Why Duplex Flanges Are Best for Tough Industrial Settings

 The ramifications of a pipeline failure at a chemical processing facility or an offshore oil rig aren't limited to just repair costs. The costs associated with safety concerns, downtime, and dealing with regulatory issues quickly add up. It's no surprise to see materials engineers and procurement departments view Duplex Flanges as a well-reasoned, long-term investment, rather than a fancy, optional expense.

 

If you're considering making the switch from standard stainless steel, here’s what you need to know before your next purchase.

Duplex Steel Explained

Duplex stainless steel is a blend of ferritic and austenitic microstructures that exist in roughly equal proportions. This hybrid allows you to have the corrosion resistance of austenitic steel and the strength of ferritic steel within the same material.

Duplex steel has some unique and truly impressive features, including:

Twice the yield strength of austenitic grades like 304 or 316

Superior resistance to chloride stress corrosion

cracking

Excellent performance over a broad temperature range

Lower levels of nickel which keeps the material costs

more affordable

In the case of flanges, that combination is hugely important. Flanges are the places within a piping system where pressure and corrosive media are combined with the potential for stress and vibration.

 

Where Are Duplex Flanges Typically Used?

 

Duplex flanges carry significant loads in some of the most demanding applications because conventional materials are unsuitable. Common applications include:

Oil and Gas — Onshore and offshore applications where exposure to and immersion in seawater occurs and where pressures can be significant

 

Chemical Processing — including plants that process acids and chlorides and where aggressive process fluids are present

Desalination — where exposure to seawater occurs

Power Generation — including Geothermal and Nuclear applications which may have very high temperatures.

Pulp and Paper — Bleaching and processing have very hostile environments

Duplex flanges are generally covered in the ASME B16.5 dimensional standard with sizes from ½ inch to 24 inches and pressure classes from 150 to 2500 PSI. Typical grade specifications are ASTM A182 F51 (S31803) and F53 (S32750).

 

Selecting the Proper Type of Duplex Flange

 

Not all flanges are the same. Here are the basic flange types:

 

Flange Type Best Used For

Weld Neck High pressure and high temperature

Slip On Low pressure, high temperature

Blind Closing the end of a pipe/vessel

Socket Weld Small bore - high pressure

Threaded Low pressure, non-weldable

 

Determine the pressure, temperature and process to determine the proper type of flange. When in doubt, contact your flange supplier to help you determine the correct type.

 

What to Consider When Choosing a Manufacturer

Cost is not the only consideration when sourcing duplex flanges from a manufacturer. Here are some other things to consider:

Material traceability - always request mill test and raw material test certificates.

Compliance with international standards - quality control certifications may include ASTM, ASME, ANSI, DIN, and JIS.

 

In-house testing - prior to dispatch, testing of chemical composition, mechanical testing, and dimensional inspections, should be carried out.

Experience with exports - a manufacturer that exports understands the requirements for documentation, packaging, and the time commitments associated with the process.

Duplex flange manufacturing is now a well established industry in India, with suppliers based in Mumbai gaining a strong reputation in the Middle East, Europe, and Southeast Asia.

 

Final Thought

Specifying duplex flanges for your project is a smart decision. Considering the long-term benefits of decreased failures and maintenance and an extended service life, the difference in cost compared to standard stainless steel is justifiable.

Take care to ensure that your supplier is able to provide documentation for each batch and has experience in your industry whether you are sourcing flanges for a new project or a retrofit. Your system deserves this attention.