Causes and solutions of pitting corrosion in stainless steel

From the perspective of pitting corrosion factors, the main factors leading to pitting corrosion in 316L stainless steel backwash pipelines are material, quality, flow rate and time. The nature cannot be changed, and the long-term stagnation phenomenon is the same. In the treatment and transformation of backwash pipeline leakage, although drain pipelines can be installed, the effect is not obvious, because all seawater cannot be drained and completely dried, even if there is a lot of water. A small amount of seawater corrosion can still travel along the direction of gravity at the bottom of the pipeline, and the corrosion will be accelerated due to the increase of oxygen content in the solution and the evaporation and concentration of seawater.

316L stainless steel pipe

Generally, there are five basic methods to control corrosion, which are to use more suitable materials, improve the environment, use protective coatings, use cathodic protection or anodic protection, and optimize the design of systems or components. Among the acceptable ones are changing materials and using protective coatings. The pitting corrosion of 316L stainless steel can be suppressed by using impressed cathodic current protection, but it is more expensive and will aggravate the corrosion of nearby unprotected metal parts. Therefore, the effective way to solve the pitting corrosion of the backwash pipeline is to consider the enhancement of the corrosion resistance of the inner wall of the pipeline. In the actual transformation on site, the method of carbon steel pipe plus vulcanized rubber lining is used.

Stainless steel anti-corrosion method

Firstly, all stainless steel pipes are removed, and carbon steel pipes are flange-connected according to the original pipeline path design on site, and the rubber-lined pipes cannot be welded. Then the carbon steel pipes are manufactured on-site and sent to professional rubber lining manufacturers. In the rubber lining factory, the inner and outer surfaces of the carbon steel pipe section are sandblasted. Then the outer surface is coated with anti-rust primer, and the inner surface is manually glued with rubber skin. Conduct electric spark inspection on the rubber lining to ensure the continuity of the rubber lining. Use epoxy resin to repair the individual defect points, vulcanize and fumigate the rubber to harden the rubber lining, and use rubber pads for flange connections during installation. The bolts are galvanized bolts with anti-corrosion coating. After installation, the pipe surface is coated with anti-corrosion paint.

Duplex stainless steel

In addition to the above methods, duplex stainless steels can also be used. At present, with the continuous improvement of the technical level, the duplex stainless steel that can resist chloride ion corrosion is developing rapidly. Duplex stainless steel is to add a certain amount of chromium to stainless steel, and add chromium elements with higher chromium content than austenitic stainless steel, so that duplex stainless steel can achieve excellent resistance to chloride pitting and seam corrosion. In the second-generation duplex stainless steel, ammonia is added to the duplex stainless steel to promote the formation of austenite and improve tensile properties and pitting corrosion resistance.