technical report | Field joint coatings
In the laboratory, adhesion is measured by peeling a coating strip of typical 1-inch (25mm) width vertically at a constant speed of 10 mm/minute. The force to remove the 25mm wide strip coating is measured in Newtons and the final unit result is expressed as Newtons per mm (N/mm). EN12068 Class C50 requires a peel strength on steel
of between 0.5 N/mm and 1.0 N/mm for heat-shrinka- ble coatings and polymeric tapes while ISO21809-3 requires 1.0 N/mm for polymeric tapes and 2.5 N/mm for polyethylene heat-shrinkable coatings with an epoxy primer. The Polyguard RD-6 system reached 3.4 N/mm on steel during testing at KTA Tator. Lap Shear Resistance - Shear resistance is critical
Above: Polyguard’s RD-6 system being used as part of a non-weighted subsea project in South America
rock fall or the excavator arm hitting the coating surface. In the laboratory, the test consists of dropping a weight from a height. The value of the weight and the height define the value of the impact in Joules. After the impact, the coating is tested with a holiday detector (dielectric test). The impact resistance required for heat-shrinkable
coatings and polymeric tapes according to EN12068 Class C50 is 15J (joules). ISO21809-3 is requesting 4J per mm of coating for polymeric tapes and 5J per mm of coating for heat-shrinkable coatings. As the typical thickness for both systems is between 2mm and 3mm, the impact resistance fluctuates between 8J and 12J for polymeric tapes and 10J and 15J for heat-shrinkable coatings. The Polyguard RD-6 coating system success- fully passed the impact test at 15J, which is equivalent to 6J per mm of coating (at 2.5 mm thickness). Indentation Resistance - Small sharp stones can
Right: The
tension applied to the PP mesh backing in the RD-6 system during
installation
provides high soil stress
resistance in service
migrate in the soil to the coating surface of buried pipelines. They can apply a high pressure on the surface and penetrate the coating with the time. In the laboratory, penetration resistance is tested with a weight equipped with a small pin, which is applied for a couple of days on the coating surface. The pressure of the pin is expressed in Newton per square mm (N/ mm²). After the indentation test the coating is tested again with a holiday detector (dielectric test). EN12068 Class C50 and ISO21809-3 are requesting the same indentation resistance for heat-shrinkable coatings and polymeric tapes of 10 N/mm². The Polyguard RD-6 coating successfully passed the indentation test at this level. Peel Strength - Adhesion is one of the most fundamental properties of an FJC and coatings with high adhesion will certainly resist better over time. The peel strength test is designed to represent the adhesion force on the substrate (steel and plant-applied coating).
26 PIPELINE COATING | September 2015
for large diameter buried pipelines due to the high soil stress applied on the coating, especially at the four and eight o’clock positions. For heat-shrinkable coatings and polymeric tapes, lap shear resistance is measured by peeling a coating piece measuring typically 1-inch by 1-inch (25mm by 25mm) horizontally at a constant speed of 10mm/minute. The final unit result is Newton per square mm (N/mm²). EN12068 Class C50 requires a lap shear resistance of 0.05 N/mm² for heat-shrinkable coatings and polymeric tapes while ISO21809-3 requires the same value for polymeric tapes and 1.00 N/mm² for heat- shrinkable coatings (3 layer polyethylene). Tested according to ISO21809-3, Polyguard RD-6 reached 0.18 N/mm² during the test at KTA Tator Inc. Polymeric tapes exhibit poor shear resistance. They
generally fail (disbond) at the four and eight o’clock positions on large diameter pipelines and, therefore, are typically rejected today in the North American oil and gas market. The high shear resistance value from ISO21809-3 for 3LPE heat shrinkable coatings results from the hotmelt adhesive layer, which absorbs the soil
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