When a welded connection is subject to design temperatures with time-depending allowable stress values for the base metal (as per ASME II-D) :
Does the ASME-Code require approval of time-dependent stress values also for the filler metals of this connection? If not, why?

Background:
We are going to manufacture a pressure vessel made out of SA-240 Gr.304H.
This vessel is subject to design temperatures of 1350°F (735°C). The allowable design stresses provided by ASME II-D for this temperatures are TIME-DEPENDENT VALUES.
May I use filler metals which have NOT been tested in view of time-dependance of their stress values?

Jörg

Jörg,
I think the time-dependence of properties in high temperatures is also influenced by the grain size and intergranular stuff. So you can expect that any fenomenon found in wrought welding consumables can differ from behavour of weld metal after the seam has been laid. We have done gazilions of tests of a heavily heat- processed material; believe me, the creep or creep-fatigue testing results are always a surprise!

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Konrad Anikiel

Jörg,

This is a typical case where the ASME code is not addressing all aspects for the life of a vessel.
The time-dependent properties are taken into account for the base material. The weld material is qualified by the WFM manufacturer according to the SFA spec, and then by the vessel manufacturer with his PQR.

But the high temperature long-time properites are the responsibility of the manufacturer and the owner of the vessel. The Code just does not address these aspects, except for a very generic statement in UG-22 and the Foreword. The later requires ENGINEERING JUDGEMENT to be applied in adittion to the minimum requirements of the Code.

I would advise to check AD Merkblätter, for example, which is a bit more detailed in this question.

DK

Jörg,

please have a look at VdTÜV-Merkblatt 1000. This is a collection of filler metal data sheets of approved trade marks.
Acc. to my experience filler metal which are approved in long-term condition and matching the composition of AISI 304H are available only for temperatures up to 700 °C.

I recommend you the use of Ni-base filler metal e.g. ERNiCr-3. These filler metals are approved for welding austenitic steels (see also VdTÜV-1000) for operation temperatures up to 900 °C. This overalloyed welding of austenitic steels for high temperature service is common used.

But is AISI 304 the right solution for operation temperature 730°C ? For a long term use at this temperature AISI 304H will be sensitized and therefore susceptible to intercrystalline corrosion.

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Kind regards,
Juergen Fleischfresser