The structural integrity of high-strength welded pipeline steels: a review (original) (raw)
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Fatigue & Fracture of Engineering Materials & Structures, 2020
In this paper, microstructure observations and mechanical behaviour of fusion line and offsetting positions from fusion line by 1, 2 and 3 mm were analysed. For the welding of X80 pipeline steel plates, different magnitudes of heat inputs such as high heat input (HHI) 25 kJ/cm, medium heat input (MHI) 20 kJ/cm and low heat input (LHI) 15 kJ/cm were employed. Critical values of J-integral (J 0.2) and crack tip opening displacement (CTOD 0.2) for predetermined regions in the X80 weldment were determined as per ASTM-E1820a. M-A constituents of different sizes such as small (1-2 μm), large >2 μm and slender (>4 μm) were observed in the microstructure of subzones of weldments for different heat inputs. Formation of granular bainite, M-A constituents and inclusions of Ti, Si, Mo in the microstructure impaired fracture toughness property. In the X80 weldment, the fusion line (FL) for HHI was found weakest in terms of fracture resistance, which subsequently increases the risk of fracture.
Integrity Assessment of Weldment Zone of Selected Oil and Gas Pipelines
2013
this work examines the integrity of weldment zone of an oil and gas pipeline used to convey petroleum products. To accomplish this in an efficient way, experiments on a variety of welding parameters were conducted on American Society of Testing Materials (ASTM) A109SCH40 steel specimen, welded by metal arc welding. Thus, the influence of welding current, arc voltage, welding speed, pipe thickness and depths of penetration on some mechanical properties of the pipeline steel were studied. The findings from this work shown that an increase in the welding speed at a constant arc voltage and current will lead to increase in penetration until maximum penetration is achieved. The practical implications of this research show that optimal weld penetration can be achieved under certain circumstances. Further researches are needed to explain how the weldment mechanism changes with varying welding conditions.
Acta Metallurgica Sinica (English Letters), 2016
The aim of this work is to study the influence of successive weld repairs on the microstructure and the mechanical behavior of the heat-affected zone (HAZ) of an HSLA X70 steel. Detailed microstructural examination combined to grain size measurement showed that beyond the second weld repair, the microstructure of the HAZ undergoes significant change in the grain morphology and grain growth. The results of the X-ray diffraction analyzed using MAUD software indicated an increase in the crystallite size and a decrease in the dislocation density according to the number of weld repair operations. Consequently, a loss of mechanical properties, namely the yield strength and the toughness with the number of weld repairs, was recorded. Beyond the second weld repair operation, the properties of the welded joint do not fulfill the standards applied in piping industry.
Evaluation of the Weld on In-service Gas Pipeline
International Journal of Electrochemical Science, 2016
The study evaluated the condition of steel gas pipeline at the site of weld after more than 45 years of service. The deformation cycle of welding and particularly superposition of the thermal and deformation cycle, results in phase transformation and precipitation processes in the thermally affected region. The deformation cycle has a pronounced effect on ageing of the welded joint and the associated increase in its hardness and reduction in notch toughness. The hardness of the weld was measured according to Vickers HV0.05. The highest values of hardness were measured for the weld metal, namely 293 HV0.05. The values of mechanical properties of steel after more than 45 years of service of the pipeline corresponded to values defined by the respective standard. Transition temperature T T according to Charpy test was equal to-8.5 °C. From the point of view of technical practice, with regard to pipe service properties, it is important that the construction material is loaded at temperatures above the transition temperature T T. Transcrystalline brittle failure was observed on the specimens that have been broken at T T temperature.
Effect of Heat Treatment on the Microstructural Evolution in Weld Region of 304L Pipeline Steel
Journal of Thermal Engineering, 2016
In this work, the effect of isothermal heat treatments at 300 °C on microstructure evolution after welding by Tungsten Inert Gas (TIG) welding technique of 304L pipeline steel have been studied. Microstructures of the weldments were investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and hardness measurements. Microstructural evolution in welded joint was identified. Results indicated that the microstructure of fusion zones exhibited dendritic structure. The applied heat treatments affected the microstructure of the welded joint. However some defects have been observed in weld joint.
