Safety Analysis Nitrogen Vessel

Transcription

1 Safety Analysis Nitrogen Vessel Nikhef number: Item number: Date: 18/10/2010 Page: 1 of MT AA1409 Status: In Work Revision: A.6 Project: Gravitational Waves Virgo Cryogenic Link Department: Mechanical Technology Top folder: West End Tower Cryostat Created by: M.J. Kraan Checked by: M. Doets, C. Snippe Distribution list: Approved by: National Institute for Subatomic Physics Science Park 105, 1098 XG Amsterdam The Netherlands

2 Table of Contents 1 SUMMARY GENERAL DESCRIPTION SAFETY DEFINING PED CATEGORY OPERATIONAL CONDITIONS MATERIAL CALCULATION SUSPENSION APPENDICES MAIN TECHNICAL DRAWINGS BEOORDELING VAN DE CONFORMITEIT VOLGENS PED (DUTCH) ASSESSMENT OF CONFORMITY ACCORDING PED (ENGLISH) CONTENTS OF THE PED MODULES

3 1 SUMMARY Presented is a aluminium vacuum vessel which will be used at the Virgo institute in Italy. The system must comply with the Pressure Equipment Directive (PED) 97/23/CE. The vessel will be made of aluminium AL The vessel has three design conditions: 1. Internal pressure of -1 bar (vacuum at the outside of the vessel) at 150 o C (bake out of the system without liquid nitrogen) 2. Internal pressure of 1.5 bar at -196 C (liquid nitrogen; in case of a failure of the inner cold part) or at +150 C (warm nitrogen gas in case of a failure while baking out) 3. At leak test condition at a pressure of -1bar (vacuum) at 20 C. To prevent failure of the system, the system has to equip with a burst disc which opens at max 500 mbar pressure differences. With a volume of 370 liter and a design pressure PS of 0.5 bar, the vacuum vessel is not applicable to PED. Assessment of conformity according the PED is defined by an extern company and a Dutch Notified Body. Result of FEA calculations, done by Array Industries, are written in document FEA calculation Aluminum Inner Shell NIKHEF with Nikhef itemnumber: AA3196 3

4 2 GENERAL DESCRIPTION The current Virgo vacuum level needs to be improved by about a factor of hundred in order to be compliant with the required Advanced Virgo sensitivity. Such an improvement requires baking out the interferometer arms. To separate these arms from the towers that hold the mirrors and allow the bake-out, four cryogenic vacuum links will be installed. Cryogenic vacuum links are the classical solution to stop the migration of water from unbaked towers to interferometer (ITF) arms. Figure 1, the nitrogen vessel is constructed inside the cryogenic vacuum link. Inside the vacuum vessel a cold part (nitrogen vessel) of the cryolink will be constructed from aluminum Al The inner surface of this link is cooled with liquid nitrogen. This cold part is isolated from the vessel by using two air springs and designed in such a way that thermal expansion does not induce stresses in the outside vacuum vessel. The system will be building up and tested at an extern company. The final performance tests will be done at Nikhef before installing at Virgo. For this the vacuum vessel will be closed with two end caps, and one extra the support will be added. See in the next Figure 2 the nitrogen vessel in red. 4

5 Figure 2, the nitrogen vessel (red) mounted in the cryostat. 3 SAFETY To prevent failure of the system, the nitrogen system is equipped with a relief valve which will be open at 500 mbar pressure difference. The relief valve is venting through a stainless steel safety line for personal safety. See the following Figure 3: Figure 3, a relief valve is preventing the nitrogen vessel. Yellow = vacuum red = nitrogen blue = safety line. 5

6 4 DEFINING PED CATEGORY The Pressure Equipment Directive (97/23/EC) was adopted by the European Parliament and the European Council in May The PED is a European Single Market Directive that covers pressure equipment and assemblies with a maximum allowable pressure PS greater than 0.5 bar. Pressure equipment: Pressure vessel Media: Nitrogen (LN 2 ) Group: Non dangerous media Phase: Gas Vessel volume: 370 Liter Design Pressure PS: 0.5 bar PS. V = 555 [bar.l] Tabel 1. Defining the PED category for non dangerous gasses. The red lines indicate the vessel properties. Following Tabel 1, the vessel is not applicable to PED. See paragraph 7.2 and 7.3 for the assessment of conformity according PED defined by Ing. H.G. Rutgers from Tutorial Opleiding & Advies. 6

7 5 OPERATIONAL CONDITIONS Quarter of the pressure vessel is modeled, as the vessel is symmetric about XY and YZ, see Figure 4. Figure 4. the vessel is symmetric about XY and YZ. The design pressure of this nitrogen vessel is 1.5 bar. Normal operational condition is without differential pressure. The PS of 1.5 bar is a product of 0.5 bar internal pressure which is determined by the relief valve which opens at 0.5 bar pressure difference ( in case of a blocking nitrogen filling line) and a vacuum on the outside of the vessel. The operational temperature of the vessel is -196 C (liquid nitrogen at atmospheric pressure). For leak test reasons the vessel will be evacuated (vacuum) at 20 C. The inner cold part, filled with liquid nitrogen, is hanging with air filled bellows on two ribs of the vacuum vessel; see Figure 5 and Figure 6. Figure 5. Two suspensions of the cold part (nitrogen vessel) inside the vacuum vessel. Blue are the flanges and green are the suspensions of the inner cold part. 7

