Stress corrosion cracking of duplex stainless steels in caustic solutions

It is used in metal degreasing and cleaning processes in a wide range of industry applications. 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. Stress corrosion cracking of duplex stainless steels. 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. Stress corrosion cracking of an austenitic stainless steel in. 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. 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. The materials with nominal compositions are given in table 1. Duplex stainless steels and high chromium ferritic stainless steels provide superior resistance to corrosion and to scc in liquors. Stress corrosion cracking of type 304l stainless steel in. Stress corrosion cracking of welded 2205 duplex stainless steel in.

Stress corrosion cracking and corrosion susceptibility of duplex. 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. Stress corrosion cracking of stainless steels in high temperature. The stress corrosion cracking behavior in caustic solutions 200 gl sodium hydroxide, 10 gl sodium chloride of three austenitic 18cr. Stress corrosion cracking of welded 2205 duplex stainless steel in sulfide containing caustic solution. 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. These changes have led to accelerated corrosion rates in carbon steel equipment used in pulp mills. For less demanding environments, duplex steels can be used. Abstract changes in pulping methods have generally increased the cooking temperatures along with the sulfidity and alkalinity of pulp mill liquors. The most commonly available duplex in north america is 2205, at a cost roughly 20% above that of 316l. Super duplex stainless steels are used at temperatures up to about 150c. The higher alloyed duplex stainless steel alloys, ones with significant molybdenum and nitrogen additions, can be superior to 316 ss in. Stress corrosion cracking was unexpected in austenitic stainless steel aisi 316l, but. Stress corrosion cracking the international institute of.

Stress corrosion cracking of duplex stainless steels in. Laboratory tests reveal good resistance to stress corrosion cracking of sandvik saf 2205. As a general rule, the resistance to caustic solutions increases with increasing nickel content. Stress corrosion cracking scc of uns s31603 austenitic stainless steel. Scc of the 300 series stainless steels is classically transgranular. Stress corrosion cracking of duplex stainless steels in caustic solutions. This article describes the susceptibility of 316l stainless steel to stress corrosion cracking scc in a nitritecontaining chloride solution. Caustic stress corrosion cracking inspectioneering. Stress corrosion cracking of duplex stainless steels in caustic. Other forms of scc in stainless steels include caustic cracking and polythionic acid scc. The rate of corrosion may further be affected by the presence of sulfide ions in caustic solutions. Chloride stress corrosion cracking the greatest corrosion advantage for duplex stainless steels is their improved resistance to cscc when compared to the austenitic grades. The required tensile stresses may be in the form of directly applied stresses or in the form of residual.

Chloride induced cracking of stainless steels, caustic cracking of plain carbon steels, and ammonia damage to copper alloys are typical examples of this problem. May 27, 2011 duplex stainless steel is a practical solution to most 304l or 316l scc failures. However, some corrosion and stress corrosion cracking scc of dsss have been reported in different pulp. Gooch t g and leonard a j, hydrogen cracking of ferriticaustenitic stainless steel weld metal, duplex america 2000, p345 kci publishing, 2000.

The duplex steel exhibited the best performances while the n08904. 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. Article pdf available in journal of failure analysis. As a general rule, the resistance to caustic solutions increases with. Improved resistance to caustic stress corrosion cracking. Stress corrosion cracking of welded 2205 duplex stainless. Studies have shown that the corrosion and scc susceptibility of dsss depend on the alloy composition and microstructure of the steel. However, some corrosion and stress corrosion cracking scc of dsss have been reported in different pulp mill environments employing caustic solutions.

Hydrogen embrittlement cracking of superduplex steel twi. Actually, the scc of sss might occur even in caustic solutions, when the. By convention, stainless steel is an ironchromium alloy with a chromium content of more than 10. Effect of alloy element contents on caustic stress. Duplex stainless steels are far less prone to this type of corrosion. Singh, effect of welding related microstructure on stress corrosion cracking susceptibility of duplex stainless steels in caustic solutions, nace international, corrosion2006, paper no. Caustic may crack carbon as well as stainless steel.

The higher alloyed duplex stainless steel alloys, ones with significant molybdenum and nitrogen additions, can be superior to 316ss in certain. In this study, the role of material and environmental parameters on corrosion and stress corrosion cracking of duplex stainless steels in caustic. 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. 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. 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. Despite the extensive qualification of inconel for specific applications, a number of corrosion problems have arisen with inconel tubing. 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. Electrochemical behaviour of duplex stainless steels in. Stress corrosion cracking of type 304l stainless steel in sodium sulfidecontaining caustic solutions p. Request pdf corrosion of duplex stainless steels in high ph caustic solution.

Corrosion of duplex stainless steels in high ph caustic. 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 scc tests were conducted by the slow strain rate ssr technique at strain rates ranging from 5. 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. Similar to other duplex stainless steels, duplex 2205 has good oxidation resistance at high temperatures. Stress corrosion cracking of stainless alloys in alkaline. Effect of alloy element contents on caustic stress corrosion. However, many dss grades have been reported to undergo corrosion and stress corrosion cracking in some aggressive environments such as chlorides and sulfidecontaining caustic. Corrosion behaviour of type 316l stainless steel in hot.

