COMPARISON OF ASME SPECIFICATIONS
AND EUROPEAN STANDARDS FOR
MECHANICAL TESTING OF STEELS FOR
PRESSURE EQUIPMENT
Prepared by:
Elmar Upitis, PE
Michael Gold
December 16, 2005
This report was prepared as an account of work sponsored by ASME and the ASME Standards Technology,
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Comparison of ASME Specifications and European Standards
EXECUTIVE SUMMARY
A study was conducted under the ASME Standards Technology, LLC (ASME ST-LLC) to compare
ASME and European specifications for mechanical testing of steels for pressure equipment. The study
has concluded that there are no technical differences between the two systems, the ASTM/ASME
requirements and the EN requirements for material testing, that would support a position that one or the
other system of requirements is more or less conservative than the other. The systems are slightly
different, but, when used in conjunction with their respective construction codes, the European Pressure
Equipment Directive (PED) and the ASME Boiler & Pressure Vessel Codes, they assure the production
of safe pressure equipment.
There are three significant differences worthy of separate note. These are the EN requirement for
elevated temperature proof testing, the EN requirement for a minimum absorbed energy impact test value
for all pressure equipment materials, and the ASME requirement for lateral expansion values for some
materials and some equipment to be reported from impact tests, in addition to the absorbed energy.
The difference between the EN requirement for elevated temperature proof testing (equivalent to a
requirement for elevated temperature yield strength testing) vs. the ASME approach employing trend
curves for both elevated temperature yield strength and elevated temperature tensile strength, is discussed
in detail in the report. In the EN system, the maximum design stresses to be used in construction appear
in the material specifications and are based on the measured proof stress as a function of temperature.
The material manufacture is required to assure that the proof stress values adequately support the design
allowable stresses. In the ASME system, the construction code establishes the design allowable stresses,
based on data analyzed under the auspices of ASME. The material manufacturer certifies only that the
material meets the room-temperature properties listed in the specification. The material manufacturer is
not in a position to assure that the design allowable stresses are suitable, because he is not a party to their
development, other than that the material manufacturer often provides representative data as a function of
temperature to the ASME committee. ASME may analyze that data (to develop maximum allowable
stresses) either alone, or in conjunction with data obtained from other sources. The insistence by
European authorities on material having elevated temperature proof test data that assures the validity of
the allowable stresses has often prevented the use of ASME materials in PED construction. However,
even though the guaranteed proof stress values in EN material specifications may be somewhat lower
(more conservative) than the yield strength values used as part of the basis for allowable stresses in the
ASME construction codes, many studies have shown that vessels designed to the PED code are thinner
and lighter (less conservative) than corresponding vessels constructed to the ASME Code. Nonetheless,
experience shows that both systems lead to the manufacture of vessels with adequate protection against
plastic collapse, and having equivalent safety records.
As mentioned in the matrix report, the EN codes require a minimum 27 J (20 ft. lb.) absorbed energy for
all pressure equipment. The ASME code for boilers (which always operate at elevated temperature),
Section I, does not contain an explicit impact testing requirement. In fact, as explained in the report, there
are instances in which an absolute requirement for an absorbed energy minimum can lead to degradation
of the principle function of boiler materials, that of retaining pressure at elevated temperatures. The
ASME codes for pressure vessels, however, contain extensive requirements for impact testing, since these
vessels often operate at ambient temperatures and cooler. The impact testing requirements vary with
material, heat treatment condition, and thickness, as explained in the report. Neither set of requirements
can be directly compared against the other. However, both sets of rules provide reasonable protection
against brittle fracture.
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Comparison of ASME Specifications and European Standards
Finally, in addition to the requirements for meeting minimum absorbed energy requirements for certain
materials, the ASME pressure vessel codes also impose additional requirements involving the a minimum
mils of lateral expansion (MLE) of specimens used in the impact test (which, in the European system is
used only to determine absorbed energy). Some experts feel that MLE is a better indication of notch
toughness (and thus of resistance to brittle fracture) than absorbed energy, at least for high-strength steels.
While this position may not be universally accepted, MLE requirements for some materials have been
incorporated into the ASME pressure vessel codes.
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