Boiler Stack Steel Material
Boiler Stack Steel Material
(OP)
We are looking at replacing the top section of a 75foot boiler stack. The stack is a self supporting stack and has a 3.5ft inner diameter at the last 50ft.
This section was just replaced 12 years ago. It was 7/16" thick A285 Gr C carbon steel. It is eaten away by the flue gas from the boiler. We have two quotes to replace the stack with A516 Gr 70 and A36 carbon steel.
Is there a particular steel that would be better suited to handle the acid from the flue gas that stack designers know about or is this the normal life of steel boiler stacks?
This section was just replaced 12 years ago. It was 7/16" thick A285 Gr C carbon steel. It is eaten away by the flue gas from the boiler. We have two quotes to replace the stack with A516 Gr 70 and A36 carbon steel.
Is there a particular steel that would be better suited to handle the acid from the flue gas that stack designers know about or is this the normal life of steel boiler stacks?





RE: Boiler Stack Steel Material
Is the stack located in a cold weather climate where the stack metal temperature could be exposed to temperatures below -20 deg F (in the event of no flue gas during boiler outages)? If so, you need to assure adequate impact properties for the steel plate.
RE: Boiler Stack Steel Material
I have never found any record of brittle fracture in a stack even under severe low ambient temperature condtions- I don't think low temperature properties need to be considered for this type of application.
RE: Boiler Stack Steel Material
We had two metal stacks collapse in the 1950's (well before my time) at two (one is now retired) of our power stations in the Midwest. We have two metal stacks at a third station that require stack heaters during winter outages.
RE: Boiler Stack Steel Material
RE: Boiler Stack Steel Material
Could you be getting condensate in the stack, where insulating that top part might help? Just a thought.
RE: Boiler Stack Steel Material
I have at least one copy of one of the actual reports, which I can retrieve. I am going on memory here but the steel used at that time was rolled and welded A7 steel plate, which is the predecessor to A 36. The stack collapsed on one of the coldest days in winter with a brisk wind, while the unit was off on a scheduled outage. The failure was attributed to brittle fracture from one of the shell course welds. The other stack failure occurred under similar conditions at a different site, and time.
I can make a copy and send it to you. I am not sure how to get in touch with you thru this forum without having any nasty messages regarding email addresses. Any ideas?
RE: Boiler Stack Steel Material
RE: Boiler Stack Steel Material
RE: Boiler Stack Steel Material
I think before choosing material you should know the exhausht gas temperature and content of exhaust gas.Then you can choose materials.If acid formation occurs with SA285GrC the same thing occur with the SA516Gr70.If So2 content of flue gas is quite high, maybe you should try SA240 series stainless steels depending on the gas content.You can use 304TP or for worse conditions 316Ti.
RE: Boiler Stack Steel Material
RE: Boiler Stack Steel Material
RE: Boiler Stack Steel Material
Regards,
DowneastTech
DowneastTech
Mechanical Engineer
Magnus R & D, Cypress, TX