Browse the Corrosion range from Nandini Steel, held ex-stock in Mumbai with EN 10204 3.1/3.2 mill test certificates and full traceability. Browse the range below, then send your grade, form, size and quantity for a same-day quotation.
Localized corrosion: pitting and crevice
Localized corrosion is the mechanism behind most field failures in stainless equipment, because it concentrates attack in a single small spot rather than thinning the whole surface evenly. Our pitting corrosion and crevice corrosion pages explain how chloride ions break down the passive chromium oxide film at a surface defect or under a gasket, bolt head or deposit, and why molybdenum-bearing grades such as 316 and 904L resist it far better than plain 304. A related mechanism, galvanic corrosion, occurs when two dissimilar metals are in electrical contact in an electrolyte, and is a common cause of unexplained attack at a bolted or welded joint where the filler or fastener grade does not match the base metal.
Cracking: stress-corrosion cracking and sour service
Cracking mechanisms are more dangerous than general pitting because they can propagate through a wall section with little visible warning. Our stress-corrosion cracking page covers chloride SCC in austenitic stainless steels under tensile stress, and our sour service and sour service and NACE MR0175 pages cover hydrogen-induced and sulfide stress cracking in oil and gas environments containing H2S. Grades qualified for sour duty, such as Incoloy 825 and NACE-HIC tested A516 Grade 70, are selected specifically to resist these cracking mechanisms rather than general corrosion alone.
Intergranular attack and sensitization
Intergranular corrosion attacks the grain boundaries of the metal rather than the surface, and in stainless steel it is almost always tied to a specific cause: chromium carbide precipitation at the grain boundary after exposure to 425 to 815 degrees Celsius, commonly from welding. Our intergranular corrosion and intergranular corrosion and sensitization pages explain why this happens and how it is prevented, chiefly by specifying a low-carbon L grade such as 304L or 316L, a stabilized grade such as 321 or 347, or a post-weld solution anneal.
Measuring resistance: PREN
PREN, the pitting resistance equivalent number, is the single number that lets you rank grades against each other for pitting and crevice resistance before you look at a single application. Our PREN and pitting resistance equivalent page and PREN explained guide set out the calculation from chromium, molybdenum and nitrogen content, and the resulting ladder across our catalogue: 304 at roughly 18, 316 at roughly 24, 904L at roughly 34, and duplex 2205 at roughly 35. A higher PREN means better pitting resistance in chloride service, but it is only one input alongside the specific corrosion mechanism, temperature and acid chemistry in play.
How this maps to grade selection
None of these mechanisms exist in isolation on a real project. A sour-gas separator has to resist both sulfide stress cracking and general pitting at once, and a welded pharmaceutical tank has to resist sensitization and chloride pitting in the same joint. Our types of corrosion overview page is the starting point for working through which mechanisms apply to your service, and from there the comparison and grade pages on this site carry the same mechanism-specific language through to a concrete recommendation.