Comparison Table Between Different Pressure Vessel Codes

1/12

COMPARISON TABLE BETWEEN DIFFERENT DESIGN BPV CODES -

DESIGN Item

Description Theory and Design

1

Minimum Thickness

2

Div 1 Membrane- Maximum Stress, generally elastic analysis.

Little if any stress analysis required, pure membrane without consideration of discontinuities controlling stress concentrations. Div 1 is more based on design by rules (cookie cutter formulas). The Code philosophy is such that requirements and details under the design rules provided in the Code cannot and must not be overruled by engineering judgments and analysis.

1.6 mm (0.0625 in), after forming, regardless of product form and material (exceptions listed in 4.1.2).

Thk for cylindrical shell , t = PR/(SE-0.6P). For ellipsoidal heads, t= PD/(2SE-0.2P).

Additional to this , a corrosion allowance has to be specified to arrive at a final nominal thickness. tn = tr +tc

ASME VIII - 2007 Div 2 Design by analysis. ASME Div. 2 was first developed in the early sixties to provide alternatives to the rules of Section VIII, Div 1. However, it was completely rewritten for 2007 and the basis for failure of theory was changed from the maximum shear stress theory to the maximum distortion energy theory (von Mises criteria).

Provisions are made so that design analyses may be carried out to overrule mandatory requirements through the use of Div 2 rules. Thus it is possible now to use engineering analysis to overrule requirements established as rules.

Thickness calculation is given by t= D/2(exp(P/SE)-1) for cylindrical shell, always lower than Div 1. The user shall determine the required thk (minimum : 1/16"), including the tolerance thk over the life of the vessel and specify such in the User’s Design Specification. The Manufacturer shall add the required allowance to all minimum required thicknesses in order to arrive at the minimum ordered material thickness. Under any circumstance shall the required thk be less than that specified in 4.1.2. (exceptions). Formula for calculating thickness of a cylindrical shell is the same as that used in PD 5500 for Div 2, but for ellipsoidal heads, formula is according to Code Case 2260, or the use of Part 5 Design by Analysis Rules, if D/t > 2000

Div 3 Applies to high pressure vessels ( 10,000 psi ). Same as Div 2. Maximum Distortion Energy Theory (von Mises criteria) is the backbone of the whole Code. Written in the same fashion Div 2. was re-written. Some design rules provided; fatigue analysis required; fracture mechanics evaluation required unless provenleak-before-burst; residual stresses become significant and may be positive factors (i.e. autofrettage).

PD 5500-2003

Thicknesses are given by: PD/(2S-P), for ellipsoidal and torispherical ends the design shall be according to Figure 3.5-2 and Table 3.5-1.

EN- 13445 (2004)

PED- 2009

Comments

A reference, but not mandatory, way of demonstrating conformity to the Essential Safety Requirements of the PED is to use the new European harmonised standard EN 13445 (Unfired Pressure Vessels). This was prepared

by CEN TC54 and was cited in the EC Official Journal in 2002. EN 13445-5:2009, Annex C specifies requirements for the design of access and inspection openings, closing mechanisms and special locking elements.

Code divided into two sections: Simple Pressure Vessels and Pressure Equipment Directive. The rule is that the product of P (operating (bars)) x Volume (capacity(litres)) of vessel shall not exceed 30,000 for SPVD.

Div 2 provides a better engineered vessel with calculated stresses closer to real stresses (because of more detailed design and analysis requirements), combined with more rigorous testing, allows for savings in material costs (thinner parts may be used than otherwise required by Div 1), but is more expensive to fabricate with. Which one to use is an economical decisicion that has to be evaluated for each vessel. Code 2 offers two options for the design of a vessel: Design by Rule, in accordance with the rules of Part 4. Design by Analysis, in accordance with the rules of Part 5. Detailed Stress and Fatigue Analysis are carried out for Div. 2 vessels, resulting in higher allowable stresses being used depending on the specific application in service for the vessel and the actual loads it will encounter in reality, as opposed to "Open Cycle Design" of Div. 1, where vessel is designed with a certain thickness irrespective of future loads (or combination of them). Div. 2 Code vessels are engineered for 3000 psi and up, and can also go into the lower design pressure spectrum of Div 1.

The differences in the wall thicknesses resulting from the designs according to EN 13445 and ASME VIII Div. 1 are low, and, thus, the resulting material and fabrication costs are similar.

The additional costs for the ASME vessels if PED conformity assessment is required are also rather small (some wall thicknesses marginally increased for ASME VIII Div.1, higher testing requirements for the materials) – presuming that the results of the material tests fulfil the requirements.

