Electrochemical studies of stress corrosion cracking of sensitized aisi 304 stainless steel in polythionic acids s. Cracking seems to have developed after shutdown and exposure to atmosphere. The resistances of aisi 308 and 309 weld metals to polythionic acid intergranular stress corrosion cracking were discussed regarding their use in direct desulfurizing reactors. Both 347 and 321 offer good resistance to polythionic acid stress corrosion cracking, encountered in oil refineries.
Exposure of nonstabilized austenitic stainless steel to temperatures in the sensitizing range will cause the precipitation of chromium carbides at grain boundaries. Why does chloride stress corrosion cracking and pascc only. Pdf stress corrosion cracking of sensitized austenitic. However, in some instances, stabilized austenitic sss have been found to be susceptible to pitting, crevice. These characteristics are consistent with stress corrosion cracking due to polythionic acids. Polythionic acid stress corrosion cracking in heater pipes. Overview of polythionic acid stress corrosion cracking pascc. Weldments may be sensitive to haz intergranular corrosion in oxidizing acid environments, and to polythionic acid stress corrosion cracking.
Ambient temperature stresscorrosion cracking of sensitized stainless steels. Stress corrosion cracking scc may be defined as the delayed failure of alloys by cracking when exposed to certain environments in the presence of a static tensile stress. The stress corrosion cracking sco of sensitized type 304 stainless steel. Stress corrosion cracking issues in syngas plants that may be. Transgranular stress corrosion cracking in type 304 austenitic stainless. The austenitic stainless steel tubes in these services can be susceptible to polythionic acid stress corrosion cracking. Electrochemical characteristics of polythionic acid stress corrosion cracking have been examined mainly on sensitized type 304 stainless steel. Has anyone developed a recommended cleaning, excavation and weld repair procedure. The types 321, 347 and 348 alloys are particularly useful under conditions which cause polythionic acid stress corrosion of nonstabilized austenitic stainless steels, such as type 304. Stress corrosion cracking of sensitized austenitic. I have a large diameter ss304h flange that has several cracks in the process exposed face. The cracks are intergranular and narrow with no significant branching.
Stabilized austenitic stainless steels sss have since been widely used in the petroleum refining industry because of their resistance to sulphidic corrosion and polythionic acid stress corrosion cracking scc, as well as of their excellent strength and toughness. Polythionic acid cracking is a type of intergranular corrosion affecting sensitized stainless steels in refineries processing sulfur containing feedstocks. The commonly used types of stainless steels, 304304h and 316316h are. Examples of polythionic acid scc pascc in a sensitized austenitic stainless steel and caustic scc in carbon steel equipment are presented. Two examples of stress corrosion cracking scc in refinery equipment are presented to highlight the lessons learned to prevent recurrence of such failures.
Experience with polythionic acid stress corrosion cracking in reactor 0707 petroleum 14 feb 07 10. What are the industrial practices being followed in. Polythionic stress corrosion cracking of stainless steel tube environment. Intergranular and transgranular stress corrosion cracking of the aisi 316l stainless steel at polythionic acid environment 8. If the cracking has been correctly diagnosed as chloride stress corrosion cracking, and the problem is confined to small drain, flush fittings, etc. Results show that alloys 304 and 304l, in the solution. Stress corrosion cracking issues in syngas plants that may.
Polythionic stress corrosion cracking of stainless steel tube. Alloy 347347h heat resistant stainless steel plate. It can lead to unexpected sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. It can also be used in chloride or fluoridefree caustic. The high temperature oxidation resistance of 347 is similar to that of 304 stainless steel. This damage mechanism primarily affects standard and high carbon stainless steels, but low carbon and chemically stabilized stainless steels may also be vulnerable under certain conditions. Polythionic acid stress corrosion cracking pascc is an affliction of many. Stress corrosion cracking of sensitized type 304 steel in low temperature borated water has been observed. Polythionic acid stress corrosion cracking deterioration mechanisms heaters used in hydrodesulfurization, hydroforming, hydrocracking, and similar processes often have austenitic stainless steel tubes and usually process reactor feed or recycled gas containing hydrogen sulfide and sulfur compounds. Examples of polythionic acid scc pascc in a sensitized austenitic. It is a very severe, rapid form of intergranular scc that attacks sensitized austenitic stainless steels such a weld hazs in type 304. Cracking of sensitized stainless steels inspectioneering. Ambient temperature stresscorrosion cracking of sensitized. Stress corrosion cracking of sensitized type 304 stainless steel in thiosulfate solutions r.
These acids form during downtime turnarounds after air enters the. Type 304l shares disadvantages of 304h it does sensitize at high temperature, however and can be susceptible to polythionic acid stress corrosion cracking during shut down, especially if the regenerator is water washed. Subsequently, this particular form of intergranular scc was called polythionic acid stress corrosion cracking pascc. During the scc test, the steel specimen was subjected to threepoint bending with constant strain at room temperature, and. Sem fractograph of intergranular scc of type 316 stainless steel in polythionic acid showing brittle features.
