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Fuel Station Services Underground Tank Testing 1


Testing

Tank testing helps determine the integrity of your tank, and whether or not it’s safe to continue using. If the tank isn’t safe, Brustech can recommend repairs or remove the tank so it doesn’t cause any further damage to the building, soil and groundwater. Typically issues that arise after tank testing are related to the fill, vent, and supply piping. Corrosion to the threads of the piping, or loosening of the pipes over time, can produce a failed result during the test. Damaged sensors and gauges can also affect the test and need to be replaced.

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Brustech offers technologies of testing open and low pressure tanks used for storing liquid inflammable, poisonous and caustic materials as well as piping system.

TECHNICAL METHODS: gas pressure with indirect leak-proofness measurement via testing of pressure and underpressure drop, hydrostatic with magnetostrictive measurement of liquid level, measurement of mass change of liquid via displacement probe and acoustic sound in gas part, with helium detector of leakiness (pressurized, pressurized-vacuous, vacuous)

INTRODUCTION The subject of technology are requirements of leak-proof testing with gas pressure method with indirect leak-proofness measurement of a tank through testing of pressure drop with the use of air or other non-liquefactive inert gas. This innovative method has been worked out according to criterion of method approved by Technical Supervision Office and with technical conditions of open and low pressure tanks for storing liquid inflammable materials (Dz. U. [Journal of Law] No 113 item 1211), as well as poisonous and caustic materials (Dz. U. [Journal of Law] No 63 item 572) and parameters given in the standard PN-EN 12285-1 Workshop Fabricated Steel Tanks - Part 1: Horizontal Cylindrical Single Skin And Double Skin Tanks For The Underground Storage Of Flammable And Non-flammable Water Polluting Liquids, American regulations of environment protection USEPA – 40 CFR 280.43 and 280.44 sec. 3 (liquid criterion converted into pressure values)

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TECHNOLOGY OF TESTING LEAK-PROOFNESS WITH GAS PRESSURE METHOD WITH INDIRECT LEAK-PROOFNESS MEASUREMENT VIA TESTING OF PRESSURE AND UNDERPRESSURE DROP The technology concerns testing leak-proofness of tanks: open and low pressure tanks Single and double skin  Interstice space and space for monitoring  With horizontal axis  Destined for storing liquid inflammable materials as well as poisonous and caustic materials  

Testing procedures Minimal testing pressure amounts:  For periodic, acceptance and immediate testing – 0,1-0,3 Bar  For control testing – 0,75 Bar  For interstice space 0,4 Bar (but not less than maximum positive gauge pressure of monitoring work)  For space for monitoring 0,2 Bar (but not less than maximum positive gauge pressure of monitoring work) Duration of Testing: up to 4 hours.

Leak-proofness testing: The tank is leak-proof when during 4 hours there is no pressure drop of more than 0,005 Bar for periodic and acceptance testing as well as 0,01 Bar for control testing and when there is no temperature deviation of testing factor more than ±0,3°C from the accepted as initial for testing.

Basic requirements Leak-proofness testing with gas pressure method with indirect leak-proofness measurement of a tank via testing of pressure drop with the use of air or other liquefactive inert gas can be conducted at the testing pressure according to techniques of testing documentation. Exploiting or acting in its behalf should agree in writing to test lea-proofness at the pressure appropriate for each testing. Leak-proofness testing is conducted separately for each space of a tank.

PRESSURE AND TEMPERATURE IS RECORDED IN A CONTINUOUS WAY. THE TESTING IS CONDUCTED WITH THE USE OF ELECTRONIC PRESSURE AND TEMPERATURE CONVERTERS CONNECTED TO THE RECORDER.

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Preparing of a tank for testing: Taking up and conducting of work in tanks can occur only when there is a written agreement given by the employer. During work in a tank there should be a constant supervision. A person giving orders of conducting such work should check whether organization and technical preparations are provided for employees during work. During work there should be a possibility of giving an employee first aid instantly at urgent need or accident as well as inform employees about:  Scope of work to be done  Types of risk which can occur  Essential collective and individual protective measures and ways of their application During leak-proofness testing the tank is disconnected from exploitation. The place of testing should be appropriately protected and marked. Disconnect from the tank all fuel pipelines and installation assembled on the tank. The tank should be partially emptied, clean the bottom of the tank (Tank Cleaning Pump System). Use explosimeter to check the level of explosive concentration in a tank (it should be included within 0-20% D.G.W.). Seal all terminals in the tank. In case of double skin tank with interstice space or a tank with a space for monitoring there must be a possibility of connecting both spaces, which are interstice space or a tank with a space for monitoring with storage space. Assemble measuring equipment. Connect nitrogen generator which produces positive gauge pressure in the tank. Test leak-proofness according to parameters given in procedures of testing.

