Nowadays, ease of accessibility to natural oil and gas wells has fallen significantly due to continuous drilling operations. The increasing demand for oil and gas has pushed drilling and exploration industry to drill ultra-deep or use complex methods like horizontal or directional drilling to reach for the oil and gas in deeper level. However, due to more complex conditions in these wells, Rods generally fail. This failure occurs in rod JOINTS as they are the weakest link. In this research, API NC46 standard TOOL joint has been investigated considering real oil well condition. The goal is to find the weakest points in the drilling rod and present an economical and practical solution to increase the life time. Results show that the maximum stress occurs in the first engaged thread of pin and last engaged thread of box which makes these areas more vulnerable. In the following, using optimization of joint main parameters including threads geometry, make-up torque and shoulder sealing design, a new plan will be presented which has higher fatigue life than the similar API standard TOOL joint. Maximum stress concentration factor of improved TOOL JOINTS relatively decrease from 3.47 to 2.86 compared to standard joint. In addition, experimental tests show that the average fatigue life of improved joint is 2.3 times more than the standard TOOL joint.

In this study, the effect of welding heat input on microstructure and mechanical properties of dissimilar JOINTS of API-X42 and API-B pipeline steels was investigated. Evaluation of the microstructures showed that increasing the welding heat input decreased acicular ferrite in weld metal microstructure, while amount of Widmanstatten ferrite, polygonal ferrite and grain boundary ferrite increased. Also, results of microhardness test showed that by increasing the heat input, hardness of weld metal and the heat affected zone decreased. Tensile test results showed that as the heat input increased, fracture transferred from base metal of API-B to the heat affected zone. Impact test results also showed that increasing the welding heat input could sharply drop the impact energy of the heat affected zone for both base metals due to extensive grain growth.

In this article using axisymetric elements in ANSYS standard code, threaded TOOL JOINTS of drill strings, which expose to failure in vertical drilling more than other members, have been modeled. Also, for modeling the contact between surfaces contact elements are used. Axial tensile and compressive forces, internal and external pressures arising from drill fluid on pipe, exerted torque by the motor on the top of the well, and bending moment caused by drill collars buckling are the main loads exerted to the model. According to the API standard, some preloads are also exerted to the TOOL joint to improve the fatigue behavior. Different types of loading composed of tension and compression, pure preload and combination of them are applied to the model. Some conclusive results have been drawn from the analysis including the location and value of maximum stress concentration factor in Pin and Box, the effect of preload on the stress concentration factor and as a result on the fatigue life of the TOOL joint and the contact stress distribution on the screw threads. Finally, convergence of the contact pressure on the contact surfaces has been investigated.

The aircraft aluminum alloys generally present low weldability by traditional fusion welding process. The development of the friction stir welding has provided an improved way of producing aluminum JOINTS. In this present work the influence of process and TOOL parameters on strength properties of AA7075-T6 JOINTS produced by friction stir welding was analyzed. JOINTS were fabricated by varying process parameters and TOOL parameters. Strength properties of the JOINTS were evaluated and correlated with the microstructure and hardness of weld nugget. This investigation demonstrates, JOINTS fabricated at rotational speed of 1400 rpm and welding speed of 60 mm/min using the TOOL with 15mm shoulder diameter, 5mm pin diameter and 45 HRc TOOL hardness, yielded higher strength properties.

The axial force measurement plays an important role in TOOL designing and identification of its restrictions. Also, it is vital in design of machine mechanism and optimization of welding process parameters. In this study, a friction stir welded butt joint on AA7075-T651 aluminum alloy plate is investigated. With change of some parameters, factors including axial force, mechanical properties, microhardness and weld morphology, are studied. For measuring the axial force, load cell was utilized and a servohydraulic machine was applied to evaluate the mechanical properties. The results show that by increasing the welding speed and in the same rotational rate, the axial force and microhardness increase but the weld appearance quality decreases. However, by increasing the rotational rate in the same welding speed, there is not any certain relationship among the axial force, hardness and weld morphology. Also, by changing the TOOL tilt angle from zero to 2.5 degrees, the weld morphological feature is enhanced. The results illustrate that the proper change in welding speed and TOOL rotational rate have great effects on optimizing the welding friction stir process.

Friction stir welding is a relatively new solid state joining process, which is suitable for welding similar and dissimilar materials. The present research work concentrates on the effect of TOOL rotational speed on the tensile, microstructural properties and microhardness of the friction stir welded JOINTS of different grades of austenitic stainless steel sheets. Four different TOOL rotational speeds are used in the experimentation while the other process parameters like traversing speed and the TOOL tilt angle are kept constant. The tensile testing, micrography and microhardness measurements were carried out in the welded samples. It is observed from the results of tensile testing that the joint made at the TOOL rotational speed of 1320 rpm has the maximum strength among the experimented speeds. The measured microhardness values at heat affected zone and parent metal zone have shown higher hardness than the weld zone. Fine and equi-axed grains are observed in the welded region at all experimented speeds with a negligible amount of transformation of austenite into martensite. These results have impact on the development of welding procedure for dissimilar stainless steel friction stir welding process.

In this research, the effect of nickel powder as an interlayer and the TOOL penetration depth on the microstructure and mechanical properties of lap JOINTS between aluminum 1050 (top sheet) and pure copper (bottom sheet), both with a thickness of 2 mm, was investigated. Nickel powder was added through a machined groove with a width and depth of 1 mm at the base of the aluminum sheet. Friction stir lap welding was performed using a hot work steel TOOL with a shoulder diameter of 16 mm, a pin diameter of 4 mm, a pin height of 2.1 mm, a rotational speed of 950 rpm, a feed rate of 85 mm/min, a TOOL tilt angle of 2°, and varying TOOL penetration depths of 0, 0.05, and 0.1 mm. The results revealed that in the sample with a 0 mm penetration depth, due to insufficient heat generation, defects such as tunnel voids were formed. Increasing the penetration depth to 0.05 mm resulted in the formation of uniform and thin intermetallic layers, including Al3Ni2, Al7Cu4Ni, and Cu3.8Ni at the interface, which enhanced joint quality and increased tensile strength to 185.2 MPa with a fracture strain of 8.7%. In the sample with a 0.1 mm penetration depth, thicker and less uniform intermetallic layers were formed, which, despite locally increasing hardness, led to a decrease in tensile strength and fracture strain to 136.6 MPa and 6.7%, respectively. This study demonstrates that under the conditions of this research, a TOOL penetration depth of 0.05 mm provides the optimal conditions for FSLW of aluminum-copper alloys using nickel powder.