Piping Exposed to slightly higher design temperature

[NovaStark]

Hello all,

Currently at my site, we have some piping that is designed to 1100 psig and 650 degF.

However due to operating issues, the piping has been exposed to 900 psig (normal operating) and 670-690 degF (max).

From my basic check, thickness is sufficient for the elevated temperature, flange rating is okay (tho everything is welded on this system).

So the only thing not checked as yet is the nozzle loading and pipe support loads via stress analysis. However for a 40 degF differential, should loading be so significant ?

Is there anything else that should be typically assessed here ? From appendix V in B31.3, this seems to deal with piping within the creep range, but this system is below that threshold.

 

[XL83NL]

Degradation mechanisms of materials which may or may not come into play. You haven’t mentioned the material yet. 690 short term isn’t damaging to most materials, but it’s just one of those checks that needs be verified.

Furthermore, does app V only apply to creep? IIRC it is also for below creep.

Flange ratings is another one to be checked. Soft goods for sealants maybe? And instruments which may have another rating?

Huub

 

[NovaStark]

@XL83NL

Yes instrumentation and damage mechanism would need to be taken into account as well. The material would be ASTM A358 Gr. 304 pipe (so stainless).

The application section of App V, states:

This Appendix covers application of the Linear Life Fraction Rule, which provides a method for evaluating variations at elevated temperatures above design conditions where material creep properties [see para. V302(c)]control the allowable stress at the temperature of the variation.

So based on that, the piping isn't in the creep range from API 571.

 

[XL83NL]

Correct. Isn’t there some other application in B31.3 that allows for short excursions above design conditions? Somewhere in para 302? Don’t have the code at hand so I could be wrong.

Huub

 

[NovaStark]

@XL83NL: Yes there is a paragraph that states for short durations e.g. 50h but not more than a certain number of times per year.

But I am referring to longer usage in the order of months rather than re-rating a piping system.

 

[mk3223]

It looks that you want to operate the system at higher temperature condition.
You may need to recalculate the material A358-304 using the allowable stress per B31.3 A-1 table at higher temperature and verify if the existing pipe is suitable for it.

IMO, B31.3 para 302 is applied for the occasionally overpressure condition, but not for the over-temperature condition. Need to verify it.

 

[KevinNZ]

If you want operate (not short event) above the original design temperate then the whole design needs to be repeated with the a higher design temperate. That means all original calculations, hoop, sustained, thermal, seismic, wind, support loads, gaps on supports etc.

 

[NovaStark]

@mk3223/KevinNZ

At this point in time, the operating limits of the system are now back into specification. So to check if anything "detrimental" happened to the piping, it seems that an essential stress analysis at the elevated temperature would need to be done. Am I interpretation that correctly ?

 

[0707]

The creep depends on time and temperature and pressure if your pipe is TP304 at 355ºC you are far from creep range for this material any way, 63Kg/cm2 is an high pressure, If the thicknesses of your pipes are ok I think you are working safely.

luis

 

[mk3223]

So to check if anything "detrimental" happened to the piping, it seems that an essential stress analysis at the elevated temperature would need to be done

It's correct that this is one thing to check. In additional to the pipe material, you may verify other components in the Specification for any temperature sensitive material, such as seating, packing, etc.

 

[NovaStark]

Thank you all for your contribution!