In the year 2008, Indian Oil Corporation Ltd. selected 100% Solids Polyurethane Coatings to rehabilitate approx. 2 x 7.5 kms of 24” diameter Chaksu – Mathura Section of the Salaya Mathura Pipeline. 100% Solids Polyurethane Coatings are the international coating of choice for Pipeline Rehabilitation and are covered under “Coatings for Repair and Rehabilitation of the External Coatings of Buried Steel Pipelines,” NACE International, USA Technical Committee Report Task Group T-10D-17/T-6A-63 (dated July 1999)
Surveys had indicated that the Coal Tar Enamel coating had deteriorated and was in urgent need of rehabilitation. Rehabilitation work was awarded to two companies; M/s Shree Ambha Associates and M/s Jay Gauri Projects. Both companies are long standing contractors of IOCL for pipeline rehabilitation works. Shree Ambha Associates and Jay Gauri selected Purethane, 100% Solids Polyurethane Coatings for the project and in Sept.-Oct. 2008 awarded the supply orders to Amchem. Despite having extensive experience of applying Tape coatings, both companies were new to 100% Solids Polyurethane Coatings. Amchem arranged for supply of the Graco equipment and training of crews of both companies in line with tender requirements. Amchem deployed skilled applicators at both sites 24×7 to ensure proper application as per written standards.
The pipeline was excavated and earth supports retained at approximately 8m intervals to avoid disruption in operation. The deteriorated coating was scraped manually from the pipeline and surface blast cleaned to SSPC SP-10 with 75+ Microns Anchor Profile using Granulated Copper Slag (single use). The pipes were coated with 1,250 Microns nominal thickness of Purethane® – 100% Solids Polyurethane Coating using state of the art plural component airless spray equipment from Graco Inc., USA. The coating sets in minutes and cures quickly. A single medium spray tip can spray about 120 litres/hour or about 60 RM (running metre)/hour of 24” diameter pipeline and Graco’s equipment could support multiple tips – upto 5!
The applied coating is thus seamless, very strongly adhered to the surface, extremely tough, with a very high electrical resistance. Furthermore, there is no “tenting” or air gaps over weld seams as in the case of Tapes. Purethane® can operate at 90° C continuous & 121° C intermittent. Cold applied tapes however can only be used up to 49°C and are likely to sag in hot climates such as India, UAE, etc. The cold tapes are further prone to soil stress damage whereas Purethane®, on the other hand, has excellent adhesion and can effortlessly prevent any damage from soil stress.
Presently Purethane® PLX are recommended for pipeline rehabilitation due to its ability to withstand high Cathodic Protection currents required to protect adjacent poor and degraded coatings on the pipe.