comparativa en13445-asme viii

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Comparative Study: EN 13445 –

ASME VIII

Workshop on the Pressure Equipment Directive

Bucharest, February, 2007

Dr. Reinhard Preiss

TÜV Austria

Krugerstrasse 16

A-1015 Vienna, Austria

Tel. +43 1 51407 6136

e-mail: [email protected]

http://www.tuev.at

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Introduction

Background: A harmonised standard related to a "New

Approach" Directive does give the manufacturer the advantage

of the presumption of conformity to the Essential Safety

Requirements of the Directive itself, but to be accepted and

applied, it must also bring economic and/or technical

advantages.

This study compares the economic and non-economic

implications arising from the application of (a) EN 13445 and, (b)

the ASME Boiler & Pressure Vessel Code plus major related

codes when appropriate (TEMA, WRC Bulletins), for the design,

manufacture, inspection and acceptance testing of 9 benchmark

examples of unfired pressure vessels.

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Introduction

The consortium which carried out the study, based on a

contract with the EC / DG Enterprise, consists of TUV Austria

and of Consorzio Europeo di Certificazione (CEC) – both are

Notified Bodies according to the PED.

The detailed design of the benchmark examples was

performed by the consortium. To evaluate the economic

factors concerning individual and/or serial production of the

benchmark vessels, pressure equipment manufacturers from

Italy, France, Germany and Austria took part as

subcontractors.

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Benchmark Examples - Overview

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Benchmark Examples - Overview

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Conformity Assessment

For estimation of the costs the following combinations of codes and conformity

assessment routes were considered:

EN 13445 and conformity assessment according to the PED (CE-marking).·

ASME Section VIII (Division 1, Division 2 if applied) and conformity

assessment according to ASME (U-stamp, or U2-stamp).

ASME Section VIII (Division 1, Division 2 if applied) and conformity

assessment according to the PED (CE-marking).

The exercise is based on compliance with the corresponding requirements in a

situation where there are no pre-existing qualifications or supplementary data

which could be used from other similar equipment

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Conformity Assessment

In the case of application ASME Section VIII (Division 1, Division 2 if applied) and

conformity assessment according to the PED additional requirements were made:

Materials: material properties used in the design must be those affirmed by the

material manufacturer. This may include hot tensile properties (yield strength

according to ASME II Table Y-1), impact properties for carbon steel at MDMT but

not higher than 20°C with a minimum value of 27J.

Hydrostatic test Pressure: The hydraulic test pressure Ptest shall not be smaller

than 1.43 PS, 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 1.25x.. requirement is not used, but if it would be the governing one, the

NDT level is increased to at least 0.85.

Permanent joining and NDT: welding operating procedures and personnel, NDT

personnel: requirements as given in the PED have to be fulfilled

Fatigue design: ASME unconservative for welded regions?

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Benchmark Example 1 – CNG Storage Tank

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Benchmark Example 1 – CNG storage tank

DBA according to EN 13445 is advantageous in this case

Higher costs for the ASME design are basically caused by higher

material costs, due to larger wall thicknesses, and to some extent

by the post weld heat treatment costs. 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 .

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Benchmark Example 1 – CNG storage tank

No considerable cost differences due to NDT

Test coupons required for EN design, but not for ASME. Thus,

higher costs for EN for this task.

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

hydraulic test pressure given by the PED is required.

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Benchmark Example 2 –

Hydrogen Reactor

Diameter 2200 mm, cylindrical length app.

8000 mm, hemispherical ends, max.

allowable pressure 180 bar, max.

allowable temperature 400°C.

Forged courses: 11CrMo9-10 / EN 10222-

2; SA-387 Gr. 22 Cl. 2.

Welded courses: 12CrMo9-10 / EN

10028-2; SA-336 Gr. 22 Cl. 2.

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Benchmark Example 2 – Hydrogen Reactor

Differences in the design wall thicknesses (e.g. for the main cylindrical

shell / forged courses 190 mm for EN 13445 DBF, 181 mm for ASME VIII

Div.1, and 151 mm for ASME VIII Div. 2; and for the main cylindrical shell

/ welded courses 124 mm for EN 13445 DBF, 181 mm for ASME VIII

Div.1, and 151 mm for ASME VIII Div. 2) are mainly caused by the

different allowable stresses.

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Benchmark Example 2 – Hydrogen Reactor

The costs are do mainly depend on the wall thicknesses, there

are no considerable cost differences due to NDT, and test

coupons required for both routes.

Again, 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

hydraulic test pressure given by the PED is required.

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Benchmark Example 4 – Stirring Vessel

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A fatigue analysis was performed for the fluctuating load components of the stirrer,

considering a requirement of an infinite number of load cycles. A fatigue analysis for the

upper end, leading to the allowable number of (specified) batch cycles, was also

performed.

The fatigue results differ substantially: the required reinforcement of the mounting

flange to obtain stresses which result in a design for an infinite number of load cycles is

different for the two code routes. Furthermore, the allowable number of batch cycles

according to EN is 13100, but that according to ASME is 2x108.