Weld Joint Efficiency is a new parameter introduced into the Div 2. (It has been used extensively and continuously in Div 1. since the later's conception, and even before Div 2. was ever written). The concept of "weld joint efficiency" depends on the type of weld, as well as the degree on NDE. Div 2. prior to 2007 did not allow anything less than 100% RT and did not have a joint efficiency. Range of applicability to much thinner shells (D/T > 2000).

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Item

Description Heads

Div 1 Different cross-section thicknesses for the same head (for knuckle and crown) NOT allowed under Div 1.

3

Design Temperatures

Div 1 rules extend into creep Div 2 2007 Edition (design range temperatures for the by rules option) now allows into design temperatures that materials used. exceed the creep temperature for the materials used (with the exception of a Code Case). The analysis rules of Part 5 may be used only if the design temperature does not exceed the creep temperature (with minor exceptions).

Materials

Ample choice of materials from Section II, Part D of the Code. However, some material specifications used in Div. 1 do not meet the intent of Div. 2.

4

5

ASME VIII - 2007 Div 2 Div 3 Torispherical Heads with different crown and knuckle thicknesses (cross-section) are allowed . Knuckle thicknessess are calculated as per procedure for knuckle elastic buckling of dished head under internal pressure as described in Div 2 (section 4.3.6.1.b) and dome thicknesses's section is calculated by the spherical shell formula (according to paragraph 4.3.5). Most of thes rules are consistent with the rules of Code Case 2286.

They are based on the test data and the analytical work presented in WRC Bulletins 406 and 462. The design factor used in the elastic buckling range is 2.0 and linearly reduced to 1.67 when the mode of failure becomes yielding.

More restrictive list of materials than offered for Div 1. SA-36, SA-283 and SA-240316 L (Ti) are banned from use.

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments According to Div 2, the minimum required thickness of a spherical shell, or hemi-spherical head, subject to internal pressure, is given by the equation: t= D/2(exp (0.5P/SE)-1)). Part 4 rules.

Div 2 has more restrictive design details and margins for error than Div 1. However, the ASME approach is not always in conformity with some general rules of PED Annex I.7 and PED Annex I.4.31, nor is it set up on the same basis as the European Codes, making them someimes very difficult to compare side-by-side. But as given by the cost estimations of the manufacturers, the extra costs for ASME designs to meet the PED requirements are in general small.

Doesn't cover a range of nonferrous materials covered by other Codes, because of "lack of demand" from the industry.

Use of Design-by-Analysis according to EN 134453 Annex B can decrease the material costs considerably in some cases, especially for more advanced or complex design or in serial production. The increased design costs are easily compensated by the savings for materials and – if applicable – by the savings of the post weld heat treatment costs.

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Item

6

Description

Div 1 Allowable Stresses at Room Prior to 1999, an increase of Temperature 14% under current code, allowing a proportional reduction in thickness. DF started as 5.0 for Div. 1 in 1914. In 1942 it was dropped to 4.0. In the 2007 Code, it is 3.5. For Stainless Steels, higher stress values exceed 2/3 but do not exceed 90% of the yield strength at temperature. Prolonged expose of materials to these values may lead to dimensional changes due to permanent strain.

Life

Corrosion Allowance and/or material used generally define the life for a Div 1 vessel.

OverPressure Protection (PSV)

Vessel can handle With the decrease in design overpressures up to MAWP of factor, PSV & PRV proper vessel. Alternative codes for control should be monitored. design of PSV devices are used: API 520, 521, and API 2000 (Tank Venting).

7

8

ASME VIII - 2007 Div 2 Prior to 2007, an increase of 25% under current code, allowing a proportional reduction in thickness.

Div 3 The stress allowables (below the creep temperature) in all international Codes, for most materials are set to not exceed the lower of the following: - 2/3 of the minimum specified yield strength. - The minimum specified ultimate tensile strength divided by a Design Factor (DF). This value varies significantly from one Code to the other, but generally European Code (including PD 5500) use values of DF ranging from 2.0 - 2.4.

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments Allowable Stresses are higher for Div 2 than those of Div 1, but the material design and fabrication requirements are more restrictive than Div 1. Up until 2007, allowable stresses for most common materials ( Carbon and low alloy steels) in Division 2 were about 10 -15% higher than those of Div 1.

For these same materials, the 2007 Edition allowable stresses in Div 2. are about 45% higher than in Div 1, providing a greater incentive to use Div 2. See table 5.6 of Div 2. Code for examples of Stress Classification according to Design by Analysis Rules. Primary General Membrane Stress, Primary Local Membrane Stress, Primary Bending Stress, Secondary Membrane plus Bending Stress and Peak Stresses are all taken into account when designing according to Part 5 of Div. 2 Code. Div. 1 ignores such considerations, and just computes thicknesses based on Primary (Principal) Stresses.

