Tomoyuki Yokota

Development of TMCP Type Alloy625/X65 Clad Steel Plate for Pipe

Demand for CRAs (Corrosion Resistant Alloys) clad steel is getting increased for pipeline application of oil and gas industry because of economic advantage over solid CRAs. CRAs clad steel consists of a CRAs layer for corrosion resistance and a carbon steel for mechanical properties. Nickel based Alloy625 is known to be suitable for harsh environmental condition such as high temperature and high pressure H2S (hydrogen sulfide) condition.In this paper, the corrosion resistance of Alloy625/X65 clad steel plate for pipe produced by TMCP (Thermo-Mechanical Control Process) was investigated. TTP (Time - Temperature - Precipitation) and TTS (Time - Temperature - Sensitization) diagram of Alloy625 indicated precipitation nose, e.g. M6C and M23C6 which would cause deterioration of corrosion resistance. TMCP enable Alloy625 to avoid long time exposure to the precipitation nose. In Huey test, the corrosion rate in TMCP was almost the same as that of solution treated Alloy625 and smaller than that in Q-T (Quench and Temper). In ferric chloride pitting test, no pitting was observed in Alloy625 layer of TMCP type clad steel. In addition, the corrosion test simulating service environment using autoclave apparatus was conducted under the condition of 0.39MPa H2S - 0.53MPa CO2 - Cl− solution at 200°C. Alloy625 clad steel produced by TMCP showed neither SSC (Sulfide stress corrosion cracking) nor crevice corrosion. All the mechanical properties of base carbon steel satisfied API 5L grade X65 specification by optimizing TMCP conditions. It is notable that 85% SATT of DWTT was below −10 °C. Thus, Alloy625/X65 clad steel plate for pipe produced by TMCP with both superior corrosion resistance and low temperature toughness has been developed.Copyright

A Study of Deformation Behavior of Double Jointing Girth Welds

Demand for double jointing technology is increasing to improve pipeline construction productivity. Submerged arc welding (SAW) utilized for double jointing is likely to cause a much wider heat affected zone (HAZ) than those of typical field welding by gas metal arc welding (GMAW), and it should be taken into account for strain-based design of high strength line-pipes. However, guidelines for SAW welds properties to ensure strain capacity of high strength line-pipes such as X80 have not been established yet.In this study, a submerged arc weld joint was produced using tensile strength (TS) over-matching welding consumable. API standard type transverse weld tension test was conducted to measure local elongation at weld metal, HAZ, and base material. Elongation at weld metal increases prior to base material, but soon after that elongation at the HAZ softening region and base material adjacent to the HAZ catch up with the elongation in the weld metal, and finally, deformation concentrates at the HAZ softening region before final fracture.Deformation behavior of the joint was analyzed to verify applicability to double jointing girth welds for strain-based design. From finite element (FE) analysis of notched wide plate test which characterizes tensile strain capacity of a pipeline, it is suggested that ductile crack would not initiate before base material start necking in this particular TS over-matching weld joint in which the defect size is 1mm of notch depth and 25mm of notch length. Thus, the weld joint would be applicable for double jointing girth welds based on strain-based design.Copyright