Clad Tubesheet for High Temperature application

[MikeG7]

Please can the forum members advise on suitable carbon steels for Hydrogen service 465 Centigrade tubesheet design according to ASME UHX and please note the tubesheet is clad. Is the cladding ignored in the design calculations for the thickness? Cladding is stainless steel. Does the Hydrogen service require any additional checks (e.g. embrittlement?)
Regards
MikeG7

 

[SnTMan]

MikeG7, carbon steel SA-516-70, SA-350-LF2, etc. could be used in the application, but the allowables will take a hit. Hydrogen service should not present any special problems from a material standpoint, but fabrication details are important, especially avoidance of unvented crevices. Stainless clad should be OK.

Cladding should not be included in the thickness for Part UHX calculations. It can be treated as corrosion allowance although this presents some difficulties such as when a pass groove is used, and with any uncorroded output data.

Can't remenber offhand but your design temp may put you in the time-dependent property region, if so, particular requirements in allowables and in Part UHX calculations come into play.

Maybe a lo-alloy would be a better choice.

Regards,

Mike

 

[MikeG7]

Mike, thanks. This is a replacement tubesheet. The existing one employs SA182 gr.12 which seems to hold it's allowable strength according to section II at these temperatures. I have recently done some work with A516-70 at around 360 C but that was about the start of the creep range, maybe a bit higher towards 400 C.

I haven't done much creep work so I am not sure, just a question: Are the time dependent (creep) requirements not already taken into account in the reduced allowables?

Sorry, but I don't get what you mean by "uncorroded output data"? Please clarify.

Thanks once again
MikeG7

 

[SnTMan]

MikeG7, yes, creep requirements are addressed by the allowables, but there are also other restrictions in the Code when in the creep region. See for example UG-23(e) and UHX-13.7.2

By uncorroded output data I am referring to any "New & Cold" data (such as MAWP) that may be calculated. For example if cladding is treated as corrosion allowance, the thickness it represents is assumed to be present, but its allowable is assumed to be the same as the base metal. Any calculations based on the new thickness are therefore not correct. True, the errors may be small, but they will be present.

I have not seen software that will account for the difference in allowables as per Part UCL-23(c).

Regards,

Mike

 

[MikeG7]

Mike, once again thanks. I have a bunch of questions about creep but will leave that for another time.
Regards
MikeG7

 

[SnTMan]

MikeG7, thats good, I am not the guy to answer detailed creep questions, but those guys are here

 

[jamesl]

If the equipment is in hydrogen service, you don't want to use carbon steel at 465 deg C. It may be OK for 465 deg F, but definitely not OK for 465 deg C. Go check API 941.