Carbon steel tank exposed to above 775F
Carbon steel tank exposed to above 775F
(OP)
We have three carbon steel steam drains tanks at our combined cycle power plant. High energy drain lines are connected to the tank including main steam and hot reheat drains. The drains are attemperated before entering the tank. The tank is atmosperic and is designed for 800F at 50 psi. We have experienced many problems with the tanks including thru-wall cracking and structural unsoundness. The plant became operational in 2003.
Just recently, we obtained historical data which indicated the tank design temperature had been exceeded for several years. The tanks are only used during start-up and shutting down the units. The tanks seem extremly volatile when there is an issue preventing a normal start-up and the high energy drains continue to be directed to the tank for 2-3 hours. It was also noted that the condensate pumps were shut off to early (condensate supplies attemperation to the drains before being directed to the tank).
I'm looking for advice if it is safe to continue using the steam drains tanks. With the main steam at 1006F and hot reheat at 1020F, what type of testing is required to determine the fitness-for-duty of the tank? The header connecting to the carbon steel tank is p11 material. Do you think the tank should have been manufactured with alloy material?
I'm particularly concerned with the dependency of the condensate attemperation to protect the tank from exceeding design temperature.
Is there a reference Code that addresses the design temperature of the tank being exceeded? Your advice is greatly appreciated.
Regards
Just recently, we obtained historical data which indicated the tank design temperature had been exceeded for several years. The tanks are only used during start-up and shutting down the units. The tanks seem extremly volatile when there is an issue preventing a normal start-up and the high energy drains continue to be directed to the tank for 2-3 hours. It was also noted that the condensate pumps were shut off to early (condensate supplies attemperation to the drains before being directed to the tank).
I'm looking for advice if it is safe to continue using the steam drains tanks. With the main steam at 1006F and hot reheat at 1020F, what type of testing is required to determine the fitness-for-duty of the tank? The header connecting to the carbon steel tank is p11 material. Do you think the tank should have been manufactured with alloy material?
I'm particularly concerned with the dependency of the condensate attemperation to protect the tank from exceeding design temperature.
Is there a reference Code that addresses the design temperature of the tank being exceeded? Your advice is greatly appreciated.
Regards





RE: Carbon steel tank exposed to above 775F
rmw
RE: Carbon steel tank exposed to above 775F
I don't understand your use of the word "volatile" but if it means what I think it means I would use the word 'violent' to describe what parts expsed to these applications undergo.
There is a tremendous amount of energy being expended in this service, and equipment involved usually suffers in the process. I've seen some mighty strong looking metal parts bent like pretzels by these drain streams.
We still need to know the actual temperatures that the tank has been exposed to in order to be able to offer an opinion regarding your question.
rmw
RE: Carbon steel tank exposed to above 775F
Thanks
RE: Carbon steel tank exposed to above 775F
1. I would have some TC's placed on the tank to evaluate actual metal temperature. By the time the steam reaches this tank you might be surprised as to the actual metal temperature.
2. During a scheduled outage I would have internal visual and NDT inspections performed of the tank girth, seam and nozzle attachment welds using wet fluorescent MT. In addition, I would have thickness testing performed. These tests would provide enough information to evaluate the condition of the tank.
3. Based on the results of 1) and 2) above, you can decide on an action plan going forward. Like adding attemperation to reduce steam temeprature to the tank or internal baffles, etc.
RE: Carbon steel tank exposed to above 775F