Boiler Tube Failure 4

[NDA277]

At least some boiler systems I have evaluated do NOT have a high TUBE temperature (not high steam temp)shutdown.

I would appreciate comments as to why a boiler would not have high TUBE temperature shutdown instrumentation to protect the tubes from overheating and failure.

Thanks...

 

[metengr]

Because in a watertube boiler feedwater level and flow are your critical parameters, operationally and to prtect the entire bolier from failure.

Yes, you can add TC's to monitor tube metal temperature in a waterwall circuit. However, you have maintenance associated with TC's and after time they fail in agressive service environments. I can deal with tube failures with little impact on safety versus an entire watertube boiler that is starved of feedwater and suddenly water is added.

 

[davefitz]

Large utility boilers usually are provided with tube metal temperature thermocouples on a few tubes of each bank's outlet header , and short term and long term alarms are annunciated in the DCS. Whether or not the operator acts on them or ignores them is the operators perogative.

There have been cases where the unit was operated for over 1 yr at final steam ( and metal) temperatures more than 100F over the design limit, and the result was catastrophic failure of the transfer pipe with fatalities ( Mohave 1987). So I think the state regs should recognize the issue and ensure the licensed operators recognize it.