Concrete Coating of Line Pipe

Delaminated concrete coat on pipe.
Voids in concrete (blue area) as shown in petrographic analysis.
Improper compaction as shown in petrographic analysis.
Unsual needle-like hydration products. (scanning-electron micrograph, SEM)
Unsual needle-like hydration products. (scanning-electron micrograph, SEM)
Unsual needle-like hydration products. (scanning-electron micrograph, SEM)

Creole Trail Pipeline Project, New Iberia, Louisiana

Breakages in a set of batches of concrete weight coating for offshore under-seafloor-lying pipes prompted an evaluation to determine the most probable cause(s) of these defects.

Samples of concrete from six coated pipes were submitted to our laboratory for evaluation by petrographic analysis and scanning electron microscopy.

The evaluation pointed to the choice of cement as the principal cause of the problem. A re-formulation of the mix of the mix was recommended. The cement causes generation of above normal heat, essential for early strength gain, but produces a harsh mix which is not easy to form around the pipe.  Inadequate consolidation creates voids in the concrete matrix and defects on the exterior coated pipes.  The voids in the concrete matrix along with variable compressive strength contribute to the unusual brittleness of the concrete coat.