The author uses three recent international pipeline projects as examples, to illustrate that the typical surface profile height and abrasive blast cleaning requirements in today’s coating standards and specifications have not been sufficient to define the adequate level of the abrasive blasting in order to provide wetting and adhesion of the pipe coatings to the pipe substrate, partially causing the pipeline coating disbondment. Adhesion mechanisms, limitations of the current standards of defining surface profile, and recommendations for future pipeline coating projects are discussed.
Fusion bonded epoxy (FBE) and three-layer polyolefin (polyethylene or polypropylene) are the most common external coating systems for new oil and gas pipelines. These FBE primed pipeline coatings have long track records of successful use, but there are occasional challenges and problems that must be addressed as part of the pipe installation process. One of these challenges and problems often met in the pipeline coating industry is pipe coating disbondment, a delamination normally between FBE and steel at cutback or along the body of the pipe.
Pipeline Project Case #1 – In 2014 and 2015, cracking and coating disbondment failures were observed on a significant number of pipes, during the handling and field cold bending processes along the right of way (ROW) of a major natural gas pipeline project in North America (Figure 1a). The 42” OD × 14.27-20.62 mm WT, X70 pipes were coated with a single layer FBE coating. The company pipe coating project specification followed both NACE International (NACE) ? SP0394 (Formerly RP0394)1 standard and The American Petroleum Institute (API)? RP 5L92 standard.
Pipeline Project Case #2 – In 2015 and 2016, at various construction sites of a key natural gas pipeline in South Asia, a dual layer 2LFBE coating applied to 28” OD × 7.14-12.70 mm WT, X70 pipes disbonded randomly on the cold bends along the ROW of the pipeline project. Poor coating adhesion of non-bent pipes was also reported (Figure 1b). The company pipe coating project specification followed also the NACE SP0394 (Formerly RP0394) standard.