Stress corrosion cracking scc can lead to an unexpected failure of normally adaptable metal alloys jeopardized by a tensile stress, frequently at higher temperatures. H 2sinduced stress corrosion cracking scc process fluids in wet and sour service within the oil and gas industry often contain a certain amount of hydrogen sulphide, h 2s. Computer software h2compass can be used to determine when pwht or preheating is required. The impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material. Stress corrosion cracking international institute of. Stresscorrosion cracking may occur in combination with hydrogen. Mechanisms that have been proposed to explain embrittlement include the formation of brittle hydrides, the creation of voids that can lead to bubbles and pressure buildup within a material and e. The required tensile stresses may be in the form of directly applied stresses or in the form of residual. The chlorideinduced stress corrosion cracking scc resistance of nitrogenalloyed, powder metallurgically pm produced and hot isostatically pressed hip duplex stainless steels dss was investigated and compared to the scc resistance of two commercial wrought forged dss. In the absence of residual stress or external loading, environmental hydrogen. It is a form of hydrogen related cracking and can have two distinct morphologies.
Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small. Firstprinciple studies available in the literature are used for characterizing the process of. The stress can either be applied in the form of residual stress. On the other hand, hydrogen may have an important effect in metal matrix, i. Elements scc capabilities help to quickly evaluate the susceptibility of metallic materials to cracking and determine the size and scope of the problem before the failure occurs, avoiding major. The threshold stress intensity factor is calculated for each. Liquid metal cracking lmc, usually a physicochemical process. The normalized threshold stress intensity factor of scc, k ik iscc, was much lower than that of hydrogen induced cracking, k ik ih 14,15, and most scc cracks originated from the pits 16 19. This type of failure is referred to as stress corrosion cracking scc. When steel is embrittled and fails by cracking due to exposure to hydrogen in the presence of stress, the failure mechanism is known as hydrogen induced stress corrosion cracking hiscc 3. Metallurgical factors in stress corrosion cracking scc and hydrogeninduced cracking hic article in journal of solid state electrochemistry 7. Sulfide stress cracking an overview sciencedirect topics. This term should not be confused with stress corrosion cracking scs, since this is anodic in nature.
Ansinace mr0175hd2003sg metals for sulfide stress cracking. Stress corrosion cracking and hydrogen embrittlement dtic. Stress corrosion cracking and hydrogen embrittlement of high. Environmentally assisted cracks in linepipe steels are initiated either as a result of stresses in combination with environmental effects, as in stress corrosion cracking scc, or as a result of trapped hydrogen in the steel, as in hydrogeninduced cracking hic. Stress corrosion cracking of ferritic steel weld metal. Sulfide stress cracking sulfide stress cracking ssc is a form of hydrogen embrittlement which is a cathodic cracking mechanism.
Cracking mechanism an overview sciencedirect topics. There are two important damage modes in pipeline steels including stress corrosion cracking scc and hydrogen induced cracking hic. Sulfide stress cracking ssc is a type of hydrogen cracking which presents a cathodic embrittlement mechanism. The threshold stress intensity factor is calculated for each environment using the multiple specimen technique. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. The blistering damage tends to form parallel to the surface and to the direction of hoop stress. The scc cracks are those cracks which are induced due to the combined. Four factors, are required before stress corrosion cracking can occur. It is a growing crack formation in a corrosive atmosphere and highly chemically specific. Hic usually occurs due to the effects of aqueous hydrogen charging of steel in wet h2s refinery process. For good resistance to h 2 s induced stress corrosion cracking scc an alloy with high nickel content is recommended, and for most sour environments this type of alloy is now used.
Hydrogen embrittlement he also known as hydrogen assisted cracking hac and hydrogen induced cracking hic, describes the embrittling of metal after being exposed to hydrogen. From the chemical composition point of view, corrosion resistant nickel based alloys are categorized as pure nickel, nickelcopper alloys, nickelmolybdenum alloys, nicrmo alloys and nicrfemo alloys. Highstrength carbon steel bolt failures due to hydrogen. Additionally, hydrogen atoms diffuse through metals and coalesce. Also high strength structural steels which are welded are exposed to a certain hydrogen pickup which means a risk at fracture and blistering due to hic.
Hydrogen formed on the surface of the steel by a cathodic corrosion reaction can diffuse into the material, causing embrittlement, and, if the region is subject to tensile stress, cracking can result. Because stress corrosion cracks frequently initiate at pits, and pits. Ferritic stainless steels, on the other hand, tend to be fairly resistant to hydrogen stress cracking due to their comparatively low hardness. Hydrogen embrittlement also known as hydrogen assisted cracking and hydrogeninduced cracking, describes the embrittling of metal after being exposed to hydrogen. Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogeninduced cracking and liquid metal embrittlement. According to the electrochemical theory, this requires a condition along grain boundaries that makes them anodic to the rest of the microstructure so that corrosion propagates selectively along them.
