are as follows:– Internal or external design pressure.– Weight of the vessel and its normal contents

under operating or test conditions.– Superimposed static reactions from the

weight of attached equipment (e.g., motors, machinery, other vessels, piping, linings, insulation).

– Loads at attached of internal components or vessel supports.

– Wind, snow, and seismic reactions.– Cyclic and dynamic reactions that are caused

by pressure or thermal variations, or by equipment that is mounted on a vessel, and mechanical loadings.

– Test pressure combined with hydrostatic weight.

– Impact reactions such as those that are caused by fluid shock.

– Temperature gradients within a vessel component and differential thermal expansion between vessel components.

MAXIMUM ALLOWABLE STRESS VALUE

• The maximum allowable stress value is the maximum unit stress permitted in a given material used in a vessel constructed under these rules.

• The maximum allowable tensile stress values permitted for different materials are given in Subpart 1 of Section II, Part D.(see UG-23).

MAXIMUM ALLOWABLE WORKING PRESSURE

• The maximum allowable working pressure for a vessel is the maximum pressure permissible at the top of the vessel in its normal operating position at the designated coincident temperature specified for that pressure.

• It is the least of the values found for maximum allowable working pressure for any of the essential parts of the vessel and adjusted for any difference in static head that may exist between the part considered and the top of the vessel.(see UG-98)

CORROSION• The user or his designated agent shall specify

corrosion allowances other than those required by the rules of this Division. Where corrosion allowances are not provided, this fact shall be indicated on the Data Report.

• Vessels or parts of vessels subject to thinning by corrosion, erosion, or mechanical abrasion shall have provision made for the desired life of the vessel by a suitable increase in the thickness of the material over that determined by the design formulas, or by using some other suitable method of protection. (see UG-25)

THICKNESS SHELLUNDER

INTERNAL PRESSURE

(CYLINDRICAL SHELL)See UG-27

CIRCUM STRESS (LONGITUDINAL JOINT)

t = minimum required thickness P = internal design pressure R = inside radius of the shell course

under consideration, (pertimbangkanC.A.)

S = maximum allowable stress value(see UG-23 and the stress limitations specified in UG-24)

E = joint efficiency for, or the efficiency of,appropriate joint in cylindrical orspherical shells, or the efficiency ofligaments between openings, whichever is less.

OR

LONGITUDINAL STRESS (CIRCUM JOINT)

OR

CONTOHThickness for Internal Pressure• Inside Diameter - 10’ - 6”• Design Pressure - 650 psig• Design Temperature - 750°F• Shell & Head Material - SA-516 Gr. 70• Corrosion Allowance - 0.125 in.• 2:1 Semi-Elliptical heads, seamless• 100% radiography• Vessel in vapor service

• The minimum thickness or maximum allowable working pressure of cylindrical shells shall be the greater thickness or lesser pressure as given by formula Circumferential Stress (Longitudinal Joints) or Longitudinal Stress (Circumferential Joints)

SPHERICAL SHELL

THICKNESS OF SHELL AND TUBES

UNDEREXTERNAL PRESSURE

SYMBOL DEFINED

• A = factor determined from Fig. G in Subpart 3 of Section II, Part D. Cylinders having Do /t values less than 10, see UG-28(c)(2).

• B = p factor determined from the applicable material chart or table in Subpart 3 of Section II, Part D for maximum design metal temperature

• Do = outside diameter of cylindrical shell course or tube• E = modulus of elasticity of material at design temperature.

Taken from the applicable chart in Subpart 3 of Section II, Part D.

• L = total length, in. (mm), of a tube between tube sheets, ordesign length of a vessel section between lines of support.

