The material performance in these environments is governed by the stability of the passive surface film, which develops as a function of alloy microstructure, chemical composition, and associated environmental. The corrosion of stainless steel in hot caustic environment has been the subject of a number of investigations, typically with a focus on kraft pulping liquors 1,2,3,4,5,6,7,8,9,10,11. The duplex steel exhibited the best performances while the n08904. It has general corrosion resistance similar or better than alloys 304l and 316l but with yield strength nearly double that of austenitic stainless steels. Feb 22, 2001 chloride induced cracking of stainless steels, caustic cracking of plain carbon steels, and ammonia damage to copper alloys are typical examples of this problem. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature.
In this study, the role of material and environmental parameters on corrosion and stress corrosion cracking of duplex stainless steels in caustic. Chloride stress corrosion cracking clscc is one the most common reasons why austenitic stainless steel pipework and vessels deteriorate in the chemical processing and petrochemical industries. The effect of alloying elements and how these elements affect the electrochemical response in 50% naoh environments can be assessed, by comparing individual alloy responses. Stress corrosion cracking and corrosion susceptibility of. A sandvik grade with very good resistance to this form of stress corrosion cracking is sanicro 28. Stress corrosion cracking international institute of. Stress corrosion cracking of stainless steels in high. Corrosion of duplex stainless steels in high ph caustic. Stress corrosion cracking scc of uns s31603 austenitic stainless steel.
Caustic stress corrosion cracking, also referred to as caustic embrittlement, is a form of degradation that is caused when a component operates in a caustic environment. The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress. The resistance of commercial austenitic, ferritic, and duplex alloys to stress corrosion cracking in a 5% naoh2% na 2 s2% na 2 co 30. The materials with nominal compositions are given in table 1.
Effect of alloy element contents on caustic stress corrosion. Caustic stress corrosion cracking inspectioneering. Gooch t g and leonard a j, hydrogen cracking of ferriticaustenitic stainless steel weld metal, duplex america 2000, p345 kci publishing, 2000. Stainless steels types 304 and 316 can be considered resistant below 80 degc, up to the limit of solubility. Scc of the 300 series stainless steels is classically transgranular. Hydrogen embrittlement cracking of superduplex steel twi. Corrosion of duplex stainless steels in high ph caustic solution. Stress corrosion cracking of duplex stainless steel scc stress corrosion cracking is a form of corrosion which occurs with a particular combination of factors. Effect of alloy element contents on caustic stress. Resistant to chloride stress corrosion cracking and temperatures of up to about 302f 150c the presence of ferrite provides for good performance of duplex 2205 in caustic environments. Improved resistance to caustic stress corrosion cracking. Stress corrosion cracking of welded 2205 duplex stainless. Stress corrosion cracking of duplex stainless steels in caustic. For less demanding environments, duplex steels can be used.
Rebak lawrence livermore national laboratory, livermore, ca, 94550 abstract caustic environments are present in several industrie s, from nuclear power generation to the fabrication of alkalis and alumina. However, some corrosion and stress corrosion cracking scc of dsss have been reported in different pulp mill environments employing caustic solutions. The typical crack morphology for chloride stress corrosion cracking consists of branched transgranular cracks. Stainless steels are damaged by stress corrosion cracking in conditions containing chlorides at the high temperatures. The relative superiority of duplex stainless steels dss over austenitic grades with regards to stress corrosion cracking scc is discussed. Chloride induced cracking of stainless steels, caustic cracking of plain carbon steels, and ammonia damage to copper alloys are typical examples of this problem. The duplex stainless steels were developed to exhibit comparable general corrosion resistance as 316ss, but with reduced susceptibility to chloride stress corrosion cracking. Stress corrosion cracking scc of duplex stainless steel. As a general rule, the resistance to caustic solutions increases with. Studies have shown that the corrosion and scc susceptibility of dsss depend on the alloy composition and microstructure of the steel. Duplex stainless steels are far less prone to this type of corrosion. Stress corrosion cracking of stainless alloys in alkaline sulfide solutions.
Duplex stainless steel is a practical solution to most 304l or 316l scc failures. Electrochemical behaviour of duplex stainless steels in. The stress corrosion cracking behavior in caustic solutions 200 gl sodium hydroxide, 10 gl sodium chloride of three austenitic 18cr. The duplex stainless steels were developed to exhibit comparable general corrosion resistance as 316ss, but with reduced susceptibility to chloride stress.
