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: prr@tuev.or.at
http://www.tuev.at
1
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
4
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 (CEmarking).·
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
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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 102222; 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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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
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15 that according to ASME is 2x10 .
according to EN is 13100, but
Benchmark Example 4 – Stirring Vessel
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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Benchmark Example 4 – Stirring Vessel
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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Discussion on ASME reply
According to the paper “Comparison of Pressure Vessel Codes
ASME Section VII & EN 13445” by Antalffy et.al. ([2], PVP 2006ICPVT-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 reply
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 !
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