Chlorides can be introduced into the system through the feed andor through the makeup hydrogen gas. A lesser understood and, at times, more menacing aqueous corrosion problem in these units has been due to chloride salts. Unfortunately, many common alloys such as common austenitic stainless steels are not suitable replacements because they are susceptible to chloride stress corrosion cracking ciscc in these environments 7. Certain austenitic stainless steels and aluminium alloys crack in the presence of chlorides. This is collated information from various sources but is of limited quality. Deterioration by clscc can lead to failures that have the potential to release stored energy andor hazardous substances. The combined action of tensile stress with corrosive environment can lead to chloride stress corrosion cracking cscc. Corrosion resistance and cryogenic toughness of stainless steels. Copper alloys can also suffer stress corrosion cracking and other forms of attack in ammonia service.
Stress corrosion cracking studies of austenitic stainless. All concentrations are given in weight% and the solvent is water. I am specifying pipes for a water system with 500 ppm chloride in solution. 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. Material corrosion resistance guide fluid technology. Pdf effect of temperature and concentration of ammonium. The effect of varying the temperature and the concentration of ammonium nitrate solution on the stress corrosion cracking scc susceptibility of mild steel is studied. Assessment of stress corrosion cracking susceptibility for austenitic stainless steels exposed to atmospheric chloride and nonchloride salts nuregcr7170. It occurs in austenitic stainless steel under tensile stress in the presence of oxygen, chloride ions and high temperature. High residual or applied stress, temperature above 6571c 150160f and chlorides increase the likelihood of cscc.
This mode of attack is termed stress corrosion cracking scc. Effect of ammonium bisulphite and chloride on the pitting and stress corrosion cracking resistance of super duplex stainless steel pipes under combined internal. Chloride stress corrosion cracking of austenitic stainless. This limits the usefulness of austenitic stainless steel for containing water with higher than a few ppm content of chlorides at temperatures above 50 c. This report documents the results of a systematic study on the stress corrosion cracking scc susceptibility of austenitic stainless steel exposed to these. A stainless steel seems like a better choice for this application. Ordinarily we would specify 316l stainless steel to limit the corrosion, but i was asked if we could instead specify carbon steel pipe with a corrosion allowance. Chloride stress corrosion cracking clscc is a type of stress corrosion cracking scc and is one of the most well known forms of scc in the refining and chemical processing industries. Ammonium bisulfide has been the well known main culprit of aqueous corrosion in hydroprocessing units. When wet ammonium chloride salt is present, the corrosion rate of carbon steel is generally considered unacceptably high. Investigation of the effect of low temperature aging on the mechanical properties and susceptibility to sulfide stress corrosion cracking of 22%cr duplex stainless steel author links open overlay panel s. Pitting corrosion of a stainless steel is illustrated in the figure 1. So instead of the typical schedule 40 pipe, could i. The standard 304304l and 316316l grades are most susceptible.
In all cases of failure by stress corrosion cracking, the following three factors must be present. Chloride corrosion of carbon steel pipe engineering. Among corrosion phenomena and degradation mechanisms are high temperature sulfidation, high temperature hydrogen attack, ammonium bisulfide corrosion, sulfide stress cracking, ammonium chloride corrosion, chloride stress corrosion cracking ciscc, and embrittlement of low alloy steels. Corrosion resistance table of stainless steel nickel monel iconel the table below indicates the approximate corrosion resistance of selected corrosion resistant metals to a range of common chemicals. Effect of ph and chloride concentration on the corrosion of duplex stainless steel. Corrosion of carbon steel and alloys in concentrated. This study evaluated the stress corrosion cracking scc susceptibility of asreceived and sensitized type 304 stainless steel exposed to ammonium nitrate mixed with sodium chloride salts. Mild steel cracks in the presence of alkali boiler cracking and nitrates. Chloride stress corrosion cracking in austenitic stainless. Increasing nickel content above 18 to 20% or the use of duplex, or ferritic stainless steels improves resistance to cscc.
The austenitic stainless steels are impact tough at cryogenic temperatures. Investigation of the effect of low temperature aging on. These corrosion data are mainly based on results of general corrosion laboratory tests, carried out with pure chemicals and water solutions nearly saturated with air the corrosion rate can be quite different if the solution is free from oxygen. The rate of corrosion depends on the type of metals that come into contact with these chlorides. Prediction, monitoring, and control of ammonium chloride. Austenitic stainless steel may be susceptible to chloride stress corrosion cracking cscc. Chloride stress corrosion cracking inspectioneering. What is temperature it is more important than concentration of chloride and anything higher than room temperature higher is worse. Copper heaters will react with the salt water and turn the pool green.
