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?

 

[XL83NL]

This is one of the reasons I try to stay away from EN 13445 for creep applications.

Bet lets give it a shot, Im happy to learn from others regarding creep design in Eurocodes

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?

Wouldnt that be defined in Chapter 19?

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.

Chapter 19 relates to Annex M as well. That may answers your question(s).

-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

Im not familiar with DBA (let alone DBA w/ creep). not sure where in Annex C you're looking at - I'm looking at C.8; if you're unfamiliar with DBA/FEM and creep, I suggest you hire an expert. This is not an easy task, nor something that can be learned on the job. Look at some posts of e.g. TGS4 here at ET and learn from him to understand the complexity of this work.

 

[GD2]

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?

You should revisit your design. The top part of 310S you said will be operating at creep (650-675C) and 100,000 hrs. (say 12 operating years ). One of the things designers overlook is the design life when taking stress values from BPVC Sec II Part D. For vessel that predominantly operates in the elastic range but intermittently works in the creep (say during start up, shutdown, upset conditions), this 100,000 hrs design criteria is acceptable. But your case is not this. The Creep is your operating case.
For creep design, The Larsen Miller Parameter (LMP) will kick in and you have to treat the upper part similar to a furnace heater tube. The LMP provides the relationship between the stress, design life and the temp. Using this relationship, you can determine the design life based on the material selected, temp and design stress (not allowable) given. Read WRC 541 to get hang of the concept.