Vessel life is monitored in terms of cyclic service. (10 8 cycles being the normal parameter taken). Corrosion allowance is already incorporated into any vessel thk calculation in the nominal thickness used. Annex 3.F provides formulas for calculating the allowable number of cycles for any calculated equivalent stress.

Annex J of PD 5500 gives recommendations for pressure relief protective devices. See also 3.13.2 and 3.13.3 for overpressure setup of discharge (reseat) pressure (5-10 % above the operating pressure).

Div. 2 can be used economically for vessels with internal pressures exceeding 3,000 psi, vessels with lesser pressures where exceptional savings in material costs can be realized, or vessels with fluctuation temperature cycles. To put it simply, it is used for vessels which are of sufficiently rigorous duty or are sufficiently complex so as to require more comprehensive calculations and more sophisticated procedures with which to construct safe as well as economical vessels that are fit for their intended purpose. The rules of Div 2. cover vessels, only to be installed at a fixed location for a specific service. Thus neither the location nor the service can be altered during the useful life of the vessel.

The intent was that both Divisions provide the same degree of overall safety, and that at very high temperatures both Divisions would ultimately give the same yield stresses for any and all materials used. When compared to En 13445 DBF ( Clauses 7 to 16) the ASME Codes Div 1, 2 and 3 (DBF and DBA) are considered to be nonconservative in comparison with procedures in major European pressure vessel Codes.

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Item

Description Fatigue Analysis Methodologies and Evaluation

Div 1 Not applicable. Since Div. 1 has no rules, the stress and fatigue analyses rules of Div.2 are normally used.

9

Safety Factors

10

Longitudinal, Tangential Shearing and Bending Stresses (Horizontal Vessels) 11

The Code traditionally allowed for a maximum allowable design stress using a design factor of 5. This factor was lowered to 4 in the 1950's. In 1998 Code Cases were established to use a design factor of 3.5.

ASME VIII - 2007 Div 2 Div 3 Two (2) provided under Part Not applicable.

5. Provides rules for stress analysis and fatigue analysis (if a Div. 1 vessel is subject to loadings for which no formula is provided, such as thermal loadings, or is subject to cyclic operation, it still needs to be analyzed).

Annex 3.F provides the design fatigue curves (formulas) for elastic fatigue analysis. It also provides parameters for the generation of the welded joint design fatigue curves.

The procedures for protection against plastic collapse mode of failure are documented in Paragraph 5.5.2. Three different alternative methods are allowed for this type of failure: elastic stress analysis, limit load analysis and elastic-plastic analysis.

See column on EN 13445 to gather a comparison between the two Codes as regards fatigue analysis.

Difference between maximum allowable design stresses of the two Code Divisions became smaller. (Design factor for Div 2 didn't move lower). When Div 2. was first published in 1963, DF = 3.0.

In 2007, it was reduced to 2.4 on the tensile strength for almost all materials below Buckling in the inelastic Use of beam theory range, the Tangent Modulus (cantilever approach) to calculate all related stresses is used, to acount for nonand moments. All K values (1 linearities. Annex 3.D - 10) are identical as in PD provides a method for 5500 calculating the Tangent Modulus from a master stressstrain curve. Alternatively, this value may be obtained from the old external pressure curves, which are still in Section II, Part D.

PD 5500-2003

The design factors based on tensile strength range from 2.35 to 2.5 for different material bands.

Use of beam theory (cantilever approach) to calculate all related stresses and moments. The same equations used as in Div 1.

All K values (1 - 14) are identical as in Div 1. also.

EN- 13445 (2004) Fatigue design according to ASME Sec. VIII Div. 2. Part 5 for welded regions is considered to be nonconservative in comparison with procedures in major European pressure vessel codes (e.g. EN 13445, ADMerkblatt3, PD 55004). Thus, ASME fatigue design for these regions is not considered to meet the requirements of PED Annex I. Taking this into account, the results of alternative design procedures may be required for fatigue evaluation. The main technical issue to arise from this concerns the fatigue evaluation, which includes cyclic thermal stresses. This was initially performed according to both EN 13445-3 clause 18, and ASME VIII Div. 2 Part 5. The results differ substantially: the allowable number of cycles according to EN is 33576, whereas that according to ASME is larger than 106.

PED- 2009

Comments The design margin on minimum specified ultimate tensile strength is 3 for Div 2 and 3.5 for Div 1.

Rules provided to address each mode of failure individually. The forms of failure addressed by Div 2. Part 5 include: plastic collapse, local failure, buckling and fatigue. With few exceptions, the analysis rules of Part 5 may be used only if the design temperature does not exceed creep temperature of the material at the operating point. Old Div 2. only used elastic analysis method to determine plastic fatigue. Old rules used Maximum Shear Stress Theory to calculated "Stress Intensity", whereas the new Div. 2 uses "Equivalent Stress" using the Maximum Distortion Energy Theory (Von Mises Theory). Load Case Combinations for the different failure criteria are summarized in Table 5.5. Fatigue Analysis is not allowed if the number of cycles , of any range, exceeds one million.

