Nozzle reinforcement for high temperature stainless steel vessel 3

[jt1234]

Dear all,
I have a stainless steel (SS321) vessel with design temperature 1050F, not heavy wall, not cyclic service. In general, do you use re-pad for nozzles ? or use integrally reinforced nozzles due to high temperature ?
(If for low alloy, we do use integrally reinforced, but not sure for SS, so that is my question)

 

[DriveMeNuts]

What is the Code?
Is this stainless steel suitable for pressure vessels? I can find it in ASME BPVC.

 

[XL83NL]

With SS I’d even be more concerned in using repads for high temp. Since the coefficient of thermal expansion is higher. So you definitely need to go for integrally reinforced design here.
In general, above 350 I’d stop using fillet welds in any design. ASME BPVC only has certain provisions, afaik, in appendix 2 for certain of flanges that use fillet welds. EN 13445 is more prescriptive and does not allow fillet welds for more occasions beyond certain temperatures.

PS; we always use cjp at these temperatures.

Huub
- You never get what you expect, you only get what you inspect.

 

[CuMo]

Be careful what grades materials you are using because certain aren't even allowed in ASME VIII-1 (if this is the design code)(SA-479 BAR comes to mind) , not to even mention ASME III.

Check ASME II D first what materials are permitted and their upper temperature limits.

To other design codes - the upper temperature limit might not be as high as you need it to be.

 

[Christine74]

Vessel manufacturers typically prefer to use reinforcing pads as integrally reinforced nozzles are quite expensive, especially true for stainless material. However there are some exceptions, for instance if a Long Welding Neck flange meets the required area replacement of the opening then that may very well be less expensive than installing a reinforcing pad, especially if its a small diameter nozzle.

I'm not sure I buy that thermal expansion would be an issue here as you would surely be using 321SS for the reinforcing pad as well and the vessel would be insulated, so everything would expand at the same rate. You didn't specify which code you're using but ASME Section VIII Div. 1 doesn't have any upper temperature limit for using reinforcing pads.

I have seen reinforcing pads prohibited for vessels operating in cyclic service, Lethal/toxic service, and hydrogen service.


-Christine

 

[CuMo]

Christine74, you also have to take into account the cost of NDT to be performed on each nozzle & pad.
Sometimes it might work out cheaper to UT + Dye Pen nozzle to shell using a LWN nozzle, than UT+Dye Pen nozzle to shell, pad to shell, pad to nozzle and X-Ray + Dye pen the pipe to a RFWN flange.

 

[XL83NL]

ASME VIII-1 App. 2, para. 2.4(c); fillet welds are limited to 370°C. API TR 942B also has several references where fillet weld design has shown to be susceptible to (a.o.) SRC.
The specs Ive seen have all prohibited fillet welds for anything greater than say 350-400°C.

Huub
- You never get what you expect, you only get what you inspect.

 

[jt1234]

Thank you all who understand or not understand my question.
I dug out from SHELL DEP pressure vessel spec and found out it does say re-pad shall not be used for temp above 900F with P8 material. Trusting SHELL has done diligent research to come up with this requirement, I will do the same by using integrally reinforced nozzles. Case closed.

 

[GD2]

In principle, any repad welding whether in the form of nozzle repad or pipe supports is limited to 427 -500 C 9depending on MOC. This is due to the fact that the repad forms an extended surface like fin and the differential thermal gradient and therefore, expansion of the base metal and the repad causes the weld to crack.
It is common to see this limit in many Owner's specification.

GDD
Canada

 

[r6155]

Never use nozzle with reinforncing pad when thermal insulation is required.

Regards

 

[jt1234]

r6155, never heard of that for hundreds of towers and drums I have actually designed and purchased for the past 30 years.

 

[YuJie_PV]

agree with XL83NL,it's also my experience.