Have posted this article at other sites and hope it is useful to you on heat exchanger inspection methods.
Did I think up all these methods? No! But I did actively search on heat exchanger inspection methods and the following are methods that I found. For those that want one single never fail method for inspecting heat exchangers. There is none. Think about it. Would you inspect a Pulse heat exchanger the same way as a clamshell heat exchanger , a clamshell heat exchanger the same way as a tubular heat exchanger ? No you wouldn't nor should you. With equipment, knowledge and training you can become more proficient at inspecting heat exchangers.
Also check your local building codes. They may list further defects other than the ones listed requiring heat exchanger or equipment replacement.
Types of Heat Exchanger Failures
1. Cracks.
2. Rust perforations.
3. Over 50 percent of the heat exchanger wall thickness has rusted away.
4. Leaking heat exchanger seams.
5. Loose or missing screws securing cells.
6. Broken crimped rings
7. Broken or leaking seals or gaskets, including cemented seals.
8. Missing factory welds on seams.
9. Clean out port gaskets missing or leaking.
Inspecting Heat Exchangers
1. Flame deviation test. Burner flame moves when the circulator blower comes on. If you do not locate a crack or perforation the heat exchanger seams can be leaking or the metal may have pinholes rusted through.
2. Visual inspection of burner chamber area and exterior of heat exchanger using a flashlight with high candlepower such a rechargeable Mag Lite as at the top. Jet engine mechanics use high candle lights to inspect turbine blades and illuminate cracks.
Flexible lights are good for getting a light right on a suspected area. Having a light almost on the crack will highlight the defect. Flex-A-Light from Sears or the inspection light from SnapOn Tools Stock#: GA481B
Sometimes you can even pickup odd looking lights such as this one that uses a rechargeable Makita battery.
By shining a light on the outside or the inside of the heat exchanger area and examining the opposite side look for light penetration.
Use a variety of mirrors. Small round and oval mirrors that have long telescoping reach are available at most welding supply stores. A large round mirror with long reach is also available through Sears. Large mirrors can be used for drum type heat exchangers.
For older heat exchangers have a mirror made at local glass shop 1/4" thick x 1-3/16" width x 24" length. A suitable carrying case can be made from 1-1/4" PVC pipe and fittings. Use a male threaded cap for one end. Install a small piece of foam such as rubatex in both ends. Tool plastic coating can be sprayed on the back side for protection and at one end for a hand grip.
3. Water Spray Test.
Remove furnace blower assembly and the fan/ limit to prevent damage to these components. Spray the exterior of the heat exchanger with a water/soap solution 1 gallon water/ 1 tablespoon soap using a garden sprayer. Inspect the interior of heat exchanger with mirror and flashlight observing for evidence of water indicating a crack, rust perforation or crimp leak.
Don't eliminate the need to pull and fill a heat exchanger with water. Had to do that once on a brand new secondary heat exchanger to find that it had several leaking rivets causing the pressure switch not to close.
4. Measuring for CO in the plenum.
A CO detector cannot tell you if a heat exchanger is good. A CO detector can indicate a heat exchanger is cracked only if all of the following conditions occur simultaneously:
a. The flame generates enough CO (lack of oxygen, excess fuel, high temperature).
b. Enough exhaust gases are emitted from the heat exchanger crack or perforation.
c. The exhaust gases from the crack are not diluted too much before coming in contact with the sensor. A cracked heat exchanger may leak CO in a small stream. You may measure high concentrations only an inch away.
d. The heat exchanger is the only possible source for the CO detected.
Note: I have not tried this but have heard of some that will spray WD-40 or Gunk penetrating oil into the burner chambers (not the outside) of heat exchangers of furnaces with inshot burners to generate CO to see if CO will leak to the outside of the heat exchanger.
5. Combustion meter measuring undiluted flue gases.
One sign of a cracked heat exchanger is a change of oxygen concentration in the flue gases of greater than 1 / 2 % oxygen, or a change in the carbon monoxide level greater than 25 ppm. This change is measured by comparing readings before and after the circulation blower has turned on. For this test to be valid , CO levels must be present in the flue gas.
Check Bacharach's site Checking for Cracked Heat Exchangers
http://www.bacharach-training.com/Tips/Cracked.htm
6. The American Gas Association developed FURNACE HEAT EXCHANGER LEAKAGE TEST injecting a nitrogen/methane gas mixture into the burner chamber. The heat exchanger outlet of the heat exchanger is plugged and a combustible gas detector is used to check for gas leakage on the exterior of the heat exchanger. A detailed fact sheet on the AGA test procedure is available at
http://www.aga.org/pdf/publicinfo/co...facts8612b.pdf
Test Products International advertises the J&N Associates H.E.T. Kit and HXG-2 Combustible Gas Detector on their web site which does the above AGA test.
http://www.testproductsintl.com/gas.html
7. Magnehelic gauge test. Tape shut burner chamber openings and flue outlet. Connect magnehelic gauge to inducer pressure sensing port. Operate circulator blower. Movement of gauge needle indicates leakage into the heat exchanger either from cracks, rust perforations or leaking seals or gaskets.
Photo courtesy of the Baldloonie
8. Vapco H.E.A.T. Spray catalog number HT-1Q. Sprayed into the blower compartment on opposite side of motor. If burner flame changes color there is a leak in the heat exchanger.
Vapco
http://www.vapcoproducts.com/catalogPDF/P19-outline.pdf
9. Magna Flux dye penetrant test. Using cleaner then penetrant and then cleaner over suspected area developer is then sprayed. Penetrant which has seeped into cracks, perforations or pinholes is pulled out by the developer agent. Full length of crack is seen not just what may be seen without this test. Magna Flux cleaner, developer , red penetrant and zyglo fluoroescent penetrant is available through welding supply stores. It was originally developed by the military and has a mil standard labeled on the cans
9A. A flourescent dye spray and UV light test has been devloped by
Visible Defects. The dye is sprayed on the exterior of the heat exchanger. The interior is then checked with the UV light. Picks up cracks, rust holes and faulty seams and welds. They also have a camera system. The lens head diameter is smaller than a dime.
http://www.visibledefects.com
10. Smoke Bomb test. Smoke bomb is placed inside burner chamber and lit. Evidence of smoke on the exterior of the heat exchanger indicates leakage.
10A. Smoke puffer test at the burner inlet and watching the smoke if it sprays away from the burner opening you may have a leak in the heat exchanger.
Linear Mode
