SOIL-AIR INTERFACE COOLING WATER PIPING CORROSION 4

[MAG1985]

HI ALL.
IT'S MY PLEASURE TO JOIN THIS EXPERTISE FORUM.
i am not sure is my question in the right place or not.

I experince lately a frequent fialure of piping just below the ground surface and it threathens the plant operation. it would be appreciated if i can get help of how to inspect and repair.

thanks

 

[brimmer]

You need to provide many more details of your situation to get a response

 

[MiketheEngineer]

Probably simple rust - caused by constant water soaking and leaching of some ground chemicals and then air dyring and repeat above about 4 times a month or more!!

What kind of pipe are you using. If steel - I am guessing rust!!

 

[BigInch]

Mike is on the track. Soil air interface, water air interface (splash zone) when offshore are the two most critical zones for corrosion protection. Moisture in the soil, moisture in the air condensing near the coolest portion of the pipe near the ground, rain water splashing up on the pipe after hitting the ground, waves wetting the pipe every 6 seconds, an easily available oxygen supply... it just doesn't get any better than that to start corrosion and keep it going. Always use the best protective coating that you can afford to buy in those air/water/oxygen interface regions.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[MAG1985]

BigInch, Mike and brimmer.
BigInch is typically pinpointing our case which we got severe corrosion at that area and mostly found as exteranlly attacking all round the pipe just like a wide ring or corrosion.

normally, we used expoxy wrap during installation 20 years back, the time comes to have more effective protection. if any body can help of which protection would be more more effective for external protection.

 

[BigInch]

20 years ago, you most likely used a polyethylene tape.

See what you think of these,

http://solutions.3m.com/wps/portal/...ion/Coatings/ProductInformation/PipeCoatings/

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[brimmer]

Here are some of the coatings I have used for pipeline risers at soil to air interface

2 part eopxy - such as SPC or Denso. These would be best. Only thing is they are not UV resistant, so at the interface and where the come above ground wrap over them with any UV resistant coating, or paint over with a UV resistant topcoat. If not covered, these will generally chalk at about 1 mil per year.

Vicous-elastic coating such as Viscotaq or Stopaq - wrap like a tape, but at soil to air interface where there are a lot of soil stresses highly recommend to put their outer composite wrap over top of this to help stop any movement / resist soil stresses

If you must use a tape wrap, then I recommend you look at Polyguard UV 350 or Tapecoat H50. These tapes are UV resistant, thicker, and resist soil stresses much better than a regular tape. You could go cheap and use a different tape, but if you do you will want to put the outer fiber wraps (example Denso Fiber-wrap) over top to resist soil stresses, coating movement (these wraps typically cure in water and are expensive, so you won't really save much money using a tape). If you use a tape remember to always wrap from the bottom going up, this way the overlaps face down and don't trap water.

You could even use shrink sleeves if you wanted to, most are UV resistant. Not the best for this application.

Remember anything but the eopxy is going to shield CP. I always recommend the eopxy first.

Proper surface preparation is the key, don't just stip the old coating and put the new coating on.

 

[MAG1985]

greet inputs by all, appreciate

 

[cvg]

good comments, but may not be the right approach, hard to know without at least some more info. for instance, what type of pipe and fittings, or is it welded? what existing coatings, what is the wall thickness, soil and groundwater properties, any overhead or nearby buried high voltage electrical? perhaps a different type of pipe would be a better approach, or maybe cathodic protection, who knows.