Sulfide Stress Cracking Research Articles

Weldability evaluation of X80 sour line pipe using a combination of thermal simulation and actual girth welding

The weldability studies of API 5LX80 pipes developed for sour service are very recent and limited information about its heat-affected zone (HAZ) properties can be found. This paper presents a comprehensive evaluation of HAZ using both thermal simulation and the production of actual girth weld joints. The test methodology included microstructural analysis, Charpy impact test, hardness (HV10), microhardness (HV0.1), and sulfide stress cracking tests (SCC). The intercritical coarse grain HAZ presented impact toughness reduction from values above 300 J to less than 50 J at 0 °C when heat input is increased above 1.5 kJ/mm. It can be explained by grain coarsening and martensite-austenite (MA) formation as a ‘necklace’ structure at previous austenite grain boundaries. Hardness and microhardness values for both simulated and actual HAZ were below the maximum limit of 250HV usually specified by industry. Specimens submitted to the sulfide stress cracking (SSC) tests did not present any crack demonstrating that the welded joint is appropriate for sour environments. Finally, a maximum heat input of 1.5 kJ/mm is recommended for field welding. For higher heat inputs, a deeper evaluation of HAZ toughness should be done. The results contribute to supporting the application of this material as an alternative for long-distance high-pressure pipelines with H2S.

Notch sensitivity and short cracks tolerance in a super 13Cr stainless steel under sulfide stress corrosion cracking conditions

Abstract Notch sensitivity under sulfide stress corrosion cracking (SSC) conditions is quantified in this work, considering its tolerance to short cracks that start at notch tips and become non-propagating after growing for a short while. The considered material is an UNS S41426 super 13Cr5Ni2Mo martensitic stainless steel, frequently used in pipelines to transport aggressive fluids in offshore applications. Tolerance to short SCC cracks depends on the notch size and shape, on the stress gradient ahead of its tip, and on basic material resistances to crack initiation S SSC and growth K ISSC inside the aggressive environment. The proposed notch-sensitivity model can be a powerful and economical alternative design tool to substitute traditional pass/non-pass criteria normally used to choose materials for SSC and similar environmentally assisted cracking (EAC) service conditions. This model is validated by testing the steel into an aqueous solution of 100 g/L of Cl−, pH 4.0, 25 kPa of H2S, and 75 kPa of CO2, at 23 ± 2 °C. After measuring S SSC (461 ± 23 MPa) and K ISSC (36.9 ± 0.6 MPa√m), short crack tolerance predictions are verified on notched specimens loaded under a peak stress at their tips σ max = 0.95⋅S Y >> S SSC, where S Y = 826 MPa is the yield strength of the tested steel.

Microstructure evolution and SSCC behavior of strain-strengthened 304 SS pre-strained at room temperature and cryogenic temperature

In this work, microstructure and sulfide stress corrosion cracking (SSCC) of 304 stainless steel (SS) pre-strained at cryogenic and room temperature were studied. 304 SS exhibits extremely high SSCC susceptibility, which increases as pre-strain rises for the acceleration of AD and HE. Cryogenic pre-strained specimens present higher SSCC resistance. Pre-strain leads to the formation of strain-induced ε and α' martensite and increase of crystal defects such as deformation bands, twins, stacking faults and dislocation, which accelerates SSCC. Cryogenic deformation produces more martensite, and the uniform occurrence of microstructure evolution only plays a limited role in SSCC.

Effects of Ce and La on microstructure and sulfide stress cracking susceptibility of API-5CT-C110 casing steel

This study investigated the effects of Ce and La addition on microstructure and sulfide stress cracking (SSC) behavior of API-5CT-C110 casing steel. The role of rare earth (RE) elements on the SSC resistance was assessed via uniaxial tensile testing and double cantilever beam testing (NACE TM0177 A and D methods). The experimental results show that the appropriate addition of RE is beneficial to the improvement of SSC resistance without compromising strength. RE addition is found to refine prior austenite grains and carbides, and modify the coarse inclusions into spherical RE oxysulfides. The electron backscattered diffraction analysis indicates that the steel with RE has lower high angle grain boundary and kernel average misorientation, which could effectively hinder crack propagation and thus reduce the SSC susceptibility. Furthermore, the proportion of deformed grains is reduced significantly due to RE addition, and substructure grains with low storage energy are increased, which is also a vital factor enhancing the SSC resistance.

