Chloride Stress Corrosion Cracking Research Articles

Failure Analysis of the Crack and Leakage of a Crude Oil Pipeline under CO2-Steam Flooding

This paper presents the failure analysis of the crack and leakage accident of a crude oil pipeline under CO2-steam flooding in the western oilfield of China. To analyze the failure behavior and cause, different testing, including nondestructive testing, chemical composition analysis, tensile property testing, metallographic analysis, and microanalysis of fracture and chloride stress corrosion cracking (SCC) testing, are applied in the present study. The obtained results showed that the pipeline under the insulation layer of high humidity, high oxygen content, and high Cl− environment occurred pit corrosion, and the stress concentration area at the bottom of the corrosion pit sprouted cracks. Besides, it is demonstrated that the cracks were much branched, mostly through the crystal, and the fracture showed brittle, which is consistent with the typical characteristics of chloride SCC. Meanwhile, the insufficient Ni content of the pipeline material promoted the process of chloride SCC, and the high-temperature working conditions also aggravated the rate of chloride SCC. In addition, efficient precautions were provided to avoid fracture.

Firefly Algorithm and Neural Network Employment for Dilution Analysis of Super Duplex Stainless Steel Clads over AISI 1020 Steel Using Gas Tungsten Arc Process

Traditional low-carbon steels provide the strength needed to satisfy industrial demands. Low-carbon steel’s poor corrosion resistance is one of its main drawbacks. Due to this restriction, corrosion-resistant materials such as super duplex stainless steels are frequently used for cladding onto the surface of low-carbon steel. The cladded surface possesses superior chloride stress corrosion cracking resistance, pitting and crevice corrosion resistance, yield strength, ductility, and impact toughness. Mild steel with measurements of 300 × 300 × 12 mm has been selected as the substrate material, and super duplex stainless steel (S32950) with an electrode diameter of 2.4 mm has been selected as the filler wire. Gas Tungsten Arc (GTA) cladding was performed onto the surface of low-carbon steel for experimentation. The clad was deposited in the flat position with four different currents, i.e., 120 A, 130 A, 140 A, and 150 A. Cladding was performed on different layers of each current level, i.e., single layer, double layers, and triple layers. After experimenting and overviewing the outcomes, it can be concluded that the optimum input parameters would be a 3-layered clad at a 140 A current level. Cladding of the super duplex stainless steel over mild steel improves the corrosive properties. The percentage ratio of reactivation current density to activation current density (Ir/Ia%) improves from 29% (mild steel) to 4.1% at the top layer and 11.9% at the intermediate layer. The microhardness of the clad decreases with an increase in both the current level and the number of layers. Microhardness varies between 191–248 at the clad, 170–189 at the HAZ, and 143–153 at the substrate for a 1 kgf load. Dilution refers to the change in the cladding alloy composition due to the mixing of the molten matrix. The composition of the clad changes under a high dilution, resulting in a decrease in the mechanical as well as corrosion properties of the clad. However, if the dilution is too small, the bond between the substrate and the clad is poor. Therefore, dilution is one of the most important process control parameters and the key to obtaining high-quality cladding. Thus, the dilution effect is also analyzed on all three clad layers deposited at various current levels using the firefly algorithm (FA) and artificial neural network (ANN). It is observed that dilution levels are found to be more approachable to the experimental setup data with FA in comparison to ANN for various current levels.

Application of Magnetic Adaptive Testing for Nondestructive Investigation of 2507 Duplex Stainless Steel

Duplex stainless steels are two-phase alloys, which contain ferritic and austenitic phases in their microstructure. Their duplex structure provides exceptional resistance to pitting and chloride stress corrosion cracking, and their strength is about twice that of austenitic stainless steels. Due to their good properties, they are widely used in chemical and petrochemical industries as a base material in pressure vessels, pipelines and containers. Duplex stainless steel samples were nondestructively investigated by measuring sets of magnetic minor hysteresis loops using the method called magnetic adaptive testing (MAT). Several series of heat-treated and cold-rolled 2507 duplex stainless steels were measured, and the magnetic parameters were compared with the results of the DC magnetometry of the samples. It was found that the changes in the material properties that were generated by heat treatment and mechanical deformation could easily be followed by magnetic measurements. In contrast to DC magnetic measurements, good correlation was found with the magnetic parameters determined by MAT method and Vickers hardness. Based on our experiments, MAT seems to be a powerful tool for the nondestructive characterization of duplex stainless steels.