Actions after finishing leak-proofness testing After finishing of testing power supply should be turned off and disconnected from the measuring equipment. During opening ball valve reduce value of positive gauge pressure to the atmospheric pressure value. Dismantle meter circuit. Restore the tank to the state from before testing.

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DIAGRAM OF CONNECTING MEASURING EQUIPMENT FOR TESTING SINGLE SKIN TANKS

RECORDER

RECORDER SUPPLY

MANOMETER CONVERTER NITROGEN GENERATOR

DN15

DN15 CONDUKTOR

OUTLET PIPE

TEMPERATURE SENSOR

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MEASURING PIPE


DIAGRAM OF CONNECTING MEASURING EQUIPMENT FOR TESTING DOUBLE SKIN TANKS

RECORDER

RECORDER SUPPLY

MANOMETER CONVERTER NITROGEN GENERATOR

DN15

DN15

DN15

MONITORING FERRULE

CONDUCTOR SECOND SKIN

OUTLET PIPE

TEMPERATURE SENSOR

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MEASURE PIPE


TECHNOLOGY OF CONDUCTING LEAK-PROOFNESS TESTING VIA HYDROSTATIC METHOD WITH MAGNETOSTRICTIVE MEASUREMENT OF LIQUID LEVEL IN A MEASURING PIPE The following technology has application in conducting leak-proofness testing in storage tanks for liquid inflammable, poisonous and caustic fuels with magnetostrictive measurement of liquid level in a measuring pipe. The method consists in filling the tank with a testing factor up to half of a measuring ferrule. This instruction has been worked out on the basis of:  American regulations of environment protection USEPA – 40 CFR 280.43 and 280.44 sec. 3  The instruction of functioning and installing of a level measurement system The tested tank is filled with testing factor up to half of a measuring ferrule. In the a measuring ferrule meter circuit is installed with measuring probe. After stabilizing of conditions in the tank (no changes of temperature higher than ±0,6°C)during one hour the change of level of testing factor is measured. During testing the temperature of a testing factor is also recorded with the use of temperature sensors installed in measuring probe. The tank is found leak-proof if during one hour the level of testing factor in the tank will not reduce more than 0,378 l., and the temperature of the testing factor in the tank will not reveal changes more than ±0,6°C.

Tank preparation for testing 1 Turning of the tank from exploitation consisting in shutting down consumption installation as well as tank valves.

2 Visual checking of the condition of external surface of the tank in order to detect potential possibilities of

leak of a testing factor during its filling. In case of visible leak of working factor from the tank during its filling, one should:

3 Stop filling

Remove excess of working factor Seal the place of leak  Continue filling the tank  

4 Closing ferrules installed in the cover 5 Installing measuring equipment with measuring probe (fig. No 1) 6 Filling the tank with testing factor up to half of a measuring ferrule 7 Checking levelling of meter circuit with measuring probe relative to the tank with a level. 8 Preparation and configuration of system in order to conducting the test:  

Connecting probe conduits do recording box Connecting voltage supply (220V) do the system

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Determining sensitivity the real leak-proof testing one should determine the sensitivity of testing. Determining the sensitivity of testing consists in adding to the tank with the use of measuring ferrule a specific amount of testing factor, e.g. 100ml or 200ml and observation of level change. Specific doses one should add as long as the recorder shows a visible level change in millimetres (min 5mm). Received value in millimetres converted according to the following example for the volume gives the sensitivity of the method.

Example: 200cm3 = level change in measuring pipe by 5mm 200 : 5 = 40cm3 Level change in measuring pipe by 1mm causes volume change of a liquid in a tank by 40cm3.

