By thineshraaj jaya raman 16371 bachelor of engineering hons. Causes and prevention of corrosion on welded joints. Attempts to control pwc have previously involved making minor additions of noble metals e. Corrosion behavior of welded stainless steel corrosion resistance of stainless steel weld metal depends on an understanding of the nature of the protective passive film that gives the steel its stainless characteristic by t. Flow accelerated preferential weld corrosion of x65 steel in.
Webcorr provides corrosion consultancy services, corrosion expert witness and corrosion short courses for inhouse training, online and distance learning. On the other hand, eroglu and aksoy 3 investigated the effect of initial grain size on mi. Pdf the influence of hydrodynamics on the preferential weld. Preferential corrosion of welds usually occurs when the environment in contact with the material has a high electrical conductivity, such as seawater, but can also occur in low conductivity co 2 containing environments. The primary objective of this study is to investigate the weldment structure and the microstructures of parent metal region, heataffected zone and weld metal region of an api 5l x52 grade carbon steel pipe. The performance of a commercially available oilfield corrosion inhibitor to control preferential weld corrosion in co 2saturated brine was assessed. Carbon or carbon or low alloy steel low alloy steel weld metal buttering layer of pure ni copper steel electrode copper carbon or low alloy steel joint parts material thermal exp. In particular, this has been on weldments made by the manual metal arc mma. High temperature carbon steel weld preferential corrosion. Preferential weld corrosion pwc has been an issue in the oil and gas industry for a number of years. The weld segments consist of parent metal, haz and weld metal that causes corrosion due to potential difference.
Investigation on preferential corrosion of welded carbon. Alterations to the environment, such as the addition of a biocide, can change the corrosion characteristics of a system. A submerged impinging jet sij was utilized to test carbon steel parent metal and a 1% ni 0. However, after these inspections were completed, a pinhole leak occurred on a weld in the crude distillation unit cdu heavy gasoil hgo circuit. Although emphasis has been placed on carbon steels and stainless steels, nonferrous alloys such as highnickel alloys, aluminum alloys, and titanium alloys also are covered.
The general consensus from authors is that environmental effects take precedence over the weld chemical composition and microstructure. A 2014 the influence of hydrodynamics on the preferential weld corrosion of x65 linepipe steel in flowing brine containing carbon dioxide, nace corrosion 2014, paper c20143796, 2010. Preferential weld corrosion2011 connecting repositories. Used in food, chemical, oil production and power generation industries. Corrosion of carbon steel weldments can be due to metallurgical effects, such as preferential corrosion of the heataffected zone haz or weld metal, or it can be associated with geometrical aspects, such as stress concentration at the weld toe, or creation of crevices due to joint design. Niekie is right in telling that pwht will decrease corrosion rate for the reasons hes explained. Preferential weld corrosion of x65 pipeline steel in flowing. In particular, this has been on weldments made by the manual metal arc mma process using electrodes containing ni or ni plus cu. Preferential weld corrosion of carbon steels knovel. The influence of hydrodynamics on the preferential weld. Preferential weldments corrosion of carbon steels has been investigated since the 1950s, commencing with the problems of ice breakers, but the problem continues today in different applications. Preferential corrosion of carbon steel welds is usually a consequence of the higher silicon content of the weld as compared with the plate from which the digester was constructed. In the welding of cmn steels, the siliconkilled steels are the most anodic and the unkilled steels with low silicon content are the most cathodic. However, the mitigation has not been effective as the feco 3.
Assessment of preferential weld corrosion of carbon steel pipework in co2saturated flowinduced corrosion environments article in nace international corrosion conference series 311. Mar 23, 20 carbon steels are used extensively in construction of oil and gas pipes but they exhibit poor corrosion resistance properties because of internal corrosion. The influence of hydrodynamics on the preferential weld corrosion of x65 linepipe steel in flowing brine containing carbon dioxide. Basic understanding of weld corrosion asm international. Corrosion professionals, asset integrity specialists and engineers responsible for risk management will find a comprehensive literature survey, detailed description of the pwc problem in its different aspects, and clear guidance on how to manage pwc in both new projects and maturing. Therefore, the primary approach is to ensure the correct corrosion inhibitor selection. Pdf investigation on preferential corrosion of welded carbon. This book addresses the detection, assessment and control of preferential weld corrosion pwc of carbon steels. Preferential weld corrosion of x65 pipeline steel in flowing brines containing carbon dioxide. Figure 1 shows an example of severe pwc in a carbon steel pipeline which failed after only a few months in service 1. Stainless steels corrosion of carbon steels and low alloy steels is poor in severe environments. The location and morphology of the preferential corrosion is. Effect of welding on microstructure and mechanical properties.