CLEVELAND-CLIFFS 444

Abstract Cleveland-Cliffs 444 is a low carbon, low nitrogen, dual stabilized ferritic stainless steel that provides pitting and crevice corrosion resistance superior to most ferritic stainless steels and some austenitic stainless steels. It is equivalent to Type 304 austenitic stainless steel in many corrosion environments and has a lower coefficient of expansion and better thermal conductivity. Cleveland- Cliffs 444 has superior chloride stress-corrosion cracking resistance to Type 304 and Type 316 austenitic stainless steels. It is oxidation and creep resistant at elevated temperatures, making it a preferred material for the most demanding applications in automotive exhaust. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming and joining. Filing Code: SS-1355. Producer or source: Cleveland-Cliffs Inc.

Investigations of Welding Parameters Impacts on Mechanical & Corrosion Behavior of Steel Welds

Now days while the welded product of duplex stainless steels (DSS) is to be used for Cl- containing environment & sour service applications for example petrochemical, off-shore platforms, oil, gas, paper & pulp industries etc. The resistance to chloride stress corrosion cracking (CSCC) during service application has always been a threat for the manufacturer & the end user of the product. Resistance regards SCC under chloride existing environment based on current ferrite content under carefully welded duplex (ferrite-austenitic) stainless steel framework. DSS ferrite specifications required by various organizations are 30 to 60%, 30 to 70 Ferrite Number, 35 to 75%, etc. In this study, DSS 2205 material all weld metal consumable test coupons within ferrite content range 14% to 30% or 20 FN to 40 FN have been prepared & investigated. Investigations have shown that yield strength & tensile strength needs regards base metal & filler metal classifications was higher at every ferrite levels observations & no SCC cracking analysed after 1000 hours exposure at ferrite level below 15%.

Stress corrosion cracking of U tube heat exchanger used for low pressure steam generation in a hydrogen unit of petroleum refinery

The reformer effluent is serially cooled down to produce hydrogen in the hydrogen unit of an oil refinery. The process heat from effluent is effectively utilized for low pressure steam generation using heat exchanger. The exchanger shell and tube side fluids were boiler feed water and process gas, respectively. Several tubes of this heat exchanger were failed especially within tube sheet after 4 years of useful service. Therefore, failed exchanger tube was subjected to engineering failure analysis to determine the cause of failure. Initially visual inspection was conducted using videoscopy in heat exchanger dry condition and evidenced circumferential crack. Subsequently, all failed tubes were separated from U tube bundle. Selected tube was subjected to visual inspection, dye penetrant and dimensional measurement. No evidence of visual deformation and thickness loss observed in the failed tube. Further investigated tube was subjected to chemical analysis and confirmed the required metallurgy as per design specification. The fracture surface was subjected to elemental analysis, fractographic, metallographic and hardness investigations. The micro hardness of an exchanger tube at failure location was higher than specified hardness value. Investigation also revealed that exchanger tubes were expanded from tube inner surface to establish tube to tube sheet joint according to specified design drawing. Tube expansion was done prior to start of service and attributed to residual stress within tube material. The results revealed that presence of chloride in the accumulated deposits within tube to tube sheet joint favored conducive environment for chloride stress corrosion cracking. Recommendations were suggested for failure prevention. Achievement in this paper may supplement the similar heat exchanger tube failure database and mitigation of failure will be possible by good engineering practices.

Analyzing the Effects of Heat Treatment on SMAW Duplex Stainless Steel Weld Overlays

Duplex stainless steel (DSS) has a reasonably high resistance to chloride stress corrosion cracking for offshore and marine applications. However, DSS weld overlay has not been successfully demonstrated due to some inherent problems in achieving pitting and crevice corrosion resistance. In this research work, isothermal heat treatments (350, 650 and 1050 °C) with and different cooling rates have been performed DMR249 Grade A by using shield metal arc welding (SMAW) with an E2209 electrode. Micrographs have shown two phase microstructures of the DSS weld metal, the amounts of austenite phase increased with increment of post-weld heat treatment (PWHT) temperatures. The dilution has maintained consistent values except solution annealing that has shown the disappearance of the heat affected zone in micrographs. The weld metal hardness values increased with PWHT temperatures and remained low at solid solution annealing temperatures. The major alloying elements (C, Mo, Cr, Ni, N, and Fe) were analyzed, as these elements can contribute to intermetallic phases. The results showed that C and Cr content slightly increased with PWHT except for solid solution annealing, Mo showed consistently low content due to dilution effects. Ni maintained higher content, although the heat-treated samples showed slight fluctuations. Nitrogen produced consistent values, as recommended to prevent critical involvement in nitride precipitation.

