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 SystemsDan 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 PlugsPrimary 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

Ff1 = μN1

N1

2θ

Ff = μN2N2

BlowoutAlternativeBlowout

Why Plugs Fail (2)

Friction and normal force competition

Ff1 = μN1

N1

2θ

Ff = μN2N2

BlowoutAlternativeBlowout

Why Plugs Fail (3)

Friction and normal force competition

Ff1 = μN1

N1

θ

Ff1 = μN1

N1

θ

1. As installed 2. Possible In use

Why Plugs Fail (4)

Friction loses the competition

Ff = μN

N

θ

Nx >Ffx , even the slightest amount and plug slips

FfxNx

Ny

Ffy

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 loosenOnce it begins it tends to continue to loosen

A different mechanical approach:InstaPlug™

InstaPlug™ A non-wedge based plug

NITINOL REPRESENTATION

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

0 0.02 0.04 0.06 0.08 0.1

Strain (in/in)

Str

ess

(psi

)

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

As machined d+~0.004” Reduced diameter for installation

Heat treatment

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

a. Place in clean tube end

b. 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.