octagonal ring joints. 3

[tel2man]

Can anyone give me any guidance on how many times you can safetly re-use an octagonal ring joint. At present I am getting conflicting information and i am opening out my options.
Thanks.

 

[saxon]

tel2man, Once. Any gasket or seal when used ought to be replaced. The reasons are too numerous to mention. This also applies to bolts and nuts.

Hope this helps.

saxon

 

[Zapster]

I agree with Saxon about replacing the ring joint every time the flanges are separated; however, many folks incorrectly reuse the ring joint. Provided that the stud bolts have not been over tightened they can be used again. If stud bolts are stretched, they should be discarded. The problem is being able to determine if the bolts were over tightened in the past.

Many years ago, I worked for a major oil field service company that would reuse the rings and hammer the stud nuts tight. The stud bolts were never torqued, and as such, I have no idea if we were over tightening them. The same company did not change the packing on their coil tubing equipment as scheduled by contract. They saved $$ by not doing the job correctly. Fortunately, I had the good sense to quite before their reckless practices created an oil spill or injury while I was in the field.

Because you don’t know who tightened the stud bolts in the past, it may be good insurance to replace the stud bolts and nuts every time as well.

 

[DSB123]

tel2man,
I agree with Saxon. Joint rings are made of softer material than the flanges and are designed to "deform" to make the seal. When you loosen the flange they do not "recover" and as such it is dangerous practice to re-use the ring in a joint since it will not be located in exactly the same orientation and "local" irregularities will cause leakage. Always opt for a new ring and the sealing faces should be checked for damage.

 

[tel2man]

Thank's to you all, based on your comments and my own preference i shall alway's be using joints and bolting once.
Just out of interest have any of you heard of KAMOS ring joints which are on the market.

 

[PAN]

RTJ VS RF FLANGES IN 900# SERVICE
thread378-96151

 

[moffen]

The KaMOS gaskets have sucessfully been used in several project world wide and references says it is very time, cost and safety efficient. What did you have in mind??

 

[unclesyd]

As stated in the reference from PAN It is possible to reuse RTJ gaskets, but one has to be very selective in doing so. Everything is determined by the competency of the mechanic that is doing the flange makeup. Watch some of the people working on turnarounds/overhauls today I would not recommend the reuse. I just witnessed a very large overhaul of a system that has a tremendous number of RTJ’s by the majority of mechanics that should have been classified as “hardcore unemployable”. There were more leaks on one system than I had witnessed in 42 years as an employee.

I have never seen a problem with the reuse of studs, B7 or B16, used in the above systems or any system where the stud has been protected from the enviroment. If a stud is tightened properly and has no physical damage there is no reason that it can’t be returned to service. The studs used in the above system have been reused many times and some are the old Crane alloy studs, precursor to B7, over 40 years old. I ran a dimension test on 1000 each of B7 & B16 studs that had been inservice many years by using a thread rolling die. There were only 2 that had been stretched enough not roll on the die. I conducted this survey 3 times over a 20 yr period.

The other half of the plant uses B8 class 2 studs were the reuse, probably 80% is more limited by damage, mainly galling. The original B8's had a much lower reuse factor for the above reason plus having more that had been stretched.

 

[khalidkhattak]

DPT of studs and play of the nuts should be checked... Ring joint sealing surface should be checked...I m working in a petrochemical ... we do not replace ring joint unless we find scratches on sealing areas of ring joint... however for a toxic service (Ammonia) better to replace....

 

[tel2man]

Hi Moffen, this is a late reply but we are using the Kamos to reduce the cost of gross leak testing. We are using 316 st st joints in carbon steel lines and we are torquing/tightening as per Hedley Purvis procedures. It looks a very good cost effective solution as we could re test the joint each time using small amounts of nitrogen thus giving a safer testing enviroment. Our client now wishes to use these gaskets only once hence the reason for the census of opinion.