PRESSURE TESTING FEEDWATER HEATERS AND POWER PLANT AUXILIARY HEAT EXCHANGERS

Stanley Yokell’s paper on hydrostatic testing feedwater heaters and auxiliary heat exchangers Paper No. 2010 – 27106 has been accepted for presentation at the July PowerGen conference in Chicago. The paper demonstrates that pressure gage divisions of typical gages used in hydrostatic testing are too coarse to disclose minute leaks such as weeping from the channel through the tube-to-tubesheet joints during the half-hour TEMA-required hydrostatic test time hold time.

The paper uses as an example testing a U-tube, closed feedwater heater at 4600 psi and a leak volume of 10 drops of water over the half-hour hold time. It shows that the change in pressure resulting from such a leak would be so small that it would not register on the test gage that would typically have 50 Psi graduations.

In most feedwater heater designs and in some auxiliary tubular equipment, the back side of the tubesheet cannot be visually inspected. Because the hydrostatic testing does not disclose minute leaks such as weeping, defined as 10 drops over the half-hour test hold time, Purchasers are advised to require Manufacturers to perform leak tests described in the ASME Code’s section V. As a bare minimum Purchaser’s should require the Manufacturer to perform a Gas-Bubble test. However, it is more preferable to perform both the Gas-Bubble test and a Helium sniffer leak test (mass spectrometer leak test).