Selected Answers

From luiz de miranda of ECOPROTEC on February 2, 2015:
Alfredo’s case study is very impressive. Here in B ...read more Alfredo’s case study is very impressive. Here in Brazil,the number of like phenomena is enormous, notably at welding junctions. I support the avoidance of  stainless steel's "fetishism." Coatings based on niobium pentoxide applied on mild steel prevent a large number of corrosion problems.

From Tom Schwerdt of Active Transportation Advocates on January 30, 2015:
Alfredo, the result you saw does not surprise me a ...read more Alfredo, the result you saw does not surprise me at all. 304 is unsuitable for marine exposure, particularly if it is welded.

From Alfredo Claussen of Instituto Mexicano del Petroleo on January 26, 2015:
Years ago,we saw several stainless steel type 304 ...read more Years ago,we saw several stainless steel type 304 vessels (packed towers) that were installed on an offshore platform in Campeche Bay, Mexico that got terrible pitting and even tunneling corrosión in the moist, tropical air, WITHOUT being used at all! The platform developed structural problems and was abandoned for several years, and the towers were never filled with process fluid. Therefore, beware of  marine environment effects on type 304 SS.

From William Slama of International Paint/Ceilcote Products on January 26, 2015:
In our experience, most stainless steel vessels ha ...read more In our experience, most stainless steel vessels have been coated because the chemical service proved to be too severe for the stainless steel and the stainnless steel required protection by a lining or coating system. Note that many stainless steels must not be contaminated by iron that is commonly present in the blast abrasive, such as black beauty and copper slag. A non-iron containing abrasive such as garnet or aluminum oxide should be used.. The same blast requirements apply as when coating carbon steel with a stated profile depth. Another situation occurs when a vessel has both stainless steel and carbon steel components. When thick linings are used over the carbon steel there is no problem, but if thin coatings are used, the possibility of a local flaw or damage to the coating can cause rapid attack due to the galvanic corrosion and the large cathode posed by the stainless steel surfaces. In those cases, it was decided to coat the stainless steel to cover (or reduce) the cathodic surface area of the stainless steel.

From luiz de miranda of ECOPROTEC on January 23, 2015:
 Tom, obviously, I agree with you since each ...read more  Tom, obviously, I agree with you since each case has specific conditions. However, I do claim there should be a reduction in the use of stainless steel. In fact, unless it is here in Brazil, stainless steel  is employed everywhere, notably in the petroleum industry. Many problems, such  as stress corrosion, could be minimized by using mild steel coated with niobium oxide, for example, instead of stainless steel.

From Terry Aben of Hempel (Canada) Inc. on January 22, 2015:
Please remember that coatings can contain reactive ...read more Please remember that coatings can contain reactive chlorine that can contribute to stress corrosion cracking of stainless steels. For example, the majority of epoxy coatings can be problematic with stainless steels, and most coating manufacturers will have one or two epoxy products that are formulated with low residual reactive chlorine content to specifically address this issue. If you are going to coat stainless, make sure you have prequalified the coating to ensure it is suitable.

From Tom Schwerdt of Active Transportation Advocates on January 22, 2015:
Luiz,  you would coat stainless steel when th ...read more Luiz,  you would coat stainless steel when the conditions on different areas of the item are in different exposures (such as inside and outside of a pipe)  and one of the conditions requires stainless, while the other condition is damaging to stainless. As an example, maybe you are piping acetic acid, which will trash most coatings (it's often worse than the strong acids), but the outside of the pipe needs to be insulated, or is exposed to high chlorides.

From luiz de miranda of ECOPROTEC on January 20, 2015:
If it is necessary to coat a stainless steel, why ...read more If it is necessary to coat a stainless steel, why not use coated mild steel instead? It is much less subject to stress corrosion and welding decay, and it is less expensive.

From Dwight peabody of peabody and associates on January 19, 2015:
Stainless steel needs to be coated not only for&nb ...read more Stainless steel needs to be coated not only for  protection from corrosion. The coating also protects the stainless from being stolen by thieves because its color hides the shiny metal's identity. 

From keyoor limbasia of essar projects on November 14, 2014:
Stainless steel should be coated to protect it fro ...read more Stainless steel should be coated to protect it from chemicals in the form of liquid or gas in the complex design of oil and chemical plants.

From OM PRAKASH JAT of Galadari Engineering works on November 3, 2014:
Stainless steel coating is compulsory when the sur ...read more Stainless steel coating is compulsory when the surface is exposed to corrosive atmospheres of sulphide, fluoride, chloride or marine atmosphere conditions. Stainless steel also needs to be coated when in direct contact with brass, bronze or other noble alloys of metals.

From Geir Christianslund of Aker Solutions MMO on November 3, 2014:
Stainless steel should be painted if it is to be i ...read more Stainless steel should be painted if it is to be insulated, and we must also paint stainless steel to prevent chloride stress corrosion cracking related to temperatures and types, for 316, 60 C; for 22% duplex, 100 C; for 25% duplex,110 C;  and for 6Mo 120 C.