31968562 pressure vessel design12

7/30/2019 31968562 Pressure Vessel Design12

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DESIGNof

PRESSURE VESSELDisusun oleh : Agus Suwarno PUSPETINDO - GRESIK


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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.


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Main Pressure Vessel Components- Shell - Head - Nozzle - Support


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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.


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HEAD Head is part/component to close at both end of shell. Heads are typically curvedrather than flat. Curved configurations are stronger and allow the heads to bethinner, lighter, and less expensive than flat heads. Heads can also be used inside a vessel.


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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.


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Nozzles are applications:

used

for

the

following

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).


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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 thevessel is not a consideration in the design of the support since the support isnot pressurized. Temperature may be a consideration in support design from thestandpoint of material selection and provision for differential thermal expansion.


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Material Selection Factors The main factors that influence material selection are: Strength Corrosion Resistance Resistance to Hydrogen Attack Fracture Toughness Fabricability


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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


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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 addresscorrosion in pressure vessels is to specify a corrosion allowance. A corrosionallowance is supplemental metal thickness that is added to the minimum thicknessthat is required to resist the applied loads.


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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 approximately600F (315,5C), monatomic hydrogen not only causes cracks to form but also attacksthe steel. Hydrogen attack differs from corrosion in that damage occurs throughout the thickness of the component, rather than just at its surface, and occurswithout any metal loss. In addition, once hydrogen attack has occurred, the metal cannot be repaired and must be replaced. Instead, materials are selected suchthat they are resistant to hydrogen attack at the specified design conditions.


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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 bedetermined by the magnitude of the impact energy that is required to fracture aspecimen 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.


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Fabricability Fabricability refers to the ease of construction and to any special fabricationpractices 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.


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DESIGN 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.


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DESIGN PRESSURE Generally, design pressure is the maximum internal pressure, that is used in themechanical design of a pressure vessel. For full or partial vacuum conditions,the design pressure is applied externally and is the maximum pressure differencethat 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)


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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.


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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 tothe liquid level in the vessel. System pressure drop. Normal pre-startup activities or other operating conditions that may occur (e.g., vacuum), that should beconsidered in the design.


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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 temperatureused in design shall be the lowest expected in service.


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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.


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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 designpressure. Weight of the vessel and its normal contents under operating or testconditions. Superimposed static reactions from the weight of attached equipment(e.g., motors, machinery, other vessels, piping, linings, insulation). Loads atattached of internal components or vessel supports.


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Wind, snow, and seismic reactions. Cyclic and dynamic reactions that are causedby pressure or thermal variations, or by equipment that is mounted on a vessel,and mechanical loadings. Test pressure combined with hydrostatic weight. Impactreactions such as those that are caused by fluid shock. Temperature gradients within a vessel component and differential thermal expansion between vessel components.


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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 1of Section II, Part D.(see UG-23).


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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)


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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 notprovided, 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 inthe thickness of the material over that determined by the design formulas, or byusing some other suitable method of protection. (see UG-25)


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THICKNESS SHELL UNDER INTERNAL PRESSURE(CYLINDRICAL SHELL)See UG-27


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CIRCUM STRESS (LONGITUDINAL JOINT)t = minimum required thickness P = internal design pressure R = inside radius ofthe shell course under consideration, (pertimbangkan C.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 or spherical shells, or the efficiency of ligaments between openings, which ever is less.

OR


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LONGITUDINAL STRESS (CIRCUM JOINT)

OR


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CONTOHThickness for Internal Pressure Inside Diameter - 10 - 6 Design Pressure - 650 psg Design Temperature - 750F Shell & Head Material - SA-516 Gr. 70 Corrosion Alloance - 0.125 in. 2:1 Semi-Elliptical heads, seamless 100% radiography Vessel invapor service


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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)


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SPHERICAL SHELL


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THICKNESS OF SHELL AND TUBES UNDER EXTERNAL PRESSURE


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SYMBOL DEFINED A = factor determined from Fig. G in Subpart 3 of Section II, Part D. Cylindershaving Do /t values less than 10, see UG-28(c)(2). B = p factor determined fromthe applicable material chart or table in Subpart 3 of Section II, Part D for maximum design metal temperature Do = outside diameter of cylindrical shell courseor tube E = modulus of elasticity of material at design temperature. Taken fromthe applicable chart in Subpart 3 of Section II, Part D. L = total length, in.(mm), of a tube between tube sheets, or design length of a vessel section between lines of support.