The purpose of this paper is to investigate stress corrosion cracking scc for 304, 316, and 321 stainless steels in petroleum. Amine corrosion refers to the general andor localized corrosion that occurs principally on carbon steel in amine treating processes. Scc is highly chemically specific in that certain alloys are likely to undergo scc only when exposed to a small number of chemical environments. The applications for stainless steels in petroleum refining are many and varied. An austenitic stainless steel for sulfuric acid corrosion environments. Samans, stress corrosion cracking susceptibility of stainless steels and nickelbase alloys in polythionic acids and acid copper sulfate solution, corrosion. Influence of cold rolling on sensitization and intergranular. The alloy can be utilized in most diluted organic acids at moderate temperatures and in pure phosphoric acid at lower temperatures and up to 10% diluted solutions at high temperatures. Alloy 347 stainless steel plate resists polythionic acid stress corrosion cracking in hydrocarbon service. In the presence of sulfide corrosion products, such conditions are met during shutdown, when moisture originates from general humidity, washing or steam out and oxygen as air enters the unit upon opening to atmosphere. This paper reports the observed susceptibility of type 304 austenitic stainless steel to stress corrosion cracking in the corrosive media and its high resistance to uniform corrosion of below 0. The drip procedure from the standard test method for evaluating the influence of thermal insulation on external stress corrosion cracking tendency of austenitic stainless steel astm c 69295a was used to research the effect of halogens and inhibitors on the external stress corrosion cracking escc of type 304 stainless steel as it applies to nuclear regulatory commission.
The sensitization curves for solutionannealed wrought stainless steels, which had been held for varying times at temperatures. Effect of polythionic acid concentration on stress. Stresscorrosion cracking of sensitized type 304 stainless steel in thiosulfate solutions r. Sensitization was evaluated by double loop electrochemical potentiokinetic reactivation method and igscc studies were carried out using slow strain rate tests in polythionic acid pta. Stress corrosion cracking scc is the growth of crack formation in a corrosive environment. To add this web app to the home screen open the browser option menu and tap on add to homescreen. Type 321 is a good choice for service in the stressrelieved condition in environments which might otherwise cause intergranular corrosion for unstabilized alloys. Stress corrosion cracking of sensitized austenitic stainless. The alloys 321 and 347 are particularly useful under conditions which cause polythionic acid stress corrosion of nonstabilized austenitic stainless steels, such as alloy 304. Alloy 347 stainless steel plate does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid.
Cracking investigation of a pressure transmitter tapping line. Mar 23, 2010 the purpose of this paper is to investigate stress corrosion cracking scc for 304, 316, and 321 stainless steels in petroleum. Stresscorrosion cracking of sensitized type 304 steel in low temperature borated water has been observed. Stress corrosion cracking behavior of cold worked and sensitized type 304 stainless steel using the slow strain rate test.
Polythionic acid is a generic term used to describe acids of the form h 2 s x o 6. The test solution was prepared by passing sulfur dioxide gas into deionized water for 4 hours and then bubbling hydrogen sulfide for 3 hours. The temperature of the column in the region of the cracking is approximately 70c 158f. Polythionic acid stress corrosion cracking pascc is a type of intergranular stress corrosion that affects sensitized stainless steels in refineries processing feedstocks containing sulphur. Experience with polythionic acid stress corrosion cracking in. In stabilized grades of austenitic steel, titaniumniobium are added which have stronger affinity to form carbides than chromium, thus protecting corrosion resistance.
Polythionic acid stress corrosion cracking pascc is an affliction of many refineries processing sulfur containing feedstocks, and since that is the norm these days, most refiners reduce their susceptibility to pascc by selecting resistant alloys orby neutralizing exposed surfaces during shutdowns. Intergranular stress corrosion cracking scc mechanism in sensitized stainless steel type 304 was investigated experimentally. Based on this analysis the leaks were caused by cracks that initiated on the id surface. Polythionic acid stress corrosion cracking deterioration. Effects of fluoride and other halogen ions on the external. Corrosion behavior of austenitic stainless steel in. Often in many product forms, the grain size and carbon content can meet both the 347s and 347h requirements.
Alloy for resistance to polythionic acid stress corrosion cracking for. Ambient temperature stress corrosion cracking of sensitized stainless steels. Polythionic acid stresscorrosion cracking pascc occurs in refinery units processing sulfurous streams. Stress corrosion cracking behavior of cold worked and. Ae monitoring from various types of stress corrosion cracking scc has been conducted for the past 15 years in our laboratory. Alloy 321 does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid service. Type 321 is a good choice for service in the stress relieved condition in environments which might otherwise cause intergranular corrosion for unstabilized alloys.
Corrosion is not caused by the amine itself, but results from dissolved acid. Polythionic acid stress corrosion cracking pascc occurs in refinery units processing sulfurous streams. Refer also to nace rp0170, protection of austenitic stainless steels and other austenitic alloys from polythionic acid stress corrosion cracking during shutdown of refinery equipment. Results reveal that the stress corrosion life decreases rapidly on increasing the concentration from 0. Are there any methods that can be used to give a 100% picture of the status of the pipes whilst they are mounted in the heater. A tetrathionic potassium k 2 s 4 o 6 chemical solution was used to mimic polythionic acid scc which the most aggressive scc type.