On the sulfide stress cracking resistance of a 125 ksi grade high-strength low-alloyed steel for oil country tubular goods

Excellent sulfide stress cracking (SSC) resistance was achieved in a 125 ksi grade high-strength low-alloyed steel with increased C content and Cu alloying. Results showed that increased C content allowed tempering at higher temperature, obtaining low dislocation density without decreasing strength. Moreover, Cu alloying refined martensite blocks and inhibited dislocation annihilation, but hardly influenced the precipitation of Cr-rich carbides. The decrease in dislocation density was the main reason for improving SSC resistance, and sufficient precipitation of Cr-rich carbides came in second. Despite Cu alloying failing to improve the SSC resistance, it increased the yield strength without sacrificing SSC resistance.

LABORATORY AND OPERATING TESTING OF HIGH-ALLOY STEEL PIPES MADE BY THE LATEST TECHNOLOGIES

The purpose of the research: evaluation of the quality and durability for pipes made of high-alloyed austenitic and ferritic-austenitic steels, which are manufactured at PJSC "CENTRAVIS PRODUCTION UKRAINE" using the latest technologies, by conducting complex laboratory studies and long-term operational tests at chemical industry enterprises. Materials and methods: the research materials were experimental pipes made of high-alloyed austenitic and ferritic-austenitic chromium-nickel-molybdenum steels of the new generation, manufactured using the latest technologies. The microstructure of the pipes was investigated by metallography and electron microscopy using developed and improved methods. Corrosive researches in laboratory terms included a test on firmness against the local types of corrosion inherent in high-alloy steels: intergranular corrosion (IGC), pitting corrosion (PC), corrosion cracking (CC) and sulfide stress corrosion cracking (SSCC). The mechanical properties of the pipes were determined by tensile and impact bending tests. Long-term operational tests of pipes were carried out in conditions of industrial production at chemical industry enterprises in apparatus for the urea and caustic soda production. Research results: A high content of special low-energy grain boundaries in the theory of coincident nodes’ lattices (SG CSL) was established in the structure of pipes manufactured according to the latest technologies (≥ 75 %); high resistance of pipes against various types of the most dangerous local corrosion compared to existing analogues, a high level of mechanical properties, as well as high corrosion resistance during long-term operational tests in environments at chemical industry enterprises. The implementation of the obtained results will contribute to increasing the efficiency of production and operation for highly alloyed steel pipes in demand on the world market and increasing the competitiveness of domestically produced pipes on the European and world markets.

Localized Environment Enriched with Hydrogen Sulfide for Inducing Sulfide Stress Cracking on Type-430 Stainless Steel

Exposure tests to hydrogen sulfide environments are frequently used to evaluate hydrogen sulfide stress corrosion cracking (SSC) in steel. However, there are many safety restrictions in handling hydrogen sulfide, and the maintenance of the facilities is very costly. To improve this situation, an electrochemical measurement method that can be used even in laboratories to simulate hydrogen sulfide stress corrosion tests easily. Specifically, a safe hydrogen sulfide corrosion test method was developed using a local hydrogen sulfide concentration environment near the steel surface.A local acidic environment of pH 3-4 was induced by constant potential anodic polarization of a platinum electrode below 2 VSHE in an aqueous sodium sulfide solution. Exposure of the carbon steel surface to a local acidic environment resulted in the formation of iron sulfides such as FeS and FeS2 on the surface, accompanied by a negative shift of the carbon steel electrode potential and an increase in the microelectrode current. Local acidification of a potentiostatically polarized type-430 steel surface confirmed the existence of a critical potential at which the steel surface begins to depassivate and actively dissolve. It was suggested that the substitution of iron oxide for iron sulfide in a hydrogen sulfide environment determines the sulfidation of the steel surface. Using this method, furthermore, the formation of cracks was successfully induced on the surface of type-430 steel under tensile stress loading.

