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1 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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Comparative Study: EN 13445 – ASME VIII

Comparative Study: EN 13445 – ASME VIII

Workshop on the Pressure Equipment Directive

Bucharest, February, 2007

Dr. Reinhard PreissTÜV Austria

Krugerstrasse 16A-1015 Vienna, AustriaTel. +43 1 51407 6136e-mail: [email protected]

http://www.tuev.at

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IntroductionIntroduction 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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IntroductionIntroductionThe 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 - OverviewBenchmark Examples - Overview

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Benchmark Examples - OverviewBenchmark Examples - Overview

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Conformity AssessmentConformity AssessmentFor 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 AssessmentConformity AssessmentIn 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

Benchmark Example 1 – CNG Storage Tank

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Benchmark Example 1 – CNG storage tank

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

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

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

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

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

Benchmark Example 4 – Stirring Vessel

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Benchmark Example 4 – Stirring Vessel

Benchmark Example 4 – Stirring Vessel

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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Benchmark Example 4 – Stirring Vessel

Benchmark Example 4 – Stirring VesselSince 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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Benchmark Example 4 – Stirring Vessel

Benchmark Example 4 – Stirring VesselThe 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 SummaryOverall SummaryThe 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

Overall Summary – Cost Comparison Table

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Overall SummaryOverall SummaryMaterial 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 SummaryOverall 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 SummaryOverall 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 replyDiscussion 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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Discussion on ASME replyDiscussion on ASME replyAccording 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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Discussion on ASME replyDiscussion on ASME replyAccording 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

Comparative Study: EN 13445 – ASME VIII

Thank you for your attention !

Questions and comments welcome !