Dealing in extremes – part one

Geoff Addicott, Exova, UK, explains how a unique testing methodology tackled the issue of pipeline coating performance at sub-zero temperatures.

We take protective coatings, and how they perform and protect things in our everyday lives, for granted – for example, the paint on our car, the paint on our garage door, etc. But how would these coatings cope within extreme environments?

With ever more challenging environments being explored and developed, it has never been more important for the oil and gas sector to understand how materials and processes will perform in extreme conditions.

Across the globe, different temperatures and conditions prevail and, for many of these, laboratory tests including impact testing in accordance with ISO 21809-1 Annex E, and in conjunction with high voltage holiday testing in accordance with ISO 21809-1 Annex B, give accurate data on anticipated coating performance. In a recent customer project, Exova deployed a high voltage holiday detector that finds pin holes or flaws in the continuity of a surface coating. For this to work, the substrate, which the equipment is connected to, must be conductive in order to complete the circuit and in this case the test specimens were steel pipes. As Figure 4 shows, results can be seen in action as the spark jumps from the brush to the pipe through a crack in the coating to make the connection with the conductive substrate.

However, for new gas lines being installed to cross the Black Sea at a depth of 2.2 km, and then crossing Eastern Europe and into Austria, the specific conditions of depth and distance bring their own issues. Exova’s customer needed a better understanding of the coatings’ performance to address concerns relating to the properties of polypropylene coated pipes, which can become brittle at low temperatures. This can cause cracks to appear in the coating and can lead to complete failure in some circumstances, with the coating shattering and becoming detached all around the pipe. Therefore, Exova specifically needed to have an insight into how these coatings perform during handling and installation processes. For example, should these pipes accidentally collide with each other, would the coating withstand the impact and protect the pipeline before, during and after installation? Clearly a bespoke solution was required and the company worked in close partnership with the customer team to create the answer.

Pushing the limits of testing

Such specific testing had never been conducted before, putting Exova at the forefront of this technically demanding test. A specialist climate chamber located on the outskirts of Paris, with the ability to go to temperatures as low as -80°C, provided the ideal base for the team to work from. This allowed testing at temperatures between -10 to -40°C, providing information and precise data on how coatings would perform in such extreme conditions.

A purpose-designed impact tester (2 m in length) was fabricated at Exova’s laboratory and workshop in Salford, Manchester. The tester was calibrated, ensuring it was traceable to national standards and compliant with the required standards under correct operation, to guarantee the delivery of accurate data.Individual samples were supplied by two different pipe mills. In order to meet the specification for extreme sub-zero test conditions, the pipe samples were fitted with thermocouples at various points and depths in the pipe substrate, and also at the surface of the coating to enable precise temperature measurement, before, during and after the test.

The following information was recorded for each pipe tested:

• Pipe mill supplier.
• Heat number.
• Pipe number.
• Coating applicator.
• Coating material.

Written by Geoff Addicott, Exova, UK, and edited by Hannah Priestley-Eaton

Read the article online at: https://www.worldpipelines.com/special-reports/01062015/extremes-part-one/