In the China National Standard GB150-89 for steel pressure vessels , a factor of 3.0 or higher is used.

Other Stds. establish MADS based on yield strength only. Although MADS may at times be higher at room temp. and moderate operation temperature conditions, there is significant material testing and third party involvement during material manufacturing and other considerations to ensure a reasonable level of safety.

Three classes of vessels were originally proposed with " Class 3" pressure vessels having a "relatively large design margin" of 3 on tensile strength, and the lowest design margin of 1.875 for "Class 1" vessels (now changed to 2.4) and an intermediate factor of 2.4 for "Class 2" vessels.

The only pressure vessel stds that have a design factor below 2.35 are typically for transportation or handling (portable) purposes, generally requiring design testing as well as periodic testing and recertification, considerably more expensive than for vessels built for stationary purposes.

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Item

Description Yield Strength

Div 1 Safety Factor of 1.5 used on the specified yield strength of the material to determine Maximum Allowable Design Stresses.

12

Tensile Strength

13

14

15

ASME VIII - 2007 Div 2 Div 3 Safety Factor of 1.5 used on the specified yield strength of the material to determine Maximum Allowable Design Stresses. Relatively large design margin of 3 on tensile strength.

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments Three classes of vessels were originally proposed with " Class 3" pressure vessels having a "relatively large design margin" of 3 on tensile strength, and the lowest design margin of 1.875 for "Class 1" vessels (now changed to 2.4) and an intermediate factor of 2.4 for "Class 2" vessels.

The only pressure vessel stds that have a design factor below 2.35 are typically for transportation or handling (portable) purposes, generally requiring design testing as well as periodic testing and recertification, considerably more expensive than for vessels built for stationary purposes.

ie- Tensile Strength of SA516-70, MADS = 20,000 (17,500 psi previous to the 1999 addenda or the Code Cases)

ie- Tensile Strength of SA516-70, MADS = 23,300 (at elevated temperatures (above 500 F), when the yield strength may be the controlling factor, the stresses for the two Codes will be the same).

Ultimate Tensile Strength Listed in Tables under Section Annex 3.D includes values of Yield based with reduction II, Part D, for temperatures yield strength and ultimate factor for yield to tensile ratio up to 500 F (260 C). tensile strength , as well as less than 0.7. strength parameters as a function of temperature.

These allow us to generate a cyclic stress-strain curve for elastic-plastic fatigue analysis. Tangent Modulus is also determined from this Annex. Annex 3.E provides tables for a number of physical properties, including Young's Modulus, Coefficient of Thermal Expansion, Thermal Conductivity, Thermal Diffusivity.

Pressure Equipment Safety As a simple comparison, the Over Pressure Protection Rules Listed in Part 9. 23,300 maximum allowable design psi under the existing Section stress at room temperature VIII, Division 2. The increase for the same SA516-70 material under the new Code, in the MADS will be more will now be 25,300 psi significant for materials with (instead of 29,200 psi since high minimum specified yield the material's specified stresses, such as SA517 minimum yield stress of Grade A. 38,000 psi governs) versus 20,000 psig (or 17,500 psi previous to the 1999 addenda or the Code Cases) under Section VIII, Division 1.

Factors affecting pressure equipment safety include but are not limited to: owner's design specification, designer's competency and thoroughness, design assumptions and details,integrity and quality systems of material manufacturers/suppliers and the actual properties of materials supplied; fabrication processess and procedures; welder's competency and welding consumables; quality of testing and examination; manufacturers' compliance to design specifications; operators training and competency; plant operation procedure;change management and quality program;plant maintenance and integrity management; a plant's physical environment; relevant legislation and a host of other considerations.

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Item

Description Use of Stiffening Rings (External Pressure Design)

16

ASME VIII - 2007 Div 2 Div 3 Rules have been added for braced and stayed surfaces (similar to Div. 1). Rules for sizing stiffeners have been very much refined and are less conservative than the old Div. 2 rules. As always, the choice of increasing the shell thickness vs. adding stiffeners to reduce this thickness, is made on an economic basis.

User's Design Specification and Manufacturer's Design Reports

Not applicable. Since Div. 1 has no rules, the stress and fatigue analysis rules of Div.2 are normally used. No Professional Engineer required, or certification of design specification or design report.

Junctions

For Cone-Cylinder Junctions, a totally new procedure, using limit analysis, has been included. The procedure, although more refine and accurate than those of Div 1. or the old Div 2. is cumbersome and tedious to apply by hand. Step by step procedures are provided in Paragraph 4.3.11, which easily lend themselves to computer programming techniques. These procedures cover junctions with a flare or knuckle, as well as junctions without such transition.

