High concentration caustic solutions are known to cause stress corrosion cracking in carbon steel at elevated temperature. 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. In this study, the role of material and environmental parameters on corrosion and stress corrosion cracking of duplex stainless steels in caustic. Stress corrosion cracking facts and how to reduce the risk. Most of those who own solid stainless steel equipment operating in the cui temperature range are likely to experience ecscc at some point. The environmental factors that increase the cracking susceptibility include higher temperatures, increased chloride content, lower ph, and higher levels of tensile stress. Stainless steels are more resistant to general corrosion compared with carbon steel.
Presence of caustic in a specific range of concentrations. The temperature is around 600700c and the corrosion can be coal ash corrosion or oil ash corrosion. In the case of coal ash, a low melting salt, na,k3fe so 4 3, is produced. However, high corrosion rates will occur if tantalum is used in caustic applications such as sodium hydroxide, even at room temperature. 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 scc tests were conducted by the slow strain rate ssr technique at strain rates ranging from 5. It becomes increasingly more corrosive with increasing temperature and concentration.
Stress corrosion cracking international institute of. Generally, the corrosion resistance of caustic soda usually increases with the increase of nickel content. Stress corrosion cracking of carbon steel in carbonate solutions. Environments that may cause stress corrosion cracking in nickel alloys include hot caustic solutions, high temperature water and hot and wet hydrofluoric acid. Austenitic alloys tested included type 300 series stainless steels, monel alloy 400, inconel alloys 600, 625, 690, incoloy alloys 800, 804, 825, hastelloy alloy c, and nickel 201. Stress corrosion cracking the international institute of. Stress corrosion cracking scc is characterized by cracks propagating either. 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.
Corrosion by caustic sodium or potassium hydroxide at all concentrations is easily handled at room temperature with a variety of metals and alloys, including carbon steels. Stress in the metal above some level generally undefined. The stress corrosion cracking behavior in caustic solutions 200 gl sodium hydroxide, 10 gl sodium chloride of three austenitic 18cr10ni2. Corrosion resistance the primary driver for specifying a stainless steel basically, candidate materials must resist corrosion in the service environment 2. In many ways, caustic scc of stainless steel represents a forgotten phenomenon, since it was researched, studied and quantified in the 60s and 70s. As with other forms of stress corrosion cracking, caustic cracking will. 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. Caustic stress corrosion cracking cscc is a failure mechanism affecting both the carbon and austenitic stainless steels. This means that all environments do not cause scc on all of the alloys. In the case of superheater or reheater tubing, liquid ash can also cause corrosion, leading to tube thinning and stress rupture failure. Figure 2 illustrates the resistance of 300 series stainless steels in pure caustic. External chloride stress corrosion cracking ecscc is a specific form of cui that occurs in austenitic stainless steels 300 series ss.
Caustic stress corrosion cracking inspectioneering. For cscc to cause a failure, a number of factors and conditions must be. Stress corrosion cracking scc is the formation and growth of crack through materials subjected to tensile stress and a specific corrosive medium. Stress corrosion cracking of stainless steels in high. At higher temperatures, stress corrosion cracking and corrosion fatigue are possible. Caustic stress corrosion cracking creative engineers, inc. Both 304 and 316 stainless steel types are resistant to a wide range of concentration and temperature. Metalenvironment combinations susceptible to cracking are specific. Mechanical propertiesalong with alloy strength, consider hardness, fatigue, impact and stressrupture properties selectaloy method.
Chloride stress corrosion cracking in 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. 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. Anodic polarization, curves at selected temperatures, 316 stainless steel rod. This due to high concentration of the caustic soda added to the boiler water to control ph ph 9. Prediction of stress corrosion cracking in 10% caustic soda solutions at 315 c. Caustic stress corrosion tests for the lltr technical report. Over the range of temperature, caustic concentration and heating rate tested the stainless steel stressed to 90% of yield or above suffered cracking. Stress corrosion cracking of stainless steels in high temperature.
This calculation establishes the conditions where heat of dilution will not cause the solution temperature concentration to exceed the boundary for stress corrosion cracking as established by nace international. Stress corrosion cracking and hydrogen embrittlement of high. Consequently, caustic corrosion called caustic embrittlement more accurately, a specific kind of stress corrosion cracking was engendered on the carbon steel tubes under both concentrated naoh and tensile stress because the operational pressure of the tube side was larger than the shell side, and corrosion products including na 3 feo 3, na. Deaeration increased the corrosion rate of type 316l stainless steel in hot caustic naoh environment, but exposure to 30 wt% naoh at rt showed the opposite trend. 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. For cscc to cause a failure, a number of factors and conditions must be present in the correct amounts. 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.
