The resistance of pressure equipment is currently tested, before commissioning or at periodic maintenance, by means of normal pressure tests. Defects occurring inside materials during the execution of these tests or not seen by usual non-destructive techniques can remain as undetected potential sources of failure . The acoustic emission (AE) technique can detect and monitor the evolution of such failures. Industrial-size helium cryogenic systems employ cryogens often stored in gaseous form under pressure at ambient temperature. Standard initial and periodic pressure testing imposes operational constraints which other complementary testing methods, such as AE, could significantly alleviate. Recent reception testing of 250 m3 GHe storage vessels with a design pressure of 2.2 MPa for the LEP and LHC cryogenic systems has implemented AE with the above-mentioned aims

Barranco-Luque, M

Cherfaoui, M

Hervé, C

Margaroli, C

Sergo, V

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsLHC Project Report 218AbstractThe resistance of pressure equipment is currently tested, before commissioning or atperiodic maintenance, by means of normal pressure tests. Defects occurring insidematerials during the execution of these tests or not seen by usual non-destructivetechniques can remain as undetected potential sources of failure . The acousticemission (AE) technique can detect and monitor the evolution of such failures.Industrial-size helium cryogenic systems employ cryogens often stored in gaseousform under pressure at ambient temperature. Standard initial and periodic pressuretesting imposes operational constraints which other complementary testing methods,such as AE, could significantly alleviate. Recent reception testing of 250 m3 GHestorage vessels with a design pressure of 2.2 MPa for the LEP and LHC cryogenicsystems has implemented AE with the above-mentioned aims.Presented at ICEC’17 Conference – 14-17 July 1998 – Bournemouth - UKAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandGeneva, 31 July 1998Quality Testing of Gaseous Helium Pressure Vessels by Acoustic EmissionM. Barranco-Luque 1, M. Cherfaoui 3, C. Hervé 3, C.Margaroli 2, V. Sergo 11 LHC Division, CERN, Geneva (Switzerland); 2 TIS Division, CERN, Geneva (Switzerland)3 CETIM, Senlis (France)2Quality Testing of Gaseous Helium Pressure Vessels by Acoustic EmissionM. Barranco-Luque 1, M. Cherfaoui 3, C. Hervé 3, C.Margaroli 2, V. Sergo 11 LHC Division, CERN, Geneva (Switzerland)2 TIS Division, CERN, Geneva (Switzerland)3 CETIM, Senlis (France)The resistance of pressure equipment is currently tested, before commissioning or atperiodic maintenance, by means of normal pressure tests. Defects occurring insidematerials during the execution of these tests or not seen by usual non-destructivetechniques can remain as undetected potential sources of failure . The acousticemission (AE) technique can detect and monitor the evolution of such failures.Industrial-size helium cryogenic systems employ cryogens often stored in gaseousform under pressure at ambient temperature. Standard initial and periodic pressuretesting imposes operational constraints which other complementary testing methods,such as AE, could significantly alleviate. Recent reception testing of 250 m3 GHestorage vessels with a design pressure of 2.2 MPa for the LEP and LHC cryogenicsystems has implemented AE with the above-mentioned aims.1  INTRODUCTIONNowadays cryogenics has become  an important user of large pressure containers for its process fluids whenstored in the gaseous state.The LHC, the 27 km circular proton-proton collider presently in the initial stages of construction atCERN in Geneva (Switzerland), will use a cryogenic system employing ~ 96000 kg of liquid helium ascooler of the chain of its ~ 2000 supraconducting main magnets and disposing of ~ 50 buffer and storagevessels of 250 m3 each corresponding to a total capacity of  ~ 12.500 m3 at 2.2 MPa for gaseous helium  atambient  temperature.In the framework of the application of the most advanced techniques also for safety testing, a relativelynovel non-destructive (ND) global detection technique, Acoustic Emission (AE ), has been associated withthe normal mandatory pressure tests in order, firstly,  to detect , locate and survey in real time defects whichare sometimes hardly recognisable using other ND techniques and, secondly, to keep track of theirevolution during the operational life of the vessel. A description and comments concerning the test criteriaand