Is it the shear strength between the concrete and PE that you are more interested in to prevent pipe slippage on a laybarge?  The pipeline engineers should be able to calculate the minimum shear strength required for the water depth and lay configuration when the pipe is sitting in the tensioners.  The next question will be how to test it.  We used instrumented jacks during concrete coating procedure qualification to monitor the force required to get the concrete to move.  For coal tar enamel, the concrete would exceed the required value easily and would spall before slipping.

Steve Jones
Petroleum Development Oman LLC
Muscat
Sultanate Of Oman

Thanks Steve,

I have see a typical instrumented hydraulic jacks during concrete coating procedure qualification of NKOSSA project.
During this project the contractor (Bredero) assured a shear strength between concrete and PE of more than 5kg/cm2.

By my experience, the minimum value of concrete shear strength, that contractors can assure is about 2kg/cm2.
I know how to calculate the minimum required concrete shear strength according to water depth and lay configuration but I don't know if 2kg/cm2 is a "typical-normal" value.
Sometimes when we required a concrete shear strength of 5 kg/cm2 instead of 2 kg/cm2, contractors requires additional cost. To overcome this we normally aggre on 3kg/cm2 without additional cost.

Do you remember the concrete shear strength value between concrete and coal tar enamel in your project?


Antidio Magnani

One possible solution is to increase the 'roughness' on the PE: Mannesman produced a three layer system (I'm afraid I can't remember if it was PP or PE) where the top layer had ridges about 1-2mm high running along it, that they claimed increased the protection against backfill... I was offered it in the late 90's for a onshore line, but thought it was a bit of a gimmick, and asked for a normal top layer.  However, if they still do it, and the coating system is acceptable, these ridges might increase the adhesion between the coating & the weight coating?

Antidio,

The experience I was referring to was at Bredero Ras Al Khaimah on DN400 pipe.  Our spec was 5 kg/cm2 and it was exceeded.  I can't remember what was finally achieved but, in the end, the concrete started to disintegrate still without slipping. As to the cost aspect, it was an EPIC contract so, we as operator, weren't able to assess any  impact of demanding 5 kg/cm2.

Steve Jones
Petroleum Development Oman LLC
Muscat
Sultanate Of Oman