Hydrostatic Testing on Fossil Fuel Boilers 2

[Michaelk2]

What is the formula for calculating hydrostatic test pressure maximums on fossil fueled boilers? Also, I am assuming the boiler safety valve pressure settings are 1.5x MAWP on the same boilers. Please correct me if I am incorrect in that. I appreciate your wisdom in advance.

 

[yogibear1]

Safety valve settings do not follow the 1.5 multiplier that is used in hydro testing of pressure parts. This is partly due to the temperature difference between the two conditions and the relative strength of the materials at those temepratures. The low set safety valve on drum type boilers is set for the maximum allowable drum pressure which is higher than the pressure at Maximum Continuous Rating (MCR). I have seen steam drums on large utility boilers with 4 to 6 safety valves. But that (low set on the drum) is not the lowest pressure setting overall. The lowest setting would be on the superheater outlet (which is at a higher temperature than the drum).

 

[metengr]

The hydrostatic test pressure is as follows;

1.5 X maximum allowable working pressure (MAWP) or design pressure


No, safety valves on boilers are set to pop at the design pressure of the boiler. Anytime a hydrostatic test is performed, the safety valves must be gagged or blanked off to avoid popping the valve at higher pressure.

CAUTION; I would not recommend performing hydrostatic tests on boilers that have been in service for over 25 years. My reasoning is that the boiler design has been proven and using the hydrostatic test to look for "weak links" or areas of deterioration or degradation can result in more harm than good. Most of the materials used in the steam circuits of boilers age resulting in a lower toughness or older boilers were constructed of materials that had exhibited lower toughness, thus requiring an increase in water/metal temperature prior to conducting a hydrostatic test. Second issue is back filling of superheaters that cannot be isolated from the steam drum and would otherwise not see water during normal operation.

There are many advanced condition assessment techniques that can be utilized in place of a hydrostatic test.