Pipe exposed to hydrogen flame

[ashfaqanwer]

Recently, we had an incident at our Plant when a thermowell got detached from a Syn Gas piping and the gas caught fire. The flame completely damaged the nearby insulated piping and the bare piping then exposed to the flame for about 25 minutes.

The nearby piping is in different materials including A333 Gr. 6, A106 Gr. B, A335 P11 and A335 P22. We have visually examined the piping and there are some apparent marks of flame exposure plus burned insulation / cladding.

In order to ensure the mechanical integrity of piping, we have taken hardness readings on the piping which was directly impinged by flame. The hardness reading for that specific piping in A333 Gr. 6 material is coming out to be 80 BHN which is a too low number. Unaffected metal hardness is in the range of 140-160 BHN. Based on this hardness check, we are planning to replace this affected portion of piping.

Should we do any additional checks also before replacement of pipe or hardness is OK in this specific case as it's too low? Is there any other reliable method like some sort of heat treatment to increase the hardness of the affected portion?

Need your value comments.

[arcpro]

The hardness value is too low and with any of the heat treatment you cannot get that mush rise with sound mechanical properties.
Replacement is the way to go in my opinion.

[irish]

The complete evaluation of such fire damage is assessed in line with API 579.
API 579 defines the whole set of evaluation and takes you through the stages of assessment.
But just to confirm, you are on the safer side with the replacement decision as the hardness is too low. You cannot live with this much of hardness.
How much is the affected portion?

[ashfaqanwer]

Thanks arcpro and irish.
irish, the affected portion having hardness lower than the sound area is almost of 10" diameter. And we are replacing the whole pipe length between the two adjacent butt welds (2.4 m long). Pipe is of 16" NPS 36 mm thk.
I will attached the sketch to bring more clarity.

[qaisarabbas]

Apart with replacement of affected piping, DPT and MT of nearby welds should also be carried out to assess any possible effect on welds.

[ashfaqanwer]

Here is the sketch attached of the piping area directly exposed to flame during the incident.
Hardness readings have also been marked.

[arcpro]

What's your plan for the small bore piping / tapping or branch connections attached to the affected piping?

[ben]

Your decision is correct as far as replacement of the affected portion is concerned.
Was there some other piping impinged by the flame (indirectly) or faced the heat especially the low alloy one you have mentioned? If yes what checks you practiced for the health assessment?
See part 11 of API 579 in detail to carry out the necessary checks before taking the whole piping in service.

[ashfaqanwer]

Thanks for referring me to Part 11 of API 579. It includes detailed analysis.
For other piping which faced the heat, we have undertaken Magnetic particle and spot hardness checks.

Should we replace the threadolet also from which thermowell got detached?
Hardness check is OK and threads look fine. Request your opinion in this.

[ashfaqanwer]

Thanks for referring me to Part 11 of API 579. It includes detailed analysis.
For other piping which faced the heat, we have undertaken Magnetic particle and spot hardness checks.

Should we replace the threadolet also from which thermowell got detached?
Hardness check is OK and threads look fine. Request your opinion on this.