During daily use, stainless steel flanges should be kept clean and protected from prolonged contact with strong corrosive media such as acids, alkalis, and salts. They should also be protected against moisture, scratches, and high-temperature oxidation. During installation and operation, the tightness of the sealing surfaces, gaskets, and bolts should be checked regularly to prevent leaks caused by loosening or corrosion, thus ensuring the safety and service life of the pipeline connection.
Under normal storage conditions, stainless steel flanges can generally be stored for more than 10 years. If the storage environment is dry, well-ventilated, and avoids contact with moisture and corrosive media, and if dustproof and rust-proof packaging is used, some 304 and 316 stainless steel flanges can even be stored for a long time without affecting their performance.
Daily Guide for the Use and Maintenance of Stainless Steel Flanges
How to choose flange materials?
The material, pressure rating, and sealing surface type of stainless steel flanges must be strictly matched to the operating conditions to avoid premature failure due to incorrect selection.
Material Selection: Choose the appropriate grade based on the characteristics of the medium (e.g., acidity/alkalinity, chloride ion content), temperature (-196℃~800℃), and environment (e.g., high humidity in coastal areas, chemical corrosion). For example: 304 stainless steel is suitable for general corrosive environments; 316L, containing molybdenum, has stronger resistance to pitting and crevice corrosion and is suitable for seawater and chemical media; 321, containing titanium, has better resistance to intergranular corrosion and is often used in high-temperature pipelines.
Pressure Rating: Must comply with standards such as GB/T 9112 and ASME B16.5. Select the flange with the corresponding pressure rating (e.g., PN16, Class 150) according to the design pressure (PN series or Class series). Overpressure use is prohibited.
Sealing surface matching: Raised face (RF) is suitable for medium and low pressure conventional operating conditions; MFM and tongue and groove (TG) have better sealing performance and are used for flammable and toxic media; Ring joint (RJ) is used for high pressure (Class 600 and above) scenarios. It is necessary to ensure that the sealing surface forms of the mating flanges are consistent.
2.Precautions Before Flange Installation
A thorough pre-installation inspection can effectively mitigate 80% of subsequent leakage risks.
Appearance and Dimension Check: Inspect the flange surface for cracks, scratches, and rust (especially the sealing surface). Minor scratches can be polished with fine sandpaper; scratches deeper than 0.5mm require replacement. Verify the nominal diameter (DN), pressure rating, and bolt hole center distance to ensure compatibility with pipelines, valves, and other equipment.
Sealing Surface Protection: The flange sealing surface (especially the water line on the RF side) must be protected from scratches by hard objects. Cover with plastic film or rubber gaskets during storage. If the sealing surface is contaminated with oil, wipe it clean with acetone or anhydrous ethanol. Do not use steel wool or strong corrosive solvents for cleaning.
Gasket Compatibility: The gasket material must be compatible with the medium (e.g., oil-resistant rubber gaskets for fuel pipelines, PTFE gaskets for highly corrosive media, and spiral wound gaskets for high temperature and high pressure). The gasket size must match the width of the flange sealing surface (e.g., the inner diameter of the gasket on the RF side should be 1-2mm larger than the flange inner diameter to prevent media erosion).
3.Precautions during flange installation process
During stainless steel flange installation, proper alignment is essential to prevent leakage. The two flange faces should remain concentric to avoid uneven gasket pressure, and bolts should be tightened gradually in a diagonal sequence to ensure uniform force distribution. Forced assembly is not recommended when gaps are excessive, as this may cause flange deformation or sealing failure. When welding stainless steel flanges to carbon steel pipes, insulation measures should also be used to reduce overheating and sensitization risks.
Pressure Testing After installation, conduct a pressure test — hydraulic test pressure should be 1.5× the design pressure, and pneumatic test 1.15×. Hold pressure for at least 30 minutes and inspect the flange sealing surface and bolt areas for leaks. If leakage occurs, release the pressure first, then readjust the gasket or bolt torque.
Daily Maintenance: Regularly check flanges for rust, cracks, loose bolts, and sealing surface damage. In humid or underground environments, apply anti-corrosion coatings and insulation to prevent crevice corrosion.
Special Conditions: In chloride environments such as seawater, control flow rate and monitor wall thickness regularly. Under high temperatures, inspect bolt loosening or creep and use heat-resistant bolts like 35CrMoA when needed.
What Should We Know About the Use of Stainless Steel Flanges?
1.To avoid intergranular corrosion during welding, the welding current for stainless steel flanges should be lower than that used for carbon steel. Short arc welding and fast cooling between layers are recommended.
2.Welding electrodes must be kept dry before use. Titanium-calcium electrodes should be dried at 150°C, while low-hydrogen electrodes should be dried at 200–250°C to maintain good welding quality.
3.Repeated heating during welding may cause carbide precipitation, which can reduce the corrosion resistance and strength of stainless steel flange pipes.
4.Chromium stainless steel flanges may harden and crack after welding. Preheating and slow cooling are recommended, especially when using G202 or G207 welding electrodes.
5.Alloying elements such as Ti, Nb, and Mo help improve the corrosion resistance and welding performance of stainless steel flanges. Proper welding materials should be selected according to working conditions.
Characteristics and Advantages of Stainless Steel Flanges
Stainless steel flanges serve as critical connectors in piping systems. They are usually joined using bolts and gaskets, ensuring strong, leak-proof connections.
These components allow easy assembly and disassembly, making pipe maintenance and replacement more efficient.
Main advantages include:
Excellent corrosion and oxidation resistance
High pressure-bearing capacity
Convenient installation and replacement
Compatibility with various pipe types and materials
Stainless steel flanges come in several types, such as:
Threaded flanges
Slip-on (plate welding) flanges
Socket welding flanges
Weld neck flanges
Blind flanges (flange covers)
Lap joint flanges
Swivel and anchor flanges
Their versatility makes them indispensable in industrial systems, including oil and gas pipelines, chemical plants, and boiler rooms.
304 vs 316 Stainless Steel Flange Maintenance Difference
304 stainless steel flanges are commonly used in general industrial piping systems, while 316 stainless steel flanges offer better resistance to chloride corrosion.
304 Stainless Steel Flanges
Suitable for:
Water pipelines
General industrial use
Indoor systems
316 Stainless Steel Flanges
Recommended for:
Marine environments
Chemical processing plants
High humidity areas
Chloride-containing media
Although 316 offers stronger corrosion resistance, routine inspection and cleaning are still necessary under harsh working conditions.
Conclusion
Proper maintenance is essential for maximizing the service life of stainless steel flanges. Regular inspection, correct cleaning methods, suitable storage conditions, and proper installation practices all help improve sealing performance and reduce the risk of corrosion or leakage.For industrial projects operating in harsh environments, selecting the correct flange material and following a routine maintenance schedule can significantly improve long-term pipeline reliability and safety.
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