Investigation on size tolerance of pore defect of girth weld pipe

Abstract

Welding quality control is an important parameter for safe operation of oil and gas pipes, especially for high-strength steel pipes. Size control of welding defect is a bottleneck problem for current pipe construction. As a key part of construction procedure for butt-welding of pipes, pore defects in girth weld is difficult to ignore. A three-dimensional non-linear finite element numerical model is established to study applicability of size control indices based on groove shape and softening phenomenon of material in heat-affected zone of practical pipe girth weld. Taking design criteria of pipe as the basis, basic tensile, extremely tensile and extremely compressive loading conditions are determined for pipe stress analysis, and failure criteria based on flow stress is employed to perform stress analysis for pipe girth weld with pore defect. Results show that pipe girth welding stresses of pores at various radial locations are similar. Whereas, stress for pores of different sharpness varied significantly. Besides, tolerance capability of API 5L X90 grade pipe to pore defect of girth weld is lower than that of API 5L X80 grade pipe, and size control index of 3 mm related to pore defect in current standards is applicable to API 5L X80 and X90 grade girth welded pipes with radially non-sharp pore defects.

Quality evaluation of welding joints by different methods

“…Two types of tests determine the mechanical properties and quality of the weld joints. The quality of welds is assessed in welded metal, heat affected zone (HAZ) and in unaffected base metal [17,18].…”

Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment

“…Lu et al [29] obtained the equation of the residual strength of an incomplete full penetration defect model at the root of a girth weld pipe via the stress function method, which was in good agreement with the finite element results. According to the flow stress failure criterion, a stress analysis was performed on a pipe girth weld under extreme compression [30]. In general, the current research on the failure of pipe girth welds focuses mainly on the specification design and fracture mechanics.…”

Fatigue and burst tests of full-scale girth welded pipeline sections for safe operations

“…-Developing of newer non-destructive testing methods in order to identify the girth weld defects in operating pipelines [17][18][19]] -Achieving FEM calculations in order to investigation of defect size tolerances in girth welds [20], describing the damage process [8,9], or to preparation of fracture mechanical analyses [21,22] -Performing investigations on specimens in order to determine and analyze the tensile and toughness properties [23], yield strength mismatch [24], or fracture properties at low temperatures [25] of girth welds; to develop novel test method for mechanical properties of characteristic zones of girth welds [26]; to develop "field girth welding simulation" procedure evaluating properties in HAZ of girth welds [27]; or to ensure the safe operation of a pipeline transporting environments with hydrogen content [28] -Applying local approach to fracture in order to analysing of full-scale pipeline tests containing girth weld defects [29] -Performing investigations on full-scale pipeline sections for describing the behavior of the pipelines under different loading conditions [5,30,31], furthermore for the comparison of the results based on full-scale pipes and small-case specimens [32] -Applying engineering critical assessment (ECA) methods [33,34] based on different standards (e.g., [35,36] -Developing survival analysis models for girth weld failure prediction [37] In [29] publication, the full-scale test was played an intermediate role between numerical simulations and specimen tests. A full size test was carried out on a welded pipeline segment containing a girth weld defect; the pipe was subjected to internal pressure and superimposed bending.…”