Creep design - EN 13445

[ElCidCampeador]

Hi,
I'm designing a pressure vessel, O.D.1800mm, height=4500mm, mat. SS316 acc. to EN 13445.
Vessel has 2 shells (upper&lower) which are connected by a body slip on flange made by plate. Lower shell is 2,5m, higher shell 2m.
Shells are welded to 2 elliptical heads (at bottom and at top) with some minor nozzles.
My client has just changed data project for the upper shell and top head (with their nozzles): material shall be SS310, with design temperature of 675°C. Pressure is irrelevant (<1 bar).
The lower part is still designed with old material and data project (SS316 and lower temperature)
I've calculated thicknesses of all parts but for the upper shell my calculation software shows me 3 big warnings:

-See EN 13445-3 Annex M for guidance on monitoring of vessels operating in creep
-See EN 13445-3 Annex A for pressure bearing welds non allowed in creep range
-See EN 13445-2 Annex C for weld creep strength reduction factor

Calculation I've made are only to check pressure vessel parts, so what I understand is that I need to run a dedicated calculation for creep, right?
Regarding points above:

-For Annex M: it describes NDT and destructive ones during lifetime in order to monitor creep behaviour, correct?
-For Annex A: it shows what welds are allowed in creep range. Ok, no problem.
-For Annex C: I don't completely understand it, since I've no experience in creep test. It seems that tests are necessary to find parameter to be used in the creep calculation, am I right?

Do you know a sort of procedure to follow in this case, to check creep acc. to EN 13345?

Thank you

 

[Trestala]

What is your normal operating temperature and how long would the metal temperature exceed the creep temperature of SS310?

 

[ElCidCampeador]

What is your normal operating temperature and how long would the metal temperature exceed the creep temperature of SS310?

I don't exactly know, my client told me that upper nozzles are very close to a burner, which means that fluid entering the upper part of vessel would be at high temperature, estimated about 650°C, but 675°C is the worst scenario. I don't think that vessel will be subjected to a thermal fatigue, since when design temperature will be reached, it will be kept constant as soon as burner will operate.

At the moment, by the use of software for pressure parts, I've followed this road:

-Assumed 100000h as specified lifetime in creep range
-Assumed weld reduction factor in creep range 0,8 (WCSRF)
-Chosen ASME SA 240 310S as material with its allowable stress acc. to ASME II PART.D

Taken note of this, I've design all upper parts. I suppose that formulas used by software are the same for non-creep design of pressure parts, but with these differences:
-WCSRF seems to be multiplied to z in joint efficiency in the pressure part formulas
-Allowable stress used are related to values included in ASME II PART.D
Am I right? Am I missing some other relevant calculation?

Thus I have the following problems:
-Annex C, since WCSRF is assumed equal to 0,8, is no more applicable, right? Which means that all creep tests shown in that annex are not more mandatory?
-Annex M is still mandatory? Among other things, I was told that metallographic replicas are very important and relevant, right?