The chief applications of hastelloy alloys are in the presence of hot chloride solutions. One of our 2000 liter tanks has been found with a large discoloration on the tanks sidewall. Pitting or crevice corrosion can occur on most stainless steel grades. Stainless steels are more resistant to general corrosion compared with carbon steel. Carbon steel in caustic service corrosion engineering. Resistance of the ati 904l alloy is further aided by presence of 4. Chloride stress corrosion is a type of intergranular corrosion and occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions, and high temperature. Corrosion of stainless steel by hot caustic research using solutions of chemically pure caustic sodium hydroxide naoh led to the development of a diagram that attempts to delineate the param eters of concentration and tem perature governing stress corrosion. Through an investigation of the field failure analysis and laboratory experiment, a study on stress corrosion cracking scc behavior of steel and aluminum was performed. This form of corrosion is controlled by maintaining low chloride ion and oxygen content in the environment and use of low carbon steels.
Improved resistance to caustic stress corrosion cracking can be given to inconel by heat treating it at 620 o c to. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. These alloys can however suffer from caustic stress corrosion cracking at caustic concentrations above 70% at temperatures above 290crmo c 550f. Improved resistance to caustic stress corrosion cracking can be given to inconel by heat treating it at 620 o c to 705 o c, depending upon prior solution treating temperature. Similar but accelerated laboratory test was subsequently conducted in such a way as to mimic the field failures. It is used in metal degreasing and cleaning processes in a wide range of industry applications. A discussion started in 2003 but continuing through 2019. Overview the temperatures required to produce fully oxidized white liquor are capable of causing stress corrosion cracking scc on the 300 series of austenitic stainless steels 304l316l.
It may occur in equipment of carbon steel, low alloy steel, ferritic steel. Stress corrosion cracking of steel and aluminum in sodium. Aug 18, 2008 naoh is attacking 316 stainless steel tank. Stress corrosion cracking of 316 stainless steel in. Caustic embrittlement or caustic cracking occurs when the alloy material cracks under the action of tensile stress and corrosion medium in alkaline solution. Corrosion of duplex stainless steels in high ph caustic.
Discussion caustic stress corrosion cracking of steels is one of the oldest known forms of scc, dating back to the days of the early steam locomotives, when it was responsible for countless explosions of riveted boilers trethewey et al. Inverted stainless steel funnels were welded to the. Mild steel corrosion and caustic cr4 discussion thread. Residual sodium carbonate, which is used for the softening process, undergoes hydrolysis, forming sodium hydroxide at high pressures and temperatures. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. There is caustic stress corrosion cracking when carbon steel is exposed to concentrated caustic solution. No evidence of caustic cracking was found in the stress corrosion tests for. Austenitic stainless steels are known to be susceptible to caustic stress corrosion cracking scc above approximately 121c. 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. Localized corrosion, mostly pitting, took place when the caustic soda solutions became dilute. Risk of stress corrosion cracking attack caustic stress corrosion cracking occurs at higher temperatures than chloride stress corrosion cracking which can occur at temperatures as low as 60 degc. Stress corrosion cracking of type 304l stainless steel in.
As with other forms of stress corrosion cracking, caustic cracking will occur only when. 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. Greg murphy engineer brisbane, queensland, australia. Stress corrosion cracking scc is the formation and growth of crack. Selection stainless steel for handling sodium hydroxide. 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. Caustic embrittlement focuses on the stressed parts of the boiler, including cracks, bends, rivets and joints. Specialized corrosion doehdbk1015193 corrosion ch02 rev. Percentage elongation and reduction in crosssectional area were used to investigate the scc of the steel.
