Introduction：

Stainless steel flange as the core component of pipeline connection, its quality is directly related to the sealing and safety of the whole system. Flange products on the market seem to be similar in appearance, but due to different testing standards, the actual performance may vary several times. In this article, we will analyze the testing methods and quality differences of stainless steel flanges in an easy-to-understand way to help buyers avoid the “low price trap”, and at the same time, we will show how we can ensure that each piece of flanges can withstand the test of harsh working conditions through the whole process of quality control.

I. Basic testing dimensions and core methods

  

  1. Material composition testing: to eliminate “defective products for good products”

• Detection method:

      --Spectrometer rapid scanning: handheld device can detect the content of chromium (Cr), nickel (Ni), molybdenum (Mo) and other key elements in 3 seconds (accuracy ± 0.01%).

      --Chemical reagent verification: use nitric acid spot test method to quickly distinguish between 304 and 201 stainless steel (304 has no obvious reaction, 201 will turn black).

• Characteristics of inferior products: nickel content is insufficient (such as 304 requires nickel ≥ 8%, inferior products may be only 5%), using manganese instead of nickel to reduce costs.

• Our practice:

100% spectral testing of raw materials before warehousing, provide third party SGS material report for each batch.

   2. Dimensional accuracy inspection: millimeter-level error control

• Key inspection points:

       --Flange outer diameter, bolt hole center distance (error > 0.5mm will lead to installation misalignment).

       --Sealing surface flatness (using a knife edge ruler detection, gap > 0.05mm may leak).

• Detection tools:

      --Digital vernier caliper (accuracy 0.01mm)

      --Coordinate measuring machine (detection of complex surfaces)

• Our Advantage:

Using Japan Mitutoyo measuring equipment, flange thickness error control within ± 0.1mm (national standard allows ± 0.5mm).

   3. Surface quality testing: the hidden dangers invisible to the naked eye

• Detection Focus:

       --Cracks and air holes: use red penetrant to coat the surface and observe whether it penetrates into the defects after 5 minutes.

       --Scratches and dents: Surface roughness meter to detect Ra value (Ra≤3.2μm for high quality flanges).

• Common Problems:

      --Incomplete pickling leads to oxide skin residue and accelerates corrosion.

      --Inferior quality products are sanded with grinding wheel to cover the cracks.

• Our promise:

All flange sealing surfaces are made by precision turning process, with roughness Ra≤1.6μm, and provide 10 times magnifying glass re-inspection service.

II. Performance testing: let the data speak for itself

   1. Strength and toughness testing

• Testing method:

       --Hardness test: measured by Rockwell hardness tester (304 flange normal value HRB 70-90, too low indicates that the heat treatment is not qualified).

       --Tensile test: intercept the specimen and pull it until it breaks, test the tensile strength (≥520MPa is qualified) and elongation (≥40% is good).

• Risk case:

       A project using substandard 316L flanges, cracking around the bolt hole under 6MPa pressure, resulting in media leakage.

• Our guarantee:

       Sampling 3% of each production lot for destructive testing to ensure that the mechanical properties are 100% up to standard.

   2. Corrosion resistance testing

• Laboratory method:

       --Salt spray test: place the flange in 5% sodium chloride spray, 304 material requires 720 hours without red rust.

       --Intergranular corrosion test: Boil with sulfuric acid-copper sulfate solution for 24 hours, no crack after bending is qualified.

• Quick judgment on the spot:

       Rub the non-sealing surface of the flange with a copper brush: no obvious metal shavings fall off from high-quality products, and inferior products will fall off         powder (due to insufficient chromium content).

• Our technology:

       Add 48 hours double concentration salt spray test to flanges for chemical projects, corrosion resistance increased by 30%.

   3. Sealing performance measurement

• Testing method:

       --Hydrostatic test: pressurize to 1.5 times the design pressure (e.g. PN16 flange test 24Bar), hold pressure for 10 minutes without leakage.

       --Helium Leak Detection: Detect tiny leaks with helium mass spectrometer.

• Risk of low-cost products:

      Pressure tests are skipped to reduce costs and flanges are deformed at 80% of design pressure.

• Our standard:

      All flanges are hydrostatically tested 2 times before leaving the factory (rough + fine inspection), and helium leak detection is added to the flanges used for critical equipment.

Ⅲ.The poor quality of the flange “four big traps” and crack methods

   Trap 1: substandard materials

• Common means:

Using 201 stainless steel to pretend to be 304 (nickel content difference of more than 3%)

Recycled material remelted resulting in impurities exceeding the standard

• Breaking method:

Require suppliers to provide spectrometer real-time testing video

We support customers to factory supervision and sampling

  

    Trap 2: Cutting corners on size

• Typical problems:

Reduce the thickness of the flange (such as the national standard PN16 flange thickness of 18mm, inferior products only 15mm)

Insufficient number of bolt holes (e.g. DN100 flange should be equipped with 8 holes, inferior products do 4 holes)

• Cracking method:

Carry simple calipers to measure the key dimensions on site

We provide free sample comparison service

   

   Trap 3: Process Simplification to Reduce Costs

• Risk Points:

Failure to do solution treatment (excessive hardness prone to cracking)

Insufficient pickling time (surface passivation film is not formed)

• Breaking method:

Observe the flange cross-section: the fracture of high-quality products is silver-white, inferior products gray (due to coarse grains)

We use vacuum solid solution furnace to ensure the uniformity of material organization.

Ⅳ. Why choose us?

   

   1. Industry-leading testing equipment

        Equipped with German Zeiss spectrometer and U.S. Niton handheld detector, material analysis is completed in 3 seconds.

   2. Implementation standards are stricter than the national standard

        Increase on the basis of national standard GB/T 9119:

            Material composition deviation ≤ 0.3% (national standard allows 0.5%)

            Sealing surface hardness uniformity error ≤ 5% (national standard does not require)

   3. Full traceability system

        Each flange is laser coded with a unique number for traceability:

            Raw material furnace number, production team, testing records.

            20 years of files stored in the cloud, accessible at any time.

   4. Real cases to verify the strength

         Exported to Europe 5000 pieces of PN40 flange, 95% through the EU PED certification

Ⅴ.Conclusion

The quality gap of stainless steel flanges is often hidden in the inspection details. Choosing a professional supplier is not only buying a product, but also a security guarantee. We have been deeply plowing into the field of flange manufacturing for 16 years, establishing 128 testing nodes from raw materials to finished products, proving our strength with data and accumulating reputation with cases. Every choice you make is the best recognition of our professionalism.