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HomeHomeDiscussionsDiscussionsMaterial Select...Material Select...why ASTM A312 TP 304 pipe used for dimeneralised waterwhy ASTM A312 TP 304 pipe used for dimeneralised water
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6/24/2005 9:00 AM
 
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I have following technical querries, can anybody help me resolve this. 1. Recently we have used ASTM A312 TP 304 SS pipe for dimeneralised water in our butadiene plant piping. Question is why TP 304 pipe used for DM water ?? what will happen if we use A106 grade B or A312 TP304L pipes for this service. Is it something to do with chloride stress corrosion cracking, can anybody explain what is chloride stress corrosion cracking. Please note dimineralised water is slightly acidic i,e PH value is less than 7. 2. Can anybody tell me what is NACE piping, for what all fluid service NACE rules are applicable ?? What is the difference between simple ASTM A 106 grade B pipe & A 106 grade B NACE pipe ?? what are the additional test requirement for NACE pipe? 3. What is the role of Carbon content in ASTM A 312 TP 304 & A 312 TP 304L, we know that carbon content in TP304 is 0.03 wt % whereas carbon content in TP304L is 0.08%, what impact less carbon will have on material properties ?? Does less carbon improve the material strength ?? Narayan Acharya Piping Engineer Mumbai India
 
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6/24/2005 9:00 AM
 
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Narayan You are making some mistake on carbon content of SS TP304. TP 304 has a carbon 0.08 max. wile TP 304L is the low carbon grade with a carbon 0.035 max. Because of its lower carbon, TP 304L is less susceptible of carbides precipitation on grain boundaries and for this reason more resistant to CSCC than TP304 A106 Gr B is not good for use in Demineralised water services. The difference between A106 Gr B and A106 Gr B NACE is the carbon content “Chloride SCC One of the most important forms of stress corrosion that concerns the industry is chloride stress corrosion. 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. It is thought to start with chromium carbide deposits along grain boundaries that leave the metal open to corrosion. Maintaining low chloride ion and oxygen content in the environment and use of low carbon steels controls this form of corrosion.” Regards Luis Marques
 
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6/24/2005 9:00 AM
 
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Generally 304 piping is used for DM water. The reasons for this usage in DM water is - DM water is a very good solvent and will corrode the CS. The corrosion rate is not important. However, by this process DM water will be degraded. Also, if any O2 or CO2 absorption has taken place in DM water, it will become quite corrosive. SS 304 L piping is much costlier and generally not reqd (not a service requirement). Sensitization is the precipitation of Cr rich carbide (M23C6) at grain boundaries, when heated betn 450-650 C as happens during welding etc. NACE piping are for application in H2S & Sour water service etc. where service induced cracking chances are high. Generally these NACE piping has much stringent controls S&P. 'Hope it helps Regards
 
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6/25/2005 9:00 AM
 
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DM Water is often callled 'Hungry Water" as it invites metals in it. Normal carbon steel easily looses it's elements in DM Water because of poor corrosion stability and hence SS used. Even in SS you have to maintain a minimum flow rate and if there is any stagnancy SS can also get pitted and punctured due to local concentration cell. with compliments to Luis and Chakra
 
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