It was later known as stress corrosion cracking which is in turn replaced by caustic cracking. In these media, many stainless steel grades suffer from crevice corrosion, pitting corrosion and stress corrosion cracking. Stress corrosion cracking scc tests were conducted by the slow strain rate ssr technique at strain rates ranging from 5. It is used in metal degreasing and cleaning processes in a wide range of industry applications stainless steel types 304 and 316 can be considered resistant below 80 degc, up to the limit of solubility both 304 and 316 stainless steel types are resistant to a wide range of. Caustic embrittlement is also known as stress corrosion cracking. Caustic embrittlement was first used to describe the cracking of riveted mild steel boiler plates due to local deposition of concentrated hydroxide at temperatures of 200 to 250 o c 400 to 480 o f. Stress corrosion cracking of 316 stainless steel in caustic solutions. Caustic stress corrosion cracking inspectioneering. For this reason pure nickel is generally specified for heating coils, even in tanks for 50% caustic. The important general point is that those environments that cause stress corrosion are frequently highly specific to the particular. Caustic cracking of pressure vessels mainly occurs in steam and other places prone to repeated evaporation and concentration or in hightemperature vessels in contact with caustic soda. 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. Thus, the addition of caustic soda to boiler feed waters to reduce the corrosiveness of the latter towards mild steel can result in the form of stress corrosion frequently referred to as caustic cracking. Mar 04, 2019 caustic alkali generally refers to caustic soda and caustic potassium, namely sodium hydroxide and potassium hydroxide.
However, when sulfides are present in caustic solutions the scc of austenitic stainless steels has been reported to occur at lower temperatures. Store in cool, dry conditions in well sealed containers. Published corrosion rates for steel in pure caustic at the elevated. There is an additional risk of stress corrosion cracking scc at. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Austenitic stainless steels suffer from scc in chlorides, caustic, and polythionic acid. Jenkins westinghouse savannah river company aiken, south carolina, usa, 29808 abstract solution chemistry of wastes from us atomic weapons production is controlled to inhibit corrosion of carbon steel tanks used in containment and storage. Stress corrosion cracking of stainless steels in high.
Risk of stress corrosion cracking attack caustic stress corrosion cracking occurs at higher temperatures than chloride stress c orrosion cracking which can occur at temperatures as low as 60 degc. Rebak october 11, 2005 corrosion 2006 conference and exposition san diego, ca, united states march 12, 2006 through march 16, 2006. The rate of corrosion may further be affected by the presence of sulfide ions in caustic solutions. Pitting corrosion has been reported from household bleach spills on stainless steel 304 type sinks in domestic environments.
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 stainless steels in high temperature caustic. The stress corrosion cracking scc behaviour of medium carbon steel mcs in caustic soda, potash and a mixture of these reagents was studied by fracturing this material on a tensometer after every seven days of immersion in these media. The intersection of the naohho boiling point curve with regions of caustic scc are. The useful safe limit of carbon steel is approximately 150of65oc, both with re. Corrosion of carbon steel in hot naoh solutions under heat. Mild steels steels with low carbon and low alloy content and stainless steels will. The duplex steel exhibited the best performances while the n08904 steel had the worst scc resistance. Carryover of caustic soda naoh in the steam path caused. Carbon steel was fairly passive in naoh solutions of 0.
Stress corrosion cracking of 304l stainless steel in. Pdf a case study on caustic corrosion in refinery piping. The mechanism is similar to that of chloride stress corrosion. Which alloy material is most resistant to caustic soda. Stainless steel types 304 and 316 can be considered resistant below 80 degc, up to the limit of solubility. The corrosion behavior of carbon steel, austenitic stainless steels, nibase alloys, and nickel in hot, concentrated caustic soda solutions at the active potential range was investigated. So, lack of pwht will increase susceptibility, mostly from residual tensile stresses, and not just hardness. Improved resistance to caustic stress corrosion cracking can be given to inconel by heat treating it at 620oc to 705oc, depending upon prior solution treating temperature. Stress corrosion cracking behavior of nickel base alloys. Resistance to chloride stress corrosion cracking is correlated with nickel content, with the 25% nickel ati 904l alloy, showing improved resistance compared to an 8% nickel alloy like type 304 stainless steel.
Nicrmo alloys the nicrmo alloys are particularly resistant to the insidious and unpredictable forms of corrosion caused by chlorides. The useful safe limit of carbon steel is approximately 150of65oc, both with regard to caustic stress corrosion cracking cscc and corrosion. Despite the extensive qualification of inconel for specific applications, a number of corrosion problems have arisen with inconel tubing. Alloy 400 n04400 and alloy 600 n06600 also have excellent stress corrosion resistance. We use a lot of 316l stainless steel in our processes. The caustic naoh solution will be stored in the tanks at 70 c, and at 300 gl, which are made out of mild steel as149. Caustic cracking of stainless is characterized by a gunmetal blueing effect, obvious on visual examination. Caustic stress corrosion cracking is a form of degradation that is caused when a. Most caustic soda is produced as a coproduct in the production of chlorine by the.
