Stainless Steel Pipe Fittings

Performance analysis of series 317 series stainless steel

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317LXN, 317LX and 317L are austenitic stainless steels containing alloying element molybdenum, which have better corrosion resistance than common chromium nickel austenitic stainless steel. In addition, the creep resistance and stress cracking resistance of 317XN, 317LX and 317L stainless steel at high temperature are better than that of 304 stainless steel. The comprehensive performance of the three alloy is significantly higher than that of type 317 stainless steel, so the low carbon level (“L”) stainless steel will exhibit better resistance to intergranular corrosion in welding or other thermal processing, “X” and “N” meaning respectively containing high molybdenum and nitrogen components. The combined action of Mo and N can significantly improve the pitting corrosion resistance and crevice corrosion resistance of stainless steel in acidic, CI – and sulfide containing high temperature water vapor. Nitrogen also increases the strength of the steel itself. The above three kinds of stainless steel can be used in more stringent corrosion environment, such as flue gas desulfurization system.

317LXN, 317LX and 317L stainless steel in moderately corrosive medium corrosion resistance of 304 stainless steel is more excellent than conventional, but generally on type 18-8 stainless steel corrosion environment, the formation of corrosion of the stainless steel containing molybdenum is not the same, but the strong oxidizing acid such as nitric acid exception.

In sulfuric acid solution, 317LXN, 317LX and 317L are more corrosion resistant than type 304 stainless steel, and the corrosion resistance will increase with the increase of alloying element molybdenum content. The three kinds of stainless steel can be corroded with 49 and 5% sulfuric acid. When the temperature is below 38, the three kinds of stainless steel will show excellent corrosion resistance in the higher concentration of sulfuric acid.

The carbon content of the three kinds of stainless steel is less than 0.03%, and the low carbon content can significantly enhance the intergranular corrosion resistance in the process of welding or forging. They also contain more chromium, so they have better resistance to intergranular corrosion. However, it is clear that when they are exposed to the temperature range of 417-816 degrees Celsius for a long time, because of the precipitation of the delta phase, they will greatly weaken the anti crystal corrosion ability of these alloys, and will likely become brittle.

317LXN, 317LX, 317L stainless steel in acidic solution containing CI or other halogen ions in resistance to pitting corrosion and crevice corrosion ability is stronger than the 316 or 304 stainless steel, so they are often used in flue gas desulfurization system.

When welding 317L stainless steel, the welding material should contain at least 6% molybdenum; when welding 317LX and 317LXN stainless steel, the welding material should have at least 8% of molybdenum, such as using 625 alloy as welding material. In actual welding operation, if the high matching welding material can not be adopted, the post weld heat treatment and pickling can not be taken into consideration, the welding parts of the self fusion welding should be carefully considered to meet the requirements of the process conditions. The best corrosion resistance can be obtained after heat treatment and acid washing of 317LXN, 317LX and 317L self fusion welding parts.

 

Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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Stainless Steel

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