Repair of Leaking Fuel Oil Pipe

[mreale6828]

My subcontractor installed 2" threaded steel pipe for the fuel lines for new emergency generators per the engineer's specifications. The problem is leaking at the joints. He has already made repairs on (3) different ocasions without success. He has changed fittings, pipe sections and pipe dope. His latest proposed solution is to cut out the section with the leaking fittings an replace with socket welds. Does anyone know where I can find the industry standards for this procedure? I am hesitant (to say the least) to allow this subcontractor near the pipe with any type of hot work.

Thank you

 

[Mjconnol]

I would have the contractor check the dies he is using to cut & thread the pipe joints.

It wouldn't be the first time a die was used without the correct taper (or none at all like conduit)

 

[JJPellin]

I would be concerned that the piping was not designed with enough flexibility. If the diesel engine has flexible mounts, the motion of the engine could be flexing the piping and causing the leaks. If you change to socket welded piping, you will be making the piping even less flexible. The next failure could be a cracked pipe which could result in a much larger leak and a potential for fire, environmental incident, etc. A piping designer should be consulted to determine if a flexible section of line is needed to take up the relative motion of the engine versus the fuel tank.

 

[TBP]

If he's using an adjustable die head, I'd suspect that the dies aren't set correctly. Many people threading pipe also think they're somehow doing a better job if they "cut 'em deep". Threading pipe is becoming something of a lost art.

You might check the dope that's being used. Some are limited to a maximum of 1-1/2" pipe. The manufacturer will also list the fluids they're good for, along with pressure & temperature limitations.

 

[abeltio]

threaded pipe will allow dissassembly for maintenance... welded pipe may mean that for maintenance you will have to cut and re-weld.

threads leak because of the reasons mentioned in the previous posts.

vibration can also make a threaded joint leak.

in an installation with leaky threaded joints we added flexible pipe sections at strategic points (there are several manufacturers like swagelok, parker, etc) never had a leak again, and still kept the maintainability of the installation.

granted, there will be an extracost... buying the flex-pipe... but this negotiation is beyond the question raised.


saludos.
a.

 

[pmover]

i trust the emergency generator is an internal combustion engine. regardless, the design should include some type of vibration isolation device between the engine and piping system to avoid engine movement/vibration from transmitting to the piping system. also, since the pipe diameter is 2-inch and there are leaks, i would certainly question the dies used to create the threads &/or the mfg of the fittings.
my opinion only, i would never use a threaded joint > 1" diameter for a fuel piping system. even then, i would limit the number of threaded joints (test and inspection locations). i would plan the routing of pipe to avoid obstructions and ease of maintenance. socket weld and flanges with flextallic gaskets, regardless of design pressure and temperature. threaded joints are a weak joint and are eventually prone/susceptible to leakage; hence, a fire hazard. hence, my justification for not using threaded joints. as far as the welding, use a qualified welder that has successfuly passed the weld procedure/qualification. again, my opinion only.

good luck!
-pmover

 

[Latexman]

I remember hearing something about fuel oil and leaks. I did not look into it, so it could just be an urban legend. Here's what I heard. Fuel oil is very difficult to make leak free when using close tolerance fittings, because it has an extremely low value of surface tension. It'll come right through most screwed fittings, compression fittings, flare fittings, etc.

Antone know if this is true? Like I said I didn't look into it.

Good luck,
Latexman

 

[JJPellin]

Latexman,

What you said about fuel being hard to seal is more true of gas oil, especially when it's hot. Hot gas oil will seep through almost any threaded connection. Hot fuel oil can do the same thing. But the fuel oil that we are talking about here is diesel fuel (I assume) and low temperature. Cold fuel oil shouldn't be tough to seal. It could be bad threads like some posts mention or high vibration / engine movement like others mention. I believe it is probably that later. If it's an engine it has to move and the piping has to be able to take the movement.

 

[rpeng]

My experience is for Marine environments, so vibration and accidental environmental spills are a major concern. All fuel piping is welded or flanged (with appropriate containment). As noted in threads above vibration isolators / expansion joints are a must.