When or how often should flange bolts be re-torqued?

[KernOily]

Guys here's a question... I am in a debate here as to whether flange bolts on ANSI (or API) flanges should be retorqued. I have not researched the issue but it seems to me that unless the fluid service is cyclic, or subject to vibration, that there is no need to retorque flange bolts. Your thoughts?

Thanks!
Pete

 

[aybee]

if the initial torque allows for the thermal increase in the bolt length during cold-operational temp change plus an allowance for bolt/gasket relaxation which is up to 30% over time then you should not need to re-torque. this is a simplistic view though because the flanges may creep over time and rotate allowing the tension to lower..

 

[MJCronin]

74,

Another occasion when bolts must be re-torqed includes lined piping systems....particularly PTFE. Crane's resistoflex lined piping requires ANNUAL RETORQUING !

See

http://www.resistoflex.com/Flange_Bolt_Torquing.asp

Gasket Mfrs Recommendations and comments:

http://www.dracomech.com/gaskets/boltinfo.htm

It seems that most gasket manufacturers would like a retorque for any bolted application in order to ensure that gasket compression/creep has been given a chance to occur.....

Easy for them to say..... sometimes hard to implement


MJC

 

[TD2K]

Pete, I'm not familar with retorguing flanges on a routine step. When we would chill down the ethylene plant to operating temperatures, we would constantly walk the units looking for any signs of flange leakage from the thermal cycle concentrating on any flanges broken during the shutdown.

Any leaks were tightened up online (luckily, we never had any leaks we couldn't stop this way). We didn't go through the entire unit again and retorgue everything although I could see the value of it when you are chilling equipment down from ambient to as low as -160C at the coldest.

Let me check with a couple of contacts at the local refineries and see what their practice is during a T&I.

 

[11echo]

Actually ...this topic had just been addressed where I work. We have a number of steam pipeline, and if leaks start can do serious damage to the piping components. SO we started a maintance schedule to re-torque the studs AND valve bolts(bonnet bolting) once every year. This is in a oilfield application. Good Luck ...11echo