Likely damage mechanism on a boiler

[Ondas]

I have got a hot water boiler made out of CS, there's a firebox where fuel is ignited and burned off and hot gas travels through a series of tube around the firebox. There's glycol water mix on the shell side (20C in and 70C out). Operating temp is around 70 degrees C and 5 barg. What are the most likely corrosion mechanisms I could get in either of those two components?

 

[LittleInch]

Depends on the fuel and whether the flue exhaust temperature is above or below condensation temp.

No free water, gen very little corrosion but poor efficiency.

Not enough details.

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[MJCronin]

https://fossil.energy.gov/international/Publications/DECC_task_02_US_2page.pdf

MJCronin
Sr. Process Engineer

 

[TugboatEng]

Glycol isn't a corrosion inhibitor so you'll need to treat your water side with inhibitors.

On the fire side, the system is typically designed so that the flue temperature maintains s minimum of 250°F. Frequent starts and stops will complicate this.

 

[0707]

On hot side you will be dependent on fluel composition and hot flue gas temperature, on water side glycol and water mix composition
let us know more...

regards

 

[Ondas]

Fuel gas is mainly methane (around 75%wt and 15% ethane), water side is ethylene glycol+water (45%wt) mixture. Operating temperature is 70 as design temp is 90 degrees C.

 

[LittleInch]

What's Flue gas exit temperature?
What's in the other 10% of the fuel?
Design temp is your water side.

Why glycol? Is it in danger of freezing?

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Also: If you get a response it's polite to respond to it.

 

[weldstan]

As per Tug, you will deinitely need to add a corrosion inhibitor to the glycol-water mixture. I have seen severe corrosion of carbon steel in similar circumstances when corrosion inhibitor was not properly maintained.

 

[hacksaw]

Sounds like a domestic water heater is the item of concern, they are called boilers in the EU for example

 

[LittleInch]

So the questions are:

What is the flue gas exhaust temperature - i.e. does the flue gas create steam on exit (condensing boiler) or not?
What else is in the feed gas missing 10%? Any H2S or SO2?
How often does it fire?
Is the water a closed system (seems likely) or once through?
Is there anything else in the water ( small amount of Corrosion Inhibitor?)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mrfailure]

The OP never said there was an actual problem, just asked the too vague question what were the most likely failure mechanisms. I would like to point them to ASM Handbook Volume 11A Analysis and Prevention of Component and Equipment Failures to the chapter "Failures of Boilers and Related Equipment" on page 662.