Fracture Toughness Testing of a Nickel-Chromium Lined Pipe Girth Weld Using the Unloading Compliance Technique
Vitor Scarabeli Barbosa1; Diego Felipe Sarzosa1; Claudio Ruggieri1
1 Escola Politécnica da USP
doi:10.20906/CPS/CON-2016-0064
Resumo
The increasing demand for energy and natural resources has spurred a flurry of exploration and production activities of oil and natural gas in more hostile environments, including very deep water offshore hydrocarbon reservoirs. One of the key challenges facing the oil and gas industry is the assurance of more reliable and fail-safe operations of the infrastructure for production and transportation. Currently, structural integrity of submarine risers and flowlines conducting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of C-Mn steel pipelines (for example, API X65 grade steel) either clad or mechanically lined with corrosion resistant alloys (CRA), such as Inconel Alloy 625 and Alloy 825, for the transport of corrosive fluids. However, while cost effective, fracture assessments of girth welds in lined pipes become more complex due to the dissimilar nature of these materials. In particular, current standardization efforts now underway make extensive use of single edge notch tension SE(T) specimens to measure experimental R-curves which are applicable to fracture specimens made of homogeneous materials. For a given specimen geometry, mismatch between weld metal and base plate strength affects the macroscopic mechanical behavior of the specimen in terms of its load-displacement response with a potentially strong impact on the crack growth resistance curve. This work presents an investigation of the ductile tearing properties for the girth weld of a typical C-Mn pipe internally clad with Inconel 625 CRA alloy (UNS N06625) using experimentally measured crack growth resistance curves (J-Δa curves). Here, the material of the external pipe is an API 5L Grade X70 pipeline steel with a higher yield stress of 551 MPa and relatively low hardening properties whereas the inner clad layer is made of Inconel nickel-chromium alloy 625 (UNS N06625) with yield stress of 495 MPa and high hardening. The higher mechanical
Palavras-chave: integridade estrutural; curvas de resistência J-R; fratura dúctil; dutos para gás e petróleo; junta soldada