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Testing safety devices in gas pressure regulating stations
By Leif Bro Jensen, Senior Engineer Gas Distribution Technology, HMN Naturgas I/S.
Within the next two years, Danish natural gas distributor HMN Naturgas will implement the Kamstrup Inspection System for the visual and functional testing of all Distribution Metering-Regulating and District Regulator stations.
HMN Naturgas has 451 pressure regulating stations, distributed on 134 high and 193 low-pressure stations in the east (the Greater Copenhagen area) and 124 high-pressure stations in the west (Central and North Jutland).
The key function of the stations is to reduce the pressure – the high-pressure stations reduce the pressure from typically 50/40/19 bar to 25/4 bar, whereas the low-pressure stations reduce the pressure from typically 4/2.5 bar to 100/22 mbar.
From the very beginning of the introduction of natural gas in Denmark, the Danish working environment legislation contains requirements on the safety devices in the stations with one purpose: protection from unintended overpressure.
Requirements for annual testing
The gas companies assign a very high priority to security of supply, and therefore, focus especially addresses the optimal function of safety devices and working regulators.
According to the authority requirements, safety devices must be inspected and tested every calendar year at an interval of maximum 15 months.
For a part of the stations, the gas companies have increased the number of tests to ensure a high security of supply, and in addition, objects are separated for service and exchange of soft parts.
In historical terms, the security of supply from the stations in the Danish natural gas system has been high.
However HMN Naturgas has chosen to invest DKK 3.3 million in a system for visual and functional testing, and to understand why, it is important to first understand the Kamstrup inspection system.
Kamstrup Inspection System
Today, gas station inspectors test the safety devices and the regulators by installing hoses between pressure outlets and pressure gauges, and manually carry out blockings and readings.
The Kamstrup system performs these tests automatically, and a digital data collection of the function of the individual objects is performed.
In the steel influence pipes of the safety devices of the gas line, the Kamstrup safe diagnosis coupling (BMA) and safe measuring coupling (BDA) system couplings are installed to which the mobile test device can be connected by means of the flexible hoses.
Dependent on the safety devices, five or six system couplings per gas line are installed. In most stations, there is an operation line and a reserve line, and therefore, ten to twelve system couplings are installed in one station.
The mobile test device
The mobile test device is named PLEXOR.
It consists of a casing with two digital pressure gauges, a function selector for selecting the object that is to be tested, e.g. the regulator, Safety Shut-off Valve (SSV) or Safety Relief Valve (SRV) and a start handle for activating the test.
Dependent on the actual pressure range, the pressure gauges are exchangeable to ensure that the measurement is carried out with the required precision.
The PLEXOR test device is connected to the system couplings by means of the flexible stainless steel connecting hoses.
Two types of system couplings are available: BDA, the safe diagnosis coupling, and BMA, the safe measuring coupling.
The BDA coupling has a three-way valve that makes it possible to isolate the safety device, e.g. the SSV, and then apply a test pressure v