Conducting leak-proofness testing With starting the programme the process of recording data from measuring probe starts, that is level change of working factor and temperature in a tank. There is no need to determine the time of stabilizing testing factor during testing. It is found that the tank is stable if the temperature of testing factor does not change more than ±0,6°C (after judging that the condition of the tank is stable) in one hour. Leak-proofness testing is found correct if during testing there is no temperature change more than ±0,6°C. The tank is found leak-proof if during leak-proofness testing there is no change in working factor more than 0,387l during one hour and the temperature in the tank during testing is not higher than ±0,6°C. If during leak-proofness testing there is single level change of testing factor more than 0,387l during one hour without monotonic characteristics, the tank is found leak-proof. If during leak-proofness testing there is single level change of testing factor more than 0,387l per hour with monotonic characteristics, the tank is found leaky. In case of difficulties with correct interpretation of test results, one should extend testing up to two or more hours.

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Checking of the meter circuit after testing At the end of real leak-proofness testing one should add 200ml of testing factor to the tank. The recorder should record level change (in millimetres), according to points of determining sensitivity testing convert level change of working factor from mm into cm3. The amount of added factor, time, date of conducting checking as well as level change should be written on checking meter circuit record.

Disassembling of meter circuit After finishing leak-proofness testing one should:

1 Disconnect the system from power supply 2 Dismantle meter circuit with measuring probe 3 Take out the probe from the tank 4 Empty the tank from fuel up to max. Level 97% (the maximum level of filling the tank) 5 In case of doing leak-proofness testing with the use of water, one should empty the tank and dry it and water should be neutralized.

Industrial Safety during testing During preparation of the tank for testing, testing itself and after finishing testing one should obey Industrial Safety rules and regulations connected with spending in explosion hazard zone.

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DIAGRAM OF CONNECTION MEASURING EQUIPMENT FOR TANK TESTING VIA HYDROSTATIC METHOD WITH MAGNETOSTRICTIVE MEASUREMENT OF LIQIUD LEVEL IN A MEASURING PIPE

SYSTEM DRIVER

STEERING CABLE BREATHING VALVE

MEASURING FERRULE ON A LARGER SCALE

BREATHING PIPE

HEAD CASING OF PROBE MADE OF ANODISED ALUMINIUM MEASURING AXIS MADE OF STAINLESS STEEL

SUCTION FERRULE

FLOAT LEVEL OF FILLING THE TANK WITH APPROXIMATELY HALF OF MEASURING FERRULE

MANHOLE OUTLET FERRULE

ANTI-OVERFLOWING VALVE

SYPHON

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THE TECHNOLOGY OF CONDUCTING LEAK-PROOFNESS TESTING WITH THE USE OF HELIUM METHOD WITH LEAK DETECTOR (PRESSURIZED, PRESSURIZED-VACUOUS, VACUOUS) Testing During leak-proofness testing, vacuum methods are used and they can be divided into vacuum and high-pressure. Vacuum method consists in tank testing with the use of vacuum pump which is built in helium detector. Air is pumped out from a tested tank to get vacuum. Next, places which can be leaky are tested. They are fanned with helium and if helium penetrates into the tank, the detector used during testing informs the operator about the leak via sound signal and it gives absolute value of helium concentration on the liquid crystal display. In the high-pressure method a tested tank is filled with pressurized helium. If the tank is leaky, helium and air gets out through leaknesses, where it is detected with a special probe.

Detector Leak detector with mass spectrometer is a full system which localizes and measures leakiness of a product inside or outside. This method uses marking gas – helium, which fills product connected to the detector. Helium leaks to/from the tested product to the detector where partial pressure is measured and displayed on the screen. The mechanism of functioning of the detector bases on field mass spectrometer. Analysed input gas (here is helium) is ionised in vacuum. Ions of helium are accelerated through applied voltage and later it is separated in magnetic field. Ion signal, via a special detector, is changed into electric signal. This signal is accelerated and displayed on the screen in leakiness detection units. The measured signal is directly proportional to helium concentration, and what follows from the above, equals measured leakiness.

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Control leak-proofness control of tested systems with the use of helium detectors can be realized in various ways. In case of vacuum systems the helium detector is connected indirectly to the tested system, where vacuum is created. From outside of the system – for all potentially leaky elements of the system – helium is sprayed. If helium gets into the vacuum system in any place, then it is signalized but helium detector. This method enables to determine places of leak and its intensity. In other cases filling of a tested system or element is used and later it is smelt outside with the use of probe connected to helium detector. This method is perfect for localisation of leakiness, however, it gives lower sensitivity and accuracy of leakiness measurement.

