In large boiler installations such as utilities, pulp and paper mills, etc., the location of several safety relief valves are in difficult-to-reach areas. This makes it challenging to remove and send them out for testing, as in several installations the valves are welded in place. In such situations, ASME allows in-situ testing that utilizes lift assist devices attached to the spindle of the valve with adapters and pressure applied to lift the spindle.
The interval of testing of safety valves is governed by ASME standards, NBIC and local jurisdictions regulations.
ASME pressure relief valve testing standards are primarily located in Section 1 and Section VIII of the ASME Boiler & Pressure Vessel Code.
In summary, Section I of the ASME Boiler & Pressure Vessel Code provides guidance and standards for pressure applications for boiler applications. A valve conforming to the requirements of Section I is identified by a National Board “V” stamp, and usually features two blowdown rings.
Section VIII of the ASME Boiler & Pressure Vessel Code specifically refers to vessels that operate at pressures above 15 psig. Safety relief valves that conform to Section VIII standards are identified by a National Board “UV” Stamp.
There are two methods utilized for in-situ testing, both comply with ASME standards and are considered accurate and reliable.
Hydraulic Testing Method:
This method requires a bracket to be manually installed to the safety valve spindle. In this configuration, hoses from the pumping units are connected to the bracket. A compressed air-driven hydraulic pump unit is utilized to apply pressure. The operator controls the pressure to be applied, and the data is continuously recorded on a laptop. Prior to the test, software is programmed with the safety valve data/specifications and set pressure. When the required set pressure is achieved, the pressure is released. If the safety valve does not meet the lift pressure specifications, adjustments and repairs are carried out and the test is repeated.
The hydraulic system is bulky and require long lengths of hydraulic hoses. It is also sometimes challenging to test safety valves that are difficult to reach to attach the bracket and hoses.
Electronic Testing Method:
An electronic system makes use of a precisely controlled and computerized driven system referred to as set pressure verification device (SPVD). SPVDs utilize highly accurate pressure sensors to measure the process pressure and determine the lift force being applied. These sensors include automatic calibration and diagnostics by the SPVD computer-based controller to confirm the sensors are operating correctly prior to each test. The portable unit consists of a laptop equipped with a database of valve seat effective areas and lift assist device. A combination of system pressure and controlled external force is applied to the valve’s spindle to lift the valve. All data is recorded in real time, and test results are available by digital and analog mediums.
For reasons of accuracy and portability, the electronic test method is considered the preferred method of in-service testing of safety relief valves.
Anzar