High Temperature

When reviewing the code allowable stress tables, moving you finger down the page a bit past the carbon steel tubes, and pick out an alloy tube.

Read the notes for the material in SecII D.

See SecVIII Div 1 UG-20 (c)

Tankman650-

One word: REFRACTORY

As deanc pointed out, exceeding the max listed temperature is not permitted. To get a 1200°F hot wall design, you're looking at a 1¼Cr or higher material as davefitz referred to. Even then, it would be hugely uneconomical: Look at the allowable stresses at 1200°F compared to even 1000°F. You'll find a factor of roughly 6x. Sounds to me like you need to sharpen the pencil on the HAZOP (ie reduce the design contingency) or do what everyone else does and design a cold wall refractory lined carbon steel vessel. Although the design of a substantial vessel at 1200°F would be kind of fun... The vessel itself, internals, piping, L&P's...

jt

Thanks for the responses.

I am not trying to certify to 1200 F. I want to verify that the structure will not colapse under PWHT conditions. This is a non-code issue but an issue never the less.

I do have a large vessel under much dead load.


Thanks again.

Be very careful here because creep (short term) will result in distortion, which will be a concern if you have too much static load while attempting to perform PWHT of fabrication or structural attachment welds.

Make sure the vessel structure is adequately supported and if necessary stagger your PWHT schedule to compensate for loss of strength of carbon steel during PWHT.

You need to get the material properties from reference material such as ASTM Special Pub 180 (was available from UMI Out-of-Print Books on Demand) or API 579.

We would also consider creep buckling.

Tankman650-

A field PWHT. Gotta love 'em! These can get difficult though. As pointed out above, you can consider a PWHT of circumferential segments while adjacent ones carry the load. For example, divide the circumference into eight 45° sections and PWHT alternating segments with a bit of overlap. Then go back and PWHT the segments which were cold the first time. Be careful here with potentially high thermal stresses. The other approach is to PWHT the entire band at once and consider creep buckling. The ASTM publication bvi referred to might be the same one I got from the ASTM which is ASTM Data Series DS 11S1 (Supplement to Publication DS 11, formerly STP 180). If you call the ASTM they won't find it in their listing on the 'puter but with further encouragement they did find it on some other list. API-579 appendix F will provide similar data.

jt

tank,

Carbon steels can only be used to service temperatures about 775 to 800F. Above that temperature, they will degrade in a process known as graphitization.

Low chrome alloy and stainless steel materials have been developed to operate in the ~1200F range.

Try ASME SA335-P22 or P91 for your PV or ASME SA 240-type 316 or 321.

These materials all have been used in this temperature range....

My thoughts only.

MJC