Hydrogen Induced Stress Cracking Research Articles

A review on pitting corrosion and environmentally assisted cracking on duplex stainless steel

Duplex stainless steel is widely used in the petrochemical, maritime, and food industries. However, duplex stainless steel has the problem of corrosion failures during use. This topic has not been comprehensively and academically reviewed. These factors motivate the authors to review the developments in the corrosion research of duplex stainless steel. The review found that the primary reasons for the failure of duplex stainless steels are pitting corrosion and chloride-induced stress corrosion cracking. After being submerged in water, the evolution of the passive film on the duplex stainless steel can be loosely classified into three stages: nucleation, rapid growth, and stable growth stages. Instead of dramatic rupture, the passive film rupture process is a continuous metal oxidation process. Environmental factors scarcely affect the double-layer structure of the passive film, but they affect the film's overall thickness, oxide ratio, and defect concentration. The six mechanisms of alloying elements on pitting corrosion are summarized as stabilization, ineffective, soluble precipitates, soluble inclusions, insoluble inclusions, and wrapping mechanisms. In environments containing chlorides, ferrite undergoes pitting corrosion more easily than austenite. However, the pitting corrosion resistance reverses when sufficiently large deformation is used. The mechanisms of pitting corrosion induced by precipitates include the Cr-depletion, microgalvanic, and high-stress field theories. Chloride-induced cracks always initiate in the corrosion pits and blunt when encountering austenite. Phase boundaries are both strong hydrogen traps and rapid hydrogen diffusion pathways during hydrogen-induced stress cracking.

A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 1–Significance of the Three-Dimensional Phase Distributions and Morphological Properties on Hydrogen Transport

This paper is associated with a larger program of research, studying the resistance to hydrogen-induced stress cracking (HISC) of a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS), with respect to both the independent and interactive effects of the three key components of HISC: microstructure, stress/strain, and hydrogen. In the first part presented here, several material properties such as the three-dimensional microstructure, distribution, and morphology/geometry of the two phases, i.e., ferrite and austenite, and their significance on hydrogen transport have been determined quantitatively, using x-ray computed tomography microstructural data analysis and modeling. This provided a foundation for the study to compare resistance to HISC initiation and propagation of the two DSSs with differing microstructures, using hydrogen permeation measurements, environmental fracture toughness testing of single-edge notched bend test specimens, in Part 2 paper of this study (Blanchard, et al., Corrosion 78, 3 [2022]: p. 258–265).

A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 2–Significance of the Hydrogen Permeation Properties and Severity of Stress Raisers on Hydrogen Transport and Cracking

The quantified microstructural analysis performed on a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS) in the Part 1 publication of this study established the significance of the three-dimensional (3D) distribution and morphology/geometry of the ferrite and austenite phases on hydrogen transport through two DSS product forms (see Blanchard, et al., Corrosion 78, 3 [2022]: p. 249–257). This paper is a follow-up to Part 1 and focuses on the role of the other two key, interrelated components of hydrogen-induced stress cracking (HISC): stress/strain and hydrogen. For this purpose, experimental hydrogen permeation measurements, and environmental fracture toughness testing (i.e., J R-curve testing) using conventional and nonstandard single-edge notched bend test specimens were used. These particularly enabled interpretation of the hydrogen permeation and transport test data, and evaluation of suitability of environmental fracture toughness test methods for the assessment of resistance to HISC in DSSs. The latter is discussed, both from laboratory and component integrity perspectives, in the context of the findings from the 3D microstructural characterization of the two phases, the role of stress raisers and their severity, and hydrogen transport through the bulk and from the surface.

Duplex steel welding in artic conditions – Correlation of welding parameters in relation to HISC

Duplex steel is an austenitic-femtic steel alloy commonly used in the offshore and subsea oil and gas industry. Duplex steel provides a unique combination of good mechanical properties and corrosion resistance in sweet and sour hydrocarbon environment, as well as in seawater. However, the combination of tensile loading, post-weld residual stresses, cathodic protection and other factors related to subsea implementation significantly increase the probability of hydrogen induced stress cracking (HISC). This paper aims to find a relationship between the formation of residual stresses and the imperfection of the welding process carried out on Duplex steel in extremely cold conditions. Based on a finite element (FE) welding transient simulation from a thermal perspective, the correlation between the welding parameters and heat distribution is established and analysed when the welding takes place in the cold arctic conditions. Pearson parameter correlation analysis method will be used to investigate the impact of extreme ambient temperatures on the welding process. The results and conclusions provide a solid foundation for welding process optimization in connection with HISC.

