Abstract:The girth welding of steel pipelines creates a substantial heat affected zone (HAZ) within the base pipeline steel. The HAZ can be considered to be a complex graded microstructure. While there is significant concern as to the fracture and mechanical properties of the HAZ as whole, detailed knowledge about the mechanical properties of the individual microstructures is lacking. For this study, X80 is heat treated in a Gleeble simulator to create samples of bulk microstructures with differing amounts and morpholo… Show more
“…Selection of material for pipelines has a critical role in addressing this problem. However, previous studies have expressed concern on various issues encountered during welding of API pipeline steels (Gaudet, 2015). During fusion welding, heat disperses away from weld, raising the temperature of surrounding base material and creates steep microstructural gradients (Shome et al ., 2004).…”
PurposeThe key purpose of conducting this review is to identify the issues that affect the structural integrity of pipeline structures. Heat affected zone (HAZ) has been identified as the weak zone in pipeline welds which is prone to have immature failuresDesign/methodology/approachIn the present work, literature review is conducted on key issues related to the structural integrity of pipeline steel welds. Mechanical and microstructural transformations that take place during welding have been systematically reviewed in the present review paper.FindingsKey findings of the present review underline the role of brittle microstructure phases, and hard secondary particles present in the matrix are responsible for intergranular and intragranular cracks.Research limitations/implicationsThe research limitations of the present review are new material characterization techniques that are not available in developing countries.Practical implicationsThe practical limitations are new test methodologies and associated cost.Social implicationsThe fracture of pipelines significantly affects the surrounding ecology. The continuous spillage of oil pollutes the land and water of the surroundings.Originality/valueThe present review contains recent and past studies conducted on welded pipeline steel structures. The systematic analysis of studies conducted so far highlights various bottlenecks of the welding methods.
“…Selection of material for pipelines has a critical role in addressing this problem. However, previous studies have expressed concern on various issues encountered during welding of API pipeline steels (Gaudet, 2015). During fusion welding, heat disperses away from weld, raising the temperature of surrounding base material and creates steep microstructural gradients (Shome et al ., 2004).…”
PurposeThe key purpose of conducting this review is to identify the issues that affect the structural integrity of pipeline structures. Heat affected zone (HAZ) has been identified as the weak zone in pipeline welds which is prone to have immature failuresDesign/methodology/approachIn the present work, literature review is conducted on key issues related to the structural integrity of pipeline steel welds. Mechanical and microstructural transformations that take place during welding have been systematically reviewed in the present review paper.FindingsKey findings of the present review underline the role of brittle microstructure phases, and hard secondary particles present in the matrix are responsible for intergranular and intragranular cracks.Research limitations/implicationsThe research limitations of the present review are new material characterization techniques that are not available in developing countries.Practical implicationsThe practical limitations are new test methodologies and associated cost.Social implicationsThe fracture of pipelines significantly affects the surrounding ecology. The continuous spillage of oil pollutes the land and water of the surroundings.Originality/valueThe present review contains recent and past studies conducted on welded pipeline steel structures. The systematic analysis of studies conducted so far highlights various bottlenecks of the welding methods.
“…Gaudet conducted a series of weld trials on plates instrumented with thermocouples spot welded in the bottom of small holes drilled at various positions from the weld fusion line. 20 The temperature cycles, recorded in situ during the weld trials, provide critical information on the relevant heating rates, peak temperatures and cooling rates at different positions in the HAZ for gas metal arc welding (GMAW) in single- and dual-torch configurations. More recently, similar experiments were also extended to submerged arc welding (SAW) conditions in order to compare the two welding techniques and their influence on the resulting microstructure.…”
Section: Background and Experimentsmentioning
confidence: 99%
“…The first pass is defined by a peak temperature of 1200°C with t 8–5 = 7 s, and the second pass by a peak temperature of 1200°C with t 8–5 = 15 s, that is similar to what was measured in the experimental weld trials. 20 In all cases, the heating step is conducted at a rate of 100°C s –1 up to the peak temperature where the holding time is 0.5 s before the onset of cooling. 1 Simplified heat treatment cycles to simulate a single torch and b dual torch welding…”
Section: Background and Experimentsmentioning
confidence: 99%
“…12,13 In particular, a large austenite grain size and/or a high level of Nb in solid solution favours the formation of transformation products such as bainite and the associated martensite/austenite (M/A) constituents, which may have detrimental effects on weld toughness, hydrogen resistance, cold and reheat cracking. 2,14–19 A recent study by Gaudet 20 has shown the variation of tensile properties and tear resistance over a range of temperatures (20 to −60°C) for relevant microstructures found in the HAZ of the current X80 steel (with the exception of the intercritical region, which is currently under investigation).…”
Section: Introductionmentioning
confidence: 96%
“…As part of a larger project, a significant body of experimental and theoretical work has recently been conducted for a Ti-Nb microalloyed X80 linepipe steel. 4,11,[20][21][22][23][24][25] The aim of this paper is to integrate the previous work on austenite grain growth, dissolution of microalloyed precipitates and decomposition of austenite into a single model to allow for the prediction of microstructure evolution in the weld HAZ for this steel with an emphasis on relevant conditions of girth welds. Additional experiments have been conducted to validate and, where necessary, to refine the model parameters previously reported in the literature and examine the predictive capability of the model.…”
An important aspect of the integrity of oil and gas pipelines is the heat-affected zone (HAZ) of girth welds where the microstructure of the as-hot rolled steel is altered with potentially adverse effects on the HAZ properties. Therefore, it is critical to evaluate the HAZ microstructure for different welding scenarios. Here, an integrated microstructure evolution model is proposed and applied to the HAZ of an X80 linepipe steel. The model considers dissolution of Nb-rich precipitates, austenite grain growth and austenite decomposition into ferrite and bainite. Microstructure maps showing the fraction of transformation products as a function of distance from the fusion line are obtained and used to compare the effect of different welding procedures on the HAZ microstructure.
There is a complex interplay between welding procedures and the steel chemistry which determines the final engineering performance of the heat affected zone in a large diameter girth weld. This work uses a combination of experimentally determined thermal histories from laboratory scale single and dual torch multi-pass gas metal arc welding (GMAW) with phenomenological models to predict microstructure and mechanical properties in the heat affected zone (HAZ) of an X80 steel. The integrated model consists of sub-models for austenite grain growth, dissolution of Nb based precipitates and austenite decomposition. These models have been calibrated with detailed experimental studies using a Gleeble 3500 thermomechanical simulator. The models are fully integrated so that the austenite grain size and the Nb solid solution level are used as inputs into the austenite decomposition model where these two factors strongly affect the final microstructure. The decomposition model includes ferrite and bainite models with suitable criteria for transition from one model to the other and a simple first order empirical relation to predict the final fraction of martensite/retained austenite (MA). The integrated model has been applied to a variety of thermal scenarios which are derived from experimental measurements of thermal histories including dual torch conditions where, for example, the Nb solid solution level has to be tracked through both thermal excursions into austenite. Using the integrated model, microstructure maps of the HAZ can be generated for the different welding scenarios.
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