What Happened???

[TuckerMike]

I was out in my sugar shack last night, test firing my D&G 2x6 arch, looked in to the bottom of the finishing pan and could see several tiny pin holes all over the bottom of the pan and could see down in to the fire box. When I drained the pan and looked at the bottom it was wet all over (obviously), but the holes were so tiny they would only form a drip every few seconds. The flue pan also has 1 tiny hole up near the firebox, but that is all I have found so far.

I have no idea what happened. I bought this arch used and have only used it myself for 1 season. Can anyone help me out on the cause of this?

Thanks,Mike

[DrTimPerkins]

I assume this is a welded pan and the leaks are in the pan material itself (see attached photo below) and not in the welds or solder joints. Tell us more about how the pan was used and then stored last year? How did you clean it during and after the season (inside and bottom)? What fuel (or other things) are you using in the arch? What type of SS is it? Photos?

Pinhole corrosion is typically caused by oxidation (often associated with using chlorine or other strong oxidizers to soak/clean without adequate rinsing) or sometimes by carbon build-up on the bottom containing chlorine or other salt residues that get hydrated in storage. Not saying that is it, but it a common cause of these failures.

Unfortunately there is not much you can do to fix it if the corrosion is extensive. It'll get worse over time.

pitted pan.jpg

[Walling's Maple Syrup]

Is it an oil fired rig?

[TuckerMike]

I don't have any pictures of it yet. Stainless pans, welded. holes are in the bottom of the pans. For storage I did a citric acid soak and then did a chlorine rinse to kill off any "bugs" after letting it sit all summer. I thought I effectively rinsed it each time...but maybe not?

It is an oil-fired rig.

[Walling's Maple Syrup]

Did you clean bottom(underside) of pans after the season last year?

[TuckerMike]

I did clean the bottoms of the pans, but no to shiny stainless. I brushed the heavy carbon off and hosed the majority of the remaining carbon off.

[Walling's Maple Syrup]

Is there any shiny ss showing on bottoms of pans? Do you use off road diesel? #2 fuel oil? Cut with kerosene? I believe it may be oxidation of fuel oil residue.....is your Burner tuned properly? You shouldn't get too much black on bottoms if it is

[TuckerMike]

Offroad diesel (ULSD). Nothing shiny on the pans. I've always struggled with carbon buildup, but my chimney has no smoke when operating. Figured it has to do with relatively cold metal due to sap on the inside. I'm headed out to clean them up and inspect the holes. I'll post some pics when I've got them clean.

[TuckerMike]

Apparently these pans aren't made of high-grade stainless? I thought a stainless pan would be less susceptible to chemical attack than this? I get that I need to keep the equipment clean, but I work in the power industry and we certainly don't worry much about carbon residue on stainless parts on boiler equipment. This is my first commercially built pan...so I'm still learning and appreciate the responses/input.

[Cjadamec]

It's not the carbon so much that you are concerned about. Its the sulfur oxides in the exhaust getting trapped in the soot that then turn to sulfuric acid when exposed to moisture in the air. The carbon holds the acid onto the pan. This is also known as "cold end corrosion". This tends to occur most when diesel fueled exhaust is "cold" which is around 300F. Although it still happens to a lesser degree at hotter temps. A poorly tuned burner which is evidenced but excessive amounts of carbon soot makes this problem worse as well. Carbon from a poorly burning burner will generally produce "fluffy" soot and tends to form soot balls. Soot from a tuned burner tends to be harder and more tar like.

If the pin holes in the bottom of the pan are small and shiny on the inside of the pan its more than likely your corrosion issue is coming from the fire side. The area around the pins holes in the fire side will likely look dull or rusty and have a dished out look and be much larger than the hole itself.

Stainless tends to perform very poorly if moisture is held against it with a lack of oxygen. The soot layer if kept in a moist dark area will accelerate corrosion.