In Situ Investigation of Hydrogen-Induced Cracking Behavior in Linepipe Steel Under Different Environments

NACE MR0175/ISO 15156 provides the severity of a sour environment defined as a function of pH and H2S partial pressure for sulfide stress cracking. Although hydrogen-induced cracking (HIC) is also a major issue of linepipes exposed to a sour environment, the severity diagram does not necessarily correspond to the HIC susceptibility. Recently, from the viewpoint of fitness-of-purpose, the severity diagrams for HIC have been proposed based on the concept of equal hydrogen concentration. From this concept, HIC susceptibility corresponds well to the steady-state hydrogen permeability obtained from the hydrogen permeation test method. In this study, in order to clarify the relationship between HIC susceptibility and hydrogen diffusion behavior, in situ crack inspection during the HIC test and finite element method analysis of hydrogen diffusion were performed. The in situ inspection technique using phased-array ultrasonic testing which can capture the time dependence of crack distribution, and HIC initiation and propagation behaviors were clearly visualized and investigated. It was found that crack initiation and propagation stabilize as hydrogen concentration reaches a steady-state value throughout the specimen and the result was considered evidence that the HIC susceptibility corresponded with the steady value of hydrogen permeability.

The Effects of NaCl on Hydrogen Permeation and Sulfide Stress Cracking Resistance of C110 High-strength Steel

Sulfide stress cracking (SSC) limits the application of high-strength low-alloy carbon steel C110 in the oil and gas industries. Chloride ions (Cl−) play an indispensable role in SSC. This study aims to evaluate the effects of NaCl on hydrogen permeation and SSC susceptibility by electrochemical techniques including hydrogen permeation test and electrochemical impedance spectroscopy (EIS), and the novel notched tensile slow strain rate test on carbon steel C110 under wet-H2S environments. The results show that the higher concentration of Cl− reduces hydrogen absorption and enhances SSC susceptibility. However, it is widely accepted that the reduction in hydrogen absorption results in an increase in SSC resistance. To figure out the role of Cl− in the SSC mechanism, the morphology of the side and the cross-sectional surface were observed. It was found that a higher pit density in a condition with a higher Cl− concentration leads to increased SSC susceptibility as pits act as crack initiation sites. The SSC mechanism transfers from hydrogen embrittlement to pit-induced cracking when the Cl− concentration in the solution increases.

Analysis of corrosion fatigue steel strength of pump rods for oil wells

Purpose is to perform analysis of corrosion durability (fatigue) of pump rod materials in terms of various chemically active simulation environments, and study influence of economically modified rare-earth impurity on corrosion fatigue strength of pump rod materials. Methods. 40 and 20N2M steel grades have been applied as well as experimental steel (ES). Steel of the conditinal ES grade has been melted within a pilot site of Institute of Electric Welding Named after E.O. Paton of the National Academy of Sciences of Ukraine. The steel was alloyed economically by means of a micro impurity of a rare-earth element (REE) being 0.03% of cerium; in addition, it contained comparatively low concentration of sulfur and phosphorus as well as minor concentration of dissolved hydrogen. The following has been used as simulation environments: 1) NACE environment (i.e. 5% NaCl solution which contained 0.5% СН3СООН, and saturated H2S; t = 22 ± 2°C; pH = 3.8-4.0); 2) 3% NaCl solution without hydrogen sulphide. Once every day, the environment was replaced to oxygenate it up to 8-10 mg/l concentration. Findings. Stability against sulfide stress-corrosion cracking (SSCC), hydrogen initiated cracking (HIC), and corrosion fatigue of steel of deep pump rods for oil industry has been studied. It has been defined that the experimental steel, modified economically by means of micro impurities of a REE, meets NACE MR0175-96 standard in terms of chemical composition as well as strength; in turn, 20N2M and 40 steel grades have high resistance neither to SSCC (threshold stresses are < 0.8 s) nor to corrosion fatigue attack; moreover, steel grade 40 has demonstrated low resistance to HIC (CLR > 6% and CTR > 3%). Originality. It has been identified that corrosion fatigue attack results from hydrogen penetration of steel initiating its cracking and hence destruction under the effect of alternating loads accelerated by the action of corrosive environment. Further, surface micro destructions, influenced by micro stresses, transform into large discontinuities and cracks with following macro destructions. Practical implications. It has been proved that high resistance to corrosion cracking can be achieved by means of refining of pump-rod steel of ferrite and perlite type using metallurgical methods, i.e. 0.01-0.03% REE microalloying.