INVESTIGATION OF THE MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF WELDED API X70 PIPELINE STEEL
The mechanical properties of pipelines particularly those in marine environments are influenced by corrosion activity of seawater throughout their service lives. The degree to which these properties are influenced in seawater compared to those exposed to air needs to be better understood. In this study, the chemical composition of API X70 pipeline steel plate, microstructure and mechanical properties of the welded joints of same steel plates exposed to ambient air and seawater respectively were investigated. It was found that the base metal consisted of manganese (0.51wt% Mn), low carbon content (0.051 wt% C) and small quantities of alloying elements such as vanadium (0.021wt% V), molybdenum (0.118 wt% Mo), chromium (0.240 wt% Cr), copper (0.002 wt% Cu), and a carbon equivalent (CE IIW) of 0.38. Scanning Electron Microscope (SEM) showed that the microstructure of base metal sample has large grains formed in packets which have certain crystallographic orientation but contain submicron grains arranged in a chaotic interlocking manner. The tensile tests performed using a UNITED type universal testing machine confirmed that the yield strength of the base metal was 573.045MPa which conforms to API standard for X70 steel pipe. The manual metal arc (MMA) welding technique was applied to produce the welded joints. For the welded joints exposed to ambient air at room temperature, the yield strength was 680.624MPa while the compressive strength was 1500.2MPa, and the impact energy at-10°C was 112.68J. Air tests referred to tests conducted in the laboratory at room temperature. For the welded joints exposed to seawater for 12 weeks, the yield strength was 609.154MPa while the compressive strength was 1219.34MPa, and the impact energy at-10°C was 61.48J. The above results for air and seawater exposures were used to determine the environmental reduction factors of the two environments. Hardness tests conducted using Vickers hardness tester revealed variations in hardness across the base metal, the HAZ and the weld, with the weld having the highest average Vicker's hardness value (223.8HV) followed by the base metal (217.3HV) and the HAZ had the least (214.5HV)
Arc Welding 128 SCC can occur in both gas and liquid pipelines but is more common and catastrophic in gas pipelines . SCC is the most unexpected form of pipeline failure that can involve no metal loss and must not be confused with wall thinning rupture. SCC on pipelines begins with small cracks develop on the outside surface of the buried pipe. These cracks are initially not visible to the eye and are most commonly found in colonies, with all the cracks in the same direction, perpendicular to the stress applied. This chapter describes the mechanical and environmental effects as well fracture characteristics on SCC susceptibility of steels used in the oil industry using slow strain rate tests (SSRT), which were carried out according to requirements of NACE TM-0198, ASTM G-129 and NACE TM-0177 standards (NACE TM-0198, 2004; ASTM G-129, 2006;. Some tests were supplemented by potentiodynamic polarization and hydrogen diffusion tests. SSRT were performed in samples which include the longitudinal and circumferential weld bead of pipeline steels. The weld beads were produced using the submerged arc welding (SAW) and shielded metal arc welding (SMAW) process. The SCC susceptibility has been evaluated using the results of SSRT in air (as an inert environment), sour solution according to NACE TM 0177 (solution A from method A) and in some cases a simulated soil solution called NS4. The studies include the effect of pH, temperature, microstructure, effect of multiple welding repairs and mechanical properties. The steels studied are low carbon steels API X52, X60, X65 and X70.
This study was focused on wear-resistant material prepared by CO 2 GMAW method to basically determine the alloys and hardfacing technology which could be employed into mining equipment. Three flux-cored wires with different chemical compositions, marked by DM-I, DM-II and DM-III were used in welding a martensitic steel for the comparison of the microstructures and mechanical properties of the welding metals and HAZ. The results show that DM-I weld metal contains martensite plus other reinforced phases, while both DM-II and DM-III alloys lead to mainly martensitic microstructures with little precipitates. Among all of the tested materials the DM-I alloy has the highest hardness and wear resistance but the lowest impact toughness among the experimental weld metals. Meanwhile, the hardness, impact toughness and wear resistance of the DM-II and DM-III alloys are close to those of the base metal but the DM-III is not as strong as DM-II. Dimples can be found on the impact fracture of the weld metals, but the steel fracture consists of both cleavage and dimples. Thus HAZ has less risk for cracking than the welds, and the DM-II wire which produces the weld having identical mechanical properties to the base metal is suitable for further application.
Metallurgical Aspects in the Welding of Clad Pipelines—A Global Outlook
Applied Sciences
In the present work, the metallurgical changes in the welding of clad pipelines are studied. Clad pipes consist of a complex multi-material system, with (i) the clad being stainless steel or a nickel-based superalloy, (ii) the pipe being API X60 or X65 high-strength carbon steel, and (iii) the welding wire being a nickel-based superalloy or stainless steel in the root and hot pass, with a nickel or iron buffer layer, followed by filling with carbon steel wire. Alternatively, the corrosion resistant alloy may be used only. During production of the clad pipe, at the diffusion bonding temperature, substantial material changes may occur. These are carbon diffusion from the carbon steel to the clad, followed by the formation of hard martensite at the interface on cooling. The solidification behavior and microstructure evolution in the weld metal and in the heat-affected zone are further discussed for the different material combinations. Solidification behavior was also numerically estima...