Valve/Actuator Stall Test 1

[jrod47]

Hello all. I work for an EPC company and one of our vendors is having issues meeting a valve testing requirement in one of our client's specs. Does anyone have any input on the following issue?

We have a requirement in our instrumentation spec which calls for a “stall test” to be performed on actuator/valve assemblies to demonstrate that with the valve jammed at the maximum actuator output, the stem and drive train are not damaged. While the vendor believes this test will not damage the stem or drive train in any way, he has advised against this test because of potential to damage the ball and/or seats, because in their view, the only way to physically jam the valve is to put an obstruction in the ball opening.

The ball valve is a 24”x20” reduced bore, 1500# Class, Super Duplex Valve (Body and Ball). The estimated maximum actuator torque is 56,413 Nm.

So the question is, is anyone familliar with stall tests (specifically on valves this size), and if so, are there any testing standards and/or guidelines our vendor can follow so to not damage the ball and/or seats?

I'd appreciate any help. Thanks.

 

[bcd]

The vendor is correct. Installing a 20" diameter rod through the ball port and apply the full stall torque of the actuator could cause permanent deformation of the parts. Especially the edge of the ball port. A slight elongation on the corner of the ball port will cut into the seats when the valve cycles.

One option is to disassemble the valve, make test fixtures and test each part individually. Will be pretty expensive but will allow for alternate ways of holding the parts and avoid damage.

Or, use calculations. Its all pretty basic, well proven stress formulas found in a good machine design text or Roark.

Last resort, make them do the test and agree to pay for repair of any damage that occurs.

 

[jrod47]

Thanks for the response.

We also share the same concern as our vendor and are trying to push for acceptance of calculated MAST values to justify the design.