1. 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

2. 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)

3. 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

4. Why Plugs Fail (1) Forces on a stuck mechanical plug
Ff1 = μN1
Alternative
Blowout
Blowout 2θ N2
Ff = μN2

5. Why Plugs Fail (2) Friction and normal force competition
Ff1 = μN1
Alternative
Blowout
Blowout 2θ N2
Ff = μN2

6. Why Plugs Fail (3) Friction and normal force competition
Ff1 = μN1
Ff1 = μN1 θ θ
1. As installed
2. Possible In use

7. Why Plugs Fail (4) Friction loses the competitionNy
Ff = μN
Ffy Nx
Ffx θ
Nx >Ffx , even the slightest amount and plug slips

8. 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

9. A different mechanical approach: InstaPlug™

10. InstaPlug™ A non-wedge based plug
unique one-piece shape + a material with very special properties

11. 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

12. Simple positive process (1) Create the plug and shrink it
Heat treatment
As machined d+~0.004” Reduced diameter for installation

13. Simple positive process (2) Install into well prepared tube/tubesheet
Place in clean tube end
Heat to restore “memorized” interference fit

14. Insta-Plug common sizes

15. Engineering and Design
NOT the simple analysis used for exposition here
Sophisticated Finite Element Analysis for
Deflection
Force
Stress/strain distribution
Thermal analysis

16. 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.