A review on subsea process and valve technology

The world’s energy consumption continues to increase steadily. Fossil fuels (oil, natural gas, and coal) still comprise more than approximately 85% of the world’s energy consumption. Offshore oil field development and operation began by using platforms and ships, but oil producers and operators are looking for new and innovative ways to reduce production costs and improve recovery and production rates from reservoirs. As a result, subsea production solutions are becoming more popular. A subsea production system consists of subsea completed well(s), seabed wellhead(s), production tree(s), subsea tie-ins to flow line systems, and subsea equipment and control facilities to operate the well(s). The wellhead consists of the pressure-containing components at the surface of an oil and gas well that provide the interface for drilling, completion, and testing of the well, in addition to production equipment. Subsea manifolds are used to simplify the subsea system, minimizing the usage of subsea pipeline and risers while optimizing the fluid flow. Subsea valves, which are mainly ball or through conduit gate valves, are located on the trees and wellheads and designed based on API and ISO standards. They are made in exotic corrosion-resistant alloys to avoid different types of corrosion such as hydrogen-induced stress cracking, and should withstand high-pressure classes. These valves can be manual or actuator-operated with or without the help of a remote-operated vehicle. The subsea industry is shifting from hydraulic-type to electrical-type actuators for important reasons including reduced costs and faster operation. Newly designed subsea valves should pass strict qualification tests such as hyperbaric tests, endurance tests, and pressure and temperature cycle tests.

Hydrogen-Induced Stress Cracking of Swaged Super Duplex Stainless Steel Subsea Components

A recent subsea failure of two subsea connectors made of UNS S32760, a 25 wt% Cr super duplex stainless steel, led to an extensive root cause failure analysis. The components showed a single longit...

Sulfate‐reducing bacteria‐assisted hydrogen‐induced stress cracking of 2205 duplex stainless steels

AbstractThe paper presents the results of a laboratory investigation of the microbiologically assisted hydrogen‐induced stress cracking (HISC) of 2,205 duplex stainless steel (DSS). The testing of susceptibility toward HISC was performed with two different methods. Precharged in sulfate‐reducing bacteria (SRB), inoculated medium samples were subjected to slow strain‐rate testing in artificial seawater. In situ constant load tests were performed directly in SRB‐inoculated medium under hydrogen charging at 70% of the ultimate tensile strength. Samples tested in the biotic (SRB) conditions showed a considerable loss of ductility as compared to those tested in sterile conditions. Quantitative characteristics of fracture surfaces indicated increased susceptibility to HISC of biotic samples, therefore, suggesting a role of SRB in promoting hydrogen damage of DSS.

Effect of K-rate and cathodic protection potential on fracture toughness of the super duplex stainless steel UNS S32750

Super duplex stainless steels (SDSS) have emerged in the last decade or so asa candidate material to withstand harsh oil and gas production environments. However, documented cases of failure due to hydrogen induced stress cracking (HISC) have raised some concerns. The aim of this investigation is to evaluate the effect of the cathodic protection potential and K-rate on the susceptibility of SDSS to HISC. The results indicated that although the susceptibility to HISC might appear unequivocal, the tests parameters should be carefully considered since they influence dramatically on the results produced. Indeed, for more cathodic electrode potentials stronger is the detrimental effect on fracture toughness while the influence of K-rate is rather weak. However, the influence of this latter parameter becomes more relevant when the applied electrode potential is less negative.

Hydrogen embrittlement under cathodic protection of friction stir welded UNS S32760 super duplex stainless steel

Hydrogen Induced Stress Cracking (HISC) resistance of super duplex stainless steels is basically controlled by the material's microstructure. Friction stir welding is a low heat input joining process that has the potential to maintain the base metal original resistance to HISC since it does not significantly alter the proportion of ferrite and austenite. This work evaluated the susceptibility to HISC under cathodic protection of friction stir welded super duplex stainless steel UNS S32760. Microstructure evaluation revealed a recommended proportion of ferrite and austenite phases as well a refinement of the overall stir zone microstructure. Fracture toughness tests in synthetic sea water under cathodic protection of − 895mVsce indicated that the microstructure of the stir zone is actually less sensitive to HISC than the microstructure of the base metal.

