Production • Processing • Handling
Testing steel at high temperatures
Jörg Maffert and Dr Ingo Detemple look at the criteria for tensile tests at elevated temperatures on CrMo(V) steel plates.
temperatures and pressures are leading to the construction of higher capacity reactors with thicker walls. Also, more severe requirements in these steel specifications leave the steelmaker little scope to find a good balance between all the influencing parameters, in order to achieve the best possible steel design.
T Te design of pressure vessel for petrochemical
industry is based on mechanical properties and the design method, which are given by the construction code. Te design values such as ASME II-D, Tables U and Y-11
are to be used for design purpose only.
Specification writers whereas often specify acceptance criteria for tensile tests at elevated temperatures based on these tabulated values. We have seen that the level can differ between 80 and 90 per cent of the values of table U. Tis paper targets the sensibility of users of codes to take into account the real potential of high sophisticated steels, such as CrMo-steels, in accordance with ASME SA387 and SA542. Te method to verify the suitability of the given
values for testing purpose will be described in this article. Te modern technology of steel production as well as an appropriate method have been taken into account.
echnical requirements for petrochemical reactor steels have proliferated in the past decade. Te need to increase economic benefits together with higher operating
Hot tensile test Recommendations concerning elevated temperature tensile tests be come sometime mandatory, the acceptance criteria are somehow aligned to the code values, which are given for calculating purpose only. Te tested values shall not be compared to the
design values for rejection purpose. When the requirement is on a 90 per cent level of the table U, the manufacturer would try to improve the hot tensile properties. Such a product would have quite instable tensile
properties especially after long time post weld heat treatment (PWHT), which is not acceptable for an equipment running a high temperature and high pressure.
As an example we refer to APIRP 934 A2
recommendation: “Elevated temperature tensile tests, when required by the purchaser, should be performed at the equipment design temperature. Test specimens should be in the maximum PWHT condition. Acceptance values should be as specified by the owner/user…”
Acceptance criteria Te most efficient way to verify the suitability of the acceptance criteria is the ratio Rp0,2 note: Rp0,2
/Rm and Rm
(please are determined together within
the same tensile test). Subsequently, we determine typical ratios for different steel grades at ambient temperature (Fig. 1) and elevated temperatures (Fig. 2).
70
www.engineerlive.com Fig. 1. Ratio Rp0,2
/ Rm
at ambient temperature for different steel grades.
Fig. 2. Ratio Rp0,2
/ Rm
at elevated temperature for different steel grades.
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