Titanium alloys are widely used in hydrogen containing environments and under conditions in which galvanic couples or cathodic charging causes hydrogen to be evolved on metal surfaces. Cracking due to the simultaneous presence of hydrogen, the corrosive environment and tensile stresses in a metal or alloy is defined as. Cracks can develop by both transgranular and intergranular paths. Propagation of stress corrosion cracks and relevance to proposed mechanisms of stress corrosion cracking. Hydrogen induced cracking of subsea duplex stainless steel twi. Apart from the high cost of production and fabrication, one of the hindrances to its application has been corrosion, especially underperformance in severe environments due to stress corrosion. The types of corrosion that have been observed on titanium may be classified under the general headings. Despite this, titanium may suffer different forms of corrosion in severe environments. The embrittlement of a metal or alloy by atomic hydrogen involves the ingress of hydrogen into a component, an event that can seriously reduce the ductility and loadbearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials.
Hydrogen stress cracking is a form of embrittlement occurring when corrosion from certain acids causes atomic hydrogen to penetrate higher strength steels. The role of hydrogen in the mechanism of stress corrosion cracking has been known since the 1970s so that preventative measures have since been introduced. Embrittlement of hydrogen is the main mechanism related to environmental cracking, especially in alloys like titanium and steels. A small number of duplex and superduplex stainless steel components have failed in subsea service due to hydrogen induced stress cracking hisc.
Room temperature stress corrosion cracking of titanium. Although excellent performance is revealed for these alloys in most cases, hydrogen embrittlement has been observed. Hydrogen embrittlement also known as hydrogen assisted cracking and hydrogeninduced cracking, describes the embrittling of metal after being exposed to hydrogen. When the solubility limit of hydrogen in titanium about 100150 ppm for grade 2 is exceeded, hydrides begin to precipitate. Some of these types include general, galvanic and crevice corrosion, as well as stress corrosion cracking, anodic breakdown pitting and hydrogen embrittlement. At high temperatures, the absorbed hydrogen tends to gather in the grain boundaries and stressinduced cracking is then intergranular. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. This absorption was initiated by an ironnickel contamination on the areas to embrittle.
In the case of a crystal lattice becoming saturated or coming into contact with atomic hydrogen, many alloys and metals may. The path of crack growth in hydrogen embrittled steels is a function of the stress intensity factor, k mpavm. Hydrogen embrittlement he also known as hydrogen assisted cracking hac and hydrogeninduced cracking hic. Webcorr provides corrosion consultancy services, corrosion expert witness and corrosion short courses for inhouse training, online and distance learning. Hydrogen induced craking hic, also referred to as hydrogen stress cracking or static fatigue, is a typical form of hydrogen embrittlement. The blistering damage tends to form parallel to the surface and to the direction of hoop stress. Elements stress corrosion cracking scc testing evaluates the susceptibility of metals to cracking failure under tensile stress and corrosion.
Titanium is immune to general attack and stress corrosion cracking by hydrocarbons, hydrogen sulfide, brines and carbon dioxide. Hydrogen induced stress cracking hisc resistance and. Hydrogenassisted stress corrosion cracking of high. Stress corrosion cracking scc and hydrogenassisted. It is a complex process that is not completely understood because of the variety and complexity of mechanisms that can lead to embrittlement. If stress induces cracking under these conditions, the path is transgranular. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. It was observed that the relationship between hydrogen induced crack growth rate and applied stress intensity can be described by three separable regions of behavior. Stress corrosion cracking in the titanium alloys is the ability of the structure or test configuration to sustain by a moving crack front an actively corroding local site of a nonpassivating electrolyte. 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. A model has been developed which simulates the deformation of single crystal austenitic stainless steels and captures the effects of hydrogen on stress corrosion cracking. Ferritic stainless steels, on the other hand, tend to be fairly resistant to hydrogen stress cracking due to their comparatively low hardness.
Politecnico di milano, department of chemistry, materials, and chemical engineering g. Hydrogen induced cracking hic is most commonly encountered in steels but other metals are susceptible, as shown in table 33. Hydrogeninduced cracking hic refers to the internal cracks brought about by material trapped in budding hydrogen atoms. Elements hic tests evaluate material susceptibility to hydrogen induced cracking in a sour environment in accordance with nace. One key difference between hydrogen embrittlement and stress corrosion cracking, although very similar in many aspects, is their reaction to cathodic protection. The classical argument as to whether the halogen or hydrogen are the cracking species is obscure, as both are interacting to sustain the reaction. Absorption of several hundred ppm of hydrogen results in embrittlement and the possibility of cracking under conditions of stress. Ricker, national institute of standards and technology stress corrosion cracking scc is a term used to describe service failures in engineering materials that occur by slow, environmentally induced crack propagation. Sixty years on, stress corrosion and other hydrogen effects continue to be. Cathodic hydrogen absorption cha is a subset of scc. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment.