Hydrogen induced stress cracking in UNS S32750 super duplex stainless steel tube weld joint

In this work, the hydrogen embrittlement of super duplex stainless steel tubes UNS S32750 under different hydrogen charging conditions was investigated. Hydrogen charging was performed both in unloaded and in elastically stressed specimens. The tubes were charged and tested under two conditions: as-received and welded. The samples were submitted to tensile tests in order to evaluate how the mechanical properties are affected by the hydrogen inserted into the microstructure. The fracture surfaces were analyzed in order to identify the failure active micro mechanisms. Combined tensile test results and microstructural investigations indicated that elastic stress applied to samples during hydrogen charging enhanced hydrogen solubility and permeability, resulting in greater loss of ductility. As pointed by fractographies of welded H-charged tubes, the microstructural changes induced by welding increased hydrogen diffusivity. The fracture surface of the hydrogen charged as-received tubes exhibited a quasi-cleavage aspect, indicating a mixed failure mechanism composed by plastic strain in austenite and cleavage on ferrite. Otherwise, the main mechanism of failure on welded tubes was cleavage.

Hydrogen induced stress cracking in supermartensitic stainless steels – Stress threshold for coarse grained HAZ

The objective of the present work was to investigate the influence of the microstructure on the hydrogen cracking susceptibility of two typical pipeline supermartensitic stainless steels. The work has concentrated on the coarse-grained heat affected zone because this is the typical crack initiation point. The hydrogen cracking susceptibility was tested by notched tensile test samples containing a simulated coarse grained heat affected zone. The samples were tested under constant load immersed in 3.5% NaCl and subjected to a negative potential corresponding to that induced by the cathodic corrosion protection system. The load was increased by a small amount every second day in order to establish the threshold stress for hydrogen cracking during service in seawater with hydrogen being introduced on the steel surface by the cathodic protection system. A significant influence of the second heat cycle was observed. This effect was attributed to both a variation in yield strength and the influence of precipitates on hydrogen solubility and diffusion.

Thermally Sprayed Aluminum (TSA) Coatings for Extended Design Life of 22%Cr Duplex Stainless Steel in Marine Environments

In this article, evaluation of sealed and unsealed thermally sprayed aluminum (TSA) for the protection of 22%Cr duplex stainless steel (DSS) from corrosion in aerated, elevated temperature synthetic seawater is presented. The assessments involved general and pitting corrosion tests, external chloride stress corrosion cracking (SCC), and hydrogen-induced stress cracking (HISC). These tests indicated that DSS samples, which would otherwise fail on their own in a few days, did not show pitting or fail under chloride SCC and HISC conditions when coated with TSA (with or without a sealant). TSA-coated specimens failed only at very high stresses (>120% proof stress). In general, TSA offered protection to the underlying or exposed steel by cathodically polarizing it and forming a calcareous deposit in synthetic seawater. The morphology of the calcareous deposit was found to be temperature dependent and in general was of duplex nature. The free corrosion rate of TSA in synthetic seawater was measured to be ~5-8 μm/year at ~18 °C and ~6-7 μm/year at 80 °C.

Resistance Toward Hydrogen-Induced Stress Cracking of Hot Isostatically Pressed Duplex Stainless Steels Under Cathodic Protection

Abstract The resistance toward hydrogen-induced stress cracking (HISC) of forged and hot isostatically pressed (HIP) super duplex stainless steel (SDSS) according to UNS S32760 have been compared b...

Relation of room temperature creep and microhardness to microstructure and HISC

Room temperature creep experiments were performed on three product forms of one superduplex stainless steel. The results indicate that the creep behavior is different between product forms with fine and coarse microstructures. A comparison with results from hydrogen-induced stress cracking (HISC) experiments indicates that room temperature creep is a prerequisite for HISC but is not the only influencing factor. For the duplex material with coarser microstructure, HISC occurs when the material creeps. Results from microhardness measurements after hydrogen charging show that ferrite is stronger than austenite for the material with fine microstructure, but ferrite and austenite show similar strengths for the coarser material; this effect may relate to the hydrogen content in the ferrite. Because of the lower hydrogen content in the ferrite phase of a duplex stainless steel with fine microstructure, the stress concentration in the ferrite phase is not likely to be high enough to form a crack in the austenite phase, even though the material creeps.

Hydrogen Induced Stress Cracking (HISC) and DNV-RP-F112

Duplex stainless steels are widely used in subsea petroleum production installation. In many instances such steels are a robust solution to the design and manufacturing challenges. However, a number of failures have occurred, which were attributed to Hydrogen Induced Stress Cracking (HISC). Several failure investigations and extensive testing have been carried out over the last 5–10 years, and a design guideline has been established; DNV-RP-F112. The article presents HISC as a failure mode, with a brief summary of the necessary conditions and failure characteristics. The testing and research effort into HISC is described. Finally DNV-RP-F112 “Design of Duplex Stainless Steel Subsea Equipment Exposed to Cathodic Protection” is introduced and the main features are outlined.

