Evaluation of adhesive strength of polymer coatings for oilfield pipes after exposure to a CO2 environment

Problem. The effect of polymer coatings on the protection of steels against CO2 corrosion has been little
studied, and existing standards for evaluating their adhesive strength contain contradictions in the interpretation of test
results. Aim. To develop a model of changes in the adhesive strength of coatings for oilfield and tubing pipes in a CO2-
containing environment for predicting their service life. Methods. Three types of polymer coatings used for the protection
of oilfield and tubing pipes (tubing) were studied: a liquid non-thermosetting coating (coating 1) and two two-layer powder coatings (coatings 2 and 3). The tests were carried out using an autoclave complex. The conditions in the autoclave
were the following: total system pressure 10±0.5 MPa; temperature 90±3 °С; electrolyte – sodium chloride solution in
distilled water with a mass fraction of 3 %; exposure duration – 50 days. Adhesive strength was determined by the dolly
pull-off method. For microscopic analysis, cross-sections of the coatings at locations of blisters were prepared, then metallographic sections were prepared. Results. After 50 days of exposure in a CO2 environment, the adhesive strength of
the coatings decreased: for coating 1 – from 7.8 to 2.9 MPa, for coating 2 – from 27.1 to 10.2 MPa, for coating 3 – from
16.1 to 11.3 MPa. Coating 1 showed low initial adhesive strength values that did not meet industry standards. For coating 2, adhesion decreased in the 0–10 and 20–30 day intervals and then stabilised. For coating 3, an initial increase in adhesion was observed, followed by a decrease. Conclusions. After 50 days of exposure in a CO2 environment, the adhesive
strength of coating 1 decreased by 37 % of its initial strength, of coating 2 – by 38 %, and of coating 3 – by 7 %, which
recommends it for operation under similar conditions.