This paper describes the test methods and results obtained on commonly used coatings after 60 days and 120 days of hot water immersion testing. Recommendations are given as to how coatings can be reengineered to improve long-term performance under actual operating conditions. Tests used for the prediction of coating lifetime should be carried-out on samples that have been aged and not on brand new coatings. High initial adhesion strength is meaningless in terms of lifetime. A good coating is one that retains adequate adhesion after 120 days hot water immersion at maximum expected pipeline operating temperature. Long-term cathodic disbondment testing is only applicable to small areas of a pipeline where the coating has defects, it is also only carried-out on brand new coatings. For the vast majority of a coated pipe surface, the 120-day hot water immersion test is a much more powerful tool for predicting loss of adhesion after ageing. Fresh water has a higher osmotic gradient than salt water; hence, blistering or adhesion loss will be faster in fresh water. Multi-layer coatings should be system-engineered so that the epoxy and copolymer layers achieve maximum bonding to steel and good chemical bonding between layers. The use of a liquid epoxy rather than fusion-bonded epoxy (FBE) will improve bonding characteristics, as evidenced by the excellent performance of 3-layer heat-shrinkable sleeves after 120-day hot water immersion. It must be recognised that only one particular sample of three-layer polyolefin (3-LPE) was used in this test and that there are a multitude of different types available commercially which means that many more samples need to be tested in order to get a much broader picture. The aim here is to encourage research, and the goal, to generally improve coatings within the industry.


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    Title :

    The importance of the hot water immersion test for evaluating the long-term performance of buried pipeline coatings


    Contributors:
    John, R. (author) / Alaerts, E. (author)


    Publication date :

    2005


    Size :

    9 Seiten, 4 Bilder, 2 Tabellen, 2 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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