procedures for 12 of these ~50 storage vessels, already built, installed and tested, together with theplans for their future operational life, are given in Section 3 of this article.2  THE ACOUSTIC EMISSION TECHNIQUEToday’s construction and use of pressure equipment rely on the concurrent application of sciences andtechniques on materials, structural design, fabrication, inspection, testing, protection and maintenance.Standards, codes and regulations summarise all useful information for the safe realisation  and operation ofsuch equipment. On the basis of the current state of the art in the above mentioned domains thesedocuments are periodically updated according to all new advancements, especially in the field of non-destructive testing.3This is the case for AE, which is useful as a complementary global technique, capable of locating andmonitoring in real time the presence and evolution of microcrystalline  defects in large vessels or otherstructures of any size when under stress. The AE technique is based on a naturally occurring phenomenonproduced by transient elastic waves travelling within materials when strain energy, produced bymicrostructural changes inside the material, is suddenly released all around the modified region. If enoughenergy is released, the sounds produced can be audible.The present advanced state of development of this technique, mainly due to the fundamental discovery ofJ. Kaiser, at the beginning of the fifties, known as the Kaiser effect, relies on the non-repeatability of theacoustic phenomenon because of the irreversibility of the behaviour of the defects in the metallic structuresnot affected by global degradation themselves [3]. Under further loading, structures emit acoustically onlyafter exceeding the highest stress value reached during the previous loading cycles.Nowadays, the AE technique makes it possible to extend our hearing to detect sounds of higher frequenciesand lower intensities; the acoustic signals of all these intercrystalline phenomena being picked up, typically,in the ultrasonic range between 50 kHz and 2 MHz.Usually, piezoelectric sensors are used to convert the AE stress waves into electric signals that areamplified and further processed. An array of sensors  (Fig. 2) can locate the acoustic source by means of theultrasonic wave arriving at each sensor at different times [4].During the last 20 years, the AE technique has found more and more applications. Table 1 summarizes thepresent state of the art in AE standardisaton and application in the field of pressure vessel testing :Table 1  Standardisation of AE for pressure vessel testingCountry(ies) Standards DesignationUSA Yes ASTM E1419 and ASME BC 95.Sect.V1)Japan Yes JSNDIAustria  and  Germany Yes VD-TUV 369- 12/93 2)EC Std.zationCommissionsUnder preparation CEN/TC/138/WG7-Ac. Em./ Press.VesselsFrance Yes AFNOR 3)1) ASTM Standards in application since 1980.2) The TUVs accept the equivalence between the hydrostatic test  and the pneumatic test monitored by Acoustic Emission.3) In addition to these Standards, a multipartner program named CIAPES (Contrôle et Inspection des Appareils à Pression lorsde l’Epreuve et en Service) launched and steered  by the CETIM, Senlis (France), in which CERN participates with 9 otherdifferent partners from industry and research, is in progress since 1993 with the main aim to develop a real-time surveillancemethod by Acoustic Emission for ensuring the safety of proof tests on pressure vessels [5].3  ACOUSTIC EMISSION ON 250 m3 HELIUM GAS STORAGE VESSELSTwelve gaseous helium pressure vessels, at present ready for operation on CERN’s service and access sites,have each been submitted to two pressure tests : namely, a hydrostatic test, at 1.5 times the design pressure,at the manufacturer’s premises in Decin (Czech  Republic) and a pneumatic test, at 1.25 times the designpressure, at CERN after transport, handling and installation. The surveillance of these tests by means of AEhas been performed within the framework of the above-mentioned CIAPES Program [5,6,7].The aims of these tests, which led to the implementation of AE as a real-time survey techniquecomplementary to normal mandatory pressure tests on the first batch of twelve pressure vessels, were :- to acquire the best possible first-hand insight into the quality of the tanks before they leave the workshop- to collect useful data on the tanks’ structure as a support for justifying possible future requests toincrease the intervals between periodic inspections- to