Chloride stress corrosion cracking of a non-standard, ‘Borderline’ Chromium-Manganese stainless steel – Problems of counterfeits and substandard materials

Nonstandard chromium-manganese (stainless) steels are gaining popularity nowadays, but data for them are inadequate as the majority of literature is on the ‘pedigrees’ such as the standard 200 series and 300 series steels. This paper begins with a brief overview of the counterfeit problems of such steels. It then presents the slow-strain-rate test results of a chromium-manganese ‘borderline’ stainless steel in room-temperature air, 60 °C NaCl and 60 °C distilled water (the lower-bound temperature for chloride stress corrosion cracking in austenitic stainless steels). At low strain rates (10-6 s−1), grain-boundary segregation of phosphorus and sulphur (especially the latter) can cause intergranular cracking in air and in 60 °C distilled water. In 60 °C NaCl, manganese sulphides may serve as the initiation sites of transgranular cracking. Many producers of nonstandard chromium-manganese (stainless) steels lack impurity control technologies, and so users must be vigilant of this issue. The fracture mode of the ‘borderline’ stainless steel is strain-rate dependent, changing from being mainly intergranular to being transgranular and dimpled as the strain rate goes up. The reason behind this is unclear, but a plausible suggestion is given in this paper.

Experimental Study on Chloride Stress Corrosion Cracking Sensitivity of 316L Stainless Steel

The slow–strain-rate tensile test was used to study the chloride stress corrosion cracking (SSC) behavior of 316L stainless steel under the simulated condition of a CO2 gas field in the Tarim Basin, and the effects of CO2, Cl− concentration, and temperature on the sensitivity of SCC were discussed. The results show that the increase of CO2 content has no apparent influence on the chloride SCC sensitivity of 316L stainless steel. With the rise in temperature, chloride SCC’s sensitivity increases, and the change in the SCC sensitivity index Iscc is noticeable. When the concentration of Cl− increases, the sensitivity of chloride SCC also increases. The degree of influence of the three factors on the experimental results can be ranked as follows: temperature>Cl− > CO2. In this experiment, when the partial pressure of CO2 is 0.1 MPa, the temperature is 65°C, the concentration of Cl− is 1,20,000 mg/L, and Iscc of 316L tensile samples has a maximum of 26.8%.

Stress corrosion cracking failure of friction stir welded nuclear grade austenitic stainless steel

Stress Corrosion Cracking behavior of Austenitic Stainless Steels (SS) in a chloride environment has been investigated by several methods. In this investigation failure of emerging structural material for nuclear reactor (316LN grade austenitic stainless steel) and its Friction Stir Welded (FSW) joint due to stress corrosion cracking were analyzed in a chloride environment. FSW joint was fabricated between 316LN plates with optimized process parameters. Initially, hardness and tensile properties were analyzed across the weld zone to evaluate the mechanical properties of the welded joint. Microstructural characterization of base metal (BM) and weld zone were done by Optical Microscope (OM), and Scanning Electron Microscope (SEM). Grain boundary analysis was done by Transmission Electron Microscope (TEM). Microstructural evolution revealed that the FSW process is capable to refine and reduce grain size nearby 12 times that of the base metal by Continuous Dynamic Recrystallization mechanism (CDRX). Improved strength and hardness are also recorded at the weld zone compared to the base metal. Boiling 45 wt% MgCl2 solution at constant load condition as per ASTM standard G36 was used to assess SCC failure on base metal and FSW joint. Failure due to Chloride Stress Corrosion Cracking (CSCC) on weld samples were investigated and compared with its base metal samples at different tensile stress conditions (20%, 40%, 60%, 80%, 100% of base metal yield stress values). From the experimental result steady-state elongation rate (ISS), Transition time (tss) and time to failure (tf) were evaluated and generalized equations to predict time to failure of base metal and FSW weldment was generated. The impact of microstructural morphology on SCC failure of the FSW joint was investigated. The fracture location of the weld joint, nature of crack advancement of both base metal and FSW joint was analyzed by the SEM study. A study of fracture surface displayed brittle nature transgranular failure for base metal as well as FSW samples.

