08/03/2015

Inside the Hose Safety Institute - August 2015

The NAHAD Standards Committee recently completed work on updating the Hose Safety Institute HANDBOOK©. The Committee has also completed work on a new Hose Assembly Test Certification Guide to help educate Institute employees and their customers. The following is an excerpt from the new Guide, which is also reflected in the new Assembly Fabrication Guides available to Institute members on the NAHAD website.

Hydrostatic Proof Pressure Tests (Non-destructive)

Proof or hydrostatic testing refers to testing that “proves” the finished hose assembly meets the pressure rating required by the application for which it will be used, and that the end fittings have been correctly fitted and the assembly is leak free.

For assembly testing, the rating of the component with the lowest rated working pressure determines the working pressure of the assembly. There shall be no indication of failure or leakage. 

*Certain specifications may require used hose assemblies to be tested at working pressure

**unless otherwise required by the customer

A hydrostatic pressure test requires either a hand pump, a power driven hydraulic pump, or an accumulator system. Connect the hose assembly to the test pump in a straight fashion, assuring a leak tight connection. It is recommended that the hose assembly be secured in an encapsulated tank if possible for short lengths that will withstand the pressure, or sufficient restraints to prevent “whipping" if a failure occurs. The hose ends need to be restrained.  The hose must be free to move slightly when pressure is applied.

Test pressure is determined by the assembly component with the lowest pressure rating.

The following testing procedure is recommended:

1. Lay the hose out straight whenever practical, slightly elevating one end to ensure trapped air is expelled, allowing space for elongation under pressure, preferably on supports to allow free movement under pressure.
2. Blank off one end of the assembly.
3. Completely fill the hose with water; take particular care to ensure that all trapped air is released from the hose.  A bleed valve is typically used to release trapped air in a pressurized assembly.***
4. For reference, mark a line behind the coupling which is at the end of the ferrule, clamp, band, etc.
5. Gradually raise the pressure to the desired pressure rating. Hold the pressure for the time dictated by hose type and conduct a visual inspection. As the pressure is raised, watch for visual indications of permanent deformation, leakage, and coupling slippage. If any of these are noted it is cause for rejection. After the test is complete, relieve the test pressure before disconnecting the hose assembly from the test equipment and drain the water from the hose. The hose may be flushed with a drying agent to customer specifications.
6. When tested in accordance with the above, the assembly under test should be totally leak free for the duration of the test; leakage is defined as a continuous stream of water droplets emitted from a single or multiple locations.

***This is very important as a safety measure because expansion of air compressed in the hose, when suddenly released by bursting or other failure might result in a serious accident.

Unless otherwise stated by the end user, the test medium should be water.

For additional information, please consult the Hose Safety Institute HANDBOOK© chapter on Testing and/or the relevant Fabrication Guide (restricted to Hose Safety Institute members) or NAHAD’s Test Certification Guide (available soon on the NAHAD website.)