Exceeded MAWT
Exceeded MAWT
(OP)
If the MAWT of an ASME stamped vessel is briefly exceeded, is there anything (like a fitness for service calc or ???) that would be required to continue using said vessel?
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RE: Exceeded MAWT
jt
RE: Exceeded MAWT
RE: Exceeded MAWT
It is not solely restricted to flow as it is can be shown to occur in "dead leg" piping as well.
Here is one article...
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RE: Exceeded MAWT
jt
RE: Exceeded MAWT
A-All the "hydro" units I am familiar with were internally insulated; "cold wall" design. So it was very unusual for the shell temp to approach design. Is that your case ?
That being said , some of our reformer vessels had temperature sensitive paint so any hot spots could be located and measured.
B-For some vessels, coupons were cut out for creep-rupture testing (maybe a nozzle cut out); Expensive, but definitive.
C- Some bulging was tolerated (years ago) after hardness testing and crack/flaw testing were satisfactory.
D- For carbon and 1/2% Mo vessels, the possibility of high temperature hydrogen attack must be considered (that is where some of the Nelson Curve data came from). I don't think that is a concern for 2 1/4 Cr : 1 Mo; and likely 1 1/4 Cr : 1/2 Mo.
RE: Exceeded MAWT
No skin TC, yes the internals are by the "G" company. Not cold walled, material is 321 SS clad on 1 1/4 Cr. Will include a visual inspection following any temperature excursion.
RE: Exceeded MAWT
I would be inclined to follow a similar approach to ASME B31.3 Appendix V, adjusting for the caveats and limitations therein specified.
Many years ago, I devised a guideline wherein the Larsen-Miller parameter was used to generate a plot of excursion temperature versus time (for a given pressure) for a carbon steel piping system that had been designed for saturated steam but occasionally experienced superheated steam conditions. In that case, I limited the "zero time allowed" threshold to 427 C, which was the Code-accepted graphitization threshold. This produced a curve that fell below the creep rupture curve, and to which excursion monitoring and safeguards were effected. Basically, I created an envelope from which each excursion duration could be cumulatively deducted from the theoretical creep rupture life. It was approved and adopted for use in a fairly large refinery, after meeting with approval from the local Regulator. At that time, either "Appendix V" did not exist or I certainly wasn't aware of it. Nor did I have any benefit of the paper entitled "Graphitization Of Steels In Elevated Temperature Service" - Foulds / Viswanathan, Journal Of Materials Engineering And Performance, Volume 10(4), August 2001.
In this case, I suspect that creep and other damage mechanisms are more a concern than graphitization. I think ASME VIII Division 1 probably refers one to Section II Part D for properties at elevated temperature, but otherwise, I would anticipate that a creep analysis might be the course of action unless there is visually observable gross plastic deformation.
Regards,
SNORGY.
RE: Exceeded MAWT
RE: Exceeded MAWT
- original desing diff expansion expectations may have been exceeded, and bumpers / supports limits may have been exceeded with reslting high stress on attachments
- weld interface between SS cladding and 1.25% Cr shell has a thermal generated shear stress related to the difference in thermal expansion coeficients of SS and 1.25% Cr, may need to check for delamination at weld interface using UT
- if the current overheat is judged OK, its publbication may lead to operators allowing add'l overheats in future- a sort of "mission creep"- leading to later damage