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P = external design pressure. Pa = calculated value of maximum allowable external working pressure for the assumed value of t Ro = outside radius of spherical shell. t = minimum required thickness of cylindrical shell or tube, or sphericalshell, in. (mm) ts = nominal thickness of cylindrical shell or tube, in. (mm)


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CYLINDRICAL SHELL AND TUBES Hitung nilai dari Do/t.A. Bila nilai Do/t 10, ikuti step berikut: Step 1, Asumsikan nilai tebal t, danhitung rasio L/Do dan Do /t. Step 2, Lihat Fig. G pada Subpart 3 of Section II,Part D. Pakai nilai L/Do sesuai perhitungan 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.


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Step 3, Tarik garis dari L/Do ke kurva Do/t sehingga ada titik potongan. Dari titik tersebut ditarik garis lagi ke area factor A untuk memperoleh nilai factor A. Step 4, Cari nilai B, dengan memasukkan nilai 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). Tentukan kurva material/temperaturedisain yang akan dipakai.


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Contoh grafik untuk mencari nilai B


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Step 5, Tarik garis dari nilai A ke kurva material/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 nilaiB yang didapat dari step 5 dengan rumus:


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

Step 8, Bandingkan nilai Pa yang didapat dari perhitungan di step 6 dan 7 dengandesign pressure P. Jika Pa


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Bila Do/t < 10. Step1, langkah kerja sama seperti step 1s/d 5 untuk Do/t10 untukmemperoleh nilai B: Jika Do/t < 4, nilai factor A bisa dihitung dengan rumusan:

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


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

Step 3, hitung Pa2 dengan rumusan:


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Step 4, Bandingkan nilai Pa1 dan Pa2, yang lebih kecil diambil sebagai Pa. Bandingkan Pa dengan P, jika Pa


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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. Tarikgaris ke arah kurva material/temperature hingga ketemu titik perpotongan. Bilanilai A berada di sebelah kiri kurva, perhitungan Pa mengikuti step 5.


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Step 3, cari nilai B dengan menarik perpotongan ke area B. Step 4, hitung nilaiPa,dengan rumus:

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


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Step 6, bandingkan Pa terhadap P, bila: Pa


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BUKAAN NOZZLE


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


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A41, A42, A43 = cross-sectional area of various welds available for reinforcement (see Fig. UG-37.1) A5 = cross-sectional area of material added as reinforcement (see Fig.UG-37.1) c = corrosion allowance D = inside shell diameter Dp =outside diameter of reinforcing element (actual size of reinforcing element may exceedthe limits of reinforcement establish ed by UG-40; however, credit cannot be taken for any material outside these limits).


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d = finished diameter of circular opening or finished dimension (chord length atmid surface of thickness excluding excess thick ness available for reinforcement) of non radial opening in the plane under consider ation, in.(mm) [see Figs. UG-37.1 and UG-40] E = 1 (see definitions for tr and trn) E1 = 1 when an openingis in the solid plate or in Category B butt joint; or = joint efficiency obtained from Table UW-12 when any part of the opening passes through any other weldedjoint


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F = correction factor which compensates for the varia tion in internal pressurestresses on different planes with respect to the axis of a vessel. A value of 1.00 shall be used for all configu rations except that Fig. UG-37 may be used forintegrally 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 reinforcement established by UG-40.)


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K1 = spherical radius factor (see definition of tr and Table UG-37). L = lengthof projection defining the thickened portion of integral reinforcement of a nozzle neck beyond the outside surface of the vessel wall [see Fig. UG-40 sketch (e)] P = internal design pressure (see UG-21), psi (MPa) R = inside radius of the shell course under consideration Rn = inside radius of the nozzle under consideration S = allowable stress value in tension (see UG23), psi (MPa)


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Sn = allowable stress in nozzle, psi (MPa) (see S, above) Sv = allowable stressin vessel, psi (MPa) (see S, above) Sp = allowable stress in reinforcing element(plate), psi (MPa) (see S, above). fr = strength reduction factor, not greaterthan1.0 [see UG-41(a)] fr1 = Sn /Sv for nozzle wall inserted through the vesselwall. 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 orSp) /Sv fr4 = Sp /Sv


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t = specified vessel wall thickness,24 (not including forming allowances). For pipe it is the nominal thickness less manufacturing under tolerance allowed in the pipe specification. 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 wall thickness 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)


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Design for Internal Pressure. The total cross-sectional area of reinforcement Arequired under internal pressure shall be not less than A = dtrF + 2tn trF(1 fr1) Design for External Pressure The reinforcement required for openings in single-walled vessels subject to external pressure need be only 50% of that requiredin formula above.


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MODEL SAMBUNGAN NOLLZE YANG DITERIMA SESUAI UW 16.


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31968562 pressure vessel design12

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