Underground CS piping flange and bolt corrosion rates

[mechengr12]

Long story short currently have a carbon steel pipe buried underground with two exposed flanges and flanged valve all underground. Carbon steel nuts and bolts were used. Plan was to leave the hole open until the next outage in 2-3 years and then redo the piping to remove the valve and add a coating for corrosion protection. A contractor proceeded to bury the pipe with sand. Has any one experienced corrosion rates of carbon steel piping and components underground that would suggest that 3-4 yrs underground is unacceptable and a leak could occur? My thoughts are that the electrochemical reactions driving the corrosion will be low enough not to warrant us to excavate the area.

Thanks

 

[pennpiper]

Well it's too late now.

Rule #1 DON'T put Carbon Steel underground.
Rule #2 Coat the Flanges and Valve with a Tar based mastic (like they put under roofing shingles) and wrap it all with moisture resistant tape
Rule #3 As soon as possible get rid if the CS Valves and Install Cast Iron Valves and Flanges (if they can take the Service conditions).
Rule #4 Don't rely on "sand" to be a good alternative.




Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

Clean, dry sand is one thing, but typical sand is quite another story. It can hold a lot of water, salts, and be composed of various minerals. Corrosive oxygen rich, rainwater migrates easily between grains as just about anything else will do too. Sand isn't always just sand.

Electro-chemical reaction is only one method of driving corrosion. Different voltage levels, induced currents are others. There may be stray current from other nearby installations, utilities, power lines, gophers nibbling underground electrical cable insulation and varying voltage potentials driven by other pipeline CP rectifiers.

Excavate and coat all metallic materials ASAP. Use a mastic, expoxy paint, or tape coating system of your choice. Cover bolts and flanges with protection kits.

Corrosion is the single most common and dangerous form of pipeline damage. Corrosion rates can be at times very surprising. Do you want to be safe, or sorry.

 

[LittleInch]

Ok,

A few questions - Is there CP on the "pipe". Can you put any on it (sacrificial)

Was there any sort of coating or grease or anything on the flanges?

What type of flanges / gaskets or ring joint.

What's in it and at what pressure?

Where is the water table / soil conditions (dry, wet, salty??)

If negative to the first two then 3-4 years is probably a bit too long. Your real issue is probably crevice corrosion of the faces of the flange rather than corrosion of the bolts causing failure, but you will probably have to cut the bolts off when you remove it.

When you assemble all the items above then you can start to make a better assessment of a leave it for 3-4 years or dig it up now scenario.

Me - I would dig it up now and protect it better. 3-4 years has a habit of turning into 7-8....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.