The testing of pipes, whether for water or gas, is an essential stage in ensuring the safety, reliability and durability of distribution infrastructure. This process makes it possible to verify that the pipes are correctly installed, free from structural defects and capable of withstanding the expected operating pressures. The testing procedure is therefore vital for preventing future problems that could compromise the operation of the network or lead to significant leaks, with both economic and environmental consequences.
LEAX is able to carry out and certify leak tests and acceptance tests on pipelines, systems and tanks using specialist equipment.
Inspections and leak tests are essential to ensure proper functioning and compliance with regulations, and are also necessary:
All our tests are carried out in accordance with the most stringent international, national and local regulatory requirements.
TESTS AND LEAK TESTS CARRIED OUT
The testing techniques used are selected and tailored to the type of pipeline.
The tests are carried out by specialist technicians using specialist equipment certified by ACCREDIA and/or with a UNI EN ISO 17025 calibration certificate.
The following measuring instruments are used:
1) MECHANICAL CYLINDER-TYPE THERMOMANOMETER RECORDER, or THERMOMANOGRAPH, with data recorded on a paper chart.
2) Electronic DIGITAL PRESSURE GAUGE, with data logging to an SD card in Excel format.
CYLINDER-TYPE THERMOMANOMETER RECORDER
The temperature and pressure recorder, or TERMOMANOGRAPH, is a portable TEMPERATURE and PRESSURE recorder that allows both the pressure and temperature of a pipe, network or system to be recorded simultaneously.
In order to carry out a leak test or commissioning test on a pipeline correctly, it is essential to account for the drop in pressure caused by changes in temperature, so as to avoid mistaking a drop in pressure for a leak.
Using the thermomanograph, temperature and pressure are recorded simultaneously and plotted on graph paper wrapped around the instrument’s drum. It is therefore possible to correlate the pressure readings in the system with the temperature readings and avoid errors in interpreting the results. Temperature and pressure readings can be recorded on a daily or weekly basis.
The DIGITAL ELECTRONIC PRESSURE GAUGE is used for the precise measurement and monitoring of pressure in pipes, systems and networks. We use it in the plumbing sector for the testing and leak testing of pipes and systems, in the civil engineering sector to check for any ‘water theft’ from systems, in the industrial and manufacturing sectors to test fire-fighting systems and to monitor compressors and pumps, and in the chemical sector for process control measurements.
PREPARATION FOR THE LEAK TEST OR COMMISSIONING TEST
The thermomanograph is secured in a stable and safe position. (Similarly, the digital electronic pressure gauge is also connected and set to scan pressure readings at 20-second intervals. These measurements will be automatically saved to an SD card on board the manometer, directly in Excel format).
APPLICATION OF TEST PRESSURE IN POLYETHYLENE (PE, HDPE, LDPE) PIPES
The testing of a PE pipeline must take into account the visco-elastic behaviour of polyethylene and therefore follow the SPECIFIC PROCEDURES set out below.
During testing, the temperature of the pipe section must not undergo significant variations, as the visco-elastic properties of the polyethylene pipe could adversely affect the result. After backfilling, it is therefore advisable to wait at least 24 HOURS before carrying out the testing, to allow the temperature of the entire section to STABILISE. Any exposed sections of the pipe must be protected against temperature fluctuations caused by exposure to sunlight.
With reference to the attached diagram, the procedure for applying the test pressure to polyethylene pipes is as follows:,
1) PRESSURISATION
Once the vent valves have been closed, switch on the ELECTRONIC DIGITAL PRESSURE GAUGE and gradually bring the pipeline up to the test pressure PC (section A–B of the graph).
The test pressure is given by: PC = 1.5 PE
PC = test pressure, PE = maximum permissible working pressure in continuous service.
For PE100 polyethylene, it is advisable not to exceed a test pressure of PC ≤ PE + 5 (bar).
2) APPLICATION OF TEST PRESSURE CORRECTION COEFFICIENTS In the case of PE pipes subjected to test temperatures above 20 °C, the test pressure PC must be multiplied by a pressure reduction coefficient Ct, defined as: Ct = 1.260 – 0.013 T.
Therefore, in this case only, the test pressure will be: PC = 1.5 PE × (1.260 – 0.013 T)
3) MAINTAINING PRESSURE The test pressure PC is maintained for 30 MINUTES (section B–C of the graph), REPLENISHING any pressure drops with subsequent pumping, so as to compensate for the increase in VOLUME due to the natural EXPANSION of the pipe.
4) PRESSURE REDUCTION The pressure is gradually REDUCED until it reaches 3 BAR (section C–D of the graph), by draining water via the vent valve.
5) ACTIVATION OF THE THERMOMANOGRAPH
The THERMOMANOGRAPH is activated to continuously record pressure and temperature values (point D on the graph).
The ELECTRONIC DIGITAL PRESSURE GAUGE has already been activated and is therefore continuing to record pressure data.
6) CONTRACTION OF THE PIPE
Due to the visco-elastic behaviour of polyethylene, the diameter of the pipe will tend to CONTRACT, causing an INCREASE in pressure (section D–E of the graph). Pressure and
temperature readings must be recorded for at least 90 minutes (following the tapping of the pipe).
The duration of the test is, however, determined by the site manager, the test engineer, or as specified in the special tender specifications.
7) SUCCESSFUL TEST RESULT The test is passed if, during the contraction phase, the pressure is consistently RECORDED AS INCREASING (segment D–E) or STABLE (segment D–F).
The increasing trend in water pressure (section D–E) may be caused by the viscoelastic properties inherent in polyethylene.
