Corrosion In Polyethylene Reactor Bolts

[ak1965]

Dear Forum ,


I need a help to find out the criteria for deciding suitability of service for corroded Studs in a loop pipe reactor in Polyethylene plant.

Service conditions are 210 KG/ Cm.2 & 230 Deg. C temp.
Bolt material is SA 193 Gr. B7. & the size is 1 5/8" with 320 mm length.

Bolt threads are corroded due to high temperature & exposure to open atmosphere. I have pictures of corroded bolts, but dont know how to post them to forum

What should be the criteria for replacement of bolts & what NDT & destructive exmaination (on line & offline) should be conducted to decide for replacement plan?

Thanks

 

[vesselguy]

You must have at least 1/4" or more of threads above the nut. If the threads are corroded and I assume this is part that you're saying is corroded. So when you say corroded, you do mean some threads are gone right? If so,I don't know what there is to test? It's only carbon steel studs.. If I'm not wrong it is cheaper than the reactor and way cheaper than insurance payout for dead workers. Suggest you just replace them at a shutdown. No worries after that.

 

[ak1965]

Dear Vessel Guy,

Thanks for sharing your thoughts. Infact, threads under the nut can not be checked at this stage because the vessel is in service. However, These bolts are very difficult to open therefore, we wish to become doubly sure before recommending for replacment.

Any other idea to share please !!!

 

[vpl]

ak1965

You commented that you have pictures, but don't know how to post them. One of the links in my tagline is to a FAQ on how to post images.


Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

Want to post an image? Look at the FAQ's in forum559

 

[gr2vessels]

ak1965,
Please read again vesselguy's reply. If the thread on the studs above the nut have corroded away, those stud bolts are not safe anymore for use and must be replaced for safety reasons. I imagine that the difficulty you mentioned is not the removal of the studs, but the plant shut-down for the opening of the vessel. I also imagine that you don't have a qualified field inspector and you have to make the painful decision of informing the owner of the vessel that those stud bolts must be replaced.
Please inform your superiors that will cost much less to replace the stud bolts, than performing some ndt's and other tests on those corroded bolts. The bolting can be ordered with PTFE coating to help with the external corrosion problem. I don't believe the temperature is an issue, because at 230 deg C the external moisture would evaporate instantly. I do believe however, that the bolting real temperature is under 100 deg C and you do have moisture on the end of those bolts, helping with the corrosion of the threads.
By the way, if ak1965 is related any way to the Kalashnikov machine gun, I can imagine the pressure you are under, recommending the replacement of those bolts.
Cheers,
gr2vessels