Drift in Ductile Brittle Transition Temperature (DBTT) 2

[GasGuy]

I am trying to determine an appropriate temperature margin to account for drift in the ductile-brittle-transition-temperature due to pressure vessel age.

I have used API RP 579 to determine the minimum allowable temperature for the vessel thicknesses / materials but want to add a margin to this. The vessel is a reactor at an oil refinery and is made from ASTM A204 Gr.A (C-1/2Mo) and ASTM A182 F11 (1 1/4Cr-1/2Mo).

Any ideas or references on where to look for this information would be appreciated.

 

[metengr]

GasGuy;
Too little information to provide any help. What are you really attempting to do? Are you wanting a reason to derate or decommission the vessel because of concerns with service induced embrittlement or simply old age?

There is more to embrittlement than simply age of the vessel. Normally, the concern with a shift in the original ductile to brittle transition temperature (DBTT) is a combination of exposure to elevated service temperature and time at temperature. In some cases, the increase in DBTT can be as much as +150 deg F or more, it all depends on actual service temperature and the chemical composition of the steel.

If you need to estimate minimum design metal temperature or DBTT for these steels, API 579 is the way to go and do not unnecessarily invoke more conservative measures.

 

[davefitz]

is it feasible to remove several sample coupons and test in a lab?

 

[GasGuy]

Metengr;
Not looking for a reason to decommission vessel, but wanting to ensure I have accounted for everything in my DBTT calculation. This reactor vessel has been operating for 30 years at temperatures up to 400-500°C and the client is concerned there may be a drift in transition temperature that can occur with reactor age.

We have no sample coupons that can be tested. Is there any other way to determine if DBTT drift is occuring?

 

[metengr]

From my experience, the F11 material should not really suffer from embrittlement (shift in DBTT) in this temperature range.

The concern I would have is the potential for graphitization in the C-Mo material. The service temperature for this material should be limited to 800 deg F or less. If you have this material exposed to higher service temperatures for prolonged periods, graphitization is a possibility. In this case, I would perform some field metallography to evaluate the microstructure of the pressure vessel steel plate (A 204). This is a nondestructive test method.

 

[davefitz]

F11 , P11 and T11 have been used in section I service up to 1000F for decades, but with issues. It is the most likely upgrade from carbon steel if teh design metal temp is 800-900 F, or if mitigation of erosion-corrosion is required.

The latest "state of the art" of drift in ductile brittle transition temp may be found in the 2006 PVP ( Vancouver), paper ICPVT11-93652 by M.T EricksonKirk , and his referenced papers.