Effect of ammonium bisulphite and chloride on the pitting. From the same topic i can quote stainless steels the three conditions that must be present for chloride stress corrosion to occur are as follows. Carbon steel, alloy steel, and highstrength, quenched and tempered steel, when under applied or residual stress and especially when cold formed andor welded without subsequent thermal stress relief, are subject to failure by stresscorrosion cracking scc in aircontaminated dry ammonia. Ammonium chloride corrosion is characterized by general or localized corrosion, often pitting, normally occurring under ammonium chloride or amine salt deposits, and often in the absence of a free water phase. Corrosion resistance and the behavior of carbon steel and alloys in high concentration ammonium chloride nh4cl solutions were investigated. What is the maximum chloride in ppm that can be allowed in. Selection of stainless steels for handling ammonia nh3. Corrosion under insulation cui is a severe problem for 304 stainless steel pressure vessel. Immersion tests were performed under boiling 20 wt% and 40 wt% nh 4cl solutions. Ammonium chloride n f f n f g g g 210s 210 210 g n g g. Copper alloys can be attacked by carbon dioxide depending on what oxidants, including dissolved oxygen, are present.
The combination of tensile stress and a specific corrosive environment can crack stainless steels. Corrosion resistance table of stainless steel nickel monel. The actual pitting corrosion phenomenon is shown on propeller shaft of high speed craft, and the pit depth was measured with dial. The intergranular corrosion of a sensitized steel can be insidious, in that after such attack the steel. The most common environmental exposure condition responsible for scc of stainless steels is the presence of chlorides. Chloride ions are present in the environment dissolved oxygen is present in the environment metal is under tensile stress austenitic stainless steel is a nonmagnetic alloy consisting of iron. Ammonia is not corrosive for stainless steel without presence of water or condensate. This paper described the mechanism of chlorideinduced stress corrosion cracking of oil tube as a result of. What is the minimum concentration of chloride ion required. This study was conducted to better understand material performance in severe nh 4cl corrosive environments in refineries. Chloride stress corrosion cracking cscc is a type of intergranular corrosion.
The susceptibility of the 300series stainless steels to stress corrosion cracking in aqueous ammonium chloride solutions was determined by exposing highly stressed, sensitized wires to the test solution and recording the time to failure. Since automobiles are made of steel or various alloys and aluminum, magnesium or a combination, the corrosive effects are varied and one needs to consider proper coatings. Ammonium chloride these corrosion data are mainly based on results of general corrosion laboratory tests, carried out with pure chemicals and water solutions nearly saturated with air the corrosion rate can be quite different if the solution is free from oxygen. Effect of ph and chloride concentration on the corrosion. Stresscorrosion cracking of steels in ammonia with. Application of duplex stainless steel in the chemical. The main issue is the cryogenic toughness of stainless steels at around 40 degc, compared to carbon steels, which can also be considered for ammonia service under these conditions. The salts have a whitish, greenish or brownish appearance. Corrosion resistance and the behavior of carbon steel and alloys in high concentration ammonium chloride nh 4cl solutions were investigated. Ammonia stress corrosion cracking is a form of stress corrosion cracking that commonly occurs in brass tubes in cooling water service that has been contaminated with ammonia due to biological growths or other contamination. Nace 2014 paper scc of type 304 stainless steel exposed.
Methods of minimizing chloride stress corrosion cracking. It can be detrimental to austenitic stainless steels, one of the main reasons these steels are not considered a cureall for corrosion problems. Salt water pools are high in free chlorides, which will cause chloride stress corrosion cracking in stainless steel heaters. This study is to identify factors responsible for loss of production due to problems in plant and equipment. This cracking can also occur when ammonia is intentionally added to process streams as a neutralizer by someone unaware of its potential effect on brass tubes. Ammonium chloride corrosion in hydrotreating units description of damage. Ammonium hydroxide stainless steela ahow good resistance to all concentrations of ammonia. Laboratory stress corrosion cracking examinations by means of drop evaporation tests det showed that duplex stainless steels have a better stress corrosion cracking resistance in alkaline chloride containing solutions than highnickel alloys. Chloride stress corrosion involves selective attack of a metal along its grain boundaries. Welding operations, for example, may leave an area near the welds in such a corrosionsusceptible or sensitized condition.
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