Choosing between a polypropylene encapsulated flange and a traditional steel flange affects everything from installation cost to long-term system reliability. Here’s how they compare.

Weight and Handling

Polypropylene encapsulated flanges — like Stu Piping’s PPDA and DF2DI ranges — can be up to 50% lighter than conventional steel backing rings. That translates directly into easier on-site handling, lower crane/lifting requirements, and reduced freight costs, especially on large projects with hundreds of flange connections.

Corrosion Resistance

Steel flanges, even coated ones, remain vulnerable to corrosion in aggressive or wet environments — a major concern in water treatment, aquaculture, and marine applications. Polypropylene-encapsulated flanges eliminate this risk entirely at the flange body, since the ductile iron core never contacts the process fluid or atmosphere.

Installation and Bolt Tension

One overlooked advantage of convoluted PP flange designs (like the DF2DI) is bolt tension retention. The flexible cross section helps bolts maintain tension over time, reducing the need for re-torqueing — a common maintenance task with rigid steel flanges.

Cost Considerations

While the upfront unit cost of a PP-encapsulated flange can be comparable to or slightly higher than steel, the total installed cost is often lower once you factor in reduced freight weight, less handling equipment, and lower long-term maintenance from corrosion.

When Steel Still Makes Sense

Steel flanges remain the right choice for very high-pressure applications outside the PN/Class ratings of encapsulated flanges, or where local project specifications mandate all-metal construction.

Which Flange Range Fits Your Application?

Stu Piping’s PPDA, PPDI, PL2DI, DF2DI, and PPFL ranges cover butt welding, socket welding, ANSI, and plate-style connections across water, gas, mining, marine, and aquaculture industries. [Contact us] to discuss your project’s flange specification.