Crack principle and protective measures of stainless steel seamless tube

Crevice corrosion is a form of local corrosion cracks when surface passivation layer of surface sediment or shielding area is destroyed.


There are cracks in the welding process or design of the stainless steel pipe joint at the other joint. In effective corrosion sites, the crack must be wide enough to allow corrosive electrolyte to enter the stagnant zone. The width of the corrosion crack is several meters wide, but it is not absolute. The critical crack size leads to corrosion.


In particular, the negative chlorine ions have high activity. Therefore, if there is an external body solution of the crack, the metal ions with positive charge are easily attracted to the narrow cracks. The cracks (usually chromium) in the metal chloride formed to form hydrochloric acid, reduce the pH value to passivate the pH value and passivate. The cracks in the membrane were destroyed and further pitted. Events should be passivated, corrosion will be fast and self - sustaining, especially when the bulk solution has provided chloride ion.


The chromium and nickel elements which prevent crevice corrosion in stainless steel seamless pipes support the stability of the passivation layer and promote the stability of the passivation layer of the stainless steel. Although chromium metal ions are more supportive than ion or nickel anode reactions in crevice corrosion, the improvement of chromium content of alloys is more resistant to crevice corrosion. For specific chromium content steel, austenitic stainless steel seems to be more tolerant of erosion than low nickel ferrite steel. Molybdenum and nitrogen are very important for improving corrosion resistance. Generally speaking, stainless steel (such as 6% molybdenum austenitic stainless steel) can provide the best crack resistance. Ordinary stainless steel has a good effect of reducing crack resistance. Cracks can not be completely penetrated into the welding bead produced during the welding process.


The permeability of complete root dissolution is crucial because the round and smooth solder bead in the inner bead to the base metal area is not the bottom groove.