Paper presented at 29th international conference on offshore mechanics and arctic engineering omae 2010, shanghai, china, 611 june 2010. Here we examine the corrosive of a range of media on commercially pure and near commercially pure titanium alloys table 1. 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 impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material. Similar failure modes were observed in fractographic examinations of surfaces produced by. Ferritic stainless steels, on the other hand, tend to be fairly resistant to hydrogen stress cracking due. Darpa is exploring a number of advanced materials for military applications, including amorphous metals and titanium based alloys. Initiation and early slow growth of stress corrosion cracks in tial alloys in methanolhcl solutions occurs by slip induced grain boundary splitting. Mechanisms of stress corrosion cracking of titaniumaluminum. Stress corrosion cracking of titanium preliminary report. By virtue of their excellent physical, mechanical and chemical properties, titanium alloys have tremendous application potential. The significance of these failures has led to research to.
It involves atomic hydrogen, which is the smallest atom, that diffuses into a metallic structure. In addition to help, absorption induced dislocation. Similar failure modes were observed in fractographic examinations of surfaces. Titanium, like any other metal, is subject to corrosion in some environments. Crevice corrosion stress corrosion cracking anodic breakdown pitting hydrogen embrittlement galvanic corrosion references. General corrosion, localized corrosion, stress corrosion cracking, hydrogen induced cracking, microbially influenced corrosion, a. Stress corrosion cracking scc is difficult to predict and identify, and it can lead to catastrophic failure, often without any prior warning. Corrosionpedia what is hydrogeninduced cracking hic. Hydrogen embrittlement and stress corrosion cracking. Environmental cracking is a broad term that includes corrosion fatigue, hightemperature hydrogen attack, hydrogen blistering, hydrogen embrittlement, liquid metal embrittlement, season cracking, caustic embrittlement, stress corrosion cracking, stepwise cracking, sulfide corrosion cracking and sulfide stress cracking. 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. Cracking of a metal due to stress relaxation during pwht or in service at elevated temperatures is most often observed in heavy wall sections. It is characterized by the brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material.
The most vulnerable are highstrength steels, titanium alloys and aluminum alloys. This is a type of deterioration which can be linked to corrosion and corrosion control processes. Active path compounds and intermetallics are formed along preexisting paths such as grain boundaries. This chapter provides a summary of the present knowledge on stress corrosion cracking of titanium and its alloys with due emphasis on hydrogen enhanced cracking. Stress corrosion cracking the international institute of. Stress oriented hydrogen induced cracking sohic stress orientated hydrogen induced cracking occurs in the area of grain enlargement in weld heat affected zones. Hydrogeninduced cracking an overview sciencedirect topics.
Hydrogen cracking its causes, costs and future occurrence p h m hart weld metal hydrogen cracking in pipeline girth welds, proc. 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. Hp hydrogen produced by corrosion and ha hydrogen absorbed into the material 274. Hydrogen embrittlement and stress corrosion cracking of titanium alloys caused by cleaning processes 850709 hydrogen was absorbed by titanium alloys in an alkaline scale conditioning bath. Hydrogen may be produced by corrosion reactions such as rusting, cathodic. The relationship between these three types of failures can be showed in figure 1 where the eac domain is the union of the three circles, each one representing the three failure modes. Hot salt stress corrosion cracking in ti 6246 alloy has been investigated to elucidate the chemical.
Stress corrosion cracking international institute of. Mechanisms of stress corrosion cracking of titanium. Hydrogen atmospheres at high temperatures as well as wet h 2 s and hf acid services, also accelerate hydrogen embrittlement damage. Embrittlement atoms of hydrogen diffuse onto the crack tip and cause embrittlement to the metal. Experimental studies show that hydrogen produced during the corrosion of titanium alloys by halide salts and subsequently absorbed by the titanium is responsible for cracking of these alloys. Stresscorrosion cracking, materials performance and. Stress corrosion and hydrogen embrittlement in an aluminum. Jun 05, 2017 the difference between stress corrosion cracking and hydrogen embrittlement. Hydrogen embrittlement of titanium alloys hydrogen damage of titanium and its alloys is manifested as a loss of ductility embrittlement andor reduction in the stress intensity threshold for crack propagation. Corrosion of ti gr 7 and other titanium alloys in nuclear. This book presents proceedings which give an account of knowledge and understanding of hydrogen embrittlement and stress corrosion cracking from the viewpoints of the authors. Hydrogen embrittlement and stress corrosion cracking asm. Roles of hzs in the behavior of engineering alloys.
