New steam flange bolts coming loose multiple times

Galvar2439

We installed new 8" flanged gate valves on a 60psi steam line. In the last 9 months it has developed leaks between the flanges. Gaskets were changed, The nut and bolts always get loose and we have to re tighten them. I have never had this happen before. Any ideas? Thank you in advance

Ironman

Double nut the bolts.

pecmsg

Tighten them.
Come back in a day or 2 and snug them up while hot.

I ASSUME lock washers are in use.

EdTheHeaterMan

LockTite® or double nuts with star washers between the nuts

Expansion and contraction happening. This crushes the gasket. Then the gasket does not expand back to its original thickness. The bolts are now loose when cold. Snug up nuts and bolts after about 20 hot to cold cycles. Then do it again after 20 more cycles. Each retorquing will need less tightening. Then again after 20 more cycles. That should be the last time you need to do it. Then do the double nut/lock washer thing

Jamie Hall

And torque them adequately, using a torque wrench. Base the torque on the specification grade of the bolt and the diameter. Don't guess. Also use some sort of criss-cross pattern to torque them up -- don't just go around the circle. If you are in doubt as to the technique, check YouTube for videos on torquing engine cylinder heads.

ScottSecor

We rarely work on high pressure steam. That being said, we see a lot of undersized hardware on all types of flanges. Make sure the bolt diameter is not too small. We often see 5/8" bolts and nuts used on 6" or 8" flanges, most often they should be at least 3/4" diameter.

Any chance the gasket is the wrong type for high pressure steam? Hate to see you go through the re-0torqueing process only to find the gaskets are not rated for the pressure (and resulting temperature).

EBEBRATT-Ed

What did you use for a gasket? You need a metal "Flexatallic" gasket for high pressure.

I have never seen bolts get loose and you don't need lock tight or lock washers. As the pipe expands the bolts should tighten as the heat expands everything.

You may need an expansion joint in the piping if the piping is constrained and can't move.

retiredguy

Do what @EBEBRATT-Ed said, and use "flexatallic" gaskets and also, never use red rubber for the gaskets. If this is a steam line that someone may work on at a later date, I would use "anti seize" on the gasket. In fact, I used anti seize on almost every gasket for water controls for steam boilers since they are supposed to be serviced every year.

Hap_Hazzard

I'd also like to know what the gasket material is. If it's creeping under pressure, that will make the bolts lose tension and loosen up. Also, what are the bolts and flanges made of? Differential expansion rates might be the culprit too.