Titanium Flange Selection Guide for Critical Parts of Refining Units

Titanium flanges, with their corrosion resistance, high specific strength, and wide-temperature-range stability, have become the preferred materials for two critical sections in refining and chemical plants: the reaction zone and the sour water stripping unit. Precise selection of titanium flanges is central to ensuring long-term, safe operation of the unit. Based on actual working conditions, this article outlines the logic behind titanium flange selection.

• Contains hydrogen sulfide (H₂S), chlorides, naphthenic acid, hydrogen, etc., with extremely strong corrosivity under high temperature and pressure.

• Temperature: 300-600°C; Pressure: Several MPa to tens of MPa.

• Risks include hydrogen embrittlement, sulfide stress corrosion cracking (SSC), and high-temperature sulfur corrosion.

• Materials require a combination of high-temperature strength, creep resistance, and resistance to complex corrosion.

• Treats sour wastewater containing hydrogen sulfide, ammonia, cyanides, and phenols. pH is low, and chloride ion content can be relatively high.

• Temperature: 100-150°C; Pressure: Moderate.

• The medium is sensitive to pitting and crevice corrosion.

• Flange connections are prone to corrosion perforation due to medium stagnation in crevices, requiring materials with excellent resistance to pitting and crevice corrosion.

• TA2 (Gr2): Economical and practical pure titanium. Suitable for oxidizing environments (e.g., seawater, nitric acid, wet chlorine gas) with excellent corrosion resistance. Widely used in sour water stripping and chloride ion environments.

• TA9 (Gr7) / TA10 (Gr12): By adding palladium or molybdenum and nickel to the TA2 base, these grades significantly enhance resistance to reducing acids (e.g., dilute sulfuric acid, hydrochloric acid) and high-temperature, weakly reducing media. Suitable for the complex corrosive environments in reaction zones.

• TC4 (Gr5) Titanium Alloy: High strength and excellent creep resistance, with a yield strength exceeding 900 MPa. Suitable for parts in the reaction zone requiring high mechanical strength under high temperature and pressure.

• Weld Neck Flange (WN): Suitable for high-pressure, high-temperature, and severe cyclic conditions. The integrated tapered hub provides a smooth transition, reduces stress concentration, and offers excellent fatigue and vibration resistance. It is the standard configuration for high-temperature and high-pressure pipelines in reaction zones.

• Lap Joint Flange (SO/LJ): Suitable for applications requiring frequent disassembly for maintenance or for use with special, expensive pipe materials to save costs, but has lower pressure-bearing capacity.

• Sealing Face Types:

  • Raised Face (RF): Most common, but caution is needed for flammable, explosive, or highly hazardous media.

  • Male & Female Face (MFM) / Tongue & Groove Face (TG): Recommended for leak-prone, hazardous media. The self-sealing action prevents gasket blow-out, ensuring reliable sealing.

  • Ring Type Joint (RJ): Specifically designed for high-pressure applications, using a metal ring gasket. Used in ultra-high-pressure parts of the reaction zone.

• Determine the Nominal Pressure (PN) or Class based on design pressure and temperature.

• Forging Level is a key quality indicator: According to standards (e.g., JB4726), for titanium flanges with PN ≥ 10.0MPa or operating temperature ≤ -20°C, the forgings must meet Level Ⅲ or above, ensuring a dense structure without defects.

• Ensure the flange products comply with the international or national standards required by the project, such as ASME B16.5, GB/T 9112, etc.

• Possess complete material certificates, heat treatment records, and non-destructive testing reports (UT/PT).

• Forging is superior to casting: Forging results in a denser structure and better mechanical properties, making it the preferred process for high-pressure flanges.

• Surface Finish: The surface roughness of the sealing face must be strictly controlled to ensure an effective seal.

PART.03 Quick Reference Table for Section-Specific Selection Recommendations

As an expert with two decades of deep involvement in the titanium industry, Lihua Titanium not only provides high-quality titanium flange products that meet global standards but also aspires to be your "Materials Advisor." Connecting the world, and more importantly, connecting safety. Let every choice you make become a solid guarantee for the stable, long-term, and efficient operation of your unit.