Dynamical In Situ Study of Morphological Variations on Stainless Steel in a Sour Corrosive Environment

It is still unclear how environmentally assisted cracking, especially sulfide stress cracking (SSC), is caused by corrosion and fracture behavior. In this study, a new in situ technique for an SSC visualization challenge was established and applied for the visualization of microcrack propagation resulting from a single pitting on the steel surface of 13% Cr martensitic stainless steel during four-point bending SSC tests and discussed by combining ex situ x-ray computed tomography (XCT) and electron backscatter diffraction (EBSD). The dynamic behavior of microcracks was visualized successfully, and the microbubbles behavior with the corrosion reaction was also captured. Regarding the relationship between internal structure and microstructure for cracking, it was found that a cavity was formed in the interior of prior to the cracks seen on the surface by XCT, and cracks by EBSD were propagated along prior austenite grain boundaries. On the basis of in situ observations and complementary ex situ analyses, the actual situation of crack on the steel surface was revealed and discussed with both corrosion and fracture over time. This approach provides an opportunity to clarify the SSC occurrence process based on actual SSC tests and contributes to the determination of phenomenological criteria. Furthermore, by combining this in situ technique with commonly known electrochemical measurements such as polarization curves, open-circuit potentials, and electrochemical impedance spectroscopy, it is possible to directly discuss various electrochemical data corresponding to corrosion and fracture behavior, including dissolution and gas evolution.

Microstructure and sulfide stress corrosion cracking of the Inconel 625/X80 weld overlay fabricated by cold metal transfer process

The use of cold metal transfer process (CMT) is an excellent alternative to depositing nickel-based alloys on oil and gas pipelines due to the relatively small dilution. However, sulfide stress corrosion cracking (SSCC) of dissimilar weld joints has proven to be an issue. Therefore, this study investigates the microstructure and SSCC behavior of an Inconel 625/X80 weld overlay fabricated CMT process focusing on the tempering effect. Four-point bending tests show a high SSCC susceptibility of the non-overlap zone due to the formation of coarse structure in the heat affected zone and narrow martensite layer along the fusion boundary. However, microstructural characterization indicates a tempering effect in the overlap zone, producing homogenized microstructure and less residual strain in the heat affected zone. Therefore, the SSCC resistance is greatly improved, especially for the fusion boundary, because reversed austenite in the martensite layer could decrease the accumulation of hydrogen at lath boundaries.

Welding heat input for synergistic improvement in toughness and stress corrosion resistance of X65 pipeline steel with pre-strain

The microstructure, hydrogen embrittlement sensitivity, fracture toughness, and influence of pre-strain on the sulfide stress corrosion cracking (SSCC) sensitivity of the coarse-grained heat-affected zone of X65 pipeline steel with large deformation were studied to determine the optimal welding heat input in an acidic H2S environment. After pre-straining, the microstructures of the specimens changed insignificantly, but their ductility decreased. The acicular ferrite microstructure obtained under a low heat input demonstrated the synergistic improvement in the SSCC resistance and fracture toughness under pre-strain, especially at t8/5 = 20 s. The M/A constituents interface potentially causes microcrack initiation and interconnection under pre-strain.

Hydrogen embrittlement of high-strength API carbon steels in H2S and CO2 containing environments

This study aims to understand the Sulfide Stress Cracking (SSC) resistance of API carbon steels exposed to wet sour environments containing CO2. A mini-pipe specimen was cut from API grade tubulars and placed in an SSC test cell to perform the investigation. The specimen was highly strained and internally pressurized while exposed to the corrosive environment for seven days. The partial pressure ratio (PPR) of CO2 (i.e. ratio of partial pressure of CO2 to the total pressure) was varied to study the effect of CO2 content on SSC. Experiments were performed while maintaining a constant H2S concentration and temperature. The steels' variations in mechanical properties (ultimate tensile strength and plastic strain before failure) after exposure to the sour environment are used to quantify the embrittlement. In addition, the specimens were examined using optical microscopes to assess the severity of the SSC corrosion based on shear deformation patterns and crack features. The SSC resistance of the tested steels was minimized when the PPR of CO2 was approximately 20%. Results demonstrate that the materials have adequate SSC corrosion resistance to be utilized in the environment containing 280 ppm H2S. Nevertheless, their SSC resistance reduced noticeably between 10 and 30% PPR of CO2.

