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Insta-Plug ™ New low-pressure Feedwater heater and condenser tube plug Not to leak or fall out for the life of the exchanger. American Power Systems Dan Bina Hollaender Enterprises, Inc. Roger Adelman. Plugging tubes: A problem with many solutions. Metallurgical Plugs

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Insta-Plug™New low-pressure Feedwater heater and condenser tube plug Not to leak or fall out for the life of the exchanger

American Power Systems

Dan Bina

Hollaender Enterprises, Inc.

Roger Adelman


Plugging tubes a problem with many solutions
Plugging tubes: A problem with many solutions

  • Metallurgical Plugs

    Metallurgical bonding mechanisms:

    • Welded, brazed, soldered

    • Explosive (kinetic)

  • Mechanical Plugs

    Friction/interference mechanisms:

    • Tapered cylinders

    • Tapered cylinder in mating sleeve

    • Taper around a cylinder (Screws/Compressors)


  • Mechanical plugs
    Mechanical Plugs

    • Primary Advantages:

      • Quick to install

      • Simple to install

      • Relatively low cost

      • Effective for lower pressures

  • Primary Disadvantages:

    • Failure, particularly with cycling


  • Why plugs fail 1 forces on a stuck mechanical plug
    Why Plugs Fail (1)Forces on a stuck mechanical plug

    N1

    Ff1 = μN1

    Alternative

    Blowout

    Blowout

    N2

    Ff = μN2


    Why plugs fail 2 friction and normal force competition
    Why Plugs Fail (2)Friction and normal force competition

    N1

    Ff1 = μN1

    Alternative

    Blowout

    Blowout

    N2

    Ff = μN2


    Why plugs fail 3 friction and normal force competition
    Why Plugs Fail (3)Friction and normal force competition

    N1

    N1

    Ff1 = μN1

    Ff1 = μN1

    θ

    θ

    1. As installed

    2. Possible In use


    Why plugs fail 4 friction loses the competition
    Why Plugs Fail (4)Friction loses the competition

    Ny

    N

    Ff = μN

    Ffy

    Nx

    Ffx

    θ

    Nx >Ffx , even the slightest amount and plug slips


    Why plugs fail 4 how can that happen
    Why Plugs Fail (4)How can that happen?

    • Differential behavior of tube and plug

    • Changes in coefficient of friction

    • Mechanical dynamics

    • Infiltration of intermediate material

    • Other (micro cracking, etc.)

    IT IS A FAIL “UNSAFE” CONDITION:

    Once it begins it tends to continue to loosen



    Instaplug a non wedge based plug
    InstaPlug™A non-wedge based plug

    unique one-piece shape + a material with very special properties


    Nitinol or memory metal
    NiTiNol or “Memory Metal”

    • Nickel/Titanium alloy

    • Exists in two allotropic forms (atomic structures)

      • Martensite (at lower temperatures)

      • Austenite (at higher temperatures)

    • Special processing gives two important properties

      • Ability to “remember” a first shape after being in second

      • Superelasticity – almost six times “normal” metals

    • Inert enough to be widely used in medical implants

    • Retains large elastic energy when press-fit


    Simple positive process 1 create the plug and shrink it
    Simple positive process (1) Create the plug and shrink it

    Heat treatment

    As machined d+~0.004” Reduced diameter for installation


    Simple positive process 2 install into well prepared tube tubesheet
    Simple positive process (2) Install into well prepared tube/tubesheet

    • Place in clean tube end

    • Heat to restore “memorized” interference fit



    Engineering and design
    Engineering and Design

    • NOT the simple analysis used for exposition here

    • Sophisticated Finite Element Analysis for

      • Deflection

      • Force

      • Stress/strain distribution

      • Thermal analysis


    Conclusion
    Conclusion

    • We believe that we now have cost effective, and reliable means in the Insta-Plug™ that will:

      • not fail in service regardless of the cycling conditions

      • provide for installation that is fast, safe and simple

      • be cost competitive with other mechanical plugs

      • account for real world service demands e.g. thermal cycling

    • We intend that Insta-Plug™, like our experience with explosive welded plugs for high pressure feedwater heaters, will “last the lifetime” of the heat exchanger.


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