There is no established method of measuring load accurately in a threaded connection at working temperatures exceeding 500°C. At these conditions conventional methods can not be used due to the sensitivity of the instruments and it is suggested that a non contact method should be used. The laser strain gauge was developed by the Loughborough University Optical Research Group and it is a non contact way of measuring surface strain. With the help of finite element analysis (FEA) a special nut was developed that can be used to measure the load on the connection by relating the surface strain of the nut to the load. Experimental work later revealed that due to the threads sticking in the connection there is hysteresis present between the load and surface strain relationship. To eliminate the hysteresis a new part was added to the connection which could be used to relate the surface strain on it to the load without any hysteresis. This new part was a specially designed washer with three grooves to allow easy access for the user to measure the surface strain using the laser strain gauge. Part of the design specification was that the load has to be determined to an accuracy of 0.5%. Using sensitivity analysis the washer was analysed in terms of how manufacturing imperfections affect the accuracy of the load measuring device. The results revealed that to achieve the required 0.5% accuracy the washer would have to be manufactured to very tight tolerances. To achieve these tight tolerances the manufacturing process would not be cost effective so it was proposed that individual calibration is required for each load measuring washer. Tests showed that with sufficient calibration the specially designed washer and the laser strain gauge can be combined and used as an accurate non contact load measuring device. As it is a non contact method it can be used in extreme environments including high temperatures. This thesis describes how background research, finite element analysis and experimental testing were used to develop the load measuring washer. Also it is shown, how in-depth sensitivity analysis was used to determine the accuracy of the prototype and that how manufacturing imperfections influence the working life of a threaded connection.

Silver is a precious metal that has traditionally been used for jewellery and money. It also possesses desirable properties such as being corrosion resistant and having good electrical conductivity, resulting in its use for industrial applications. Furthermore, it is also recognised for its tribological properties in non-cost prohibitive applications. Silver can be used as a surface coating and can be deposited using an electroplating process. The utilisation of silver as a surface coating is advantageous and sustainable, as the substrate material properties are enhanced while usage of silver is kept to a minimum. On the other hand, electroplating has been used for over a century. It is a process which is able to produce a layer of uniform and dense coating that adheres well to the substrate metal, thus modifying the properties of the substrate. It benefits from being relatively low cost and is scalable. Silver is electroplated onto stainless steel threaded compression fittings to prevent galling. Traditional silver electroplating, which contains the use of cyanide as a complexing agent in the electroplating bath, is still in use within industry, even to this day. Cyanide, in its various forms can be poisonous, toxic and even lethal, which presents a risk during the silver electroplating process. Furthermore, the toxic wastes created during the cyanide silver electroplating process are detrimental to the environment. The aim of this work is to develop a self-lubricating non-cyanide silver PTFE composite coating suitable for use in threaded compression fittings of the ferruled type. The composite can be considered self-lubricating when a concentration of 8% or more by volume of the self-lubricating PTFE substance is incorporated. My original contribution to knowledge is firstly the successful development and characterisation of a self-lubricating non-cynanide Ag-PTFE coating on stainless steel without a strike resulting in improved CoF of 0.06 from the CoF of 0.6 based on an unlubricated surface. Secondly is the application of a non-cyanide Ag-PTFE MMC for threaded compression fittings. Thirdly is the characterisation of the make-up process of threaded compression fittings through the proposed use of the torque-angle slope in assessing coating performance for threaded compression fittings during make-up. Conclusions that can be drawn for the work are that the performance non-cyanide Ag-PTFE coating exceeded the performance of the pure Ag coating made using the same non-cyanide process. Moreover, the performance of the Ag-PTFE coating shows promising results when compared to the performance of the commercial silver cyanide coating. As a viable replacement to the current silver cyanide process, the self-lubricating non-cyanide Ag-PTFE coating, will improve the working conditions and have a positive contribution to the environment. Moreover, a thinner coating with has the potential to reduce raw material usage and electroplating waste disposal costs.

This thesis work was conducted at Luleå University of Technology in collaboration with Sandvik Rock Tools. The aim of the work was to determine the influence of carbon content on the wear performance in carburized steel in the dry contact interface of threaded connections between drill rods. In order to investigate this, samples of drill rod steel were carburized to three different carbon concentrations and shot peened to replicate the production process of a drill rod. The samples were wear tested by utilizing a twin-disc wear tester with one disc rotating at 100 RPM and the other at 3000 RPM to mimic the operating conditions in the threaded connection between drill rods. The results was evaluated by wear rate, surface topography, hardness as well as optical analysis by light optical microscopy and scanning electron microscopy. The results show that an increased surface carbon content provide a decrease in wear rate and an increase in hardness in the surface layer that undergo microstructural changes due to the frictional heat and contact pressure during wear testing. The primary wear mechanisms were identified as plastic deformation, adhesive scratching and material removal through delamination.