THERMAL SHOCK/STRESS

[Deleted User]

Hot boiler, cold system, 15 HP circulator, 5" piping.

richard lampson

THERMAL SHOCK/STRESS

does anyone out there have an explanation of thermal shock ?? and how thermal shock differs from thermal stress ?
relating to cast iron and especially copper tube boilers and water heaters.
thank you

Alan R. Mercurio

"Boiler Thermal Shock" can be loosely defined as sudden thermal changes that occur within the boiler causing rapid and uneven contractions of the boiler's cast iron or steel material. An example is placing a cold glass under hot water -- the glass cracks because of the extreme temperature change. In thermally shocked boilers, the fractures or cracks occur where the temperature difference is greatest -- usually in the back of the boiler near the nipple joints or the furnace area where the cold water enters. Surfaces exposed to cold water are contracting while surfaces exposed to fire are expanding.

Causes of Boiler Thermal Shock Several conditions can contribute to boiler stressing and eventual boiler shock. All involve introducing excessively low temperature water, or cool temperature water at high flow rates, into the hot boiler: Returning water at too low a temperature Cool return water at too great a flow Firing the boiler and heating up water before system circulator is turned on Moving the burner into high fire with boiler water at too low a temperature

You can learn more about this at : http://www.bellgossett.com/Press/thermalshock.htm

Your friend in the industry,
Alan R. Mercurio