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A second-generation cast pin tear test (CPTT) that is capable of ranking the weldability of Ni-base superalloys has been developed at the Ohio State University. The CPTT utilizes an optimized testing procedure and apparatus design that provide controllable and repeatable testing conditions, and yield reproducible and reliable test results.The CPTT provided a weldability ranking of four highly alloyed stainless steels that is in very good correlation to the results of a round robin study on six externally restrained weld hot-cracking tests. The solidification microstructure of the test samples (cast pins) closely simulates the microstructure of low to medium heat input welds, such as those made by the GTAW process. The CPTT fracture surfaces exhibit dendritic "eggcrate" fracture morphology, which is a characteristic of solidification cracking. This fracture morphology is similar to the high and medium temperature regime of solidification cracks generated using the Varestraint test. The nature of crack nucleation and propagation, and the crack healing phenomenon in CPTT closely resemble weld solidification cracking.The CPTT technique was applied for evaluating the solidification cracking susceptibility of a series of high performance turbine engine alloys. These alloys were ranked in order of decreasing susceptibility to solidification cracking as follows: René alloys 142, 125, and 77, alloy 718, René 80, Waspaloy, and alloy 600. These rankings are in good correlation to field experience with the solidification cracking susceptibility of the tested alloys.The second generation CPTT proved to be capable of ranking the solidification cracking susceptibility of both "difficult-to-weld" alloys and "standard" alloys, and to differentiate their solidification cracking behavior. It also provides an efficient and inexpensive tool for weldability testing in the process of alloy and consumable development. Pin Tear Test

High pressure tubing and associated tubing couplers are critical components required for the operational control of subsea oil and gas production equipment. Tubing couplers used in subsea oil and gas developments are commonly made from Nitronic 50 HS® (N50HS) due to its high strength, corrosion resistance, and resistance to galling. Nitronic couplers are typically welded to several dissimilar metals including super duplex stainless steel (SDSS) control tubing using SDSS filler metals such as AWS A5.9 ER2594. Recent evaluations have found that sigma (σ) phase forms in N50HS weldments and its effect is not broadly understood by industry. During N50HS solidification, Scheil solidification conditions establish compositional gradients in the unmixed zone located along the fusion line adjacent to the N50HS base metal. This solidification-induced segregation promotes compositions that are susceptible to interdendritic intermetallic compound formation when they are reheated by subsequent weld passes such as in multipass welding or at weld start-stop locations. Decreasing heat input is a common approach to reduce or eliminate the formation of intermetallic compounds in SDSS. Although decreasing heat input can reduce the amount of energy available to drive the solid state transformation from ferrite to σ, it does not change the solidification mode (AF) or solidification conditions from Scheil to para-equilibrium within the range of cooling rates possible with arc welding processes. As such, the compositional gradients that promote intermetallic compound formation along the N50HS fusion line can only be minimized through heat input control and cannot be eliminated in arc welds regardless of the heat input used. The effects of σ on toughness and corrosion resistance of Nitronic weldments were evaluated. N50HS solidified samples with up to 2 volume percent σ were found to have CVN of >40J at −40°C, and no evidence of pitting at 25°C in the ASTM G48 test.

To meet the increasing worldwide demand for natural gas, there is a need to safely and economically develop remotely located resources. Pipeline construction is a major activity required to connect these remote resources to markets. Such pipeline routes may cross areas containing geohazards such as discontinuous permafrost, active seismicity and offshore ice gouging. These pipelines may be subjected to longitudinal strains above 0.5%. To safely design pipelines for such conditions, a strain-based design (SBD) approach can be used in addition to conventional allowable stress designs (ASD). Significant pipeline construction cost savings can be achieved with the use of higher strength steels (X70+) due to reduced pipe wall thicknesses (less steel) and faster girth welding. However, a robust welding technology for higher strength SBD pipelines is often a technology gap depending on the target level of longitudinal strain that needs to be accommodated, since such applications often demand excellent weld toughness at low temperatures (−15°C) and high tensile strength (>120ksi). This paper discusses the development of an enabling welding technology that offers a superior combination of strength and toughness compared to commercially available technologies. Acicular ferrite interspersed in martensite (AFIM) has been previously identified as a useful high strength weld metal microstructure that can be applied in field pipeline construction. This paper describes how this microstructure has been used to create welds with excellent strength overmatch and good ductile tearing resistance for X80 SBD pipelines. This approach has been implemented for mainline, double-joining and repair welding applications. This paper describes the welding procedures, mechanical properties achieved, estimated strain capacities, and the results of a full-scale pipe strain capacity test.