Formulas are provided for applied axial force and moment, as well as for internal pressure. Some limitations are specified on the range of geometric Non-circular vessels have Rules are provided for been taken into consideration cylidrical, conical and from the beginning. spherical shells. Design rules for non-circular vessels have been added (similar to Div. 1). For those shapes for which design rules are not specifically provided, the analysis rules of Part 5 must be used.

17

18

Geometry

19

Div 1 According to UG-29 and UG30. Stiffeners can be attached by continuous, intermitent or a combination of continuous and intermitent welds or braces. Formulas are based on Available Moment of Inertia Area > Required Moment of Inertia Area for correct thickness/spacing of shell/stiffeners used.

The existing Section VIII, Division 2, requires that the user prepare a User s Design Specification detailing the intended operating conditions and other requirements and the document must be duly certified by a Professional Engineer who is experienced in pressure vessel design.

PD 5500-2003

EN- 13445 (2004)

According to 3.6.2.2 to 3.6.3.3.3. No intermitent welds allowed. Welding can only be continuous. Formulas are based on elastic instability of stiffeners as a function of the spacing these have relative to each other and to the perimeter of the vessel cross-section and the maximum stress the stiffener is able to withstand.

Rules in Clause 8 of EN 13445-3 are based almost entirely on the rules in British Standards Institution (BSI) document PD 5500 , itself a continuation of the previous BS 5500. The rules have been in BS 5500, the British Standard for unfired pressure vessels, since about 1973.

PED- 2009

Comments The similarity between PD 5500, EN 13445 and Div 2 . is striking for external pressure calculations of shell thickness. Even the formulas for calculating the different FS (Design Factors) are very similar indeed. The safety factor is now shown explicitly in the formulae ( new EN- 134453 re-written from BS 5500) and the distinction between light and heavy stiffeners is clearer. The values of elastic limit (yield stress) have been changed slightly. For more on this subject refer to PD 6550: Part 3: 1989, an explanatory supplement to BS 5500 on external pressure, published by BSI. It is the responsability of the User (or its hired agent, such as a Consulting Company) to prepare and provide a UDS (User's Design Specification).

This Specification must be certified in acordance with Annex 2.A of the Code.

When Part 4 does not provide design rules for certain geometry or loading, Part 5 must be used.

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Item

Description

Div 1

ASME VIII - 2007 Div 2

Div 3

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments

FABRICATION Materials

All ferrous materials must meet the requirements of paragraph 3.3. Fabrication requirements are in Part 6.

Paragraph 6.6 has specific requirements concerning high strength quench and tempered materials. These materials with high strength are achieved by heat treatment. Because of their high strength, these materials are very difficult to work with.

Layered Vessels (Cladding)

Rules in new Div. 2 for cladding of vessels have been kept and expanded.

20

21

Heat Treatment

22

23

Data Reports and Fabrication Drawings

PWHT (Post Weld Heat Treatment) can take a number of forms, not all require the whole vessel parts to undergo the same HT intensity. See UCS- 56.

Test specimen for materials required to be subjected to essentially the same heat treatment as the vessel.

These requirements are tied to the material P-number (which is a measure of weldability). Except for preheat requirements of Section IX, preheat is not mandatory. RT and UT are interchangeable, with a few exceptions.

Materials of Carbon content greater than 0.35% may not be welded on.

The higher costs for EN design for forged courses are basically caused by higher material costs, higher fabrication costs and to some extent by the post weld heat treatment costs. The higher costs for ASME design for welded courses are also basically caused by higher material costs, higher fabrication costs and to some extent by the post weld heat treatment costs. For ferritic steels, the safety factor of 2,4 put on the ultimate strength at 20° C impedes efficient use of the new modern high yield strength steels (Thermo-Mechanically rolled and Quenched and Tempered steels). Therefore Annex B of EN 13445-3, DBA Direct Route, allows the use of a reduced safety equal to 1,875, but still giving a margin of safety of 2 towards burst for vessels with moderate notch effect (e.g. weld details of testing group

Material costs are frequently greater using the ASME code. In some cases, savings attributable to lower material costs with EN 13445 are partly offset by additional costs of weld testing and NDT when compared with ASME requirements

The P-number and Group number are listed in the stress allowable tables of Section II, Part D, as well as Section IX. These requirements of Div. 2 for PWHT are much more extensive and detailed than those of Div. 1 (or old Div. 2). The need of PWHT ultimately depends on the P-number and niminal thickness. The definition of nominal thickness governing PWHT is in Paragraph 6.4.2.7 and must be carefully studied. (see Table 6.8 Div. 2). PWHT costs are frequently greater for the ASME designs, since the PWHT requirements depend on the wall thicknesses.