Which alloy material is most resistant to caustic soda. Introduction stress corrosion cracking scc of austenitic 304 stainless steel in chloride environment is a common problem in industries. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. Stress corrosion cracking behavior of alloy 600 coupled to.
Stress corrosion cracking of duplex stainless steels in. From observations of the characteristics of nitrate and hydroxide solutions, known to promote stress corrosion cracking scc in carbon steels, and from the form of potentiodynamic polarization curves and the structural dependence of the corrosive attack, it was predicted that carbonate solutions would also produce intergranular stress corrosion in carbon steels. Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. Stress corrosion cracking susceptibility and general corrosion are reported. Stress corrosion cracking caustic embrittlement of super. Hydrogen stress cracking is the same mechanism that is responsible for sulfide stress corrosion cracking in wet h. Other problems that have been observed with inconel include wastage, tube denting, pitting, and intergranular attack. Stress corrosion cracking of stainless steels in high temperature caustic solutions. Another source suggests that the corrosion rate of alloy 800 in boiling 50 % caustic 300 o f148 o c is excessive 39 mpy. Caustic corrosion an overview sciencedirect topics.
A summary of the temperatures and caustic concentration ranges that can result in caustic scc for carbon steel and type30 stainless steel is given in figure 1. Also the temperature, the oxygen and chloride contents and the presence of any. This is a type of deterioration which can be linked to corrosion and corrosion control processes. As a general rule, the resistance to caustic solutions increases with increasing nickel content. It may exhibit a higher temperature limit, based on cscc. Stress corrosion cracking behavior of nickel base alloys. Stress corrosion cracking behavior of alloy 600 coupled to magnetite under high temperature caustic conditions geun dong song, jeoh han, soonhyeok jeon and do haeng hur korea atomic energy research institute, 989111 deadeokdaero, yuseonggu, daejeon 34057, korea correspondence.
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. Stress corrosion cracking testing of inconel alloys 600 and 690 under hightemperature caustic conditions. Oct 20, 2019 the exposure temperature is a key parameter in the performance of type 316l stainless steel in caustic environments, affecting the length of the passive domain and corrosion rate. The 300 series of ss also suffer caustic cracking at temperatures above 100c. 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. Rebak october 11, 2005 corrosion 2006 conference and exposition san diego, ca, united states march 12, 2006 through march 16, 2006.
There can be a risk of stress corrosion cracking scc attack at higher temperatures, which is common to both the 304 and. Below 80 degc they can be considered resistant to any concentration of sodium hydroxide, up to the limit of solubility. 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. 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. Notable in table 2 are the relatively high chromium content of g30 alloy and the relatively high molybdenum content of g50 alloy. Pdf stress corrosion cracking scc of nickelbased alloys. The ni alloys such as c276 n10276 also have useful caustic cracking resistance, however are susceptible to caustic cracking at high concentrations and temperatures. Corrosion behaviour of type 316l stainless steel in hot.
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. 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. Industrial experience on the caustic cracking of stainless. Mar 04, 2019 caustic embrittlement or caustic cracking occurs when the alloy material cracks under the action of tensile stress and corrosion medium in alkaline solution.
Stress corrosion cracking scc or environmentally induced cracking. In alkaline media, the most commonly used nickel alloys are nickel 200201, monel 400, nickel 600 and 625. Stress corrosion cracking is the cracking of a susceptible metal under the mixed. The highstrength, precipitationhardening, stain less steels have varying degrees of resistance to stress corrosion cracking and. Caustic cracking of carbon steel occurs over a wide range of caustic. Stress corrosion behavior of fecrni and other alloys in. Stainless steels have useful general corrosion resistance in a broad range of conditions, but are also sensitive to caustic stress corrosion cracking cscc at temperatures above about 200 f. It can lead to unexpected sudden failure of normally ductile metals. Stress corrosion cracking scc or called as environmentally assisted cracking eac may take place at the electrochemical potential range. These alloys can however suffer from caustic stress corrosion cracking at caustic concentrations above 70 % at temperatures above 290crmo c 550f. The resistance of various commercial alloys to stress corrosion cracking scc in 50% naoh has been evaluated at temperatures in the range 284 to 332 c. When stainless steels are fully immersed, it is rare to see chloride stress corrosion cracking at temperatures below 60 c 150 f. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. Stress corrosion cracking of stainless steel components in.
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