Reduction of Scale during PWHT?

[andrewsjo]

I am currently involved in the design of a jacketed pressure vessel. Per the ASME code, we are required to complete a PWHT. The vessel is very simple and there is nothing out-of-the ordinary with the design. However, we are concerned that a PWHT would create scale/oxidation inside the jacket that is is not accessible for cleaning/gritblasting.

Are we over-reacting? are there easy (cheap) ways to prevent oxidation/scale?

Oh yeah, the tempeprature is 1100F for 4 hrs or so...



John Andrews, PE
Mechanical Engineer
Artisan Industries Inc.

http://www.artisanind.com

 

[unclesyd]

Assuming Carbon Steel.
It will not scale at the temperature you state. You will get a little heat tint which is not detrimental to the heat transfer process.

 

[metengr]

I would agree, as well. We have performed numerous PWHT operations on carbon and Cr-Mo materials with no significant problems related to scaling from exposure to PWHT temperatures.

At 1100 deg F, you will have slight oxidation on the surface with no real scale build-up.

 

[andrewsjo]

Thanks for the responses. The idea of an argon or nitrogen blanket during PWHT has been floated to avoid even the slightest chance of oxidation. Any thoughts?

John Andrews, PE
Mechanical Engineer
Artisan Industries Inc.

http://www.artisanind.com

 

[unclesyd]

Either gas can be used but you have to be careful with the flow. Keep it very Low.

I'am a loss to the reason for the concern over the heat tint. On a lot of our equipment we purposely create a heat tint (bluing) on carbon steel jacketed equipment.

Could you post what will be inside the jacket.