mohd,

I suggest that you consult the piping design code that governs your installation. Look under the section that describes "minimum wall thickness" or "calculation of wall thickness" This section will give guideance on the maximum "gouge" size that can be tolerated without repair or replacement.

Look at the section that describes "out of roundness". This will give you some direction on the size of a dent that can be tolerated.

Good Luck !

MJC

It really does depend on the code you are bound to.  I've done a lot with natural gas pipelines in the United States following the proscriptive regulations in 49 CFR 192 and the suggested guidelines in ASME B31.8.  For lower pressure systems with small blunt plastic deformations you can do almost anything (or nothing).  That all changes when you have stress risers, pressure cycles, thermal cycles, and severe plastic deformation.  Leaking pipelines are also a different animal.

There are tons of ways to fix these defects.  The best is probably to just replace the cylinder of pipe that is damaged.  Barring that you can use full-encirclement fittings (bolt-on or welded), patch repairs, and even some composites.  You might want to check out:

http://www.plidco.com/

http://www.dressercouplings.com/gas_prod/gclamp_sleeve/gclamp_sleeve.html

http://www.allanedwards.com/steel.htm

http://www.clockspring.com/

Good luck.

CR Alexander and JF Keifner has done an in-depth study sponsored by API to determine dents on intehrity of the liquid petroleum pipeline. It appeared in the June 1998 issue of the Pipeline and Gas Industry journal (archives available in the web).

Another reference i can suggest is the pipeline welding and inspection published by AWS based on the proceeding of Conf Ag 1980. A paper again presented by JK Keifner where he talks about dents and gouges (page 77).