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Ductile Iron vs. Cast Iron

Discussion in 'Irrigation' started by PurpHaze, Nov 20, 2006.

  1. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    In doing a little research for ductile iron fittings and joint restraint fittings for push-together pipe I came across the following explaining the difference between ductile iron and cast iron. Maybe nobody else will find it interesting but we're going to these fittings more and more in our area with the increased use of push-together pipe and HDPE pipe for larger pipe sizes.


    Cast iron is a generic name for any high carbon molten iron poured as a casting. When used to refer to pipe, cast iron (sometimes called gray iron) is a specific type in which the free graphite (Carbon) is in the shape of flakes. Cast Iron pipe were introduced into the United States in 1817.

    Ductile Iron is a specific type of cast iron in which the free graphite is in the shape of nodules or spheroids. (Other names for ductile iron are nodular iron or spheroidal graphite iron.) Ductile Iron Pipe were introduced to the market in 1955.

    Although nearly identical chemically, the two irons are quite different metallurgically. The now obsolete standard for Cast Iron Pipe (ANSI/AWWA A21.6/C106) required an iron strength of 18/40 (18,000 psi Bursting Tensile Resistance and 40,000 psi Ring Modulus of Rupture.) Although tensile testing was not a requirement of this standard, a tensile test of gray cast iron pipe would give a test result of approximately 20,000 psi Ultimate Tensile Strength, with no measurable Yield Strength or Elongation.

    The current standard for Ductile Iron Pipe (ANSI/AWWA A21.51/C151) requires a minimum grade of 60-42-10 (60,000 psi Ultimate Tensile Strength, 42,000 psi Yield Strength, and 10% Elongation.) In addition, Ductile Iron Pipe manufactured under this standard are required to meet a minimum of 7 ft lbs impact resistance by the Charpy test. (Compare Gray Iron Pipe with an impact resistance of approximately 2 ft lbs or less.)

    The difference in the physical properties of these two materials is attributable almost entirely to the difference in the shape of the free graphite. The shape of the graphite is determined at the instant of solidification and is made nodular by the addition of magnesium to the molten iron bath. Although Cast Iron was the best engineering material available for pipe production for nearly five hundred years, the development of Ductile Iron Pipe provides a far superior product.
  2. BSME

    BSME LawnSite Senior Member
    from Midwest
    Posts: 829

    you're right....

    nobody else did find that interesting :sleeping:
  3. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Wow...I'm impressed. You guys on that left coast sure have a lot of time on your hands.:dizzy:
  4. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Guess if all you work with is 1" PVC or poly then there'd be no reason to even attempt to understand ductile iron fittings, joint restraint fittings, knuckle joints, HDPE pipe, mechanical joints, etc. :nono:
  5. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    By taking 2-1/2 vacation days off I end up with nine straight days off.:)
  6. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    That almost beats my upcoming 3-4 months of vacation!!
  7. Mr. Vern

    Mr. Vern LawnSite Senior Member
    Posts: 632

    I found it interesting alright. I'm just wondering what useful information had to be displaced from my brain in order to make room for it.

    Anyone seen my car keys?LOL
  8. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Guess we're about even then. Between vacation time (4 weeks/year), holidays and comp time it's a wash. I just spread mine out over the year. Oh... and I very rarely have to work weekends during the height of the season unlike many others on this forum. :)
  9. DanaMac

    DanaMac LawnSite Fanatic
    Posts: 13,156

    Yeah but I also took off mid -August through Oct 1. Heck, I'd be pretty well off if I actually worked 12 months each year. April, May and June I keep thinking "Look forward to the winter, look forward to the winter".
  10. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    And isn't that same time when you're running around chasing your tail and being a real biatch??? :laugh:

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