Computational analysis of a three-layer pipeline coating: Internal stresses generated during the manufacturing process

The presence of internal stresses in organic coatings is a current phenomenon that can generate loss of adhesion, so that it must be taken into account to achieve long-term protection. In the case of external coatings used for corrosion protection of steel pipelines, three-layer systems are often applied. They are composed with an epoxy primer, an adhesive and a thick layer of polyethylene. Some spontaneous disbondment having been observed on these coatings after only several years in service, the presence of internal stresses has been suggested to explain this behaviour.This finite element study aims at estimating the internal stress generated during the application process to compare it with the values of adhesion measured. This comparison should allow concluding if this phenomenon is responsible for the loss of adhesion observed. Three models were successively developed to estimate correctly the stress induced, including a linear thermoelastic model and a thermoviscoelastic one, with entry parameters function of temperature.

Research highlights▸ Viscoelastic model allows obtaining realistic behaviours and stress values. ▸ Stresses are concentrated near the interfaces, in the adhesive layer, at the edges of the pipe in agreement with experimental observations. ▸ Epoxy/steel interface presents significant stresses (several MPa) on the whole length of the pipe.