Test of Safety Devices on Gas Pressure Regulating Stations
Within the next two years, the Danish natural gas distributor, HMN Naturgas, will implement the digital tool: Kamstrup Inspection System for the functional testing of all MR and DR stations.
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By Leif Bro Jensen, HMN Naturgas I/S (DK) |
HMN Naturgas has 451 pressure regulating stations, distributed on 134 high pressure stations 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 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 to Denmark, the Danish working environment legislation contains requirements on safety devices in the stations with one purpose: Protection from unintended overpressure.
The basis of meeting the requirements of the Danish Working Environment Authority is the American GTPC guide (previously ASME guide) supplemented by WEA Guideline F.0.1 of July 2001. The safety devices can e.g. be safety valves or monitoring regulators. If the supply pressure is above 4 bar, two independent safety devices must be available.
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 work regulators.
According to authority requirements, safety devices must be inspected and tested every calendar year at an interval of maximum 15 month. 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. But what is then the reason for HMN Naturgas to invest DKK 3,3 millions in a digital tool for functional testing? Before answering this question, a description of the digital tool is given below.
Kamstrup Inspection System
The figure shows the individual parts of Kamstrup Inspection System.
Today, gas station inspectors test the safety devices and work 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.
On the flexible stainless steel hoses from the safety devices of the gas line, the Kamstrup system couplings BMA and BDA are installed to which the mobile test device can be connected by connecting hoses.
Dependent on the safety devices, 5 or 6 system couplings per gas line are installed. In most stations, there are an operation line and a reserve line, and therefore, 10 to 12 system couplings should be installed in one station. The system couplings are installed permanently in the stations.
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. a SSV or a SBV, 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 on the flexible stainless steel hoses by connecting hoses. Two types of system couplings are available: BDA, the safe diagnosis coupling, and BMA, the safe measuring coupling. BDA has a three-way valve that makes it possible to isolate the safety device, e.g. the SSV, and then apply a test pressure via the PLEXOR equipment to test the device.
During the test, the PLEXOR test device lets the pressure increase by 1.5 % per second, until the safety device is released. The PLEXOR test device registers all pressure conditions before and after the object.
Instructions via PDA
The figure shows how the PLEXOR test device communicates wirelessly with a PDA. On this PDA, the gas station inspector is instructed in the installation of hose connections and valve positions.
The procedure is prepared specially to the station in question, and the gas station inspector cannot use the test incorrectly or finalise the test uncompleted. The gas station inspector can read the test result on the PDA, and therefore, he can decide on site if a safety device requires service.
The software INSPECTOR is installed the PDA. This module compares the test results with the predefined criteria and informs the gas station inspector of any discrepancies.
The INSPECTOR module cannot change the set-up or procedures — such changes are only possible using the MANAGER module installed on a desktop computer at the responsible operations manager.
CONNEXION software
The key component of the Kamstrup system is the CONNEXION software package. In addition to the previously mentioned modules INSPECTOR and MANAGER, the module DIAGNOSTICS is also included.
CONNEXION controls both the visual and the functional inspection, stores all the inspection results and presents them in various screenshots, dependent on the requirements of the operating technician.
The DIAGNOSTICS module imports the data required for analysis and presents them graphically, which ease the evaluation of the states of the AMR stations.
If one of the components of the gas line requires further attention, a zoom function makes it possible to draw attention to error indications.
An essential function of DIAGNOSTICS is the possibility of comparing with previous registrations that can be included in the same diagram. This provides a good statistical basis.
Implementation
The installation of system couplings on MR stations started in August 2011 and are expected to be finalised within two years.
At the moment, HMN Naturgas works on collecting documentation for all stations, which is to be transferred to CONNEXION.
Kamstrup assists in building up the database structure, and furthermore, all procedures installed on the PDA must be in Danish. In late 2011, HMN Naturgas receives the mobile test device and software, and training in the use of the device will take place. To begin with, four gas station inspectors are trained, two in HMN east and two in HMN west. Subsequently, these inspectors must train their colleagues in their group in the use of the device.
Uniform functional testing
Back to the question about why HMN Naturgas invests DKK 3,3 millions in a digital tool for functional testing.
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Kamstrup Inspection System provides a uniform functional testing that is completely independent of the individual. The test results are stored, and the data collection means that the test will be reproducible. This means that, at an early stage, it is possible to detect if an object is soon to be renovated.
With this system, it will therefore be possible to complete predictive maintenance to a great extent and thereby reducing the spare part consumption and the time consumption of overhauls.
The functional testing is carried out with pressure on the gas line, in contrast to today, where the test is carried out without pressure. This means that the inner density of the gas line is controlled, and small leaks in valves and objects are registered, as even very small pressure changes are visible.
The system has been in operation in Holland since 2000, and in Germany, many gas companies have adopted it within the last five years. On the basis of experience gained from these markets, HMN Naturgas expects that the system in a few short years proves to be a good investment.
Kamstrup Gas Inspection System