8) FAILED TEST Conversely, DECREASING pressure values indicate leaks in the system (section D-G).
In this case, it will be necessary to carry out a LEAK DETECTION, a procedure in which we are SPECIALISED and equipped with all the best SPECIALIST EQUIPMENT.
9) DRAFTING OF THE TEST REPORT
The report on the leak test or final inspection must set out in detail the test parameters and results.
APPLICATION OF TEST PRESSURE TO STEEL AND DUCTILE IRON PIPES With reference to the diagram attached below, the procedure for applying test pressure to STEEL or DUCTILE IRON pipes is as follows:
1) PRESSURISATION
Once the vent valves have been closed, the ELECTRONIC DIGITAL PRESSURE GAUGE is activated and the pipeline is gradually brought up to the test pressure PC (section A–B of the graph).
The test pressure is given by: PC = 1.5 PE
PC = test pressure, PE = maximum permissible operating pressure for continuous use.
2) ACTIVATION OF THE THERMOMANOGRAPH
The THERMOMANOGRAPH is activated to continuously record the pressure and temperature values (point B on the graph).
The DIGITAL ELECTRONIC PRESSURE GAUGE has already been activated and therefore continues to record pressure data.
3) RECORDING OF MEASUREMENTS Pressure and temperature readings must be recorded for at least 24 hours. The duration of the test is, however, determined by the site manager or the inspector, or specified in the special tender specifications.
4) SUCCESSFUL TEST RESULT The test is passed if a STABLE pressure value is consistently recorded (section B-C).
5) FAILED TEST RESULT Conversely, DECREASING pressure values indicate leaks in the system (section B–D).
In this case, it will be necessary to carry out a LEAK DETECTION test, a procedure in which we SPECIALISE and are equipped with all the best SPECIALIST EQUIPMENT.
6) DRAFTING OF THE TEST REPORT
The leak test or commissioning report must set out in detail the parameters and results of the test.
WATER NETWORKS VS GAS NETWORKS
| WATER | GAS | |
|---|---|---|
| Test fluid | water | air, nitrogen or inert gas |
| Test type | hydraulic | pneumatic |
| Pressures | 1.5 × operating pressure | often higher than the operating pressure (depending on the regulations and the type of gas) |
| Lifespan | variable, but easier to manage | longer than for water networks, with stabilisation times |
| Leak detection | Pressure drop. Measurement of the volume of water replenished | Pressure drop. Electronic sensors. Foaming solutions applied to joints |
| Acceptance criterion | A leak is permitted within regulatory limits | Zero leakage (even micro-leaks are not permitted) |
| Critical aspects | Proper air purging. Settling of materials. Temperature has a lesser influence than gas. | High risk → strict safety procedures. Influence of temperature and volume (air/gas expand). Very restrictive regulations. |
TANK LEAK TESTS
Le prove di tenuta delle vasche servono a verificare che una vasca non presenti perdite e mantenga la sua impermeabilità nel tempo.
-Verificare assenza di perdite
-Controllare impermeabilità di strutture e giunti
-Certificare la vasca prima della messa in esercizio o dopo interventi
Esistono diverse tecniche per eseguire le prove di tenuta, a seconda del tipo di serbatoio o vasca, del liquido o gas stoccato e delle esigenze del cliente.
Ecco le più comuni:
- La prova di tenuta idraulica è la più comune
- Misurazione del livello per 24–72 ore.
- La perdita di livello rientra nei limiti ammessi
- Non compaiono infiltrazioni o trafilamenti visibili
- Prova con gas traccianti
- Si aggiunge un tracciante all’acqua
- Utile per individuare micro-perdite
- Spesso usata in vasche interrate o difficili da ispezionare
- Metodo a ultrasuoni
- Si riempie la vasca fino al livello massimo di esercizio
- L’operatore passa il sensore su pareti, fondo, giunti, passaggi tubazioni registrando il rumore di fondo.
- Si procede con la scansione sistematica ovvero ogni punto viene ascoltato, misurato e confrontato con il rumore di fondo.
- Vengono individuate le perdite, grazie al carattere distintivo del suono di perdita e alle frequenze tipiche, avvicinandosi al punto fino ad individuare il punto preciso.
- Dati della vasca
- Metodo utilizzato
- Durata della prova
- Risultati
- Esito finale (idonea / non idonea)
Questa è una delle tecniche più tradizionali e prevede il riempimento della vasca o del serbatoio con acqua, monitorando eventuali variazioni di livello o pressione nel tempo. È una soluzione efficace, ma può essere dispendiosa per quanto riguarda l’uso e lo smaltimento del liquido di prova.
Come si esegue:
Riempimento della vasca con acqua e attesa di 12-24 ore di stabilizzazione (soprattutto per vasche in CLS).
Esito positivo se:
Si tiene conto di evaporazione e temperatura.
Si possono utilizzare anche tecniche avanzate come il LEVEL SCANNER ovvero uno strumento elettronico che misura in continuo il livello dell’acqua con precisione millimetrica (o sub-millimetrica), registrando le variazioni nel tempo.
In questa metodologia, un gas come l’elio o l’idrogeno viene introdotto nel serbatoio e i rilevatori specifici individuano eventuali microperdite con estrema precisione. Questa soluzione è particolarmente indicata per serbatoi interrati o difficilmente accessibili.
Come si esegue:
La tecnologia SDT (Sound Detection Test) si basa su un principio fisico sofisticato: i sensori acustici ad alta sensibilità sono in grado di "ascoltare" e rilevare le onde sonore a bassissima frequenza generate da una perdita, anche infinitesimale.
Come si esegue:
Documentazione finale
Di solito si redige un verbale di prova con: