Online Sealing of Piping Flange Joints for High Pressure

[mthakur]

Dear all,
We all have been using the online sealing system for gas, steam and water line flanges, glands etc since ages. Do you have any experince of failure of studs/bolts while carrying out online sealing of a leaking flange. We had one incident where two studs of a 8" 600# flange joint failed, one after other while carrying out re-injection on it.
any such experince or suggestions on what precautions one should take, also your suggestions on how many re-injection are allowed.
regards,

 

[unclesyd]

Was this failure on a steam line and if so were there any deposits in the area other than the sealing compound. They would normally be white or gray with possibly some rust?

This very important to get back as you might have a problem with embrittlement if steam. If not what was the bolting material and the process material.

 

[mthakur]

hi,
this was a boiler feed line at 200 Deg F at 50 bar. there was no corrosion found on the studs either. the bolting were checked for their composition and it confirmed to ASTM A 193 Gr B7.

 

[unclesyd]

What we are looking for is embrittlement, probably caustic, of the bolting. It usually manifest itself as a deposit on the fastener or around the initial leak as a white , grey, or either streaked with rust stains. There will usually be no visible corrosion.

How long did the flange leak prior to the leak stop?
What did the fracture on the fastener look like?
Can you get the BFW treatment people involved and to do a fracture analysis on failed fastener?

Was there any “slugging” on the studs prior to the either leak repair attempt?
This will increase the fastener stresses making the embrittlement possibility worst.
Have you found any broken studs around any other flanges?

I would not recommend hot bolting, or anything around the piping until you verify the mode of failure.

None of the injection compounds that I’m familiar with will cause this type failure. This is not to say the sealing compound is ruled out.

A little anecdotal but the reason for my concern.
The scariest time in my 42 years in the chemical industry was a similar situation. Walking by a H2 plant I noticed 4 men working around a BFW Heater atop the Reformer, two were mechanics and the other two were leak repair people who were going to attempt to stop a leak on the heater head by slugging the studs then try a repair. There was no reason to be there as the system was online at 1200 psig @ 800̊F. As I climbed the ladder and looked over the edge I saw several broken bolts. I was able to get everybody off leaving everything in its place. As I walked into the Area Supervisors office to tell him he had to crash the H2 Plant, he later told me I scared him to death as I was devoid of color.