Ductile Iron Vs. Steel Flanges – Are They Interchangeable?

Setting Standards for Fittings

The American Society of Mechanical Engineers /American National Standards Institute (ASME/ANSI) recognized the importance of reliable guidelines and were the first to create a set of performance standards for valves, flanges, and fittings in . The American Water Works Association determined the ANSI/ASME pressure ratings were too conservative when used with water.

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Through testing, they determined Ductile Iron fittings with dimensions conforming to ANSI/ASME B16.1 Class 125 could be rated at 250 psi. The AWWA C110 applies to Ductile Iron and gray iron flanges and fittings ONLY. If you see a specification that calls out ANSI/ASME B16.1 then you better be careful.

Yes, AMSE B16.1 covers the class 250 flange, but this also covers the Class 125 flange, which has the same facing and drilling pattern as AWWA C110. This standard only refers to the Class 125 flange. The difference in Class 250 Flanges (sometimes referred to as EH-extra heavy) is:

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• They are costlier.
• They use special bolts.
• They have a more extended center to face dimension.
• They have a larger bolt circle.
• They have a thicker flange.
• They could have a .06 inch raised face.
• They will very likely have a longer lead time.

As these standards are designed for cold water service, their pressure ratings are higher than ASME/ANSI ratings for a fitting of similar size and material. These higher ratings are in place because ASME/ANSI fittings are expected to deal with more hazardous service situations such as steam! The Class 250 flange is an ANSI /ASME specification, not an AWWA, and it means the joint can withstand 250 psi at 373 degrees Fahrenheit. Incidentally, you will not find AWWA C110 grey iron fittings being made or sold routinely in the United States.

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