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Kane, Alexandre (SINTEF Materials and chemistry) | Osen, Vidar (SINTEF Materials and chemistry) | Ren, Xiaobo (SINTEF Materials and chemistry) | Nordhagen, Håkon O. (SINTEF Materials and chemistry) | Grytten, Frode (SINTEF Materials and chemistry) | Akselsen, Odd M. (SINTEF Materials and chemistry) | Zoric, Josip (SINTEF Materials and chemistry)
A data management system for material assessment at low temperature is developed in the context of large test programmes run in a current research project called Arctic Materials II. A generic database platform is proposed for efficient access to material data and to analyses of various materials such as steels/weldments, aluminium alloys, composites and polymers/coatings. Safe and flexible data processing accessible through a customized web interface is obtained by unifying test results, test methods, and procedures (e.g. tensile testing, fracture mechanics testing) and predictive models of fracture. The framework provides a solid support for the development of more robust solutions to account for the influence of, e.g., temperature, constraint effects, residual stresses, crack arrest, probabilistic scatter, and scaling on the material response. Its aim is also to contribute to an improved design guideline for materials requirements in Arctic conditions (down to -60°C)
The local strengths of three X-100 girth welds were tested as part of a study of the effects of heat-affected zone (HAZ) softening. While one of the welds showed obvious softening in the HAZ on all types of testing, two others showed mixed results. These mixed results allow comparisons of results from microtensile specimens, notched tensile specimens and hardness measurements as descriptors of HAZ softening. INTRODUCTION Previous work by Mohr (2003) had indicated that a combination of softened HAZ and internal pressure could cause high strain concentrations at the HAZ under conditions with plastic axial strains. Continued work in Mohr (2006) has been directed to further understand this behavior and its limits. This paper discusses mechanical testing that has been used to examine the possible softening of X-100 girth welds as part of the general assessment of the effect of HAZ softening on strain capacity. Strain-based design is used for many situations for pipelines where the loadings from forces other than the internal pressure can be the largest generators of stress and strain in the pipe wall. Such loadings can be generated by soil subsidence, frost heave, thermal expansion and contraction, landslides, pipe reeling, pipe laying, and several other types of environmental loading. Designing based on strain for these cases has an advantage over designing based on stress because these loadings tend to apply a given displacement rather than a given force to the pipe. A survey of the literature on the formation of softened regions in the HAZ of steel pipeline girth welds was performed, extended with two experimental studies. The first study used hardness measurements on existing weld cross sections from simulated girth welds in X-100 plate sections. The second study used small-scale tensile specimens and hardness measurements to determine the local mechanical properties of regions of the HAZ of girth welds in X-100 pipe. Some of the testing was reported in Mohr (2006).
Matsushita, Muneo (Joining & Strength Research Department, JFE Steel Corporation) | Kitani, Yasushi (Joining & Strength Research Department, JFE Steel Corporation) | Ikeda, Rinsei (Joining & Strength Research Department, JFE Steel Corporation) | Endo, Shigeru (Joining & Strength Research Department, JFE Steel Corporation)
As design temperatures increase and steel strength increases, the limits on yield strength of the nickel-alloy weld consumables make it more difficult to achieve overmatched weld areas, increasing the difficulty of a strain-based design assessment. Testing of Alloy 625 girth welds in X65 pipe clad with Alloy 825 found that the welds were approximately matching in yield strength to the steel in circumferential direction tests. Cross-weld tests at 20°C and 150°C found localized yielding up to 15% strain in the weld cap area followed by distribution of strain into the steel and failure in the steel.
The use of clad pipes for offshore oil and gas production has been worldwide, with multiple methods of pipe laying considered (Hval et al. 2014) (Jones et al. 2011). Assessments of the allowable flaw sizes in these girth welds generally indicate that there is value in increasing the strength of the girth welded area toward overmatching of both the yield and ultimate strength of the girth weld compared to the base metal, particularly in cases with cyclic plastic strain (Yang et al. 2009) (Tronskar et al. 2015) (Tkaczyk et al. 2015) (Carlucci et al. 2014).
There has been a desire to continue to use a single electrode for the entire girth weld to advance strength, but also provide internal corrosion resistance. Some patented methods are available for increasing the strength of girth welds, while retaining other desirable properties (Ayer et al. 2013) (Ayer et al. 2014). These methods have not widely entered welding practice, as users have primarily worked with Alloy 625 and Alloy 688 consumables.
Under these circumstances one way of improving the assessment of the allowable flaw size for strain-based design conditions would be to include a better understanding of the yielding behavior and strain aging capability of both the steel and the weld metal into models describing their behavior during reeling, installation, and service.
This phase of the project looks at the tensile behavior of example weld areas both at room temperature and at elevated temperatures.