Methods Methods of helium detection with the use of mass spectrometer can be found in standards MIL-STD-202G, MIL-STD-883H, JEDEC JESD-A109-A and PN-EN 60068-2-17. Methods which can be found there occur in two variants depending on whether the inside of the element has been filled with helium in production phase. In its basic form this method concerns such elements whose inside is not filled with helium. In this method the tested element is put into measuring chamber for a specific time and is filled with helium under specific pressure. Next, the chamber is emptied from helium, and later with the use of mass spectrometer trace elements of helium getting out from the element are detected, showing at the same time its leakiness. The standards define two types of tests. The first type of test which is called the established method, values of helium pressure in measuring chamber as well as time of testing the element are known in advance from the standards and they depend on the inside volume of the element. The second, flexible method, test time and helium pressure are taken in such a way that the amount of the remnant gas coming out of the element considered as leaky, is higher than sensitivity of mass spectrometer. Moreover, standards PN-EN 60068-2-17 and MIL-STD-202G describe a variant of judgement of leakiness concerning elements whose internal volume has been filled with helium in production phase. In this case, during the test, there is no saturation phase of a tested element with helium in a measuring chamber, and measurement is based on helium detector coming out of the element under the influence on vacuum created in the measuring chamber.

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DIAGRAM OF CONNECTING MEASURING EQUIPMENT FOR TANK TESTING VIA HELIUM METHOD

PRESSURE REGULATOR ADJUST KNOB

SAFETY RELIEF VALVE

INERT GAS INPUT PRESSURE SHUTOFF VALVE

CYLINDER FILL TUBE WITH VOLUME SCALE FUNNEL

PLEXIGLAS OUTER CYLINDER

PYREX CYLINDER WITH VOLUME SCALE DIVISIONS OF 0025 FROM 0.00 TO 0.10 GALLONS

PRODUCT - IN VALVE

PRODUCT - OUT VALVE LEAK DETECTOR REMOVED

VENT LINE

LOCATION PLUG

IMOACT VALVE PRODUCT LINE

PUMP

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DIAGRAM OF CONNECTING MEASURING EQUIPMENT FOR TANK TESTING WITH HELIUM METHOD

CONCENTRATION OF HELIUM DETECT

REGULATOR AND GAUGE

VENT AND PORTS PLUGGED FOR TESTS

REGULATOR AND GAUGE

HELIUM RISES THROUGH HOLES

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THE TECHNOLOGY OF CONDUCTING LEAK-PROOFNESS TESTING WITH THE USE OF PRESSURIZED, GAS METHOD WITH LEAKINESS DETECTOR Requirements Requirements and testing with the acceptance of pipelines are described in the standard PN-B-10725:1997. However, the standard does not include appropriate for polyethylene leak-proofness testing procedure of conduit segments because it does not take into consideration PE pipe creeping during testing which is the cause of pressure drop inside of pipeline and, at the same time, problems with finishing leak-proofness testing positively. What follows from the above leak-proofness testing of conduit segments of PE pipe should be conducted according to the procedure described in appendix A.27 do the standard EN805, whose content is presented below.

Test procedure The whole procedure of leak-proofness testing includes preliminary phase with the relaxation period which is connected with pressure drop testing and fundamental leak-proofness testing.

Preliminary phase Successful finishing of preliminary phase is the basic condition of conducting fundamental leak-proofness testing. The aim of preliminary phase is to gain appropriate initial conditions of tested system which depend on pressure, time and temperature. All mistakes should be avoided because they can influence the result of fundamental leak-proofness testing. What follows from the above, preliminary phase of leak-proofness testing should be conducted as follows:  After rinsing and bleeding of pipeline reduce pressure to atmospheric pressure level and for at least 60min let for relaxation of pipeline stress in order to avoid initial stress of internal pressure, secure pipeline against secondary air-lock  after relaxation period increase continuously and fast (up to 10 min) pressure to the level STP (System Test Pressure is test pressure,mostly=1,5xPN). Keep STPpressure for 30min by pumping up nitrogen in a continuous way with short intervals. During that time carry out Metrotech inspection H5000 pipeline in order to identify potential leakiness  during one hour do not pomp nitrogen letting the tested segment for stretching which is the result of viscoelastic creeping  at the end of preliminary phase measure pressure level in the pipeline In case of succesful finishing of preliminary phase continue tesing procedure. If pressure is lower than 30% STP, stop preliminary phase and lower nitrogen pressure of a tested segment to zero. After determining the cause of excessive pressure drop provide appropriate testing conditions (the cause can be, for example, temperature change, leakiness). Rtesting is possible after 60min relaxation period.