Traditional austenitic steels are found to be more susceptible to such attack however duplex grades are less prone to it. The duplex steel exhibited the best performances while the n08904 steel had the worst scc resistance. These alloys can be candidates for service in caustic exposure when corrosion from cooling waters is a concern. S31603, astm f8, n08904 and a duplex s31803 stainless steels. Stress corrosion cracking of welded 2205 duplex stainless steel in sulfide containing caustic solution. Aug 01, 2018 caustic cracking is a form of stress corrosion cracking most frequently encountered in carbon steels or ironchromiumnickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 482f 250c. Stress corrosion cracking was unexpected in austenitic stainless steel aisi 316l, but. This paper discusses a study of the role of sulfide in caustic solutions on scc of austenitic stainless at t50c. Although stress corrosion cracking of duplex stainless steels in chloride solution has been investigated and well documented in the literature but the scc mechanisms for dss in caustic solutions were not known. Stress corrosion cracking of an austenitic stainless steel.
The rate of corrosion may further be affected by the presence of sulfide ions in caustic solutions. This form of corrosion is controlled by maintaining low chloride ion and oxygen content in the environment and use of low carbon steels. Stress corrosion cracking of welded 2205 duplex stainless steel in sulfidecontaining caustic solution. Stress corrosion cracking of stainless steels in high temperature caustic solutions. Stress corrosion cracking susceptibility scc of the austeniticferritic stainless steels, i. Stress corrosion cracking of duplex stainless steels in. The higher alloyed duplex stainless steel alloys, ones with significant molybdenum and nitrogen additions, can be superior to 316 ss in. Normally 50 deg c but can occur at lower temperatures around 25 deg c in specific environments, notably swimming pools. Caustic stress corrosion cracking, also referred to as caustic embrittlement, is a form of degradation that is caused when a component operates in a caustic environment it is one of the most prevalent afflictions in the industry and one of many environmental cracking mechanisms that typically occur in carbon steel equipment, but it can also afflict low alloy and austenitic stainless steel.
Investigation of stress corrosion cracking of austenitic, duplex and. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. Actually, the scc of sss might occur even in caustic solutions, when the. Industrial experience on the caustic cracking of stainless. Stress corrosion cracking of an austenitic stainless steel in. It is used in metal degreasing and cleaning processes in a wide range of industry applications. Stainless steels are more resistant to general corrosion compared with carbon steel.
Super duplex stainless steels are used at temperatures up to about 150c. The mechanism of scc is shown as a simple representation in figure 1. Recent failures of dss pulp mill equipment in sulphidecontaining caustic environments,,, has necessitated the investigation of the material and environmental conditions under which different duplex stainless steel grades may become susceptible to general corrosion and stress corrosion cracking in sulphidecontaining caustic solutions. Stress corrosion cracking of stainless alloys in alkaline. Duplex stainless alloys also show resistance to caustic and caustic cracking. Stress corrosion cracking and corrosion susceptibility of duplex. The required tensile stresses may be in the form of directly applied stresses or in the form of residual. Unexpected corrosion of stainless steel in high solids black. May 27, 2011 duplex stainless steel is a practical solution to most 304l or 316l scc failures. Its duplex microstructure and low nickel and high chromium contents also allows duplex 2304 to demonstrate improved stress corrosion resistant properties compared to 304 and 316. Various techniques are utilized to grade the steel types considering their resistance to scc and the. Chloride stress corrosion cracking in austenitic stainless. Article pdf available in journal of failure analysis. The benefits of n to scc resistance of dss are provided.
In the hydroiodic acid at temperatures exceeding 177oc, alloy b2 was sensitive to transgranular stress corrosion cracking. Although duplex stainless steels offer superior stress corrosion cracking scc resistance in sulfide containing caustic solutions, but may become susceptible to. Laboratory tests reveal good resistance to stress corrosion cracking of sandvik saf 2205. Figure 1 shows the cracking that occurred on a 6mo super austenitic stainless steel n08367 exposed to 0. When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f. The higher alloyed duplex stainless steel alloys, ones with significant molybdenum and nitrogen additions, can be superior to 316ss in certain. Chloride stress corrosion cracking the greatest corrosion advantage for duplex stainless steels is their improved resistance to cscc when compared to the austenitic grades. Stress corrosion cracking behavior of nickel base alloys.
Stress corrosion cracking of welded 2205 duplex stainless steel in. Microstructural changes during fabrication processes affect the overall scc susceptibility of these steels in caustic solutions. In effect, beyond this content, under oxidising conditions oxygen in the air or oxygen dissolved in water will suffice, a thin but stable layer forms and strengthens see below for increasing cr, ni, mo contents. Singh 1 school of materials science and engineering, georgia institute of technology, 500 10th st. Stress corrosion cracking is a form of localized corrosion that will affect metal causing sudden cracks. The impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material.
