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New steam flange bolts coming loose multiple times

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
    Ironman Member Posts: 7,350
    Double nut the bolts.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pecmsg
    pecmsg Member Posts: 4,696
    Tighten them.
    Come back in a day or 2 and snug them up while hot.

    I ASSUME lock washers are in use.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,578
    edited January 19
    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
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Jamie Hall
    Jamie Hall Member Posts: 22,928
    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.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ScottSecor
    ScottSecor Member Posts: 843
    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 Member Posts: 15,329
    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
    retiredguy Member Posts: 884
    edited January 20
    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
    Hap_Hazzard Member Posts: 2,849
    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.
    Just another DIYer | King of Prussia, PA
    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24