Presenting a recent case study, Chris Todd explains how three types of protection system for gas pipelines were deployed in the UAE
DUSUP (Dubai Supply Authority) recently specified a particular liquid epoxy coating for a buried gas pipeline project in Dubai, UAE. The project was undertaken by the main contractor Global Technologies Projects and Services (GTECH) with help from subcontractors Al Raha Metal Products Factory, Al Raha Mechanical Equipment and WLL (Arm group of companies).
DUSUP required three solutions for three different types of infrastructure. Having already specified Denso Protal 7200 for the 24in diameter block valves and straight pipe lengths, it asked Denso to provide additional systems for the 2in diameter connecting valves and pipe tie-ins. Winn & Coales’ (Denso) lengthy experience in corrosion prevention enabled it to provide the following solutions.
System 1 (epoxy), for the 24in diameter block valves plus straight pipe sections.
The surface was abrasive blast cleaned to a clean near-white finish, SSC-SP 10/Nace No 2. An appropriate angular grit was used to achieve an anchor profile (63 to 127 micron). Chlorides were removed to an acceptable level of below 3 micro grams per cm2. A coat of Protal 7200 was then spray-applied over the entire area to a minimum of 508 microns and a maximum of 1,270 microns, in accordance with DUSUP’s specification.
System 2 (petrolatum), for the protection of the 2in diameter valves. After a thorough cleaning of the valve surface removing all dust, dirt and loose matter, a coating of Denso Paste was brush-applied over the entire area. This was followed by an application of Densyl Mastic to fill any voids and irregularities, creating a smooth surface for the following tape wrapping. Next, a spiral wrap of Densyl Petrolatum Tape with a 55% overlap was applied over the valve. A final spiral wrap of Denso PVC Outer Wrap with a 55% overlap completed the protection system.
System 3 (bitumen), for the protection of the pipe tie-ins. After the existing coating was profiled to a 20° angle, all dust and sand contaminates were removed. A brushed coat of Denso Primer D was then applied to the pipe area to be protected at a minimum of 150mm either side of the coating interface and allowed to dry. This was then followed by a spiral wrap by hand or pipe wrapping machine of Densopol 60HT Bitumen Tape with a 55% overlap. A final spiral wrap of the Denso PVC Outer Wrap was applied by hand or machine with a 55% overlap to complete the protective system.