Scc may be classified as an environmental assisted cracking eac, besides corrosion fatigue cf and hydrogen induced cracking hic. Later crack propagation occurs by cleavage and other forms of transgranular cracking. Hydrogenassisted stress corrosion cracking of high strength. Hydrogen blistering occurs when hydrogen atoms diffuse into the steel, and hydrogen gas nucleates at internal defects and inclusions, forming voids which eventually generate enough pressure to locally rupture the metal. Hydrogen induced cracking failures of sour gas processing equipment and transmission pipelines have been reported at facilities in libya, saudi arabia and other middleeastern plants. A hotsalt stress corrosion cracking hsscc mechanism was. Although hydrogen induced cracking and stress corrosion cracking are similar phenomena, both types of damage are usually described and treated separately. 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. 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. Hydrogen embrittlement and stress corrosion cracking of.
Under steady state conditions, in the absence of internal trapping of hydrogen, the efficiency of. Stress corrosion cracking scc and hydrogen embrittlement are differentiated by their responses to the applied current and mode of cracking. The required tensile stresses may be in the form of directly applied stresses or in the form of residual. The cracking of martensitic and precipitation hardened steel alloys is believed to be a form of hydrogen stress corrosion cracking that results from the entry into the metal of a portion of the atomic hydrogen that is produced in the following corrosion reaction. Hydrogen blistering a special case of hydrogen damage is known as hydrogen blistering.
Damage due to hydrogen embrittlement and stress corrosion. Feb 11, 2002 titanium is susceptible to corrosion in some environments despite its relative stability. Titanium is susceptible to corrosion in some environments despite its relative stability. It has been known for more than 10 years that titanium alloys suffer from intergranular stress corrosion cracking if they are in contact with chlorides. Hic usually occurs due to the effects of aqueous hydrogen charging of steel in wet h2s refinery process environments.
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. It involves the ingress of hydrogen into a component, an event that can seriously reduce the ductility and loadbearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Titanium overview titaniumbased alloys provide an excellent combination of a high strength weight ratio and good corrosion behavior, which makes these alloys among the most important advanced materials for a variety of aerospace, marine, industrial, and commercial applications. The kinetics of hydrogen induced cracking have been studied in the ti5al2. Hydrogen cracking its causes, costs and future occurrence twi. Jun 03, 2018 hydrogeninduced cracking hic refers to the internal cracks brought about by material trapped in budding hydrogen atoms. Equipment made from these materials can undergo degradation due to thermal aging, uniform corrosion, pitting, crevice corrosion, denting, stress corrosion cracking, corrosion fatigue, hydrogen induced cracking and microbial influenced corrosion. Basically, corrosion produced hydrogen from a secondary cathodic reaction is responsible for the premature failure which can occur when tensile stressed titanium alloys are exposed to chloride containing hot salt environments. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Hydrogen in hotsalt stress corrosion cracking of titanium. Word of the navys saltwater tests quickly spread, and overnight stress corrosion of titanium at room temperature was a top priority. Natta, piazza leonardo da vinci 32, 203 milano, italy.
This type of failure is known as stress corrosion cracking, often abbreviated to scc. Hydrogen induced cracking hiccauses and prevention. High strength steel offshore structures are in addition extremely sensitive to stress corrosion cracking scc 5. If applied current makes the specimen more anodic and accelerates cracking, it is a case of stress corrosion cracking. Jul 29, 2019 hydrogen induced cracking failures of sour gas processing equipment and transmission pipelines have been reported at facilities in libya, saudi arabia and other middleeastern plants. Additionally, hydrogen atoms diffuse through metals and coalesce. The presence of hydrogen atoms in a metal degrades some of its mechanical properties, especially its ductility, leading in some cases to embrittlement. Investigations of environmentassisted crack growth. The dislocation mechanism of stress corrosion embrittlement in ti. Titanium can absorb hydrogen from environments containing hydrogen gas. An improved model explains the hot salt stress corrosion cracking hsscc of titanium alloys. Modelling hydrogen induced stress corrosion cracking in. Ricker, national institute of standards and technology stresscorrosion cracking scc is a term used to describe service failures in engineering materials that occur by slow, environmentally induced crack propagation.