Influence of hydrogen from cathodic protection on the fracture susceptibility of 25%Cr duplex stainless steel – Constant load SENT testing and FE-modelling using hydrogen influenced cohesive zone elements

Laboratory experiments and cohesive zone simulation of Hydrogen Induced Stress Cracking in SENT tests specimens of 25%Cr duplex stainless steel have been performed. A polynomial formulation of the traction separation law and hydrogen dependent critical stress was applied. Best agreement with the experiments was found for an initial critical stress of 2200MPa and a critical separation of 0.005mm. Proposed threshold stress intensity factor and lower bound net section stress is 20MPa√m and 480MPa. High crack growth rates and typical hydrogen influenced fracture topography suggest large influence of the stress and strain in the fracture process zone on the hydrogen diffusion rate.

Application of hydrogen influenced cohesive laws in the prediction of hydrogen induced stress cracking in 25%Cr duplex stainless steel

Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25%Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25%Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 μm gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85–0.9 times the yield strength.

Cohesive zone modeling of hydrogen-induced stress cracking in 25% Cr duplex stainless steel

Hydrogen-influenced cohesive zone elements are implemented in finite element models of rectangular notched tensile specimens of 25% Cr stainless steel. A three-step procedure consisting of stress analysis, diffusion analysis and cohesive zone fracture initiation analysis was performed. A linear traction separation law gives a good fit with experimental results for stress levels just below the material yield stress. Hydrogen concentrations of 40 ppm at the surface and 1 ppm in bulk always produces crack initiation at the surface.

New concept for cathodic protection of offshore pipelines to reduce hydrogen induced stress cracking (HISC) in high strength 13%Cr stainless steels

Cathodic protection (CP) of submarine pipelines has generally been based on a conservative approach, as consequences of failure, to a great extent, are higher than the cost of installations. All design parameters and procedures are based on robust selections. Recent failures on pipelines with supermartensitic stainless steel (SMSS) materials have challenged this approach and laid the way for new design aspects with more realistic use of parameters. A new design concept has been introduced for the cathodic protection of offshore pipelines made from high strength stainless steel materials such as supermartensitic stainless steels (SMSS) with enhanced coating systems such as multilayer polypropylene coatings for combined corrosion protection and thermal insulation. The objectives are to reduce the susceptibility to hydrogen induced stress cracking (HISC) and coating damage. Conditions for the pipeline material, which can cause HISC have been studied and this has motivated the use of the new design concept. The study has been concerned with materials testing, CP-design parameters, CP installation and pipeline attachments, pipeline design, coating quality and direct electrical heating systems for hydrate control. The study has shown that the most critical factors for HISC are pipeline conditions with high stress and strain, especially stress concentrations, potential levels more negative than -0.80 V versus Ag/AgCl, low operating temperatures, coating failures and deep waters (high hydrostatic pressures). The paper gives a detailed overview of the new concept with regard to protection potentials for different pipeline materials; selection of design current density requirements; use of anodes with reduced driving potentials; use of subsea isolating joints; CP design principles; installation methods; compatibility with the direct electrical heating systems for hydrate control. The basis for the design has been the new ISO Draft International Standard 15889-2 on cathodic protection for offshore pipelines. Several of the new design parameters have been challenged and the new concept gives a significantly increased distance between anodes.

Variation of the Fracture Toughness of a High-Strength Pipeline Steel under Cathodic Protection

Crack-tip opening displacement (CTOD) fracture toughness measurements have been performed on longitudinal, through-wall thickness, three-point bend samples from an X-80 pipeline steel. Samples were subjected to cathodic protection in an NS-4 test solution prior to and during fracture toughness determination. Variation of the precharge time and the crosshead speed for CTOD measurement indicated that precharge times > 7 days and crosshead speeds giving rates of increase of stress intensity factor < 0.2 MPa m0.5/s were required to obtain worst-case conditions. Under the worst-case conditions, the CTOD fracture toughness for the X-80 material was reduced by 75%, to ≈ 0.17 mm, from a value of ≈ 0.70 mm in air. This reduction in fracture toughness was found to be similar at pH values down to 2.5. Although the samples were not taken with the fracture in an orientation representative of a typical pipeline defect, the reduction in fracture toughness was representative of the behavior of X-80. Comparison with literature data for conventional pipeline steels indicates that they suffer a similar loss in fracture toughness under worst-case conditions. The level of fracture toughness reduction for high-strength steels is of greater concern because they will operate under higher stresses. However, tolerable defect size calculations indicate that hydrogen-induced stress cracking (HSC) will not be a failure mechanism for X-80 steel parent material without some additional influence.