Underground galvanized pipe protection 1

[Tecnoconsult]

I have a situation in which my client is requiring that the potable water lines be underground. This is galvanized pipe and according to general specs from the client , underground pipe need to be sandblasted and covered with coal tar epoxi. is it required to do this? can I install this pipe naked?
gerardo

 

[hydrae]

It depends on how long your client wants the pipe to last, Galvanized pipe has a level of protection from the galvanizing but it does not last forever, but minor imperfections and damage in the coating are not catastrophic, because the galvanizing process penetrates the outer layer of the metal.
The method suggested by your client may last longer but only if it is installed perfectly, any pinhole in the coating caused by either poor coating application or damage during installation or by the backfill material will cause an acceleratied corrosion at the point of defect. Additional requirement of holiday detection and cathodic protection typically are included in this type of corrosion protection system.
Hydrae

 

[imok2]

Many homes in this country (USA)have been piped with Galvanized pipe and usually last about 18-25 years. burried in soil of various PH conditions

 

[PUMPDESIGNER]

An interesting note on this.
Almost all galvanized pipe failures occur in the following places:

THREADED JOINTS - Wherever the galvanized coating is removed as threads are cut, and the thread cutting reduces wall thickness by about 50%.

AIR WATER INTERFACE - Wherever there is an air water interface such as occurs where the pipe exits soil or where the pipe goes below a water table underground. The interaction of the air and water close together create extremely fast corrosion which many have seen as a line of crusty flaky rust right where the pipe enters the soil.

CONTACT WITH CONCRETE - Do not allow concrete to touch the galvanized, always sleeve the galvanized pipe where it passes through. This is especially true where the concrete may retain moisture such as floors.

Pay very close meticulous attention to those areas or all other efforts are useless.

PUMPDESIGNER

 

[CRG]

Avoid using threaded connections underground. Will your client accept Type K copper with dielectric breaks after piping comes above grade? CPVC or PVC might be a suitable product for the underground portion of this application. I would try to sell the client on something other than galvanized pipe for below grade service. If the client insists on steel piping below grade, I would try to talk him out of the galvanized coating. Then, I would recommend welded connections with cathodic protection that was prescribed by a corrosion engineer.

Is the client’s general specs for process piping? Do the specs fit the application you are trying to design? If not, discuss writing a new spec for underground potable water. Also, threaded galvanized steel pipe would not be my choice for above grade potable water, unless there was some compelling reason why it was necessary. Is there a reason why Type L copper is not used above grade?

 

[Zambo]

Have you already bought this pipe. HDPE would be a better material, there are either flange adaptors or mechanical couplers to change back to galvanised pipe when above ground.

I have a feeling (possibly wrong!) that this is a temporary site supply and the Client is making you comply with his general permanent works specs. If this is the case you could agree to remove or fill the line after use.

Zambo