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What tanks are these?

Discussion in 'Vintage Equipment Diving' started by Ghetto Diver, Oct 23, 2019.

  1. abnfrog

    abnfrog Tech Instructor

    # of Dives: 2,500 - 4,999
    Location: great white north
    well since we were talking about the nemrod double hoses at nswc here are a couple pics , I was wrong on the date these were taken it was 2001

    Attached Files:

    Sam Miller III likes this.
  2. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
    The cylinders are DOT cylinders built under the 3AA codes. They are not special permit or any other exemption that could require any form of re-validation.

    The 3AA code is covered and specified under CFR (Code of Federal Regulation) 49 paragraph 178.37. The 3AA is the most common steel cylinder code use to this day.

    On the CFR it specifies the allowable alloys and some of the material properties. The steels in the table are all chrome-molybdenum alloys. The code even provides a maximum design (yield) stress of 70,000 psi and it provides the equation to be used for this design check. Of the allowable steels, the most likely alloy used is AISI 4130.

    The age of this steel is irrelevant. There are three things that affect steel: corrosion, extreme heat (like in a fire will ruin its heat treatment), and high cycle fatigue life (the number of cycles that would affect a cylinder would require multiple fills and discharge every day).

    If the cylinder has not been exposed to fire (or extreme fatigue life), the material properties of that cylinder will be the same today as they were 47 years ago… and they will still be the same in 100 years from today.

    But don’t worry; you do not have to determine if the cylinder has been on a fire. The hydro test will measure plastic deformation. This is an indirect measurement of the material yield strength, but the measurement is conservative enough to determine material condition.

    The corrosion condition is determined by the visual inspection.

    If it passed both, the cylinder will meet the same requirements of a new cylinder.
  3. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    Usually it is "that is not vintage, but...". It seems that any discussion of old gear will find someone that knows something about it here, and a discussion ensues. It works for me.

    dead dog and Sam Miller III like this.

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