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Since the material SA-240 Grade 316Ti is not allowed for application of

ASME VIII Div. 2, and the allowable stress of SA 240 Grade 316L is

considerably lower, the application of ASME VIII Div. 2 would generally lead

to larger wall thicknesses for the shells and ends. Thus, application of ASME

VIII Div. 2 is not economic in this case.

Inner body of the vessel: differences in the design wall thicknessess are

mainly caused by different design methods for external pressure (EN design:

11 mm wall thickness, two reinforcing rings 25x125 mm; ASME design:

15 mm wall thickness, two reinforcing rings 30x160 mm). Inner dished end:

differences in the design wall thicknessess also mainly caused by the

different design methods for external pressure (EN design: 15 mm wall

thickness; ASME design: 23 mm wall thickness).

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The higher costs for the ASME designs are basically caused by higher material costs

due to larger wall thicknesses, and thus higher fabrication costs. These are partly

compensated by lower costs for NDT and for test coupons, since 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.

The additional costs for the ASME vessels if PED conformity assessment is required

are rather small and are mainly caused by higher material costs due to the required

increased wall thickness for the lower end and the costs for an additionally required

pad at a nozzle. Due to the moderate service temperature no hot tensile test is

required, and no additional impact testing is considered necessary for the austenitic

steels used. Thus, the additional costs for material testing are negligible.

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Overall Summary

The project has considered application of the new harmonised

standard EN 13445 and the ASME VIII design procedures to a set

of 9 example cases which covered a wide range of pressure

vessel types, designs, materials and fabrications .

The overall basis for comparison was one of economic cost. A

procedure was used which allowed fair comparison of three

routes: EN 13445, ASME + U-stamp, ASME + PED. While the

consortium performed the design, several EU manufacturers were

involved in the project to assess the costs.

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Overall Summary – Cost Comparison Table

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Overall Summary

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.

For standard refinery heat exchangers no notable costs differences are

reported (if TEMA requirements are considered).

In some cases the reported costs differences for different manufacturers

are larger than the cost differences resulting from the application of the

various code routes.

PWHT costs are frequently higher for ASME design, since the PWHT

requirements depend on the wall thicknesses.

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Overall Summary

Use of Design-by-Analysis according to EN 13445-3 Annex B can

decrease the material costs considerable 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.

According to the cost estimations of the manufacturers, the extra costs

for ASME designs to meet the PED requirements are in general small

for the approach used in the study.

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Overall Summary

Fatigue design according to ASME Div. VIII Sec. 2 Appendix 5 for

welded regions is considered to be non-conservative in comparison

with procedures in major European pressure vessel codes (e.g. EN

13445, AD-Merkblatt, PD 5500) and the underlying experimental

results. 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, i.e. re-assessment of the fatigue life using a European

approach would be desirable in practice, but was not performed within

this study.

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Discussion on ASME reply

According to the paper “Design Fatigue Life Comparison of ASME Sec.

VIII and EN 13445 vessels with welded region” by Kalnins et.al. ([1],

PVP 2006-ICPVT-11) fatigue strength reduction factors shall be used,

e.g. the ones given in WRC Bulletin 432. In the opinion of the authors of

the Comparative study, in the ASME code itself this is stated for fillet

weld but no there is no hint to use such factors for full penetration welds.

In a mayor code, it should be stated unambiguous if such factors shall

be used and also the reference where to find such factors shall be

given.

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According to the paper “Comparison of Pressure Vessel Codes ASME

Section VII & EN 13445” by Antalffy et.al. ([2], PVP 2006-ICPVT-11) the

vessel manufacturers providing cost estimates in the study are not based

in countries which produce the majority of pressure vessels in the world

(Japan, Korea, USA).

According to [2], the size and quantity distribution of vessels used in the

Comparative Study is generally not representative of typical chemical,

petrochemical or petroleum process facilities. The greater part of the

total cost of pressure vessels is attributed to only a relatively small

number of the higher end pressure vessels. For these high end vessels

ASME Section VIII Div. 3 can be used, which reduces wall thickness and

cost by up to 15 percent over present Division 2 requirements.

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According to [2] a review of the EN standard has shown several important and

innovative features. The ASME is in the process of rewriting Section VIII, Division

2, which will make a range of Division 2 vessels even more competitive with the

EN standard. This rewrite is an opportunity to incorporate the latest advances in

pressure vessel design, as well as new and innovative features that will enable

the ASME Code to remain the preeminent pressure vessel standard.

The survey presented in [2] concluded that throughout the global industry there

is a strong preference to use the ASME codes for pressure vessel design and

manufacturing. Even though the PD5500 or EN 13445 may have a few specific

areas or cases where there is a small economic advantage, when considering

the overall aspects of the entire organization, plant, or project cost, the ASME

code seems to provide a better overall advantage.

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Comparative Study: EN 13445 –

ASME VIII

Thank you for your attention !

Questions and comments welcome !

comparativa en13445-asme viii

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