Trends in the Development of Machinery and Associated Technology ” TMT 2009 , Hammamet , Tunisia , 16-21 October 2009 WELDING FLAWS OF PIPELINE HEAT RESISTANT STEELS (original) (raw)
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The structural integrity of high-strength welded pipeline steels: a review
International Journal of Structural Integrity, 2020
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 methodol...
Role of Welding Defects on the Failure of Sub-sea Carbon Steel Gas Pipeline
— Sub-sea gas pipeline spool made of a carbon steel alloy API 5XL grade X52 was failed at a girth weld adjacent to 45 0 elbow after 5 years of operation. The nominal diameter of the failed spool is 4″. The failed spool was received for failure analysis and data collections. Examination of the interior surface of the spool revealed moderate general corrosion with few shallow pits except the area near the girth of the circumferential welds showed severe localized pits where the corrosion attack occurred at the fusion line between weld metal and heat affected zone. Based on the macroscopic, SEM and XRD analyses, the failure was occurred due to flow enhanced accelerated localized corrosion attack related to improper welding techniques of girth welds. Undercut and / or excess bead penetration at the weld root and high heat input could be the primary causes for the localized turbulent flow conditions created around the girth welds which in turn led to this accelerated corrosion failure assisted by thermally stressed heated affect zone of the base metal. The presence of corrosive elements such as Cl &S simultaneously with localized turbulent flow results in a rate of localized corrosion orders of magnitude greater than those caused by pure erosion or corrosion mechanism. A proper welding techniques carried out by qualified welders are recommended for prevention of similar failure in the future. Index Terms—Sub-sea gas pipeline spool, carbon steel alloy, corrosion-erosion attack, welding techniques, heat affected zone.
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.
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.
The Consequences of cracks formed on the Oil and Gas Pipelines Weld Joints
International Journal of Engineering Trends and Technology, 2017
Weld cracking is one of the main failure modes in oil and gas (O & G) pipelines. Cracks are the most severe of all weld defects and are unacceptable in most circumstances. A simple existing defect on the pipeline after welding can generate a catastrophic fracture. The major cause of a crack is when internal stresses exceed the strength of the weld metal, the base metal, or both. If undetected, the cracking defects can act as stress concentration sites which lead to premature failure via fatigue, as well as offer favourable sites for hydrogen assisted cracking and stress corrosion cracking. For welded metal products such as deep sea oil and gas transportation pipes, such defects heighten the risk of catastrophic in-service failures. Such failures can lead to devastating environmental, economic, and social damage. Knowing the basics behind why cracks happen, a welder can prevent those cracks from occurring in the first place. Using different literatures, this paper reviews on the consequences of cracks on the oil and gas pipelines weld joints focusing on favourable welding processes for pipeline manufacturing, causes and effects of various types of weld cracks. It further highlights the importance of inspection, maintenance and repair of weld joints cracks. Hence, the knowledge of weld joint cracks mechanisms for any person that deals with pipelines is very important.
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.
Effect of in service weld repair on the performance of CrMo steel steam pipelines
Mater Res Ibero Am J Mater, 2006
This article presents a literature overview and discusses a practical case involving the effect of in service weld repair on the performance -behavior under creep conditions and remanent life -of low alloy CrMo steel steam pipelines with longstanding use. According to the specialized literature, several authors argue that the in service weld repair of low alloy CrMo steel steam pipes can be done successfully, while others disagree, reporting a reduction of up to 30% or more in the remanent life. According to the case analyzed here, which involves the weld repair of a 1¼Cr½Mo ferrite-pearlite steel steam pipe operating for 20 years at 480 °C, in service weld repair leads to the intragranular precipitation of Fe 2 MoC-type carbides and decreases the solute concentration of the ferrite in the base metal adjacent to the welded joint, thereby considerably reducing the pipeline's remanent life, since the estimated rupture time for the service-aged material is 3.6 times that estimated for the weld-repaired joint.
Revista de Metalurgia, 2010
Metallurgical evaluation was performed on a fractured column tube of the reformer furnace in an ammonia plant. The tubes were manufactured from centrifugally cast heat resistant steel HK 40. Optical and scanning electron microscope (SEM) were used for microstructural and fracture analysis. For composition determination of the microconstituents energy dispersive X ray spectroscopy (EDS) was used. To evaluate mechanical properties, hardness and microhardness measurements were performed. Investigations based on the microstructural features with the idea to indicate suitability of weld repair of the column were performed in this study. It was observed that the crack initiation, caused by oxidation/corrosion and thermal stresses induced by temperature gradient, appeared in the inner side of the tube wall and propagation occurred along grain boundaries. The results clearly showed the presence of an irregular microstructure which contributed to crack propagation through the tube wall. An occurrence of precipitated needle-shaped carbides/carbonitrides and brittle σ phase was also identified in the microstructure. Results of the microstructural and fracture analysis clearly indicate that reformer furnace columns made of heat resistant steel HK 40 were unsuitable for weld repair.
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.