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Jam Nuts 1

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kat6787

kat6787

Marine/Ocean
Sep 8, 2006
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I'm trying to find information about the use of jam nuts and their reliability. Is there any documentation about the benefit of using one nut versus two on a pipeline flange? Any thoughts or ideas are appreciated.

Cheers,
Kat
 
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I'm actually working on a failure analysis, and I was asked to do some research on the subject. Thus far I haven't been able to find any solid documentation. The only thing that I have found is that there is a consensus that jam nuts are unreliable and depend too much on the person installing them. That being said, I still need to have something to show for my time spent researching.

 
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I have noticed there is some interesting commentary of various locking means and effectiveness of same etc. at the sites and also the FAQ's at (it appears this site indicates conventional "jam nuts" as well as conventional washers and lock washers may not be as effective as more contemporary means or without to prevent loosening, under conditions tending to cause same).
 
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You're using JAM nuts on a pipe flange assembly? ...Well let’s walk this down. NORMALLY you use "2H" nuts on this type of installation (flange assembly). A 2H nut is taller then the standard nut, to increase it's holding strength. A jam nut is thinner by half a standard nut height, jam nuts are used as leveling device under base plate to get a particular elevation on a peace of equipment. And this space under the base plate is normally small (or height limited if you like that term better) and the use of a "thinner" nut normally aids in that type of installation. This area is grouted to insure the equipment is permanently placed. …SO I have to ask WHO thought of using jam nuts on a flange assembly?
 
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Either I was mis-informed or there are several definitions of what a jam nut is and how it works. I was under the impression that a jam nut had nothing to do with leveling a piece of equipment to get a particular elevation. The definition I was told was that a jam nut is used to lock a bolted connection. If this is not the correct definition please tell me what resource you are using so I can be better informed next time I have a similar question. As to who thought of the question, it was brought to me by a supervisor as a hypothetical question. I included the information that it would be on a pipeline flange to pre-empt the inevitable questions I would have gotten about the application of the jam nuts in question from people trying to help me find an answer to my problem.
 
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The aircraft style nut is a Nylok (sp? or Nylock)which uses a nylon compound if I am correct. It is used to ensure a nut stays tight. We used Nylok nuts a lot on submarine subsafe equipment.
Bubz
 
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Kat, You are using 'Jam nut as in "double nutting."

In my experience, the very best thing that can be done w/ flange bolts is to star torque to pre-set values w/ a compound (gear driven) torque wrench. DOuble nutting after that simply tries to maintain the first 'torque' value. Two things you need: (1) longer bolts, (b) two additional nuts per bolt plus the 10-20% normally lost. I know of no spec, code or requirement for double-mutting any offshore P/L flanges. Until then, it's not required and will raise costs (in time if not material).

We normally follw codes and specs which the client needs. If a client WANTS trhis - give it to him after explaining the labor and material cost. But remember: Its star-torquing that counts, everything else is BS.


regards.

ima-nemisis doig
 
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