I. Comparison of material core differences

   1.1Chemical Composition and Metallurgical Standards

• 2205 Duplex Steel (UNS S32205)

Typical composition is 22% chromium, 5% nickel, 3% molybdenum, and 0.15% nitrogen in accordance with ASTM A790/A789. It has a PREN value (Pitting Resistance Equivalent) of ≥35 and is suitable for use in media containing ≤20,000 ppm chlorides.

• 31803 Duplex Steel (UNS S31803)

The base composition is 21% chromium, 5% nickel, 3% molybdenum and 0.08% nitrogen, the implementation of ASTM A182 standard. Compared with 2205, the nitrogen content is reduced, resulting in welding heat-affected zone is prone to embrittlement, the need to control the solid solution treatment temperature of 1020-1100 ° C.

   1.2Mechanical performance

• Tensile strength: 2205 can reach 620-795 MPa, higher than 31803 620-760 MPa.

• Impact toughness: 2205 at -46 ℃ still maintains more than 27 J impact work, 31803 low-temperature performance is slightly inferior (≥ 20J).

• Hardness difference: 2205 typical hardness of 28-32 HRC, 31803 for 25-30 HRC.

  

   1.3Comparison of corrosion resistance characteristics

• Pitting corrosion resistance: 2205 in 6% FeCl3 solution critical temperature ≥ 35 ℃, 31803 30 ℃.

• Stress corrosion cracking: 2205 in 80 ℃, 25% NaCl solution in the withstand time than 31803 40% longer.

II. Key dimensions to consider in selection decisions

   1.1Application Scenario Matching Evaluation

• Offshore engineering: 2205 is recommended, its high nitrogen content can resist microbial corrosion in seawater (such as SRB bacteria).

• Chemical equipment: 31803 is suitable for dilute sulfuric acid environment (10%-20% concentration) with temperature ≤80℃, and its cost performance is better than 2205.

• Food processing: both meet FDA standards, but 2205 is more suitable for high-temperature acid circulation systems in CIP cleaning.

   1.2Process Adaptability

• Welding requirements:

2205 need to use ER2209 welding wire, the interlayer temperature is strictly controlled within 150 ℃.

31803 welding needs to add copper-containing welding consumables (such as E318L-16), and the implementation of post-weld solution treatment.

• Cold forming restrictions:

2205 allow cold bending radius ≥ 4 times the diameter of the pipe, 31803 need to be ≥ 5 times the diameter of the pipe to avoid cracking.

   1.3Cost-benefit balancing strategy

31803 raw material procurement costs are 8%-12% lower than 2205, making it suitable for budget-sensitive projects.

2205 has significant life cycle cost advantages: 3-5 times longer service life in Cl-containing media

III. Quality Control Points

   1.1Means of material verification

• Spectroscopic detection (PMI) to ensure that the deviation of Cr, Mo content ≤ 0.5%

• Metallographic analysis: 2205 requires α + γ two-phase ratio of 45% -55%, 31803 allows 40% -60%.

   1.2Frequently Asked Questions

• Risk of intergranular corrosion: confirm whether the steel mills implement ASTM A923 standard testing when purchasing.

• Surface defects control: 100% of the pickled steel needs to pass the eddy current flaw detection to eliminate folding, heavy skin and other defects.

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