In general, fabrication costs for Division 2 vessels are much higher than for Division 1.

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Item

Description

Div 1

Ultrasonic Examination/Testing (UT) 24

Magnetic Particle Examination / Penetration Testing (Hardness) 25

Radiographic Examination (RT) and Manufacturer's Design Report

Normally not required.

Manufacturer has to declare compliance in data report.

Failure Criteria

Membrane Stress Theory.

NDE , Hardness Testing

The requirements for test coupons according to EN 13445 increase the costs for EN design, since no coupons are required for ASME VIII Div.1.

26

27

28

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments Decision of which Code to use is usually based on overall cost of a vessel. Not simple to generalize the relative costs.

Div 2 has some additional fabrication requirements such as MT/PT of cut edges. New requirements for MT/PT of machined surfaces for forgings have been added.

Decision of which Code to use is usually based on overall cost of a vessel. Not simple to generalize the relative costs.

Old Div 2 required 100% Same as in Div. 2 Code.

Radiography (RT) of all butt welds and additional MT/PT requirements. Did not have the concept of "joint efficiency". New 2007 Edition of Div 2. provides the option of partial NDE. MDR required from Manufacturer when all work on the vessel is finished. MDR has to certufy design specification and code compliance in addition to data report.

Div 2 uses the maximum distortion energy theory (von Mises Criteria) which is more accurate than Div 1 failure criteria which is the maximum stress theory.

Manufacturer's primary responsability is to assure structural and pressure retaining integrity of the vessel. He must meet all requirements of the Code and the UDS. He must prepare a Manufacturer's Design Report (must be certifie in accordance with Annex 2.B of the Code).

Charpy V Notch Impact Test Requirement. Toughness requirements applicable to all shells, heads, nozzles and attachments essential to the structural integrity of the vessel. Two separate sets of impact exception and toughness requirement curves, for as welded and for PWHT components.

Re-Rating Option

Options provided for vessels which are outside the tolerance limits. Analysis may be in accordance with Part 5 of Dv. 2 or with the assessment methods of API579-1/ASME FFS-1

Design of Supports and Very complete coverage of Attachments (Appurtances). the design of appurtances in Div 1.

New rules added for design of saddles,skirts, lugs and leg type. Same analysis procedures, if any differences at all, as those used in the Div 1. (Zick's Analysis for Saddles of Horizontal Vessels).

29

30

ASME VIII - 2007 Div 2 Div 3 All plate and forging material 2" thick or greater must be UT examined (for the old Div.2 Code it used to be 4").

The NDT requirements according to ASME are lower than those according to EN (for the chosen weld joint efficiency) and due to the fact that no test coupons are required for the ASME route.

Div. 2 allows only for the so called fully radiographic vessels.When Radiography is not used, there are other methods of examination, such as the use of ultrasonics, dye penetrant or magnetic particle. These various additional requirements or restrictions associated with the fabrication of vessels according to Div. 2 are directed toward the prevention of brittle fracture and on the existence of structural or metallurgical notches or discontinuities. A stress report is required to be submitted, containing complete calculations and stress analysis plus drawings showing compliance with the Code requirements.

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Item

Description Nozzles (Openings) and Flanges

31

Flat Heads and Clamped Connections

Provided. See Mandatory Appendix 14 - Integral Flat Heads with Large, Single, Circular, Centrally Located Opening

Heat Exchangers

Section UHX provides rules on Heat Exchanger Design, since 2004 Edition

32

33

34

35

ASME VIII - 2007 Div 2 Div 3 Section 4.5.3 - 4.5.16 are detailed rules for nozzle design and attachment in Div 2. Paragraph 4-16 contains rules for the design of flanged joints. These rules can again be overriden by Part 5 Analysis. Nozzle external loadings according to WRC Bulletin 107 and WRC Bulletin 297 and FEA. Paragraph 4.5.17 has some rules for design of openings subject to compressive stresses.

Same as in Div 1. See Section 4.6 for detailed design of Flat Heads.

However, design of the Opening in the Flat Head is different. The maximum local primary membrane stress is calculated and then limited to 1.5 S.

Paragraph 4.18 provides Rule for the design of Shell and Tube Heat Exchangers.

Paragraph 4.19 provides new design rules for thin walled expansion joints, in heat exchangers.

Out-of-Roundness Minimum See Mandatory Appendix 13- See Rules Section 4.1.8 The maximum local deviation Constraints Vessels of Non Circular Crossfrom the true circular form Section shall not exceed the shell thickness. If shell imperfections exceed the above tolerances, there are rules for reducing the allowable external pressure of shell with such out-oftolerance.

Tolerances Many of the Carbon Steels in Local deviation from the true circular form e, must be met Div. 2 have stricter low temperature limits of to prevent local buckling.

