Boiler tubes material and diameter

[MedicineEng]

Dear All:
I am going to replace some damaged tubes in a boiler here at my plant.
The question is that the supplier is making me some questions that I cannot find an answer and I would like to see if any of you can give me some insight.
The tubes in question are ST35.8/I and 3.2mm thickness. The supplier says that he cannot find this standard in the local market and instead he is saying that ASTM A106 has the same characteristics. Is this true?
Furthermore, he is also proposing a thicker tube (3.9mm vs. existent 3.2) also due to difficulties in finding the original one in the market.
Since these pipes are going to have less internal surface area, which decrease on the heat transfer can I expect?

Thank you all for your comments.

 

[macmet]

I cannot say as I have seen ASTM A106 used for boiler tubing. I thought all materials approved for boilers had the SA designation.

Where I work we use boilers where the tube material is ASTM SA178. Our thickness varies depending on the job, but for hot water boilers is slightly less than your 3.2mm - these are firetube boilers and not watertube boilers.

 

[metengr]

The supplier says that he cannot find this standard in the local market and instead he is saying that ASTM A106 has the same characteristics. Is this true?

Reply; If your boiler was built to ASME B&PV Code, and you follow the requirements of the National Board Inspection Code for repairs, you cannot use A 106 pipe material for boiler tubing. Also, A-106 is a material specification for pipe with nominal wall thickness per ASME B36.10, not boiler tubing. Other permissible boiler tube standards are ASME SA 210, SA 192 and SA 178.

Furthermore, he is also proposing a thicker tube (3.9mm vs. existent 3.2) also due to difficulties in finding the original one in the market.
Since these pipes are going to have less internal surface area, which decrease on the heat transfer can I expect?

I would be more concerned that a thicker tube with a similar OD resulting in a smaller bore can result in circuit flow problems. Loss of heat transfer will not be significant.

 

[MedicineEng]

Dear All:
Thanks a lot for your replies. Let me just elaborate a little bit more about my system.
This boiler is installed in a recovery plant, where we burn our secondary products and use the hot gases (at 1100C) that pass trough the tubes to produce steam.

I already understood that A106 is not adequate for my application, but now it crossed my mind one doubt. And the initial tubes ST35.8/I? Are those adequate for boilers or the mistake comes from the design phase?

metengr:
Given the fact that inside the tubes it will run hot gas and not water, do you still see any circuit flow issue with the reduced internal surface?

 

[metengr]

MedicineEng;
Are the replacement tubes of the same outer diameter as original design? What is the code of construction for this boiler?