Environmental cracking is a general term that includes. Hydrogen induced cracking hic in steel is a risk problem when steels are charged with hydrogen in service as in various hydrogen sulfide environments like sour oil and gas wells and some power plants. Stress corrosion cracking commonly occurs in brass, steels, stainless steels, aluminum alloys, copper, and titanium. The material is modelled at the microscopic scale using microstructural data. Transformable ferritic steels are susceptible to hydrogen induced scc in a wide range of aqueous media. Effect of hydrogeninduced plasticity on the stress. This standard presents metallic material requirements to provide resistance to sulfide stress cracking ssc andor stress corrosion cracking scc for petroleum production, drilling, gathering and flow line equipment, and field processing facilities to be used in hydrogen sulfide h2sbearing hydrocarbon service. It is a complex process that is not completely understood because of the variety and complexity of mechanisms that can lead to embrittlement. The observed crack propaga tion is the result of the combined and synergistic interaction of mechanical stress and corrosion re actions. For less demanding environments, duplex steels can be used. The path of crack growth in hydrogen embrittled steels is a function of the stress intensity factor, k mpavm. Wet h 2 s cracking can occur in susceptible steels exposed to aqueous environments containing hydrogen sulfide.
To date only duplex stainless steels, together with supermartensitic stainless steels, have been extensively tested. Scc tests on the steel are carried out in three environments of different aggressivity based on a nace tm. An extensive failure analysis shows how many service failures occurred in the industry and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures. Hydrogeninduced cracking hic in steel is a risk problem when steels are charged with hydrogen in service as in various hydrogen sulfide environments like sour oil and gas wells and some power plants. Stress corrosion cracking scc stress corrosion cracking is the formation of brittle cracks in what otherwise appears to be sound material. This type of failure is known as stress corrosion cracking, often abbreviated to scc. Corrosionpedia what is stress corrosion cracking scc. Hydrogen stress cracking can affect several different types of metals such as high strength structural, carbon, and low alloy steels, along with titanium, nickel, and aluminium alloys. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Initiation of stress corrosion cracking and hydrogeninduced. Hydrogen induced stress cracking hisc and dnvrpf112. Metals free fulltext effects of different parameters on initiation.
In many cases, scc is really hydrogeninduced stress cracking. A corrosive medium especially chloridebearing or hydrogensulphide h 2 s media. Also high strength structural steels which are welded are exposed to a certain hydrogen pickup which means a risk at fracture and blistering. This standard presents metallic material requirements to provide resistance to sulfide stress cracking ssc andor stress corrosion cracking scc for petroleum production, drilling, gathering and flow line equipment, and field processing facilities to be used in hydrogen. Abstract the susceptibility of an x65 line pipe steel to hydrogen. Metallurgical factors in stress corrosion cracking scc. The equilibrium configuration of a dislocation pileup ahead of a scc crack is studied and it is shown that diffusing hydrogen promotes stress concentrations against microstructural obstacles and periodic microfracture along the slip planes. The cathodic process during corrosion unavoidably evolves atomic hydrogen. Process fluids in wet and sour service within the oil and gas industry often contain a certain amount of hydrogen. From my point of view chlorides from test water cannot be excluded as cause for cl induced scc if the final hydrotest of the vessels has not been performed with demineralized water in case of designs which are not gap free or at least flushed with demineralized water after hydrotest if the design is. The presence of hydrogen atoms in a metal degrades some of its mechanical properties, especially its ductility, leading in some cases to embrittlement.
The susceptibility to hisc has been confirmed in these materials. First, the part must be stressed, either from an applied force or due to residual stress usually from forming. The catastrophic cracking of steels in hydrogen sulfide h 2 s environments referred to as sulfide stress cracking is a. Sulfide stress cracking ssc cracking usually is designated as either intergranular intercrystalline or transgranular transcrystalline. Galvanically induced hydrogen stress cracking ghsc the presence of hydrogen introduced via corrosion in a metal may result in reduced ductility and increased susceptibility to cracking in the presence of tensile stress applied and or residual. Control of stress level residual or load and hardness. Finally, the effect of hydrogen on a dislocation source at a crack tip is investigated. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. A corrosive medium especially chloridebearing or hydrogen sulphide h 2 s media. Despite extensive study, much remains to be learned about the phenomena. Engineers can now rest easy, to prevent he in service due to corrosion, the engineer can simply add a cathodic protection cp system and get a good nights sleep.
Chlorideinduced stress corrosion cracking of powder. Firstprinciple studies available in the literature are used for characterizing the process of intergranular material strength degradation. Stress corrosion cracking scc is characterized by cracks propagating either transgranularly or intergranularly along grain boundaries. Hydrogen induced plasticity in stress corrosion cracking of. Stress corrosion cracking behavior of nickel base alloys. Stress corrosion cracking and hydrogen embrittlement of. The scc cracks are those cracks which are induced due to the. The chemical environment that causes scc for a given alloy is often one which is only mildly corrosive to the. Aluminum alloys that contain appreciable amounts of soluble alloying elements, primarily copper, magnesium, silicon, and zinc, are susceptible to stresscorrosion cracking scc. There are several types of stress corrosion cracking scc, for example, chloride induced scc and h 2 s induced scc. When considering the corrosivity of a sour process fluid, the partial pressure of h 2s has to be taken into account as well as the ph value.
