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Finite Element Analysis to Locate Maximum Values of the First and Second Principal Strains in the Tensile Pull-Off Test for Coating Adhesion on Large Pipes

Picture for Finite Element Analysis to Locate Maximum Values of the First and Second Principal Strains in the Tensile Pull-Off Test for Coating Adhesion on Large Pipes
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The tensile pull-off test, as in ASTM 4541, in which a round metal ‘dolly’ is glued to a coating then pulled off is a very common method for measuring adhesion of a coating to its substrate. This technique is very well known to produce joint failures that are not at the intended coating steel interface but may initiate within the coating, within the glue or at the glue-coating interface. 

Product Number: 41214-814-SG
Author: S. G. Croll, C. Siripirom, B. D. Keil
Publication Date: 2014
Industries: Pipelines, Tanks, and Underground Systems , Coatings
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$20.00
$20.00

The tensile pull-off test, as in ASTM 4541, in which a round metal ‘dolly’ is glued to a coating then pulled off is a very common method for measuring adhesion of a coating to its substrate. This technique is very well known to produce joint failures that are not at the intended coating steel interface but may initiate within the coating, within the glue or at the glue-coating interface. It also provides results that are very inconsistent in magnitude. Nevertheless, the method is used as a quality assurance procedure to evaluate the surface treatment of a steel pipe substrate and the subsequent coating application in order to assure the likely corrosion protection that the coating might provide for the pipe. This seemingly simple test is affected by many experimental and material variables. The joint will fail, and the strength be measured, in the material that suffers the most deformation. Determinations were made of the Young’s modulus and Poisson’s ratio of three coating materials, two glues and the metal dolly and substrate. Then finite element calculations were made of the stresses and strains in the coating and the dolly glue. These simple calculations show how differences in mechanical properties between glue and coating, substrate curvature and misalignment of the dolly, may determine which part of the adhesive joint suffers the most deformation and thus determines the locus of failure. Adhesion test failure modes found in practice are very consistent with the results of these calculations.

The tensile pull-off test, as in ASTM 4541, in which a round metal ‘dolly’ is glued to a coating then pulled off is a very common method for measuring adhesion of a coating to its substrate. This technique is very well known to produce joint failures that are not at the intended coating steel interface but may initiate within the coating, within the glue or at the glue-coating interface. It also provides results that are very inconsistent in magnitude. Nevertheless, the method is used as a quality assurance procedure to evaluate the surface treatment of a steel pipe substrate and the subsequent coating application in order to assure the likely corrosion protection that the coating might provide for the pipe. This seemingly simple test is affected by many experimental and material variables. The joint will fail, and the strength be measured, in the material that suffers the most deformation. Determinations were made of the Young’s modulus and Poisson’s ratio of three coating materials, two glues and the metal dolly and substrate. Then finite element calculations were made of the stresses and strains in the coating and the dolly glue. These simple calculations show how differences in mechanical properties between glue and coating, substrate curvature and misalignment of the dolly, may determine which part of the adhesive joint suffers the most deformation and thus determines the locus of failure. Adhesion test failure modes found in practice are very consistent with the results of these calculations.

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