Thermal shocking of carbon steel pipe 1

[makeup]

I've been posed with a question and would like to find out more:

We are working on a propane cooling system which has the potential under failure to expose local piping systems to flash temperatures below the recommended operating temperature range of the plant steel. Given that these flash temperatures if they occur will be short lived what are are implications on the piping. Should we engineer to the lowest possible temperature???

 

[metengr]

makeup
This is an excellent question because as the Engineer you need to evaluate the probability of occurrence. Is the exposure to the carbon steel piping external? If so, perhaps insulation would be all that you need.

 

[ash9144]

From the op I would assume the low temp comes from propane flash. As Met mentions you need to look at the probability to determine if this is a normal occurence or not. One solution would be to accomplish the flash and use one of your cold fluid streams (such as brine) to provide the heat source.

 

[EdStainless]

You also need to asses the risks. If this happened once would it lead to immediate failure or would you be able to inspect and repair afterwords?
In cases that I have seen the metal temperatures don't rise that fast (a gas cools much slower than a liquid). If the duration would be short then your real concern should focus on connections and restraints nearest the cold end of the system.
Considering the amount of gas and time involved you may choose to design part of the system to handle the conditions.

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Plymouth Tube

 

[makeup]

Thanks so much so your information.

Just to confirm, it is process pipework in question and it is the internal surface we are focusing on initially.

In brief, the project is to combine 2 propane chilling systems, one primary and one secondary. The primary system was originally designed for -12deg and the secondary -28deg operation. The primary compressor is to be abandoned and the secondary will a lower operation temperature retained.

In combining the 2 systems we now potentially have to include new standards for design, the grandfather clause is no longer suitable. One new condition for design in adiabatic flash temperatures now going down to -49deg.

This is not a problem for the areas we are proposing to modify when combining the 2 systems but it is a problem for the retained process plant/equipment/piping. We have considered putting in temperature transmitters and shut-offs but the HAZOP raised the question, what if they fail. Hence my question.

The probability/risk assessment case does sound like a very good and economical way forward as it would be nice to think that we will never have this type of event/exposure.

Thnaks once again

 

[MJCronin]

makeup....

Consider this report of a 1999 disaster of a flanged carbon steel piping system.

http://mahbsrv.jrc.it/downloads-pdf/ASTM_A_105.pdf

Also see the failure consequences contained in this report.

http://www.csb.gov/completed_investigations/docs/CSBFinalReportValeroSunray.pdf

Let us know what your final decision is and how you justify it....

-MJC

 

[nickelkid]

Within the last month we had a similar challenge presented to our office. The potential client wanted FEA to validate that brief exposures to carbon steel piping below its Minimum Allowable Temperature would be acceptable. We kindly advised them to use the correct materials without charge. NB it was an existing system.

A very helpful and relevant reply on this topic, thanks MJC; it is unsettling to think of how many of these potential disasters exist.

 

[strider6]

i think you should follow the code used to design the piping systems. for example ASME B31.3 and also EEMUA allow to go below the min temperature for a specific materials if the ratio of the stress is below a certain theshold. regarding the Risk assessment in API 581 there is a module to evaluate the risk of a brittle fracture.


S.

Corrosion Prevention & Corrosion Control