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Boiler Thermal Shock Problems

Boiler Thermal Shock Problems

Boiler Thermal Shock Problems

(OP)
We have recently designed the installation of a cast-iron sectional boiler an have experienced multiple crackings of the sections.  The manufacturer of this boiler insisted that blend pumps be installed, despite the fact that the boiler has a three-way valve on the supply that diverts hot water to the return to maintain the return temperature during warm-up and part-load operation.  
Blend pumps have been installed, and we have just experienced another crack, this time in one of the sections that had just been replaced.  The contractor has observed that these sections are much lighter than those installed in the past.  The controls contractor has observed similar problems in another instation of the same manufacturer's boiler.
Is anyone else having these types of issues?  This seems like a manufacturing or assembly problem with the boiler, and the manufacturer is denying any liability.  Any help would be appreciated.

RE: Boiler Thermal Shock Problems

The exposition does not elaborate on the Thermal Shock that appears in the title. Is it determined beyond reasonable doubt that cracking is due to thermal shock? Might it be due to assembly stresses as suggested? Would it be possible to introduce means to absorb elastically any asymmetric loads?

http://www.welding-advisers.com/

RE: Boiler Thermal Shock Problems

I would place some contact thermocouples (TC’s) at several locations on the boiler to compare temperature differentials during various operating conditions. There could be other causes for cracking, other than thermal fatigue. Several TC's well placed can help confirm or rule out thermal fatigue.

RE: Boiler Thermal Shock Problems

(OP)
The manufacturer is claiming "thermal shock" is the cause of this problem.  It has not been determined beyond a reasonable doubt that this is the problem.  We will be visiting the jobsite soon, and the cracked section has been saved.  Perhaps our observation of the crack size, type and location on the boiler section will indicated what, if any temperature gradient could have caused this.  Thank you for your suggestions!

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