Stress Corrosion Cracking of High-Pressure Scrubber in Urea Plant: A Case Study

This current work investigates the failure of high pressure (HP) scrubber lining in urea fertilizer production plant after 20 years in service. AISI 316L urea grade (UG) stainless steel scrubber lining was showed severe damage. In order to find out the root cause of failure, cracks were observed by visual inspection together with microstructure examination Chemical analysis of the base metal and corrosion products were analyzed Chemical analysis of the lining base alloy is conformed to the AISI 316L UG. Results revealed existence of chloride assisted stress corrosion cracking (SCC) initiated from pitting formed in the inner surface of the scrubber lining. Corrosion products analysis revealed existence of chloride (Cl-). Localized pitting corrosion is attributed to Cl attack. The expected sources of chloride are water during hydrostatic testing, water vapor during passivation, chloride containing atmosphere during transportation or storage the base alloy in coastal areas and water vapor in carbamate gasses (process fluid). Pits initiated at the lining inner surface act as stress concentration sites assisted SCC initiation. Chloride SCC is caused by simultaneous action of both tensile stresses and a corrosive environment containing chloride. To overcome the scrubber failure, chloride must be eliminated and residual stresses must be controlled. Upgrading the scrubber base alloy using high-alloy duplex stainless steel (Safurex) is highly recommended.

Stress corrosion testing of roof bolt grade 60 steel in simulated underground coal mine atmosphere

ABSTRACTCorrosion of roof bolts in underground mine environments could have an adverse impact on ground control, which is directly related to workforce safety. Past studies state that stress corrosion cracking (SCC) of roof bolts is a significant problem in underground coal mines, resulting in premature bolt failures. However, it has not been seriously studied in U.S. underground coal mines. As a preliminary study, the most common roof bolt material used in U.S. mines, ASTM A 615 Grade 60 steel, was studied under stress corrosion conditions. ASTM G30 standard was applied to achieve this and tested in the simulated coal mine conditions. SCC was observed on samples that were tested for 180 days. Chloride SCC (ClSCC) was found to be the corrosion mechanism resulting in cracks from the EDS data. This paper mainly discusses the test protocol, shortcomings of this preliminary testing and makes recommendations based on the observations and results.

Failure of stainless steel 304L air cooler tubes due to stress corrosion cracking caused by organic chlorides

The paper presents the failure investigation of stainless steel (SS) 304L air cooler tubes in a petrochemical company. The company encountered repeated failures of the finned tubes at the outlet section of the air cooler in its carbon dioxide manufacturing unit. A comprehensive failure investigation including visual examination, optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), fluid analysis, chemical characterization of the tubes and cyclic polarization studies were carried out for the identification of the root cause of failure. The results obtained indicated that the failure of the air cooler tubes was due to chloride stress corrosion cracking (SCC). The source of chlorides that caused the cracking was the acidic chlorides formed as a result of the decomposition of organic chloride compounds present in the process gas. The presence of acidic chlorides and the optimum temperature existed at the outlet of the air cooler resulted in the pitting and the SCC of the tubes. Recommendations made to mitigate the failure of tubes include the introduction of a scrubbing system upstream of the air cooler and the upgradation of the metallurgy of the tube to high alloy SS or nickel-base alloy.

Effect of weld metal ferrite content on mechanical properties and stress corrosion cracking resistance in 22 Cr 5 Ni duplex stainless steel

Welded 22 Cr 5 Ni duplex stainless steel is often used for chloride-containing environments and sour service applications. Chloride stress corrosion cracking (CSCC) during service poses a threat to the service life of the weldment. Yield strength and resistance to CSCC are considered to depend on the weld metal ferrite content, which is variously required to be 30 to 60%, 30 to 70 ferrite number, 35 to 75%, etc. Accordingly, the present work has been carried out in collaboration with a filler metal manufacturer to investigate the research gap pertaining to minimum ferrite content to obtain the required minimum weld metal yield strength and resistance to CSCC. In this study, 22 Cr 5 Ni weldments with weld metal ferrite content in the range of 14% to 30%, or 20 to 40 ferrite number, obtained by increasing the filler metal nickel content above the normal 9%, have been prepared and investigated. It was found that yield strength and tensile strength requirements of base metal and filler metal classifications were exceeded at all ferrite levels investigated and that no CSCC was observed after 1000-h exposure in the ASTM G 123 boiling 25% sodium chloride test.

Developing Field Test Procedures for Chloride Stress Corrosion Cracking in the Arabian Gulf

Oil and gas production and petrochemical plants in the Arabian Gulf are exposed to severe environmental conditions of high temperature and humidity. This makes these plants susceptible to chloride-induced stress corrosion cracking (CSCC). The laboratory testing fails to provide the exact field environmental conditions. A cost efficient field test setup for CSCC was designed and developed for the Arabian Gulf. The setup included designing self-sustained loading devices, samples, and sample racks. The samples were exposed to a stress equivalent to 80% and 100% of their yield strength. This paper describes the developed test procedures to establish testing with high level of accuracy and repeatability. It also discusses the design aspects and the challenges that were met.

