Qualified test benches for safe valves

Comprehensive valve testing

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In addition to the requirements for reducing emissions, a valve’s fire resistance plays an important role in its selection for many applications. Whether it actually ensures functional reliability in accordance with ISO 15848-1, API 589 and 607 or DIN EN ISO 10497 can be verified with Amtec’s test benches: the Temes valve.teq and Temes fire.safe.

Reducing volatile fugitive emissions is the goal when classifying the performance of industrial valves according to ISO 15848-1. This classification specifies the type approv-al test for assessing and qualifying valves. As a result of the amendment to the German Air Quality Control regulation (TA Luft) shortly before it came into force, this test standard will continue to grow in importance. Both valve manufacturers and industrial plant operators will need to address the issues in the near future. The type testing requirements in relation to fire safety were originally compiled by the American Petroleum Institute in various API standards
(e.g. API 589, API 607). An ISO standard (DIN EN ISO 10497) has also existed on this topic since 2004. Amtec developed appropriate test stands to ensure a systematic and reproducible test procedure for qualifying industrial valves. Amongst other things, the development process considered the criteria which are explained in the two following sections.

Classification

The performance categories for classifying industrial valves during the ISO 15848-1 type test depend on the operating conditions and the risks of the medium being conveyed; they are divided into tightness, strength and temperature class. While tightness classes are specified for the shaft or shaft seal depending on the test medium (helium or methane), only compliance with a permissible limit value must be demonstrated on the housing seal. If helium is used as the test medium, the vacuum method must be employed at the stem seal; tightness classes AH (10-5 mg/m/s relative to the circumference of the stem), BH (10-4 mg/m/s ) and CH (10-2 mg/m/s) are defined. If, on the other hand, methane is chosen, the sniffing method is sufficient; the tightness classes to be achieved in this case are AM (50 ppmv), BM (100 ppmv) and CM (500 ppmv). Regardless of the test medium, the 50 ppmv limit value must not be exceeded at the body seal using the sniffing method.

The strength classes characterise the number of mechanical cycles performed during the design test. Strength classes CO1 (205 cycles), CO2 (1500 cycles) and CO3 (2500 cycles) are defined for shut-off valves and CC1 (20,000 cycles), CC2 (60,000 cycles) and CC3 (100,000 cycles) for control valves. About half of the mechanical cycles take place at room temperature and the other half at elevated temperature. This temperature also determines the temperature class to which the valve belongs (t-196 °C, t-46 °C, t-29 °C, tRT, t200 °C, t400 °C).

Safety test according to ISO 10497

During type testing for fire safety, pressurised valves are specifically exposed to firing for a defined period of time; the flames should completely surround the test specimen. ISO 10497 specifies a burning time of 30 minutes, water as the test medium and a temperature of between 750 and 1000 °C in in the area around the valve.

The temperature is monitored with the aid of calorimeter cubes, which must be installed underneath and adjacent to the valve. Within 15 minutes, the temperature must rise to 650 °C at these cubes, which are made of carbon steel with a temperature sensor in the middle. During the remaining measuring time the average temperature must not fall below this value.

Inner and outer leakage must be recorded throughout the burning time. The test pressure depends on the seat seal and the nominal pressure level. For valves with soft seat seals and PN10, PN16, PN25 or PN40 pressure ratings as well as Class 150 and Class 300, the internal pressure must be limited to 2 bar; for all others, 75 % of the maximum permissible pressure must be set at the valve seat at room temperature.

Within ten minutes of the fire being extinguished, the specimen must be forced-cooled with water to a surface temperature of less than 100 °C. The leakage must continue to be determined during this cooling time. The maximum permissible seat and external leakage specified in ISO 10497 should be used to assess the various test phases. A leak test before firing, operability after cooling and a leak test after checking operability are also required as part of fire safety type testing according to ISO 10497.

Test equipment

The Temes valve.teq valve test bench consists of the mechanical structure, an electric (or pneumatic) actuator, a heating and cooling system and a leakage measuring device. It primarily serves to classify and qualify valves in accordance with the specifications of ISO 15848-1. Furthermore, all user-defined leakage, friction and temperature tests can be carried out both manually and automatically.

The adjustable heating device allows testing at temperatures of up to 400 °C using induction or resistance heating cables. Either helium or methane can be used as the test medium. The leakage rate can be detected with a differential pressure measuring system, a helium mass spectrometer or a flame ionisation detector. Leakage tests can be carried out both at room temperature and at maximum temperature with a maximum internal pressure of 200 bar.

All measured variables are comprehensively documented during the tests. The data acquisition unit also permits fully automatic control of the test bench and provides information on operating states.

The Temes fire.safe test bench was developed for fire safety type testing according to various API standards and ISO 10497. The central element of this test bench is an arrangement of several burner sheets in the bottom panel, which can be switched on variably according to the size of the valves or flange connections to be tested. This ensures that specimens are always completely enclosed by the flames. Since the fuel gas supply can likewise be regulated, the different heating ramps of the various standards can be individually adjusted in the test bench software.

The leakage rate is measured by collecting the leaked test medium in a container and weighing it. Leakage can thus be determined, and the type test assessed with regard to fire safety, at any time.

Once again, all measured variables are continuously recorded and stored. Subsequent evaluations of the test and the type test can hence be automated.

www.cpp-net.com

Online search: cpp0318amtec

Hall 3, Booth H85


Author: Dr. Manfred Schaaf

Managing director,

Amtec

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