Straightness tolerance , ex application. Some materials used in vessels operating to , for cylindrical and conical - 20 F have to qualify by shells subject to axial impact testing, as opposed to compression. the rules given by Div. 1 for the same condition.

Temperature Limits 36

Div 1 According to UG-36 to UG-46, nozzles. Flanges according to ASME B16.5 up to 24", and MSS SP-44-2006 (also API 16.47 -1990) Code for higher diameters (up to 60"). Nozzle external loadings according to WRC Bulletin 107 and WRC Bulletin 297.

PD 5500-2003

EN- 13445 (2004) Design of the upper end by applying Design-by-Analysis according to EN 13445-3 Annex B for consideration of the nozzle loads does not result in decreased thicknesses compared to those obtained by EN 13445 (Data Base Files).

PED- 2009

Comments Design by analysis rules of Part 5 may be used as an alternative to the design rules of Part 4. Div 2. limits nozzle diameter to shell diameter ratio to 0.35. Div 1. allows up to 0.5.

Shells having larger imperfections may have significantly less resistance to buckling.

The effect of temperature on the strength of materials during operation is not taken into account.

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Item

Description Hydrostatic and Pneumatic Test Pressures

ASME VIII - 2007 Div 1 Div 2 Div 3 Ph = 1.3 * MAWP * (S /St) For Div. 2 vessels, the 1.25 (may be exempted for (Used to be 1.5 before the standard hydrostatic and autofrettaged vessels). use of the 3.5 design factor in pneumatic tests are similar to the 1999 Addenda). that required by Division 1, except that the design pressure is multiplied by 1.25 for hydrostatic test and 1.15 for pneumatic test instead of 1.3 (for Div. 1).

37

Welding and Fabrication

Different types with buttwelds and others

Identification, handling and storing of all welding materials are some of the precautions taken prior to welding. Rules provided for repair of weld defects not present in the old Div. 2.

Extensive use/requirement of buttwelds and full penetration welds including non-pressure attachment welds.

Clad or Overlay Welding

Similar rules set out in Part UCL of Division 1

Forged Construction

Part UF of Div. 1.

Paragraph 6.5 specifies requirements for clad or overlay welded materials.

Rules also are provided for cladding material included in the design thickness.

Paragraph 6.7 has specific requirements for forged construction.

Buttwelds and extensive use of other construction methods such as threaded, layered, wire wound, interlocking stripwound, and others.

38

39

40

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments

The requirement given in the PED, Annex I clause 7.4, that the hydraulic test pressure Ptest shall not be smaller than 1.43 PS shall be adhered to even if this requires an increase in wall thickness when an “equivalent design pressure Peq” given by Peq = (Ptest x (S/Sa))/1,3 is greater than PS. The second requirement (1.25 times PS times the correction factor based on the proof strengths of ASME II-D Table Y-1) shall not be used when the resulting test pressure would be greater than the test pressure specified by the ASME Code For pressure equipment in

The additional costs for the ASME vessels if conformity assessment with the PED is required are rather small (some marginally increased wall thicknesses for ASME VIII Div.1, higher testing requirements for the materials) – presuming that the results of the material tests fulfil the requirements. In the case of ASME VIII Div. 2, no increase of the wall thicknesses due to the hydraulic test pressure given by the PED is required. Cost drivers are not severely influenced by these parameters, then.

categories II, III and IV, welding operating procedures and personnel must be approved by a competent third party (notified body or third party organisation recognized by a member state). To carry out these approvals the third party must perform examinations and tests as set out in the appropriate harmonised standards or equivalent examinations and tests or must have them performed.

For pressure equipment in categories III and IV, the NDT personnel must be approved by a third party organisation recognised by a member state. As regards ASME fatigue design for welded regions is however not considered to meet the requirements of PED Annex I.

No provisions made for transport vessels.

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Item

Description

Div 1

ASME VIII - 2007 Div 2

Div 3

PD 5500-2003

EN- 13445 (2004)

PED- 2009

Comments

INSPECTION & TESTING Material

Materials as listed under Materials have to be in Groups A,B,C and D of Tables compliance with Code in Section II, Part D. requirements. The materials allowed are listed in tables of Annex 3.A. Also listed in the allowable stress tables of Section II, Part D. For high alloy materials, two sets of stress values are not given for the same material at the same temperature, as in Div. 1. Therefore, under Div. 2 rules, the vessel engineers cannot make a choice of stress values.

Materials in new Div 2 are much more expensive than old Div 2.

Thickness

Individual thicknesses, as applied to the Code different parts. Impact testing exceptions are allowed under curves UCS -66 and UG-20 of the Code.

