Chimney Liner Problems - HCL Formation and SS

[dug320]

We live on the beach in the Pacific NorthWest and our chimney liners, now two, have corroded down to powder within years of installation.

First off we are burning seasoned Maple. Alder, Hemlock and Douglas Fir in a Regency Fireplace Insert.

The first liner was 304 SS Flex Liner that lasted three years before corroding. The next (replaced by the manufacturer under warranty) was a 316T SS smooth flex liner and it lasted 16 months before corroding.

The problem is salt (NaCl). Even the cut wood in the garage has salt settling on it when tested for salt using silver nitrate solution. Apparently, when burning the chloride is reacting with the water to form HCL. In a dry situation both types of SS have a reasonable resistance to HCL but when wet it has terrible resistance. I suspect the wet HCL is being formed at the start or end of the burn. The HCL causes micro cracks in the SS which leads to corrosion and powdered liner.


What can I do? The manufacturer will replace the liner once more but I am hesitate to see another corrode out. The manufacturer suggested a rigid system.

 

[bholler]

Or a heavy flex but i would ask them if they have an alloy that will stand up to the salt better

 

[dug320]

I am not a metallurgist but according to the corrosion charts only Ceramic and Hastelloy are resistant to wet HCL in a sold fuel situation.

 

[dug320]

I have talked to the metallurgists at my company and all have agreed vitreous enamel/porcelain is the best. The UK is a great source for this information. All sites say the max is 1.8 (4.5) feet of pipe. But, I am not passing through anything other than an existing chimney.

Any ideas?

 

[Oldman47]

Do a Google check for something called "chloride stress corrosion cracking". Stainless in a chloride rich environment will self destruct faster than mild steel in the same environment. It requires elevated temperatures and chlorides for the process to happen but guess what, both are present in your flue pipe if you are burning salt rich wood.

 

[begreen]

This sounds like a driftwood issue. Are the wood providers selling dried out driftwood? If so, the stove innards are also degrading.

 

[dug320]

I know it is not driftwood as I cut and split the wood myself. A silver nitrate test on wood I just cut, split and sitting in a covered area indicated salt.

 

[begreen]

Sounds like airborne salt is settling on everything including the wood. The suggestion of going to a rigid liner seems reasonable. Unless the wood can be sheltered from the salt accumulation all one can do is slow down the corrosion. Same thing for cars in this environment. How is the stove interior holding up?

 

[TheRambler]

Maybe this is a case to use a clay tile lined chimney? I know that isnt the norm as a liner is preferred, but just a thought.

 

[Jan Pijpelink]

We live on the beach in the Pacific NorthWest and our chimney liners, now two, have corroded down to powder within years of installation.

First off we are burning seasoned Maple. Alder, Hemlock and Douglas Fir in a Regency Fireplace Insert.

The first liner was 304 SS Flex Liner that lasted three years before corroding. The next (replaced by the manufacturer under warranty) was a 316T SS smooth flex liner and it lasted 16 months before corroding.

The problem is salt (NaCl). Even the cut wood in the garage has salt settling on it when tested for salt using silver nitrate solution. Apparently, when burning the chloride is reacting with the water to form HCL. In a dry situation both types of SS have a reasonable resistance to HCL but when wet it has terrible resistance. I suspect the wet HCL is being formed at the start or end of the burn. The HCL causes micro cracks in the SS which leads to corrosion and powdered liner.


What can I do? The manufacturer will replace the liner once more but I am hesitate to see another corrode out. The manufacturer suggested a rigid system.

As a chemist I can tell you that Hastelloy C is resistant to acids like HCl. To have a liner made from Hastelloy C will be a very expensive exercise. Another possibility is to have the liner coated by a coating company. In Bellefonte PA is a company called Silcotek. They coat everything mainly for the petro and chemical industry. They have a coating that is resistant for HCl. You can ship the liner and they will return it coated. Not cheap, but a possibility. I have contact info and names if needed.

 

[bholler]

Another possibility is to have the liner coated by a coating company. In Bellefonte PA is a company called Silcotek. They coat everything mainly for the petro and chemical industry. They have a coating that is resistant for HCl. You can ship the liner and they will return it coated. Not cheap, but a possibility. I have contact info and names if needed.

