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Intragranular tubing sulfidation prevention

Intragranular tubing sulfidation prevention

Intragranular tubing sulfidation prevention

(OP)
Greetings, I first must apologize. I am not a full-fledged engineer, just a mechanically minded guy. But nonetheless I have a problem of metallurgy that is beyond my scope.

I operate a 1260 psi, wood-fired boiler burning at approx 1300-1500 deg F. The boiler is McBurney brand and was first fired in 2005. We have intragranular sulfidation attacks on the gas side of our superheating section so bad as to render our .150" tube wall to .020" or rupture.

We are preparing to re-tube the boiler and would like to only have to do it once. So far all processes my supervisor has researched have been able to combat the sulfur content but are not sufficient to withstand the heat of continued use.

If anybody has a fantastic solution either metallurgical or chemical coating I would be greatly interested in hearing about it.

Thank you for your time.

RE: Intragranular tubing sulfidation prevention

I don't think this is job you should be taken on without the assistance of a specialist in boiler corrosion.  There are several approaches to your problem, which has to be determined by someone versed in the art.
Your boiler supplier, the tube supplier, or the insurance carrier should be able to recommend someone.

Here is a little information on some of the approaches to your problem.  These approaches don't cover all the methods used to protect tubes.
The first link is to an article about corrosion of boiler tubes.  The second is to a little information on  over layered tubes.   The third is a company that does overlay weld in the field.   

http://www.onepetro.org/google/Papers/NACE/Meetings/2003/CO
RR03/03500/03500.pdf?id=NACE-03500&soc=NACE

http://www.babcockpower.com/products/boilers-boiler-services/boiler-tube-co-of-america/products/spiral-tube-weld-overlay/

http://hi-techindustrial.com/WeldOverlay_Automated.aspx

RE: Intragranular tubing sulfidation prevention

I agree with the advice above, you should contact one or more boiler tube suppliers, even a boiler OEM that sells replacement pressure parts, to help with replacement tube selection. To combat elevated temperature sulfidation attack will require either a high chromium stainless steel or chromium/nickel alloy for this application.

RE: Intragranular tubing sulfidation prevention

(OP)
Thank you for your advice. We are investigating a number of companies regarding new alloy tube purchase, but I had not heard about the overlay process. Does anybody happen to know if overlay tubes provide better protection than alloy alone?

RE: Intragranular tubing sulfidation prevention

The spiral weld overlay tubes can perform as equally as a homogenous (one alloy) alloy tube, especially if the function of the overlay is to only provide a barrier coating against corrosion attack. This comes down to cost benefit analysis.

RE: Intragranular tubing sulfidation prevention

(OP)
Thank you both for all the information, now I will have a bit more knowledge to continue searching for the best solution.  

RE: Intragranular tubing sulfidation prevention

Out of curiosity, where does the sulfur come from?  It is not normally a constituent of wood combustion.

That asked, the advice given above is spot on.  There are fuels that are chock full of sulphur (oils, coal, black liquor and even natural gas with trace amounts) that have boiler tubing designed to survive in that type of combustion environment.

Is McBurney the actual manufacturer of the boiler or just the packager of the boiler system?  I haven't dealt with them in quite a few years, but back when I did, they packaged a variety of different OEM's boilers with the balance of the plant equipment; fuel handling, air pollution control, feedwater systems, etc in order to furnish a complete boiler system package.  If the latter, you might try contacting the original manufacturer of the boiler for their advice.

rmw

RE: Intragranular tubing sulfidation prevention

(OP)
We estimate the sulfur to be coming from the urban waste material we burn for local government agencies. Some of their fuel has more plastics and trash than fuel, but we are contractually bound to burn it. Se la Vie.

RE: Intragranular tubing sulfidation prevention

Let's just say that one should NOT assume there is no sulphur in wood!  Every wood pyro unit or gasifier I've seen has some kind of sulphur removal on it, and they're not there for fun and games...

RE: Intragranular tubing sulfidation prevention

Are you sure that Sulfur is causing all the problems and not Halogens from material like PVC or Teflon, to name a few.

RE: Intragranular tubing sulfidation prevention

So you are running for low NOx, that greatly increases the sulfur free to react in the gasses.

In general for an alloy to resist sulfidation you need high Ni.  Cr may impact overall corrosion resistance but to minimize the penetration of S take Ni.
Weld overlay has been used extensively, but it isn't perfect.  You will get cracking in the welds and localized corrosion at those locations.  It is not uncommon to see 20 cracks per inch of weld after a couple of years of service.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

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