For example, the majority of failures in welded structures in oil and gas industry are attributed to corrosion of weldments. The aim of this paper is to compare the effectiveness and electrochemical behavior of typical oilfield corrosion inhibitors with previous oilfield corrosion inhibitors under the same electrochemical techniques to control preferential weld corrosion of x65 pipeline steel in artificial seawater saturated with carbon dioxide at a pressure of one bar. Numerous models 11,12 exist for estimating the co 2 corrosion rate. Preferential weld corrosion of carbon steels ebook, 2016.
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. Pdf carbon steels are used extensively in construction of oil and gas pipes but they exhibit poor corrosionresistance properties because of internal. The corrosion could be mitigated with the formation of protective layer feco 3. Mitigation in seawater pipelines, cooling water systems, wet gas piping, heat exchangers, etc. The preferential attack of carbon steel weldments in co 2 containing systems was also shown be less in welds with low haz hardnesses. Weld decay and intergranular corrosion causes and prevention. During welding of stainless steels, local sensitized zones i. Mitigation in seawater pipelines, cooling water systems, wet gas piping, heat exchangers related equipment. Ni, cr, mo, cu to the weld consumable in order to make the weld.
Pdf effect of inhibitors on weld corrosion under sweet. Welding plays an essential role in the fabrication of components and structures such as reactor vessels, pipe work, heat exchangers etc. Preferential weld corrosion of carbon steels nace international has added a new publication to its collection of corrosion resources. Corrosion of weld joints can be avoided by the careful selection of materials to be welded, the filler metal, welding techniques and finishing. Preferential weldment corrosion pwc of carbon and low alloy steels used for. Solving preferential weld corrosion in cmn steels twi. We discuss in detail the methods of analysis of carbon steel surfaces under corrosive conditions, and in the absence and presence of corrosion inhibitors. In this research, a rotating cylinder electrode apparatus was designed so that electrodes machined from the weld metal, heataffected zone, and parent material of a welded x65 pipeline steel could be tested in high shear stress conditions. It has been found that preferential weld and heataffected zone haz corrosion. Jul 11, 2017 a welded joint can have a low resistance to corrosion due to the varying chemical composition, residual stress and metallurgical structure of the weld zone. Evaluation of techniques for measuring the corrosion activity.
Preferential weld corrosion pwc is a serious form of attack in which the corrosion rates of the weld metal wm and heat affected zone haz exceed that of the parent metal pm. Preferential weld corrosion occurs in the hydrocarbon carrying pipelines due to co 2 presence. Stainless steels contain sufficient amount of cr which forms thin protective adherent layer of cr2o3 film. Detection, assessment and control of preferential weld corrosion pwc of carbon steels. Preferential weldment corrosion pwc of carbon and low alloy steels used for pipelines and process piping systems in co2containing media has been observed increasingly in recent years.
Preferential weld corrosion is a selective form of attack, which corrodes the weld metal in wet gas environments containing co 2. Preferential corrosion of carbon steel elbow strider6 materials 27 aug 09 02. Localized corrosion of carbon steel welds has been thought to arise primarily from galvanic effects due to compositional differences between the deposited weld metal, the parent steel, and the heat affected zone induced by the welding process. Steels with a higher silicon content tend to corrode more. A case study has been conducted to examine the causes of accelerated decay during preferential corrosion of welds. It is accepted that the use of a basic flux can lead to greater corrosion rates in the weld metal than in a weld made using a rutile flux. Preferential corrosion of carbon steel elbow corrosion. The corrosion resistance of stainless steels depends on a protective. The preferential weld corrosion of x65 carbon steel pipeline. The first problem is that astm a106 is carbon steel and no carbon steel withstands corrosion from acids.
This effort came on the top of the existing refinery sulfidation inspection plan for carbon steel piping. Preferential weld corrosion pwc has posed a problem to the oil and gas industry for a number of years. Lundin2 drew the following conclusions from a detailed investigation. Preferential weldment corrosion pwc of carbon and low alloy steels used for pipelines and process piping systems in co 2containing media has been observed increasingly in recent years. Ultrasonic testing ut measurements showed no excessive corrosion on any inspected components. Assessment of preferential weld corrosion of carbon steel. Galvanic corrosion occurs due to the difference in compositions and microstructures of the weldment. A study of preferential weld corrosion in the presence of. The effect of flow rate on the preferential weld corrosion of. The aim of this research was to investigate the cause of the severe localised corrosion that sometimes occurs at welds in carbon steel pipelines carrying. Sensitization is due to the formation of chromium carbide along grain boundaries, resulting in depletion of chromium in the region adjacent to the grain boundary ref 7.