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  Hydrostatic Testing  

What is Hydrostatic Leak Testing?
Hydrostatic Leak Testing is used to test components for leaks by pressurizing them inside with a liquid. This testing method can be used on piping, tanks, valves and containers with welded or fitted sections. Leaks can be found up to about 1x10-4 std cc/sec . NOTE: Hydrostatic Testing can be a nondestructive test as well as used as a burst test.

Method
Hydrostatic Leak Testing requires that a component be completely filled with a liquid such as water. Pressure is slowly applied to the liquid until the required pressure is reached. this pressure is held for the required time at which point the component is inspected visually to locate leaks.
WDP-217 PiNPOiNT color developer for water can be sprayed on seams and welds for immediate color change and location of leak. Even if leak happened overnight and has since dried, the color change remains visible.
ODP-210 PinPOINT color developer can be used the same way if the container contains oil.
Tracer dyes can be introduced to containers filled with oil or water, for clear visual indication.
Fluorescent tracer dye can be added to the fluid in containers and leakage can be found easily with black lights.

Hydrostatic Testing - Questions & Answers
Is this test is a leak detection method, a burst test or both? Organizations such as A.S.M.E. and the Coast Guard often specify it without being clear.
Should a leak test be done before or after the hydrostatic test? If a more sensitive leak test is to also be conducted it should be done before, not after.
What about painting and insulation before the test? The ASTM standard permits, but recommends against, a test after painting and increases the normal test time of 6 minutes per centimeter of wall thickness by a factor of 10 if parts of the test object are covered by insulation.
What effect does increasing the pressure have? The hydrostatic test fluid will tend to clog small leaks and vacuum drying or heating may have difficulty in removing water vapor from leaks lxI0-6 std cm3/sec and smaller.

 

Hydrostatic Leak Testing Standard
Hydrostatic Leak Testing is covered by the Standard Method for Hydrostatic Testing, ASTM Standard # E1003-95 available from the ASTM and American Gas & Chemical Co. Ltd.

Two hydrostatic procedures are encompassed in the method:
Pressure drop procedure with a sensitivity of between IxIO-2 and 10-3 std cm/sec. This method will not locate leaks but can be used to measure total system leakage. It is significant that the method recognizes that water additives can speed up the flow of water through leaks and make the test more sensitive.
Visual inspection. This procedure can achieve a sensitivity of between lxl0-2 and lxl0-4 std cm3 /sec. This sizable jump in sensitivity is accomplished by not only reducing resistance to the fluid flow through leaks but by also enhancing the visibility of leakage indications.

There are several means of enhancing visibility - the most commonly used are developers which change color permanently as moisture is drawn through a leak (see Water Detecting Paint)  and fluorescent additives which react to black light in the same way penetrants do (see Tracer Dyes). Rockwell used this method to test fuel tanks for the B-1 Bomber.
Even with this very enhanced sensitivity the method specifically excludes either procedure as adequate for containers holding toxic gas or explosive gas. For this class of gas being held under pressure a sensitivity of lxl0-5 has often been used as a minimum tightness standard. The Colormetric Developer or a high sensitivity leak testing Bubble Fluid would be a more appropriate test method in this instance.
One of the more interesting suggestions in the ASTM standard is that it is often more useful to pulse the pressure during a test than it is to hold a steady pressure. This is especially true when the system being tested will not operate at a steady pressure or it is being tested at pressures well over those expected during normal use. The reason for this requirement is that small leaks are not always static. Some expand under pressure, some contract. Severe over pressurization may in fact close some leaks altogether.
Penetrants (usually fluorescent) can be substituted for water in a pressure test similar to hydrostatic testing. They can achieve a similar sensitivity.  Read more about Inspection Penetrants

Products for Hydrostatic Testing

 

 

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