Shear properties of pipeline coatings with elastomeric adhesives are frequently measured in the laboratory These measurements are expected to correlate with the ability of the coating to withstand the forces of soil burial and movement, The theoretical basis of choosing the parameters of the laboratory methods are given based on calculations of soil forces on pipeline coatings from an analytical model and from finite element analysis, Data obtained from two methodologies are given and discussed. The criteria used to evaluate pipeline coatings in various applications are also discussed.
The measurement in the laboratory of the shear properties of pipeline coatings with elastomeric adhesives is an important part of the evaluation of their expected performance in the ground. Each generic type of pipeline coating is affected differently by soil stress. Soil stress affects can be seen on flexible PE coatings with elastomeric adhesives as a characteristic wrinkling. However, other types of coatings can fad by blistering (FBE) or fatigue crackingl (CTE) that is exacerbated by soil movement.
The prediction of soil stress effects on coatings have been determined by burial of samples in large soil boxes or by more convenient laboratory methods? and apparatus. Extensive testing has shown that the behavior in the ground or in soil boxes is directly related to the ability of the coating to resist shear forces exerted by soil movement. This property can be directly measured by a determination of the amount or rate of shear of a sample when subjected to a known shear stress. This resistance to shear must be combined with a measurement of the resistance of the backing material to deformation and tensile force.
The two properties combine to determine the ability of a pipeline coating to resist damage by soil movement. Generally, the shear measurement is obtained as a function of temperature at a fixed normal and shear load, In this paper, we will describe the shear strength measurement methods in general use and the theoretical basis for choosing the normal and shear loads. Also, consideration must be given to the choice of criteria used for evaluating the shear strength of coatings.
