Stress-tests on the DN 1400 international gas pipeline GAZELLE

Gas pipeline DN 1400 GAZELLE in Krušné hory (The Ore Mountains)

The construction was divided into 3 LOTs. CEPS a.s. conducted in the second half of 2012 stress-tests and related activities at LOT 1B between BDS Brandov over LVS Jirkov and LVS Hrušovany to LVS Sýrovice in the length of 52.5 km.

On the pipeline leading over Krušné hory with a total elevation of almost 700 m were carried out processes of cleaning, calibration, stress-test and pressure test. At the end before the commissioning, the gas pipeline was dried up.

All activities were carried out in accordance with the Czech and also European regulations – ČSN EN 1594, ČSN EN 12327, TPG 702 04 and TPG 702 11.

By the enlargement of sections above normal limits we contributed to the acceleration of the pipeline construction

The pipeline was mainly in the mountainous parts professionally and carefully divided into sections so that all sections met the requirements for resulting MAOP (STOP), which were moving just above DP. The minimum STOP was 87.5 bar. This made possible to minimize the number of test sections while maintaining the required operating parameters.

The gas pipeline was divided into 21 sections, some of which were with regard to TPG 702 04 enlarged, namely up to twice as much. According to TPG 702 04 the maximum segment size allowed for this dimension is 6,000 m³ of the internal capacity; however the largest tested section had the capacity of 12,240 m³ at the length of 8,100 m, by which it exceeded the normative limit by more than 100%.

For this exemption it was necessary to acquire the positive standpoint of the future operator and subsequently the approval of the State Professional Supervision – Technical Inspection of the Czech Republic (TIČR).

We secured the reliable tests’ control by the extremely precise measurement

As a counterbalance to enlargement of sections were used more accurate techniques of measurement. In the course of stress-test was carried out the continuous calculation of the integral volumetric deformation in a maximum of one-second intervals, thus the deformation behaviour of pipeline was under the constant supervision, and thereby to avoid exceeding of the deformation maximum.

The actual course of tests and drying of the pipeline

Requirements for the duration of the leak tests

For the section exceeding the norm by more than 100% was put forward the requirement for the leak test in the duration of 48 hours, at other over the limit sections were the leak tests carried out for 24 hours.

The terrain accessibility

The terrain accessibility of some sections of the pipeline was very poor, despite that the tests were successfully, on time and properly implemented.

Cleaning of the section 1 of DN 1400 gas pipeline GAZELLE

Cleaning and calibration prior to testing

Each section before filling up with the water was cleaned and calibrated using the aluminium plate with a diameter of 1,325 mm.

Insertion of the calibration pig DN 1400 into the section 1

Sources of water

The entire pipeline section tested by the company CEPS a.s. took in more than 78,000 m³ of water, which was taken from the stream Svídnice, the industrial reservoir Kyjická and river Ohře.

Gas pipeline GAZELLE DN 1400 in Krušné hory – passing of water up to higher located sections

After the tests were completed, the water was sent back into streams.

Monitoring of the position of the inlet pig

The monitoring of the position of the filling pig

In the mountainous sections was monitored the exact position of the inlet pig using hydrostatic pressure and longitudinal profile.

The gas pipeline DN 1400 GAZELLE – the longitudinal profile in Krušné hory – elevation all over the entire pipeline is 704 m

On the request of the future operator, the pipeline was loaded on limit of 110% of the actual yield strength. Nevertheless, it reached an average of only 10–30% of allowed deformation limits.

Calculation of the planned load

For each tested section has been calculated the planned load at the stress-test. Each pipe in gas pipeline has been checked with inspection documents, registered its melting and the actual yield strength, attributed the geodetic load and calculated loading pressure. After that was from those pipes chosen the weakest one in the section and the entire section was adjusted to this pipe. All this was done for the entire 52.5 km of the gas pipeline, pipe after pipe.

Stress-test in the section 9 in Krušné hory

For the first time we made use of the new generation of our unique software for measurement and control of stress-tests

For measuring stress-tests was for the first time used new software, already of the 3rd generation, which allowed to effectively manage the process of stress-tests and also during the pressurization of the over limit sections. The system was based on the knowledge and experience of previous programme generations that has worked successfully on stress-tests since the mid-nineties of the last century.

General look at the stress-test control – a system of data collection, imaging software on the notebook and remote control of pumps

Development of the system of errorless data collection and subsequent imaging software lasted almost seven years, and despite a number of unsatisfactory technical solutions of data collection it was managed to get the system that fully meets the technical and operational requirements, including high-quality visualization and data outputs. Only the operating system in commercially available computers has changed three times during the development time.

Detailed look at the conducted stress-test – relation p-V

Modern computers enable to perform the control of the stress-test by displaying on more monitors, which further contributes to the control accuracy and sufficiency of information for the operation. The operator thus has at critical moments of the stress-test all the necessary data and progress of measured, calculated, and auxiliary quantities, either as a numeric value, or graphic relation. In addition to the time relations it is also possible to display relations on pumped in volume, which is crucial just for stress-test. It is possible to display up to 128 of such values.

Together with the remote control of high-pressure pumps the control engineer of measurements can when necessary (for example in case of reaching limits of stress-test) immediately stop operations of machines and to halt the further loading of the pipeline.

The course of stress-test

Despite more than doubled length of section it was managed to keep the speed of pressure rise above the normative minimum of 0.5% of the final pressure per minute. By pumping in the amount of 910 l/minute was achieved by 0.6%/minute. This required the start-up of two special high-pressure pumps; their flow was summed up together. Even so, one cycle of stress-test (its ascending part) lasted more than three hours.

Technology for implementation of the stress-test – section 13

On critical sections there was used the pipe with strengthened wall, namely up to 25.5 mm. This meant stress-test limit pressure on the limits of 190 bar. Deformation volumes amounted up to 8,000 litres. Pipe with the basic wall thickness of 18.0 mm was loaded up to approximately 135 bar.

Stress-test of the section 2 – the ultimate pressure reached 193 bar

Measuring of pressure tests was carried out on pressure recorders with increased accuracy of measurement, namely 0.1 and 0.05%. (The required accuracy is standardly 0.6%.)

Drying of the pipeline

For drying of the pipeline, which took place in two sections (19.5 km and 32.6 km), was deployed the entire capacity of dryers that CEPS has available. It was reached the instantaneous power of 1.75 m³ of dry air per second, which means 6,300 m³/hour. All this was carried out with consumption of 180 litre of diesel oil per hour in compressors with a total capacity of over 7,000 m³/hour.

Drying technology – set of compressors supplying air for drying

NET4GAS About the gas pipeline DN 1400 GAZELLE