• P = external design pressure.• Pa = calculated value of maximum allowable

external working pressure for the assumedvalue of t

• Ro = outside radius of spherical shell.• t = minimum required thickness of cylindrical

shell or tube, or spherical shell, in. (mm)• ts = nominal thickness of cylindrical shell or

tube, in. (mm)

CYLINDRICAL SHELL AND TUBES

• Hitung nilai dari Do/t.A. Bila nilai Do/t ≥ 10, ikuti step berikut:– Step 1, Asumsikan nilai tebal t, dan hitung

rasio L/Do dan Do /t.– Step 2, Lihat Fig. G pada Subpart 3 of

Section II, Part D. Pakai nilai L/Do sesuaiperhitungan yang didapat pada step 1:• Bila nilai L/Do >50, maka L/Donya=50.• Jika nilai L/Do < 0.05, maka L/Do nya = 0.05.

• Step 3, Tarik garis dari L/Do ke kurva Do/t sehingga ada titik potongan. Dari titiktersebut ditarik garis lagi ke area factor A untuk memperoleh nilai factor A.

• Step 4, Cari nilai B, dengan memasukkannilai factor A yang diperoleh ke grafik/chart tabular sesuai material yang dipakai, di subpart 3 ASME II D.(contoh fig-CS1untuk carbon steel and low alloy steel). Tentukankurva material/temperature disain yang akan dipakai.

Contoh grafik untuk mencari nilai B

• Step 5, Tarik garis dari nilai A ke kurvamaterial/temperature yang dimaksud. Pada perpotongan garis tsb, tarik garis ke arah area B untuk memperoleh nilai B.

• Step 6, hitung maksimum allowable external pressure (Pa) dengan menggunakan nilai B yang didapat dari step 5 dengan rumus:

• Step 7, Jika nilai A terletak pada sebelah kirikurva material/temperature, perhitungan Pa menggunakan rumus:

• Step 8, Bandingkan nilai Pa yang didapat dari perhitungan di step 6 dan 7 dengan design pressure P. Jika Pa<P, lakukan penghitungankembali dengan menggunakan t yang lebih tebal, sampai diperoleh Pa≥P

• Bila Do/t < 10.• Step1, langkah kerja sama seperti step

1s/d 5 untuk Do/t≥10 untuk memperolehnilai B:– Jika Do/t < 4, nilai factor A bisa dihitung

dengan rumusan:

untuk nilai A ketemu>0.10, ditetapkan A=0,10

• Step 2, Bila nilai B sudah didapat, hitungmaksimum allowable external pressure (Pa1) dengan rumusan:

• Step 3, hitung Pa2 dengan rumusan:

• Step 4, Bandingkan nilai Pa1 dan Pa2, yang lebih kecil diambil sebagai Pa.Bandingkan Pa dengan P, jika Pa<P, hitung kembali dengan menggunakanmaterial yang lebih tebal dengan langkahyang sama sampai diperoleh Pa≥P

EXTERNAL PRESSURE PADA SPHERICAL SHELL

• Step 1, buat asumsi tebal material yang dipakai, t, dan hitung nilai faktor A dengan rumusan:

• Step 2, Masukkan nilai A yang didapat ke chart yang sesuai pada ASME II D. Tarik garis ke arahkurva material/temperature hingga ketemu titikperpotongan. Bila nilai A berada di sebelah kirikurva, perhitungan Pa mengikuti step 5.

• Step 3, cari nilai B dengan menarikperpotongan ke area B.

• Step 4, hitung nilai Pa,dengan rumus:

• Step 5, Hitung nilai Pa dengan rumusberikut, bila nilai A berada disebelah kirigrafik seperti step 2:

• Step 6, bandingkan Pa terhadap P, bila:Pa<P, pakai material yang lebih tebal dan hitung kembali sampai diperoleh Pa≥P

BUKAAN NOZZLE

• A = total cross-sectional area of reinforcementrequired in the plane under consideration(see Fig. UG-37.1) (includes consideration of nozzle area through shell if Sn /Sv<1.0)

• A1 = area in excess thickness in the vessel wall available for reinforcement (see Fig. UG-37.1)includes consideration ofnozzle area through shell if Sn /Sv<1.0)

