Use of Tribological Design and Surface Engineering to Improve Riser Valve Components

This thesis is about the study of the wear behaviour of the superalloys Inconel and Incoloy, when sliding against each other within the oil and gas sector. Within riser valves, (which are used to pump oil from the seabed to the surface) there are a number of different valves which are made from superalloys. When these valves are required to open and close, they operate under high pressure and are subjected to extremely high loads. The resultant sliding of superalloys causes rapid wear and surface damage to occur, which ultimately leads to the premature failure of the components.
The wear and behaviour characteristics of superalloys, is to date relatively unknown. The following work looks to not only further understand the wear behaviour, but also seeks to provide a solution to reduce wear and early failure. In order to understand the features observed on components that have failed, it is necessary to replicate the operating conditions by conducting testing. It is also necessary to simulate the moving geometry of components using FEA analysis due to the practical limitations of conducting tests. Upon observation and comparison to original wear features, a solution was formulated based upon a thorough literature review. In the form of surface coatings, and specifically new Diamond-Like-Carbon coatings (DLC) these were applied to the materials in question and the results of testing compared. A predominant wear mechanism became a common observation galling and again it was evident that there was little work in understanding how galling develops over time. The behaviour of galling is also studied, and a criteria to define this phenomenon is also established.