apply AE real-time surveillance during the mandatory pneumatic tests on CERN’s service sites, inorder to detect and locate the appearance of any new defect in the structure and to monitor its evolution,the purpose beeing to decide immediately whether to continue with the pressurisation of the vessel or tostop it and examine the defect by means of other ND techniques.The common technical conditions for the two types of tests were as specified in the following three tables.4For the pressure vessels (see Figure1 for the dimensions and positioning of the sensors) :Table 2  Characteristics of pressure vessels Table 3  Pressure vesselsMaterial andDimensionsPressures MPa absmaterial Steel P 355 NL 2 design 2.2volume 250 m3 max. working 2.1length 28600 mm hydrostatic test 3.25diameter 3500 mm pneumatic  test 2.65thickness 22 mmTable 4  Characteristics of AE signal acquisition systemItem Type CharacteristicsSystem VALLEN AMS3 31 channels equippedPreamplifiers VALLEN 20-AP/SNGain 34 dBfilters 95 kHz – 1 MHzSensors CETIM piezoelectric, resonant at 180 kHzFigure 2 resumes three typical displays of the monitoring during one hydrostatic pressure test, showingsome triangular meshes of the localisation array based on 31 sensors.Figure 1Figure 25All 24 tests (12 hydrostatic + 12 pneumatic) were monitored in real time by an AE system with the aim ofdetecting and locating defects as they evolved, thus establishing  reference records for future tests. Allpressure vessels successfully passed the tests and no acoustic activity indicating evolving defects wasdetected.  For each tank, the acoustic activities during both the hydrostatic and the pneumatic test provedvery modest , very similar and occurred in the same regions, namely the two supports ( no evidenceindicates the presence or absence of water overload during the two tests ). The Kaiser effect regularlyappeared as expected during all the tests.4  CONCLUSIONSFor the first time, twelve important pressure vessels are starting their operational life accompanied byprecise records on the overall state of their structure which are available, as a reference for all futureinspections and tests.The experience acquired from the execution of the 24 tests assisted by the Acoustic Emission techniqueprovides indications on the simplifications and improvements to be introduced for the same tests on thepressure vessels to be built in the coming years.Increasing application experience of AE testing and the completion of development programs such asCIAPES are likely to result in EC regulations allowing its use, together with appropriate ND detectionmethods as a complementary support to the pneumatic tests where hydrostatic tests could be harmful orimpractical. This is in agreement with the spirit of what already expressed at Art. 3.2.2 of Annex I of theEuropean Directive 97/23/EC.The AE records of a pressure vessel should also facilitate the preparation of eventual waiverapplications.5  AKNOWLEDGMENTThe authors would like to thank Philippe Lebrun for his active support in the introduction of the AcousticEmission testing technique  for CERN’s equipment and J. Catty (CETIM) and L. Boyer (E.C.W.) for theirzeal and competence in carrying out the AE measurements.6  REFERENCES1 Official Journal of the European Communities. L 181, Vol. 40.(9 July 1997), Directive 97/23/C of theEuropean Parliament and of the Council of 29 May 1997 on the approximation of the laws of theMember States concerning pressure equipment.2 Kaiser J., Untersuchungen über das Auftreten von Geraüschen bei Zugversuch. - Archiv für dasEisenhuttenwesen (1953 Germany)3 Roget J., Essais non destructifs, l’émission acoustique. AFNOR-CETIM Co-editors (1988)4 Cherfaoui M., Hervé C., Acoustic Emission : New Discoveries in Acoustic Emission Checks on PressureVessels during Supervised Tests or Resistance Tests, Proc. 22nd Eur.Conf.on Ac.Em.Testing Aberdeen,(1996) 149-1545 Cherfaoui M., PROJET C.I.A.P.E.S., Compte-rendu de la réunion No. 2 du 8 juillet 1993 à la Maison dela Mécanique,6 Cherfaoui M., Hervé C., Procès Verbal du Contrôle par émission acoustique lors de l’épreuvehydraulique du réservoir d’hélium No. 36506 (FEROX)- Progr. CIAPES 2 (1998)7 Cherfaoui M., Hervé C., Procès Verbal du Contrôle par émission acoustique lors de l’épreuvepneumatique du réservoir d’hélium No. 36506 (FEROX)- Progr. CIAPES 2 (1998)

Quality Testing of Gaseous Helium Pressure Vessels by Acoustic Emission

Abstract

Similar works

Full text

Available Versions

CERN Document Server