medium carbon steels for boiler corrosion resistance

[SalmanArif]

i am working of fire tube boiler. i need to know that SA 516 grade 60 is a medium carbon steel, what sort of characteristics it posses to work correctly under chances of corrosion???
how does normalizing increases the corrosion resistance of this material??

 

[metengr]

SA 516 Gr70 is routinely used as shell material in both fire tube and water tube boilers. It is susceptible to corrosion pitting attack when exposed to oxygenated water.

Normalizing will not help corrosion resistance it helps to promote increased notch toughness, which is not important for boilers because of operating temperatures.

 

[EdStainless]

Are you concerned about corrosion from the cycle water side or from the fire side?
All of the steels are about the same when it comes to fire side issues, if you have an aggressive environment then you will need a coating or overlay of some sort.
On the cycle water side it largely comes down to water treatment. Though some alloys are better at resisting erosion in two phase flow because of small Cr levels this is not a factor in boilers themselves.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

For fire tube boilers you have combustion gases on the tube ID surface from fuel sources like oil or natural gas. The shell side will be the water side for a fire tube boiler, and as such, corrosion from oxygen cell pitting is typical. Coal ash corrosion and FAC are not damage factors.

 

[SalmanArif]

if the water is going to be properly treated before entering into boiler then the effect of corrosion is going to be minimized? is it correct?
what is optimum grain size preferred for shell of boiler?
secondly i couldn't get the micro structure of SA 516 grade 60 or 70 if anyone could help me?

 

[metengr]

Yes, boiler feedwater treatment will reduce scaling on the boiler shell ID and tube OD surfaces. There is no optimum grain size requirement for the boiler shell material because notch toughness is not a requirement for boiler shell fabrication. Not sure what you mean you could not get the microstructure. The SA 516 Gr 70 can be supplied as normalized or hot rolled plate.

 

[SalmanArif]

Do Medium carbon steels and HSLA steels are preferred because of their lower cost as compared to stainless steel? And the use of any material especially for boiler is made by keeping under considerations of environment conditions?
i am designing Fire tube Boiler using ASME Boiler and Pressure Vessel Code section 8, by the help of formulas provided there. i am not truly understanding ligaments efficiency in the tube sheet. anyone can define it???

I need to know the structure of SA 516 grade 60/ 70 either it is pearlitic + ferritic or any other phase???

I am doing Metallurgical and Materials Engineering.

 

[metengr]

SalmanArif;
First, I would suggest you find help with an engineering firm that possesses an ASME S-Certificate and can design this boiler for you. There is no reason to use material other than carbon steel for a firetube boiler shell and tubing. There is no reason to spend time evaluating the microstructure of the plate material. The basis for ASME BPV I is design by rule, which means using the published allowable stress values in BPV II, Part D based on design temperature and material.

 

[SalmanArif]

i had prepared the design by keeping under the considerations provided by ASME boiler and Pressure vessel code and my adviser has accepted it.
i want to conclude the role of micro structure into my my thesis of final year project. Thats why i had asked sir.