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 of welded 2205 duplex stainless steel in sulfidecontaining caustic solution. Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. Stress corrosion cracking was unexpected in austenitic stainless steel aisi 316l, but has on some occasions. Stress corrosion cracking of stainless alloys in alkaline sulfide solutions. Stainless steels are more resistant to general corrosion compared with carbon steel. When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f. The duplex steel exhibited the best performances while the n08904 steel had the worst scc resistance. In the hydroiodic acid at temperatures exceeding 177oc, alloy b2 was sensitive to transgranular stress corrosion cracking. These hightemperature caustic environments are found in the fabrication of alkalis, in oil refineries, in pulp and paper manufacturing and in the 0. Stress corrosion cracking is a form of localized corrosion that will affect metal causing sudden cracks. Stress corrosion cracking scc is the cracking induced from the combined influence of tensile stress and a corrosive environment. Stress corrosion cracking facts and how to reduce the risk. Traditional austenitic steels are found to be more susceptible to such attack however duplex grades are less prone to it.

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 of stainless steels in high. 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. Chloride stress corrosion cracking in austenitic stainless steel. Industrial experience on the caustic cracking of stainless.

Effect of heat treatment on corrosion and stress corrosion. 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. Most notably, pitting and cracking in this instance had initiated andor. Duplex stainless steels dsss have generally performed very well in caustic environments. Figure 1 shows the cracking that occurred on a 6mo super austenitic stainless steel n08367 exposed to 0. Stainless steels are damaged by stress corrosion cracking in conditions containing chlorides at the high temperatures. Various techniques are utilized to grade the steel types considering their resistance to scc and the. 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 an austenitic stainless steel. Investigation of stress corrosion cracking of austenitic, duplex and. The relative superiority of duplex stainless steels dss over austenitic grades with regards to stress corrosion cracking scc is discussed. When sulfides are present in caustic solutions the scc has been reported to occur at lower temperatures. 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. Duplex stainless alloys also show resistance to caustic and caustic cracking.

The impact of scc on a material usually falls between dry cracking and the fatigue threshold of that material. The typical crack morphology for chloride stress corrosion cracking consists of branched transgranular cracks. Microstructural changes during fabrication processes affect the overall scc susceptibility of these steels in caustic solutions. Stress corrosion cracking behavior of nickel base alloys. The duplex stainless steels were developed to exhibit comparable general corrosion resistance as 316ss, but with reduced susceptibility to chloride stress. Corrosion of duplex stainless steels in high ph caustic solution.

The resistance of commercial austenitic, ferritic, and duplex alloys to stress corrosion cracking in a 5% naoh2% na 2 s2% na 2 co 30. These alloys can be candidates for service in caustic exposure when corrosion from cooling waters is a concern. Duplex stainless steel is a practical solution to most 304l or 316l scc failures. Austenitic stainless steels are susceptible to caustic stress corrosion cracking scc above 121c. S31603, astm f8, n08904 and a duplex s31803 stainless steels. The duplex stainless steels were developed to exhibit comparable general corrosion resistance as 316ss, but with reduced susceptibility to chloride stress corrosion cracking. Chloride stress corrosion cracking in austenitic stainless. Stress corrosion cracking and corrosion susceptibility of.

Stress corrosion cracking international institute of. 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. 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. Normally 50 deg c but can occur at lower temperatures around 25 deg c in specific environments, notably swimming pools. Stainless steels types 304 and 316 can be considered resistant below 80 degc, up to the limit of solubility. Only the 25% nickel grades have similar cscc resistance. Unexpected corrosion of stainless steel in high solids. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. Stress corrosion cracking susceptibility scc of the austeniticferritic stainless steels, i.

It has general corrosion resistance similar or better than alloys 304l and 316l but with yield strength nearly double that of austenitic stainless steels. 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. Schematic view of stress corrosion cracking scc and corrosion fatigue cracking. This paper discusses a study of the role of sulfide in caustic solutions on scc of austenitic stainless at t50c. A sandvik grade with very good resistance to this form of stress corrosion cracking is sanicro 28. Duplex stainless steels dss with roughly equal amount of austenite and ferrite phases are being used in industries such as petrochemical, nuclear, pulp and. Stress corrosion cracking of stainless steels in high temperature caustic solutions. The mechanism of scc is shown as a simple representation in figure 1. Although duplex stainless steels offer superior stress corrosion cracking scc resistance in sulfide containing caustic solutions, but may become susceptible to.

It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Unexpected corrosion of stainless steel in high solids black. Singh 1 school of materials science and engineering, georgia institute of technology, 500 10th st. Stress corrosion cracking scc of duplex stainless steel. The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress.

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. 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. The benefits of n to scc resistance of dss are provided. The effects of alloy composition, solution composition, and test temperature on the occurrence of stress corrosion cracking were. 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. 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.