Features of residual stresses in duplex stainless steel butt welds

Duplex stainless steel finds increasing use as an alternative to austenitic stainless steel, particularly where chloride or sulphide stress corrosion cracking is of primary concern, due to the excellent combination of strength and corrosion resistance. During welding, duplex stainless steel does not create the same magnitude or distribution of weld-induced residual stresses as those in welded austenitic stainless steel due to the different physical and mechanical properties between them. In this work, an experimental study on the residual stresses in butt-welded duplex stainless steel is performed utilizing the layering technique to investigate the characteristics of residual stresses in the weldment. Three-dimensional thermos-mechanical-metallurgical finite element analysis is also performed to confirm the residual stress measurements.

Failure analysis of gas sweetening tower absorber packing

Gas sweetening tower packing was failed in the form of corrosion damage after 3 months from installation. Pieces from the failed packing as well as unused one were received for investigation to establish whether its failure was due to specific material aspects or improper use. The investigation showed that the packing was 316L stainless steel which failed due to intergranular chloride stress corrosion cracking. The root cause of the failure of the received packing could be mainly attributed to the material residual shear bands after packing sheet manufacturing process. The shear bands were formed due to lack of solution annealing after cold deformation process. Corrosion is mainly controlled by chloride ions and residual stress. It is recommended to use high quality material free from residual stresses by applying solution annealing heat treatment after cold deformation of the packing sheets and removing of the chloride ions by controlling the inlet water.

Environmental Degradation of Dissimilar Austenitic 316L and Duplex 2205 Stainless Steels Welded Joints

AbstractThe paper describes structure and properties of dissimilar stainless steels welded joints between duplex 2205 and austenitic 316L steels. Investigations were focused on environmentally assisted cracking of welded joints. The susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement was determined in slow strain rate tests (SSRT) with the strain rate of 2.2 × 10−6s−1. Chloride-inducted SCC was determined in the 35% boiling water solution of MgCl2environment at 125°C. Hydrogen assisted SCC tests were performed in synthetic sea water under cathodic polarization condition. It was shown that place of the lowest resistance to chloride stress corrosion cracking is heat affected zone at duplex steel side of dissimilar joins. That phenomenon was connected with undesirable structure of HAZ comprising of large fractions of ferrite grains with acicular austenite phase. Hydrogen assisted SCC tests showed significant reduction in ductility of duplex 2205 steel while austenitic 316L steel remains almost immune to degradation processes. SSR tests of dissimilar welded joints revealed a fracture in the area of austenitic steel.

Risk Based Inspection of Gas-Cooling Heat Exchanger

On October 2013, Pertamina Hulu Energi Offshore North West Java (PHE – ONWJ) platform personnel found 93 leaking tubes locations in the finfan coolers/ gas-cooling heat exchanger. After analysis had been performed, the crack in the tube strongly indicate that stress corrosion cracking was occurred by chloride. Chloride stress corrosion cracking (CLSCC) is the cracking occurred by the combined influence of tensile stress and a corrosive environment. CLSCC is the one of the most common reasons why austenitic stainless steel pipework or tube and vessels deteriorate in the chemical processing, petrochemical industries and maritime industries. In this thesis purpose to determine the appropriate inspection planning for two main items (tubes and header box) in the gas-cooling heat exchanger using risk based inspection (RBI) method. The result, inspection of the tubes must be performed on July 6, 2024 and for the header box inspection must be performed on July 6, 2025. In the end, RBI method can be applicated to gas-cooling heat exchanger. Because, risk on the tubes can be reduced from 4.537 m 2 /year to 0.453 m 2 /year. And inspection planning for header box can be reduced from 4.528 m 2 /year to 0.563 m 2 /year.

Failure analysis of stress corrosion cracking of 316L structured packing in a distillation tower

Abstract The present study was done to find the probable causes of AISI316L structured packings (SPs) failure in a dewatering phenol tower. In this tower, the SPs would provide a high contact surface between streams to maximize and accelerate the distillation process. Increasing vibration of discharging pump showed that there were detached pieces of SPs in pump's strainer. During plant overhaul, corrosion inspection was done and some of the broken packings were gathered for further analysis. The samples were evaluated by visual observation, optical and scanning electron microscope. Transgranular cracks in packing sheets and screws, used for restraining layers of packing together, were seen. Energy-dispersive X-ray spectroscopy (EDS) of corrosion products on packing and the fracture surface of the screw was conducted. The results showed the occurrence of chloride stress corrosion cracking. Even though the chlorine contents of tower streams were low, it seemed that process fluids have been mal-distributed leading to the local concentration of the chlorine on SPs surface. In addition to chlorine, high working temperature and applied stress provided a favorable condition for stress corrosion cracking.