WOuld the coating hold up to the heat? Have you asked your liner manufacturer about al 29-4c? It is an alloy typically used for gas appliances which exhaust allot of chlorides and that alloy is made to stand up to them so it might work i would inquire about it

 

[Jan Pijpelink]

WOuld the coating hold up to the heat? Have you asked your liner manufacturer about al 29-4c? It is an alloy typically used for gas appliances which exhaust allot of chlorides and that alloy is made to stand up to them so it might work i would inquire about it

The company I was talking about is a sister company of the company I work at. I know what they can do. The coatings are heat resistant. They are being used in and on boilers and distillation towers at oil refineries among many other things.

 

[bholler]

he company I was talking about is a sister company of the company I work at. I know what they can do. The coatings are heat resistant. They are being used in and on boilers and distillation towers at oil refineries among many other things.

Sounds interesting I was not doubting that they could just curious.

 

[Jan Pijpelink]

Sounds interesting I was not doubting that they could just curious.

Their standard coating up to 450 C (842 F) and a special up to 600 C (1112 F).

 

[TheRambler]

Their standard coating up to 450 C (842 F) and a special up to 600 C (1112 F).

Neither one of those would hold up long in a wood stove flue if that is the max heat rating. If its the normal operativg temp recommendation then thats different. I know most people run a flue temp of say 300-600, but it takes very little time to get 800+ if your not careful.

 

[bholler]

Yeah the special coating would hold up unless there was a fire then no good at all but the standard wouldn't work at all

 

[Isaiah53]

I have designed and operated industrial combustions systems with several percent HCl in the flue for 30+ years. If it is an HCl dew point issue, I don't think it is going to be cost effective for you to experiment with alternative metal liner materials or coatings. I would suggest first insulating the liner as well as possible (if you have not already) to prevent the dew point condensation. As you noted, stainless steel will work fine as long as the liner walls are above the above the dew point temperature of the flue gas. We successfully used carbon steel boiler tubes and ducts that have lasted my entire career, but they had to be well insulated and the walls maintained above about 300-400 F. If you can keep your liner that hot, you should prevent the gas from condensing and consequently the corrosion. Keep in mind that an un-insulated liner is probably about half the temperature of the bulk flue gas. You would still be vulnerable during cold starts. You could use better wood to bring it up to temperature during cold starts. Other than that, I think your best bet would be some type of ceramic or non-metallic chimney.

I would second BG's concern for corrosion to your insert. I am surprised you have not observed any damage to it. Leads me to think the situation might be manageable.

 

[dug320]

The stove seems to be fine as it shows little signs of corrosion. I asked the metallurgists about coatings and even considered chrome plating but the high temperature from a wood fire cancels out nearly all. In the UK vitreous enamel/porcelain is popular in coal fireplaces to address the HCL formation. But it is hard to find information that would apply to my situation. Unless someone who reads this thread has some insights.

 

[DougA]

Wouldn't it be easier to address the issue of where the salt is coming from and find a way to prevent it from getting on the wood? I always thought that rain could contain chemical effluent but not salt. I checked and rain can contain minute traces of salt but if the wood is stored in a garage as the OP posted, how could it get salt on it?
I would spend the time to discover where your problem originates as all of the chimney alternatives seem expensive and may not last much longer.

 

[begreen]

The OP is on the Pacific Ocean, they get constantly hammered by southwestern winds. These winds (currently gusting to 25mph) pick up salt spray from large breakers and deliver it inland. It's hard to protect against this spray.

 

[DougA]

OK, that partly answers my post BUT wouldn't a tarp covering the wood inside a garage be enough protection? I guess I just like low tech solutions that are cheap and easy.

 

[bholler]

OK, that partly answers my post BUT wouldn't a tarp covering the wood inside a garage be enough protection? I guess I just like low tech solutions that are cheap and easy.

With that much constant spray it may be in the wood as well. I agree with isaiah keep the temps up to stop condensation and i think the problem would be greatly reduced. Where the previous liners insulated?

 

[Fsappo]

Criminy, after reading most of that, how about an LP heater that uses PVC piping? seems like a load of trouble to burn wood. Or are you saving so much over LP that it may be worth installing a liner every 2 years?

 

[begreen]

LP can be pricey out here, particularly in some of the more remote areas.

 

[Fsappo]

I assumed so, but that's a hell of a problem with the salt. We dealt with salt on Long Island but nothing like what you are describing. But I suppose that the same salt will get in to anything, including a propane heater thru the combustion air intake. I almost am wondering if the suggestion above about just going with clay seems worth it.