The poorly understood failure mechanisms are difficult to differ entiate, especially in the field. Initiation of stress corrosion cracking and hydrogen. Dear muthukrishnan, i would exclude also hydrogen attack as root cause of the crack formation. Thus, there are a variety of cracking patterns that can be observed. Stress corrosion cracking and hydrogeninduced cracking in. Webcorr provides corrosion consultancy services, corrosion expert witness and corrosion short courses for inhouse training, online and distance learning. Hydrogeninduced cracking hic is most commonly encountered in steels but other metals are susceptible, as shown in table 33. The relationship between these three types of failures can be showed in figure 1 where the eac domain is the union of the three. Ammonia scc is common in brass tubes with a cooling water function that have been polluted with ammonia due to biological growths or other impurities.
Metallurgical factors in stress corrosion cracking scc and. Stress corrosion cracking scc is a progressive fracturing that occurs in metals as a result of the combined influence of tensile stress and a corrosive environment. The first part covers scc and the second covers hic. Stress corrosion cracking scc is the progressive cracking of metals and alloys caused by the combined effect of. Stress corrosion cracking scc is difficult to predict and identify, and it can lead to catastrophic failure, often without any prior warning. The first type is commonly referred to as hydrogen induced cracking hic and can occur where little or no applied or residual tensile stress exists. It is induced by the simultaneous action of tensile stress and corrosive environment. The hydrogen evolution in scc occurs at the corroding crack tip. Metallurgical, mechanical and load conditions susceptibility of steel to hi.
From my point of view chlorides from test water cannot be excluded as cause for cl induced scc if the final hydrotest of the vessels has not been performed with demineralized water in case of designs which are not gap free or at least flushed with demineralized water after hydrotest if the. Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogen induced cracking and liquid metal embrittlement. Hydrogen induced cracking can be prevented through. Hip decreases the stress intensity at the crack tip and lowers the scc risk of pipeline steels by releasing the stress concentration at scc initiation spots and enlarging deformation zone in front of the crack tip, thereby providing a possibility to optimize the cp condition.
While it is rare, formed parts can develop fractures after they are placed in service. Sulfide stress corrosion cracking occurs in presence of hydrogen sulfide. Purely mechanical forms of cracking such as brittle failure and fatigue are not considered here. Stresscorrosion cracking scc is a term used to describe service failures in engineering materials that occur by slow, environmentally induced crack propagation. Hydrogen induced plasticity in stress corrosion cracking. Scc may be classified as an environmental assisted cracking eac, besides corrosion fatigue cf and hydrogen induced cracking hic. Hydrogen stress cracking is a form of hydrogen embrittlement that occurs when corrosion from acids like wet hydrogen sulfide and hydrofluoric acid cause atomic hydrogen to penetrate hardened or higher strength steels and cause stress cracking. A corrosive medium especially chloridebearing or hydrogensulphide h2s media. The chloride induced stress corrosion cracking scc resistance of nitrogenalloyed, powder metallurgically pm produced and hot isostatically pressed hip duplex stainless steels dss was investigated and compared to the scc resistance of two commercial wrought forged dss. Transformable ferritic steels are susceptible to hydrogeninduced scc in a wide range of aqueous media. Stress corrosion cracking in aluminum alloys is characteristically intergranular. Astm f519 hydrogen embrittlement he testing element.
Gas phase water needs to be there as well even in a trace amount. Corrosionpedia what is sulfide stress cracking ssc. Structural failure due to scc can be very unpredictablefailure could occur after as little as a few hours of exposure, or the equipment could continue to function normally for. Stress corrosion cracking facts and how to reduce the. Hydrogeninduced cracking an overview sciencedirect topics. Stress corrosion cracking and hydrogen embrittlement. Metallurgical factors in stress corrosion cracking scc springerlink.
Hydrogen induced cracking hic is a common form of wet h2s cracking caused by the blistering of a metal due to a high concentration of hydrogen. This penetration can lead to the brittle fracture of materials that are normally ductile when hydrogen happens to be present in their environment. Stress corrosion cracking facts and how to reduce the risk. One of the most recognized forms of scc, chloride stress corrosion cracking appears as highly branched spiderweb cracks. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Hic usually occurs due to the effects of aqueous hydrogen charging of steel in wet h2s refinery process environments. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism. Stress corrosion cracking scc results from the combined action of three factors. Liquid metal crackinglmc, usually a physicochemical process. It is a form of hydrogenrelated cracking and can have two distinct morphologies. Cracks can develop by both transgranular and intergranular paths. Stress corrosion cracking scc or called as environmentally assisted cracking eac may take place at the electrochemical potential range. Stress corrosion cracking scc of nickelbased alloys. Request pdf metallurgical factors in stress corrosion cracking scc and hydrogeninduced cracking hic nonmetallic inclusions can affect resistance of.
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