What Pipe Coating Overlap is Needed?

 How much does my Pipe Coating Need to Overlap onto Factory Coating?

Here is an installed DIRAX - overlapping at least 3" onto adjacent factory applied coating.

     Every section of pipeline that is coated at a factory will have corrosion cutbacks on the ends of the line.  This is essentially, a section of steel at the end of the line that is NOT coated -- the PE coating could be cut off; the FBE coating could be taped off - there are a few things that are done.  Now, when the pipe gets to the field, or the lay barge; those few inches of bare steel at the end of the pipe must be coated --- after the pipe is welded together of course.  That area of bare steel would be called the cutback and someone, somewhere will know what the cutback is.  

     In the case of Fusion Bond Epoxy, it may be only 3" per side.  In the case of three layer polyethylene, it might be 6" per side.  In some cases it could be as much as 10" per side.  There are a lot of reasons why an engineer might request a specific cutback size. 

     So now we are in the field and the pipe is welded together and there may be 6", 12" or more of bare steel exposed.  Let's pretend it is 12" of bare steel.  The field joint coating will need to cover at least 18 linear inches on that pipe; coating all bare steel and overlapping onto the adjacent factory applied coating by at least 3" per side.

     Does that overlap apply to all coatings?  YES it does.  If you were working with shrink sleeves, your sleeve would need to be at least 18" wide (closest standard is sometimes 24").  If you were working with Powercrete; you need to factor in coating 18" of pipe when you're figuring your coverage requirements.  In all of those cases; coating the bare steel AND bonding to the existing factory applied coating is critical.  

Need help figuring these things out for one of your jobs?  Give me a call:  steve@jsicoatings.com  936/321-3333