Managing the Threat of Selective Seam Weld Corrosion Using a State of the Art ILI System

For many years, pipeline safety regulations in the US have defined prescriptive minimum requirements for integrity management combined with a clear expectation that operators should do more than the minimum where appropriate. The regulations have also provided operators with the flexibility to take a performance based integrity management approach leveraging as much information available to manage threats effectively. One the threats that must be managed is Selective Seam Weld Corrosion (SSWC). SSWC is an environmentally assisted mechanism in which there is increased degree of metal loss in the longitudinal weld in comparison to the surrounding pipe body. An appropriate definition is linear corrosion that is deeper in the longitudinal weld zone than the surrounding pipe body. In some cases, the surrounding pipe body may have limited or no corrosion present, and in other cases the pipe body corrosion may have occurred but at a slower rate than the local corrosion in the longitudinal weld zone. Conventional responses to potential or identified threats focus on in-situ investigations, often resulting in expensive and un-planned repairs for features reported by In-line Inspection (ILI) that when assessed properly demonstrate a remnant life well into the next inspection interval. When ILI identifies metal loss indications co-located with the longitudinal seam weld, the current prescribed response is often a blanket call for remediation. Such a response may not be appropriate if an ILI system is deployed to discriminate feature types and integrity assessment is exercised leveraging a sound understanding of the pipe’s material properties. This paper describes an approach that can be taken to manage the threat of SSWC. The foundation of the approach is deployment of an appropriate ILI system incorporating an effective ILI technology, an optimized evaluation process considering the specific threat morphology, material testing and a structured dig program. The evaluation process uses the ILI data and data from the field in combination material properties data and a susceptibility analysis to classify anomalies as “Likely”, “Possible” and “Unlikely” SSWC. This is aligned with the guidance in API RP 1176 “Assessment and Management of Cracking in Pipelines” for defining an appropriate response to ILI calls. Approaching the management of SSWC in this way allows operators to define a structured response for excavation activities to verify the process and remediate features as required. By using likelihood classification the risk to pipeline integrity can be reduced by acting on the most likely SSWC features as a priority, whilst collecting the data needed to make informed decisions on where to focus resources and efforts on what is a very complicated and difficult to manage threat. The output form this work, including a future plan for managing the remaining metal loss features, can be documented in a procedure and incorporated into an existing Integrity Management Plan.

THE PREFERENTIAL WELD CORROSION OF X65 CARBON STEEL PIPELINE UNDER CO2 ENVIRONMENT

Preferential weld corrosion (PWC) is a severe corrosion form of attack found in pipeline weldments in oil and gas industries. PWC occurs when the corrosion rate of the weld metal (WM) and heat affected zone (HAZ) is higher than the parent metal (PM). PWC was generated by galvanic corrosion mechanism due to dissimilarities in the composition and microstructure of the metal in the three weld regions.The aim of this research is to study the effect of flow rate on preferential weld corrosion (PWC) in X65 high strength pipeline steel using submerged jet impingement by investigating the mechanism of PWC on a weldment in artificial seawater saturated with carbon dioxide at 1 bar. A novel submerged jet impingement apparatus that consist of 3 rings (outer, inner and centre) was designed so that the parent material, heat affected zone and weld metal could be analysed in a high shear stress environment. Corrosion experiments were performed with X65 pipeline steel under no flow and flowing condition at 10 m/s at 30oC and pH4. The galvanic current characteristic between the weldment regions was recorded using a zero-resistance ammeter, and the self-corrosion was analysed by using linear polarisation resistance measurements. Total corrosion rates were calculated from the sum of the galvanic and self-corrosion contributions. The morphology, structure, chemical on the surface of X65 after corrosion process was investigated by means of scanning electron microscopy (SEM) and focus ion beam (FIB) to examine the corrosion product that form in brine containing dissolved carbon dioxide.In a no-flow condition, the result shows that the galvanic characteristics on all weldments were similar and the WM is cathodic and protected in comparison with the HAZ and PM. In flowing condition, the estimated flow rates associated with the different positions on the target vary depending on either (a) PM and HAZ or (b) the WM. The effects of target flow rate on WM have a similar trend, but the overall corrosion rates are greater due to PWC. The result of surface analysis after corrosion process showing that removal of hardened layer and subsurface cracking were causes of enhanced degradation.

Study on Welding Techniques of 316L Lined Bimetallic Pipe

It is well known that welding technique was often a knotty problem for bimetallic lined steel pipes to use widely. A number of failures in secession of weld cracking and weld corrosion had been observed in oil fields in recent years, which seriously disrupted the order of oil and gas production. To solve welding problems of 316L bimetallic lined pipes, works outcome about failure analysis and welding process research were presented in this paper. Failure analysis results confirmed that Welding defects, high hardness regions was the main reasons about failure problems of weld crack while structure design defects of seal weld and bad back-protection effects of flux-cored wire resulted in weld corrosion. Welding defects in the regions of seal weld became the failure source while the high hardness both in the region of seal weld and weld joint formed the crack propagation channel, and therefore both initially contributed to weld cracking. Additionally owing to the structure design of seal weld, liner layer would be heated over and over again during the period of seal weld and then it was not enough to protect CRA layers from being damaged during the period of girth weld. As a result the corrosion resistance in the welding area was reduced to become a weak area. On the basis of failure analysis, further research work was carried out to improve welding performance. Seal weld structure and girth weld process was improved. The difference of welding wires and welding process was analyzed, and their defects were described separately. Results showed that the welding performance welding by ERNiCrMo-3 and supporting technology was more reliable than ATS-F309L and supporting technology, whether seal weld or butt welding. The distribution and value of the hardness could be effectively controlled; Moreover, corrosion resistance performance was also better. Therefore, the seal weld and girth weld conducted by ERNiCrMo-3 and supporting technology was feasible.

Stress Intensity Factor Solutions for Crack-Like Anomalies in ERW Seam Welded Pipe

In response to the National Transportation Safety Board (NTSB) Recommendation P-09-1, the Department of Transportation (DOT) Pipeline and Hazardous Material Safety Administration (PHMSA) initiated a comprehensive study to identify actions that could be implemented by pipeline operators to significantly reduce longitudinal seam failures in electric resistance weld (ERW) pipe. As part of the project, Task 3 in Phase II was designed to determine more appropriate stress intensity factor solutions for non-standard, axial, crack-like anomalies in ERW seam-welded pipe. The purpose of this paper is to provide an overview of the normalized stress intensity factor solutions for cold weld (CW), selected seam-weld corrosion (SSWC), and hook crack type anomalies. ERW seams with and without weld caps are also included. The limitations on design space are discussed in the context of presenting results and interpolation and extrapolation schemes beyond that space with infinitely long solutions used as a boundary value. Results are presented in the form of surface plots for various combinations of parameters. The reports generated during the project are publicly available and are located on the following PHMSA website: http://primis.phmsa.dot.gov/matrix/PrjHome. rdm?prj=390.