A vessel according to ASME VIII Div.2 is considerably cheaper than one according to ASME VIII Div.1 due to the large differences in resulting wall thicknesses. Once governing thickness and material classification have been established for a component, the need for impact testing can be determined from Figure 3.7 and Figure 3.8.

(These curves are applicable if the general membrane tensile stress is equal to the allowable stress). Exemption Rules apply to impact testing of material according to Div 2, depending on whether governing thickness meets criteria. See Code.

41

42

NDE and Welding Requirements

43

Quality Control 44

Governing thickness, defined for different parts of the vessel. Impact testing exceptions allowed (these can be over riden depending on the governing thk > 4 ", MDMT < 32.2; specified minimum yield strength greater than 65 ksi; welded parts not subject to PWHT, having a governing thickness > 1.5"). As regards the ASME VIII Div. 2, no increase of the wall thicknesses due to hydraulic test pressure given by the PED is required.

The NDT requirements according to ASME VIII Div. 2 are similar to those according to EN. Thus, the NDT requirements should not result in considerable cost differences. Additional NDE and QC requirements, a more restrictive list of materials and design details, and additional requirements than those needed for Div 1 vessels. These requirements are in Part 7 of the Code Div. 2.

Requirements for QA/QC are summarized in Annex 2.E. Necessary to obtain Certificate of Authorization and the Stamp from ASME.

Even more restrictive than Div 2. with different requirements. Fracture toughness testing requirement for fracture mechanics evaluation.Crack tip opening displacement (CTOD) testing and establishment of Klc and/or Jlc values.

The NDT (Non Destructive Testing) requirements according to EN 13445 for the welds of the main body of the vessel are the same as according to ASME VIII Div. 1. NDT level should be at least that corresponding to a joint efficiency of 0.85, even when a smaller efficiency is permitted by ASME when the resulting test pressure would be greater than the test pressure specified by the ASME Code (1,3 x Sa/S x PS).

Inspector has the "duty" to carry out typical inspections /verifications which are summarized in Annex 7.A of the Code.

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Item 45

Description

Div 1

Experimental Stress Analysis User Specification Rqrd

ASME VIII - 2007 Div 2 Qualified Inspector has to survey and approve vessel according to Annex 7.A Qualified Inspector has to survey and approve vessel according to Annex 7.A

User's Design Specification with more specific details (see KG-310) including contained fluid data, etc. with useful operation life expected and others. Designer defined.

Yes. The same as in Div 2 only that the PE shall be experienced in high pressure vessel design and shall not sign for both User and Manufacturer.

46

Professional Engineer Rqrd

No

Yes. Professional Engineer's Certification of User's Design Specification as well as Manufacturer's Design Report. Professional Engineer shall be experienced in pressure vessel design.

Design Registration

No constraints. Vessel Marking is valid throughout its life.

Does not apply if vessel is sold individually from Plant to a new owner.

Proper Marking On The Name Plate

Same requirements - In accordance with UG 116.

Heat Treatment

Same Requirements as in Div. 2

Qualified Inspector has to survey and approve vessel according to Annex 7.A. The Proper Code stamp for Div 2. is "U2".

Qualified Inspector has to survey and approve vessel according to Annex 7.A

Pressure Testing

Same Requirements as in Div. 2

47

48

49

50

51

Pressure Equipment Safety Same Requirements as in Div. 2. UV Stamp rqrd.

52

Code Stamp and Marking 53

U Stamp with Addition markings including W, P, B, RES, L, UB, DF, RT, HT.

Div 3

Qualified Inspector has to survey and approve vessel according to Annex 7.A. Manufacturer to make sure all NDE and testing requirements are met. He has also the duty to monitor the Manufacturer's Quality Control System.

Over Pressure Protection Rules Listed in Part 9. The safety relief equipment installed on Division 2 vessels must have a "UV" stamp. All stamped vessels must pass a pressure test (over-pressure) after completion of all fabrication. Vessels designed for vacuum or partial vacuum must be tested at an internal pressure not less than 1.43 times the design external pressure. Vents at the top of the vessel are required, to purge air pockets, for hydrotest.

U2 Stamp with Additional marking including HT

PD 5500-2003

EN- 13445 (2004)

Ph = 1.25 MAWP or Ph= 1.43 MAWP (St/S), whichever is greater.

The requirements for test coupons according to EN 13445 increase the costs for EN design, since no test coupons are required for ASME VIII Div.1.

UV3 Stamp rqrd.

The beneficial effect of a higher test pressure was shown by the Research and Development programme HYDFAT, sponsored by DG Research of the European Commission.

PED- 2009

Comments

Div. 2 compliant with the European Pressure Equipment Directive (PED) in Hydrostatic Test Formulas.

U3 Stamp with additional marking denoting construction type: HT, PS, WL, M, F, W, UQT, WW, SW.

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