Stress corrosion cracking susceptibility of stainless steels. The probable role of low levels of chloride ions or sulfurcontaining ions is described including the relationship to polythionic acid cracking. It can also be utilized in chloride or fluoride free caustic solutions at moderate temperatures. The stress corrosion cracking scc of a commercial austenitic stainless steel type 316 was investigated as a function of sensitizing temperature 7500 k and test temperature 333373 k. An electrochemical study on stress corrosion cracking of. Polythionic acid stress corrosion cracking pascc occurs in. Alloy 321 stainless steel plate does not perform well in chloride solutions, even in small concentrations, or in sulfuric acid service. The alloys 321 and 347 are particularly useful under conditions which cause polythionic acid stress corrosion of nonstabilized austenitic stainless steel, such as alloy 304. Ahmad 1 oil and natural gas commission, eastern region, sibsagar785640, assam, india. Jan 27, 2020 the alloy can be utilized in most diluted organic acids at moderate temperatures and in pure phosphoric acid at lower temperatures and up to 10% diluted solutions at high temperatures. Resistant to chloride and polythionic acid stress corrosion cracking.
The cracking was found when rust stainingleaks were observed. It has general corrosion resistance similar to the low carbon 304 304l. Anybody aware of any ndt method that can be used to test for the presence of polythionic acid stress corrosion cracking in heatr pipes in a fired heater. Pascc of 304 stainless steel charge heater tubes occurred in a. Type 321 is particularly useful under conditions which cause polythionic acid stress corrosion of nonstabilized austenitic stainless steels such as type 304. Experience with polythionic acid stress corrosion cracking. Effect of polythionic acid concentration on stress corrosion. Type 321ss gave better resistance to scc than 304 and 316 ss in the three. Sensitization and intergranular stress corrosion cracking igscc behavior of deformed aisi 304 prior to aging at temperature 500 c were investigated. Stress corrosion cracking of austenitic stainless steels can occur in refinery environments where chlorides or sulfidic scales exist.
Stress corrosion tests using ubend specimens were carried out in samans solutions containing polythionic acid concentrations from 0. Intergranular cracking tendencies of fourteen stainless steels and two highnickel alloys have been evaluated by exposing numerous specimens to polythionic acid and standard acid copper sulfate solutions. They have high strength, excellent fabrication characteristics, and can readily meet a wide range of design demands load, service life, low maintenance, etc. All of the cracks observed were found underneath the coke deposits. Stressed sensitized 304, 316, and 321 stainless steels were selected and subjected to various environments that. A hydrotest at 735 psi revealed numerous leaks in four tubes from a heater. Stresscorrosion cracking of sensitized type 304 stainless.
Ctlpolythionic stress corrosion cracking of stainless. Alloy 321 resists polythionic acid stress corrosion cracking in hydrocarbon service. Severe stress corrosion cracking was observed in the csbp ltd, western australia 304l unlagged stainless steel absorber column of a nitric acid plant after 15 years of plant operation. Stress corrosion cracking susceptibility of stainless. In each failure analysis case study, the cracking is characterized using various metallurgical laboratory techniques, including metallography and fractography, in. Nace sp0170, protection of austenitic stainless steels and other austenitic alloys from polythionic acid stress corrosion cracking during a shutdown of refinery equipment, nace international, houston, tx. Failure of 321 stainless steel heater tube in heavy crude oil.
Stainless steel 321 tubes opposes polythionic acid stress corrosion cracking in hydrocarbon service. Pascc of 304 stainless steel charge heater tubes occurred in a naphtha hydrotreater during shutdown, after about 18 years in service. Pdf polythionic acid corrosion in refinery hydroprocessors. Presence of cr, carbon, exposure temperatures and presence of polythionic acids play an important role in stress corrosion cracking. This paper discusses ae results of activepath dissolutiontype scc of austenitic stainless steel in chloride solution and fused salt, fluoride and polythionic acid solutions, brass. However, it is subject to carbide precipitation in the heat affected zone haz of welds. The importance of a conjoint action of corrosion and stress as well as the nature of. How to weld repair 304h flange that has scc due to. Pdf stress corrosion cracking of sensitized austenitic stainless. Then, the stress corrosion cracking mechanism for various materials in conditions that are susceptible is discussed in detail. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Investigations were made to see the effect of mild to severe deformations ranging from 0 to 80% reduction in thickness on lowtemperature sensitization. However, to avoid scc in austenitic ss steels, exposure to conducive environment polythionic acid formation in presence of oxygenwaterchlorides along with metal sulfidesh2s to be reduced by adopting. Exposure of nonstabilized austenitic stainless steel pipe to temperatures in the sensitizing range will cause the precipitation of chromium carbides at grain boundaries.
In this chapter, the conditions for the occurrence of scc are first introduced. On the mechanism of intergranular stress corrosion. Electrochemical studies of stress corrosion cracking of. This damage mechanism primarily affects standard and high carbon stainless steels, but low carbon and chemically stabilized stainless steels may also be.
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