Stainless steels have useful general corrosion resistance in a broad range of conditions, but are also sensitive to caustic stress corrosion cracking cscc at. It may occur in equipment of carbon steel, low alloy steel, ferritic steel and austenitic stainless steel in contact with caustic soda. When sulfides are present in caustic solutions the scc has been reported to occur at lower temperatures. Caustic scc is driven by tensile stress, susceptible material and concentration of caustic. Pdf caustic soda is used in several refinery processes, for example in. 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. Failure of carbon steel piping by caustic stress corrosion cracking embrittlement and caustic gouging has been a recurring problem, several repairs attempts were made without success using patch. The duplex steel exhibited the best performances while the n08904. The area of risk in sodium hydroxide is shown on the isocorrosion diagram by the area bounded by a green line. These alloys can be candidates for service in caustic exposure when corrosion from cooling waters is a concern. On the active dissolution of metals and alloys in hot. S by means of potentiostatically controlled slow strain rate testing techniques ssrt. Rebak october 11, 2005 corrosion2006 conference and exposition san diego, ca, united states march 12, 2006 through march 16, 2006.
Selection of stainless steels for handling sodium hydroxide naoh. Chromium induces passivation in oxidizing acids, as it does in the stainless steels. How to avoid caustic cracking of carbon steel and low. Caustic soda cargo handbook the worlds largest cargo. Unexpected corrosion of stainless steel in high solids.
Improved resistance to caustic stress corrosion cracking. There can be a risk of stress corrosion cracking scc attack at higher temperatures, which is common to both the 304 and 316 types. Fracture mechanics techniques were used to study the kinetics of stress corrosion. What i am asking is whether caustic embrittlement and stress corrosion cracking will be a issue with the caustic at this temperature and concentration. The corrosion rate obtained in the boiling solution was larger than that in the hydrogensaturated solution of the same concentration and temperature in all. 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. All samples were extracted from known operating conditions from the field failures. Stainless steel is susceptible to stress corrosion cracking and also to general corrosion in hightemperature concentrated caustic. Hastelloy c276 has minor corrosion rates in reducing and oxidizing conditions. Stress corrosion cracking of 304l stainless steel in sodium. A nace task group found little difference between the corrosivity of caustic soda made by the diaphragm cell figure 1 relation of temperature and concentration of sodium hydroxide to cause stress cracking of carbon steel. How to avoid caustic cracking of carbon steel and low alloy. Singh 1 school of materials science and engineering, georgia institute of technology, 500 10th st.
The area of risk in sodium hydroxide is shown on the iso corrosion diagram by the area bounded by a green line. It is used in metal degreasing and cleaning processes in a wide range of industry applications stainless steel types 304 and 316 can be considered resistant below 80 degc, up to the limit of solubility both 304 and 316 stainless steel types are resistant to a wide range of concentration and temperature. Carbon steel in caustic service corrosion engineering eng. Stainless steel is susceptible to stresscorrosion cracking and also to general corrosion in hightemperature concentrated caustic. Selection stainless steel for handling sodium hydroxide naoh. Potassium hydroxide koh stress corrosion cracking scc caused failure of a type 304l uns s30403 stainless steel bypass in a steam methane reforming unit. Industrial experience on the caustic cracking of stainless. In alkaline solutions, the concentration of hydrogen ions is usually low and the corrosion rate in chemical media usually decreases with the increase of ph value. Naoh and carbon steel corrosion engineering engtips. Stress corrosion cracking of type 316 stainless steel in. Stresscorrosion cracking scc is a term used to describe service failures in engineering materials that occur by slow, environmentally induced crack propagation. Stress corrosion cracking of stainless steels in high temperature.
Discussion caustic stress corrosion cracking of steels is one of the oldest known forms of scc, dating back to the days of the early steam locomotives, when it was responsible for countless explosions of riveted boilers trethewey et. Corrosion of stainless steel by hot caustic research using solutions of chemically pure caustic sodium hydroxide naoh led to the development of a diagram that attempts to delineate the param eters of concentration and tem perature governing stress corrosion cracking scc of type. I am a technical services scientist at a vaccine production facility. 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 type 304l stainless steel in sodium sulfidecontaining caustic solutions p. Other problems that have been observed with inconel include wastage, tube denting, pitting, and intergranular attack.
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