Evaluation and characterisation of the tribological properties of polymeric coatings for downhole application

Bello, Jelili Olakunle (2003) Evaluation and characterisation of the tribological properties of polymeric coatings for downhole application. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

A novel evaluation of the adhesive properties of the thermoplastic and thermoset of polymeric coatings to their substrates has been performed using a truncated ASTM G8-98 standard. The test, which utilises the cathodic disbondment method, has shown that disbondment of coatings occurs at coating/primer and/or primer/substrate interfaces and the results compared with the interface indentation test adhesion method. The crack path and thus, the resistance of coating to disbondment is influenced by the shot blasted surface of the carbon steel substrate.

The wireline wear rig was used primarily to rank and characterise the wireline wear performance of the polymeric coatings currently used downhole. The results show a superior performance by the thermoplastic polyamide 11 (PA11) coating in terms of wear rate, over the rest of the coatings studies. In addition, micro-ploughing was identified as the dominant wear mechanism for thermoplastic coatings, while evidence was identified as the main cause of coating failure in the filled coatings.

Further studies were carried out on the PA11 coating using the more repeatable micro abrasion test method. Although more aggressive than the wireline, the micro-abrasion test was used to reproduce the type of wear mechanism (2-body abrasion) found in the wireline wear test. Also, the test method allowed comparative analysis to be carried out between the wireline and micro-abrasion test method. Experimental coatings were also designed with suitable fillers incorporated in the matrix of PA11 coatings and studies using the micro-abrasion test method. Results showed that TiO₂ fillers are generally detrimental to the mechanical properties of the coatings. However, incorporation of secondary filler, dolomite, was seen to offer approximately 20% more wear incorporation of secondary filler, dolomite, was seen to offer approximately 20% more wear resistance compared to TiO₂. Nevertheless, the unfilled coatings exhibited a superior wear resistance compare with the filled coatings, with approximately 30% abrasion resistance.

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