Abstract
Desert locations provide some of the toughest environments for pipeline materials and coatings. Above ground, extreme heat and humidity, combined with strong UV radiation, sand movement and sand storms test any coating. Underground, in some locations, the combination of high water table, high salinity, high temperature and soil movement provide very testing conditions.
The three-layer polyethylene (3LPE) and three-layer polypropylene (3LPP) coating systems have been successfully used on oil and gas lines in the underground conditions described above for the last ten years. For repair and rehabilitation coatings, cold applied tapes have traditionally been used but have consistently failed in the above conditions. Liquid epoxy coatings were tested for this purpose and have performed well for the past two years. For the field joints the coating the systems of choice have been co-extruded polypropylene (PP) sheet and flame sprayed PP for 3LPP lines and polyethylene heat shrink sleeve for 3LPE lines. Two new systems were successfully tested for use on field joints of 3LPP lines. These are heat assisted chemically modified polypropylene (CMPP) tape wrap and the recently marketed polypropylene heat shrink sleeve. The four field joint coating system for 3LPP lines have been given a ranking order based on performance and other considerations.
