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 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 Primary Advantages: Primary Disadvantages: 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 Ff1 = μN1 Alternative Blowout Blowout 2θ N2 Ff = μN2
Why Plugs Fail (2) Friction and normal force competition Ff1 = μN1 Alternative Blowout Blowout 2θ N2 Ff = μN2
Why Plugs Fail (3) Friction and normal force competition Ff1 = μN1 Ff1 = μN1 θ θ 1. As installed 2. Possible In use
Why Plugs Fail (4) Friction loses the competition Ny Ff = μN Ffy Nx Ffx θ Nx >Ffx , even the slightest amount and plug slips
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
A different mechanical approach: InstaPlug™
InstaPlug™ A non-wedge based plug unique one-piece shape + a material with very special properties
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 Heat treatment As machined d+~0.004” Reduced diameter for installation
Simple positive process (2) Install into well prepared tube/tubesheet Place in clean tube end Heat to restore “memorized” interference fit
Insta-Plug common sizes
Engineering and Design NOT the simple analysis used for exposition here Sophisticated Finite Element Analysis for Deflection Force Stress/strain distribution Thermal analysis
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.