• A2 = area in excess thickness in the nozzle wallavailable for reinforcement (see Fig.UG-37.1)

• A3 = area available for reinforcement when thenozzle extends inside the vessel wall (seeFig. UG-37.1)

• A41, A42, A43 = cross-sectional area of variouswelds available for reinforcement (see Fig.UG-37.1)

• A5 = cross-sectional area of material added asreinforcement (see Fig.UG-37.1)

• c = corrosion allowance• D = inside shell diameter• Dp =outside diameter of reinforcing element

(actual size of reinforcing element mayexceed the limits of reinforcement established by UG-40; however, credit cannot betaken for any material outside these limits).

• d = finished diameter of circular opening or finished dimension (chord length at midsurface of thickness excluding excess thickness available for reinforcement) of nonradial opening in the plane under consideration, in.(mm) [see Figs. UG-37.1 and UG-40]

• E = 1 (see definitions for tr and trn)• E1 = 1 when an opening is in the solid plate or in

Category B butt joint; or= joint efficiency obtained from Table UW-12

when any part of the opening passesthrough any other welded joint

• F = correction factor which compensates for the variation in internal pressure stresses on different planes with respect to the axis of a vessel.A value of 1.00 shall be used for all configurations except that Fig. UG-37 may be used for integrally reinforced openings in cylindrical shells and cones. [See UW16(c)(1).]

• h = distance nozzle projects beyond the inner surface of the vessel wall. (Extension of the nozzle beyond the inside surface of the vessel wall is not limited; however, for reinforcement calculations, credit shall not be taken for material outside the limits of reinforcementestablished by UG-40.)

• K1 = spherical radius factor (see definition of trand Table UG-37).

• L = length of projection defining the thickened portion of integral reinforcement of a nozzle neck beyond the outside surface of thevessel wall [see Fig. UG-40 sketch (e)]

• P = internal design pressure (see UG-21), psi(MPa)

• R = inside radius of the shell course underconsideration

• Rn = inside radius of the nozzle underconsideration

• S = allowable stress value in tension (see UG-23), psi (MPa)

Sn = allowable stress in nozzle, psi (MPa) (see S,above)

• Sv = allowable stress in vessel, psi (MPa) (see S,above)

• Sp = allowable stress in reinforcing element (plate), psi (MPa) (see S, above).

• fr = strength reduction factor, not greater than1.0 [see• UG-41(a)]• fr1 = Sn /Sv for nozzle wall inserted through the

vessel wall.• fr1 = 1.0 for nozzle wall abutting the vessel wall and

for nozzles shown in Fig. UG-40, sketch (j), (k),(n) and (o).

• fr 2 = Sn /Sv• fr3 = (lesser of Sn or Sp) /Sv• fr4 = Sp /Sv

• t = specified vessel wall thickness,24 (not including formingallowances). For pipe it is the nominal thickness lessmanufacturing under tolerance allowed in the pipespecification.

• te = thickness or height of reinforcing element (see Fig. UG-40)• ti = nominal thickness of internal projection of nozzle wall• tr = required thickness of a seamless shell based on the circum

ferential stress, or of a formed head, computed by the rules of this Division for the designated pressure.

• tn = nozzle wall thickness.24 Except for pipe, this is the wallthickness not including forming allowances. For pipe, use the nominal thickness [see UG-16(d)].

• trn = required thickness of a seamless nozzle wall• W = total load to be carried by attachment welds (see UG-41)

• Design for Internal Pressure.• The total cross-sectional area of

reinforcement A required under internal pressure shall be not less thanA = dtrF + 2tn trF(1 − fr1 )

• Design for External PressureThe reinforcement required for openings in single-walled vessels subject to external pressure need be only 50% of that required in formula above.

MODEL SAMBUNGAN NOLLZE YANG DITERIMA SESUAI UW 16.