Failure Analysis of a Centrifugal Compressor Impeller Made of 17-4PH Steel in the Moist Hydrogen Sulfide Environment

The impeller under consideration is a rotor wheel of a centrifugal compressor, made of 17-4PH martensitic precipitated hardening stainless steel. Its total operating lifetime was estimated to 80,000 h, but it fractured beforehand, 4 days after the scheduled overhaul without any observed pre-symptoms. The important causes of the failure were its working conditions: a moist H2S environment, the applied shaft fitting stress, and the martensitic structure of its material. In the article the post-failure analysis of an impeller is described, explaining the root cause of the impeller failure by means of both experimental and Finite Element Methods (FEM). Sulfide Stress Cracking (SSC) was found to be the primary failure mechanism for the impeller under investigation. Details of the investigations and possible corrective measures to improve performance impellers used under harsh environment conditions are discussed.

Effect of Surface Hardness and Hydrogen Sulfide Partial Pressure on Sulfide Stress Cracking Behavior in Low Alloy Linepipe Steel

TMCP (thermo-mechanical controlled process) linepipes have long been used in severe sour environments, but recently sulfide stress cracking (SSC) caused by local hard zones has become a concern. In order to clarify the hardness threshold that leads to SSC, four-point bend (4PB) SSC tests as specified in NACE TM0316 were conducted under several H2S partial pressure conditions. At H2S partial pressures of 1 bar and higher, the surface hardness threshold (at 0.25 mm from the surface) observed in 4PB SSC specimens without SSC cracking was approximately correlated to a maximum acceptable hardness level of 250 HV0.1. A stable low surface hardness of 250 or less HV0.1 was achieved by suppressing hard lath bainite (LB) and obtaining a soft granular bainite (GB) microstructure, resulting in a superior SSC-resistant property. It was found that a SSC crack propagated when the surface hardness increased due to an increasing volume fraction of the LB microstructure. Under a 16 bar H2S partial pressure condition, the crack growth rate increased in the sour environment, and hydrogen embrittlement by H2S was promoted. However, in the 4PB SSC test at 16 bar, the stress concentration and the transition to a crack were suppressed because the shape of localized corrosion was semicircular due to low localized corrosivity. This can be the reason why the SSC susceptibility was similar to 1 bar condition, especially in the 4PB SSC test using the samples with lower surface hardness level of 250 or less HV0.1.

Corrosion resistance of welded tubing of L80 strength group of different chemical composition

In previous publications, it was shown that the use of low-carbon steels with bainite hardenability alloyed with chromium, molybdenum and other carbonitride-forming elements is promising for the production of cold-resistant and SCC (sulfide stress corrosion cracking)-resistant electricwelded tubing (tubing). Tubing is often operated in CO2-containing corrosive environments, therefore, determining the steel resistance to this type of corrosion is an urgent task. It is known that the addition of chromium to steel increases not only its hardenability, but also its resistance to CO2 corrosion. Influence of other alloying elements is not obvious. For the laboratory experiment, nine variants of the chemical composition of steels for the production of welded tubing were developed. The rolled test steels were investigated. Results of the studies of corrosion resistance of these steels are shown and compared. The authors made an assessment of influence of the main alloying elements on resistance to CO2 corrosion. The steels with different contents of Cr, Mo, V, Mn, Zr were studied for resistance CO2 corrosion at different temperatures. It has been established that the steel chemical composition and the test conditions determine the composition of CO2 corrosion products, affect the process of formation and growth of corrosion products, thereby affecting corrosion resistance. Decrease in the corrosion rate of chromium-alloyed steels can be associated with the protective properties of the corrosion products formed during testing. Laboratory corrosion tests for resistance to CO2 corrosion at an elevated temperature of 65 °C and subsequent studies of the formed corrosion products revealed a positive effect of chromium and molybdenum on the rate of general corrosion by mechanism of formation of dense corrosion products that perform a protective function.

