Experimental investigation of wax deposition on multiple steel alloys

Abstract

Paraffin wax deposition is a flow assurance issue that occurs frequently in subsea crude oil and gas condensate flowlines and pipelines. While some mitigation techniques involve coatings, most wax deposition in the oil and gas industry occurs on bare pipe walls made of various steel alloys. Previously, there has not been any investigation into the possibility of differences in the wax deposition that could be attributed to the different types of steel alloys, and this study set out to fill that gap. A cold finger apparatus with interchangeable fingers was used to generate deposits. Deposits were created from waxy model oils across several bulk oil temperatures and rotational speeds. To cover a wide array of materials, six different steels were tested: A2, A36, 1018, 4130, 304, and 316. These materials range from low-carbon steels to high-chrome content stainless steels. Each cold finger's surface was finished with the same process to create a roughness of 4.6 ± 0.5 mm. Deposit mass, thickness, and composition all showed non-negligible differences between deposits formed on the steels investigated: masses varied by 5–15%, thicknesses varied by 30% or more, and deposit compositions were noticeably skewed. Alloy composition, contact angle, roughness, and thermal conductivity were discussed as possible indicators of the effects an alloy would have on wax deposition. These findings facilitate the comparison and interpretation of the results from wax research literature using different steel alloys as well as the design of laboratory wax testing that more closely resembles field conditions.