Selection of Field Applied Liquid Rehabilitation Pipeline Coatings

ABSTRACT
There are over five dozen field applied liquid rehabilitation pipeline coatings in the US market with limited performance data available from suppliers. Although there are many test methods in the literature for evaluation of pipe coatings, there are no commonly accepted test protocol and acceptance criteria for selecting coatings. End users have a great difficulty to select appropriate coatings to protect their buried pipelines. Also, no convincing technical data can be obtained from suppliers to help us determine the upper service temperature for a coating. Some coatings have long dry-to-touch time and attract insects to crawl over the wet paints at night to produce holidays which require repairing the next day. The purpose of this work is to develop a test protocol considering both application convenience and good performance and to select the coatings to rehabilitate our pipelines. The attributes for application convenience are environmental friendliness, pot life, dry-to-touch time, backfill time, etc. The coating performance includes cathodic disbondment, penetration, impact, and abrasion resistance. The acceptance criteria have also been developed to make the selection. Test methods to determine upper service temperature for the coatings were also developed. This test protocol is using standard ASTM test methods with slight modifications and can be used by both coating suppliers and end users.

INTRODUCTION
There are about two dozen liquid rehabilitation pipeline coating suppliers and over sixty products available in the US market. The suppliers are either too small in size or only a small segment of big protective coating suppliers and do not provide sufficient performance data to support the use of their products. Also, in terms of upper service temperature, suppliers normally can not provide a reasonable temperature limit with good justification. Therefore, end users can not fully depend on the technical support from suppliers to make an appropriate coating selection.

There are quite a number of tests developed by the American Society for Testing and Materials (ASTM), National Association of Corrosion Engineers (NACE), American Water Works Association (AWWA), and German DIN standard testing to evaluate pipeline coating materials. There are a number of articles (1-3) published in the literature to describe the pipeline rehabilitation coating test methods and acceptance criteria. But, there are no commonly agreeable industry test methods and acceptance criteria to qualify coatings and determine the upper service temperature.

In the field, applicators prefer the use of long potlife coatings to allow them with plenty of time to spray. However, longer potlife coatings normally require a longer time to dry too. Consequently, the insects crawl over the wet paint at night and leave holidays before they exhaust their energy to free themselves. The next day, the paint crew has to spend a wasteful effort to repair the damage. If a fast dry coating is selected, the insect problem will subside. Therefore, in the selection of appropriate coatings, we need also to consider the application convenience in addition to the performance properties.

The purpose of this work is to develop a test protocol including both application convenience and performance properties and set acceptance criteria to qualify the field applied liquid rehabilitation pipeline coatings. Also we want to develop a method to determine the upper service temperature for the coatings. We use the requirements of application properties and the performance data provided from suppliers to screen products available in the market. Then, we perform our own testing to evaluate candidate coatings.

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