Troubleshooting a Furnace Emissions Problem

We had been fighting CO flue gas emissions on our CEMS analyzer for around a year, we had indications that it was a burner problem, fixed the burners, not the CO problem, had the vendor in multiple times to look at the burners, did all kinds of tests.  Finally, we got our portable analyzer fixed, bought a high temperature probe and did a firebox survey ourselves.  We found no CO in the box, CO at the IDF.  Checked the analyzer and realized that we had a convection section leak.  We shut the furnace down, and took all the tubes out.  We found multiple holes/cracks that we think are polythionic acid stress corrosion cracks.  We have had some other small leaks on other heaters that we think are also stress corrosion cracks.  Will have lab analysis shortly.

Its an interesting story, at least to us.  Serious safety implications as we almost had a tube split open.