Effect of Tempering Temperature on Microstructure and Sulfide Stress Cracking of 125 Ksi Grade Casing Steel.

The influence of tempering temperature on the microstructure of 0.5Cr0.4W steels was investigated by scanning electron microscope, and the roles of grain boundary character, dislocation, and Taylor factor in sulfide stress cracking (SSC) resistance were interpreted using the election backscattered diffraction technique. The 0.5Cr0.4W steels tempered at 690 °C, 700 °C, and 715 °C all showed tempered martensites. The specimen tempered at 715 °C exhibited a higher critical stress intensity factor (KISSC) of 34.58 MPa·m0.5, but the yield strength of 800 MPa did not meet the criterion of 125 ksi (862 MPa) grade. When the specimen was tempered at 690 °C, the yield strength reached 960 MPa and the KISSC was only 21.36 MPa·m0.5, displaying poorer SSC resistance. The 0.5Cr0.4W steel tempered at 700 °C showed a good combination of yield strength (887 MPa) and SSC resistance (KISSC: 31.16 MPa·m0.5). When increasing the tempering temperature, the local average misorientation and Taylor factor of the 0.5Cr0.4W steels were decreased. The reduced dislocation density, and greater number of grains amenable to slippage, produced less hydrogen transport and a lower crack sensitivity. The SSC resistance was, thus, increased, owing to the minor damage to hydrogen aggregation. Therefore, 700 °C is a suitable tempering temperature for 0.5Cr0.4W casing steel.

The influence of H2S on hydrogen absorption and sulfide stress cracking resistance of high strength low alloy carbon steel C110

The application of high strength low alloy carbon steel C110 in wet-H2S environment is limited by sulfide stress cracking (SSC). The objective of this research is to evaluate the effect of the environmental H2S content on the susceptibility to SSC. Since SSC is hydrogen induced fracture, the study focusses on: (1) evaluating the effect of H2S concentration on hydrogen absorption, (2) assessing SSC susceptibility by a novel slow strain rate tensile testing (n-NTSSRT) method under both sour and non-sour environments, (3) the correlation between absorbed hydrogen concentration and SSC susceptibility. The results show that with increasing H2S concentration, sub-surface hydrogen concentration C0 increases exponentially, while critical stress intensity factor KISSC decreases. The application of n-NTSSRT methodology criteria is determined to be 1 mol% H2S, which corresponding to a C0 value of 6.66 × 10−6 mol/cm3. When H2S concentration is higher than 1 mol%, the KISSC values should be calculated by assuming the fracture is linear elastic fracture. Otherwise, the elastoplastic fracture solution J-integral should be considered.

Sour Environmental Severity for Hydrogen-Induced Cracking Susceptibility

The severity of sour environments has been determined in accordance with the European Federation of Corrosion 16 and NACE MR0175/ISO 15156-2:2015 standards for carbon and low-alloy steels, based on the experimental results of sulfide stress cracking (SSC). However, the severity map obtained from SSC test results cannot be applicable to the hydrogen-induced cracking (HIC) susceptibility. In this study, the hydrogen permeability and crack area ratio of HIC under various pH and H2S partial pressures (pH2S) were measured to establish the link between the sour environmental severity and HIC susceptibility using grades X65 to X80 steels for linepipes. In addition, the hydrogen concentration at the location of the HIC was calculated by the finite element analysis. The results showed that the sour environmental severity map obtained from hydrogen permeation tests changes with time because the hydrogen permeability reached maximum values in the early stage and steady-state values in the later stage. Then, the HIC susceptibility did not correspond to the maximum permeability, but to the steady-state hydrogen permeability. In addition, the hydrogen content at the location of the HIC did not correspond to the maximum hydrogen permeability but corresponded to the steady-state hydrogen permeability, because HIC occurred in the center segregation part and the hydrogen atoms required a certain time to diffuse from the metal surface to the mid-thickness. These results suggest that the HIC susceptibility is dominated by the severity map obtained from the steady-state hydrogen permeability.