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Integrated pressure drop testing Correct judgement of fundamental leak-proofness testing is possible provided that the content of the air inside of a tested tank is low. If it is so, one should:  at theend of preliminary phase lower rapidly pressure in a pipeline by Δp=10÷15% STP via releasing of nitrogen of a tested segment  calculate permissible loss of nitrogen ΔV accorging to the following formula and check if max

where ΔVmax – permissible loss of nitrogen [kPa] V – volume of a tested tank [litres] Δp – measured pressure drop [kPa] EW – coefficient of water comprossibility [kPa] (value 2,06 106 kPa) D – internal pipeline diameter [m] e – pipeline wall thickness ER – Young module of pipe material on the rotational direction [kPa] 9value 8×105kPa) 1,2 – improvement factor for fundamental leak-proofness testing (taking into consideration air content) released amount of nitrogen ΔV is not higher than permissible value ΔVmax.

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For correct interpretation of collected results the use of appropriate value ER is essential as well as taking into consideration temperature change and time of leak-proofness testing. Especially in case of pipeline testing with small diameters and short segments Δp and ΔV should bemeasured as precisely as it is possible. If ΔV is higher than ΔVmax one should stop testing and, after lowering of pressure to zero, bleed again the pipeline.

Fundamental leak-proofness testing Viscoelastic creeping of pipe material influenced by stress caused by STP test pressure is stopped by integrated pressure drop testing. Sudden drop of internal pressure leads to shrinking of pipeline. One should observe and record inbcrease of internal pressure caused by shrinking of pipeline for 30 min. Fundamental leak-proofness testing can be found positive is the line of pressure changes shows growth tendency and, during 30 min, which is usually enough to get appropriate, precise and determined pressure, does not show drop. If, during that time, curved line of pressure changes shows drop, leakiness of a tested segment is recorded. In case of any doubt fundamental leak-proofness testing sould be prolonged to 90 min. In this case premissible pressure loss is limited do 25 Kpa against maximum pressure value gained during shrinking phase of pipe. If pressure drops morethan 25kPa, the test isnegative. It is recommended to check all mechanical connections before visual inspectionof welded connections. Remove all indentified installation failures and repeat testing.

EXAMPLE OF LEAK-PROOFNESS TESTING Fundamental leak-proofness re-testing is possible provided that the whole testing procedure is conducted with 60min relaxation period in preliminary phase. One should notice the fact that polyethylene constitutes good isolation. After filling of pipeline with compress air via compressor (or nitrogen) fundamental leak-proofness testing can be initiated but after lowering of pipe and air temperature to the surrounding temperature, which can last even a couple of hours. Unfulfilling of this condition can be the cause of internal pressure drop not because of leakiness but it can be the cause of gas change with constant volume of tested pipeline segment the temperature drop (here nitrogen) is accompanied by pressure drop.

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Pressure

Temperature

Pressure

preliminary phase

primary phase

Temperature

Time (hours) of testing

SUMMARY Due to appearances of pressure impact during pressure testing for flexible pipes made of viscoelasticmaterials, applying the standard PN-B-10725 from 1997 is not irrational, which has been proven above. Again it is essential to underline the importance of designer,especially when determining precise rules of duration of preliminary phase, which is dependent on the type of material used in pipes. Conducting of testing is inconsistent with the standard PN-EN 805: December 2002,for modern solutions of materials from plastic, can lead to wrong interpretation of collected testing data,which can cause irrationalretesting and unnecessary increase of costs during realization of investment phase.

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ul. Toruńska 148

Fax: +48 54 423 20 33

87-800 Włocławek

kontakt@brustech.pl

Poland www.brustech.pl 20

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