Corrosion behaviour of type 316l stainless steel in hot. Request pdf corrosion of duplex stainless steels in high ph caustic solution. Duplex stainless steelsthe duplex stainless steels were developed to exhibit comparable general corrosion resistance as 316ss, but with reduced susceptibility to chloride stress corrosion cracking. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Schematic view of stress corrosion cracking scc and corrosion fatigue cracking. Effect of heat treatment on corrosion and stress corrosion. Only the 25% nickel grades have similar cscc resistance. Austenitic stainless steels are susceptible to caustic stress corrosion cracking scc above 121c. The useful safe limit of carbon steel is approximately 150 o f65 o c, both with regard to caustic stress corrosion cracking cscc and corrosion. Ssc6mo uns n08367 is a superaustenitic 6% molybdenum alloy that exhibits far greater resistance to chloride pitting, crevice corrosion and stresscorrosion cracking than the standard 300 series and standard duplex stainless steels. The main drawbacks of stainless steels is that these alloys are sensitive to chloride induced localized attack like pitting and crevice attack and stress corrosion cracking. Stress corrosion cracking of duplex stainless steels in caustic solutions.
Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. It is one of the most prevalent afflictions in the industry and one of many environmental cracking mechanisms that typically occur in carbon steel equipment, but it can also afflict low alloy and austenitic stainless steel. Microstructural changes and environmental factors, such as ph of the solution, temperature, and resulting electrochemical potential also influence the scc susceptibility of duplex stainless steels. Despite the extensive qualification of inconel for specific applications, a number of corrosion problems have arisen with inconel tubing. This article describes the susceptibility of 316l stainless steel to stress corrosion cracking scc in a nitritecontaining chloride solution. Duplex stainless steels dss with roughly equal amount of austenite and ferrite phases are being used in industries such as petrochemical and pulp and paper mills. Stress corrosion cracking facts and how to reduce the risk. Duplex stainless steels dsss have generally performed very well in caustic environments. Previous studies and field experiences have shown that duplex stainless steels dss may become susceptible to general corrosion and stress corrosion cracking in high ph caustic solutions.
Stress corrosion cracking scc tests were conducted by the slow strain rate ssr technique at strain rates ranging from 5. Other forms of scc in stainless steels include caustic cracking and polythionic acid scc. The effects of alloy composition, solution composition, and test temperature on the occurrence of stress corrosion cracking were. Unexpected corrosion of stainless steel in high solids. Stress corrosion cracking the international institute of. However, many dss grades have been reported to undergo corrosion and stress corrosion cracking in some aggressive environments such as chlorides and sulfidecontaining caustic. Singh, effect of welding related microstructure on stress corrosion cracking susceptibility of duplex stainless steels in caustic solutions, nace international, corrosion2006, paper no. Chloride stress corrosion cracking in austenitic stainless steel.
These hightemperature caustic environments are found in the fabrication of alkalis, in oil refineries, in pulp and paper manufacturing and in the 0. The most commonly available duplex in north america is 2205, at a cost roughly 20% above that of 316l. For good resistance to h 2 sinduced stress corrosion cracking scc an alloy with high nickel content is recommended, and for most sour environments this type of alloy is now used. Francis r, byrne g and warburton g r, the effect of cathodic protection on duplex stainless steels in seawater, corrosion 95, paper 290 houston, tx. Stress corrosion cracking of type 304l stainless steel in sodium sulfidecontaining caustic solutions p. Most notably, pitting and cracking in this instance had initiated andor. Similar to other duplex stainless steels, duplex 2205 has good oxidation resistance at high temperatures. Other higher nickel stainless alloys like alloy 20, 800 and 825 also resist caustic corrosion and caustic cracking better than the 300 series stainless steels.
By convention, stainless steel is an ironchromium alloy with a chromium content of more than 10. Stress corrosion cracking of duplex stainless steels. When sulfides are present in caustic solutions the scc has been reported to occur at lower temperatures. Understanding scc scc of stainless steel occurs when the stressed part is in a potential range in which a stable, selfprotective, oxiderich, passive film does not immediately reform when it is damaged fig. Abstract changes in pulping methods have generally increased the cooking temperatures along with the sulfidity and alkalinity of pulp mill liquors. Stress corrosion cracking of type 304l stainless steel in.
Duplex stainless steels and high chromium ferritic stainless steels provide superior resistance to corrosion and to scc in liquors. Stress corrosion cracking of stainless steels in high temperature. Stress corrosion cracking was unexpected in austenitic stainless steel aisi 316l, but has on some occasions. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. These changes have led to accelerated corrosion rates in carbon steel equipment used in pulp mills. As a general rule, the resistance to caustic solutions increases with increasing nickel content.
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