8 Figure 6. Detail of the suspension. Tabel 2, summary of the operational conditions Operational conditions Design Pressure 1.5 bar at -196 C and 150 C -1 bar (vacuum) at 20 C Design Temperature -196 C C Additional loads 2500 N (300L liquid nitrogen) 5.1 Material Material type: Aluminum Al 5754 Materials according to AD 2000-Merkblatt W6/1, D Temperatures valid between -270 C to C Tabel 3, Al 5754 material properties according to AD2000. Type and thickness Condition 0.2% limit -270 to 100 C [N/mm2] 1.0% limit 150 C [N/mm2] Tube (0.3 to 10) 0/H Plate (25 to 50) H Tensile strength [N/mm2] 8

9 6 CALCULATION SUSPENSION Two suspensions are used to support the nitrogen vessel inside the vacuum vessel. See the following figure for details of this stainless steel suspension M10 thread Thinnest part suspension 2 x M12 bolts Suspension: Material AISI 304L Yield strength AISI 304L 193 MPa (20 o C) Weight of the vessel 5250 N Volume liquid N liter (volume vessel = 370 liter) Density liquid N g cm 3 Weight 300 liter N N Force on each suspension = (weight vessel liter liquid N 2 )/2 = ( )/2 = 3825 N Cross section thinnest part suspension = 15 x 5 =75 mm 2 Thread cross section M10 connection = 51.5 mm 2 Tension stress suspension: Tension in M10 thread connection: 9

10 Bolt M12: Material AISI 304 Shear strength (see table 4) 117 MPa (17.5 ksi) Core diameter M mm Thread cross section M mm 2 The suspension is connected with four (4) bolts to the vessel. Calculation is done in case two bolts (one at each side) are taken all weight of the vessel: Force on one M12 bolt = (weight vessel liter liquid nitrogen) / 2 = 3825 N Shear stress in M12 bolt: The design of the suspension is such a way that extra tension/bending stress in the bolt due to temperature change of the nitrogen vessel (-196 o C o C) is negligible. Tabel 4, allowable shear stress for stainless steel bolts (from the Specialty Steel Industry of North America SSINA) 10

11 7 APPENDICES 7.1 Main technical drawings 11

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17 7.2 Beoordeling van de conformiteit volgens PED (Dutch) Met betrekking tot: Project Virgo-Cryolink, de beoordeling van de conformiteit volgens PED Vessel: cryostat assy Drawing: Vragen: 1. Hoe is dit vat ingedeeld overeenkomstig de PE D.? Het vat bevat een binnenvat (aluminium) met voornamelijk vloeibare stikstof. Het binnenvat is gemonteerd in het buitenvat onder vacuüm omstandigheden. Buiten de cryostaat assy is er een normale atmosfeer (1 bar). Het vat is verbonden met een veiligheidsventiel, die is afgesteld op 0,5 bar. De veiligheidsklep is verbonden met de open lucht. Het buitenste vat is verbonden met een breekplaat naar de open lucht. De breekplaat opent naar de open lucht op een PS van 0,5 bar. Dit betekent dat de druk in het binnenste en buitenste vat nooit een PS heeft die boven de 0,5 bar komt. Daarom is risicocategorie 3,3 van kracht en is de PED is niet van toepassing. Echter, goed vakmanschap is hier wel van toepassing, zodat risicoanalyse,-ontwerp,-berekening en controles tijdens de productie een onderdeel van het constructiedossier vormen. 2. De eindgebruiker is ook de ontwerper. Fabricage van het product wordt ingekocht. Is de eindgebruiker verantwoordelijk voor de vervaardiging en het gebruik van deze Cryostaat assy? Volgens paragraaf 3.4 van de PED, speelt de eindgebruiker de rol van de fabrikant. Daarom is de eindgebruiker verantwoordelijk voor de overeenstemmingbeoordeling van de PED, en ook verantwoordelijk voor de goedvakmanschap uitvoering. 17

18 Het bovenstaande genoemde is de beoordeling van de conformiteit volgens de PED. Dit is een zaak over de veiligheid van mensen, dus heb ik gevraagd om second opinion bij de Nederlandse NOBO genaamd "Energy Consult" gevestigd in Ede aan de Herzstraat 14. De geraadpleegde persoon was J.J. Rodenhuis en hij stemde volledig in met bovenstaande redenering en conclusie. Enschede, 14 november 2011, Ing. H.G. Rutgers Senior Consultant Tutorial Opleiding & Advies Beltstraat AA Enschede Tel: +31-(0) Mob:

19 7.3 Assessment of conformity according PED (English) Concerning: Project Virgo-Cryolink, assessment of conformity according PED Vessel: cryostat assy Drawing: Questions: 1. How is this vessel classified according the P E D.? The Vessel contains an inner vessel (Aluminum) with mostly liquid nitrogen. The inner vessel is mounted in the outer vessel under vacuum circumstances. Outside the cryostat assy there is a normal atmosphere (1 bar). The inner vessel is connected with a safety relieve valve, which is adjusted on a 0,5 bar. The safety valve is connected to open air. The outer vessel is connected with a bursting disc to open air. The bursting disc opens to open air at a PS of 0,5 bar. This means that the pressure in the inner vessel and outer vessel never reaches a PS above 0,5 bar. Therefore the risk category is 3.3 and the PED is not in force. However, sound engineering practices is here in force so the necessary risk analysis, -design,-calculation and controls during manufacturing are required. 2. The end-user is also the designer. Manufacturing will be purchased. Is the end user responsible for the manufacturing and use of this Cryostat assy? According chapter 3.4 of the PED, the end user is playing the role of manufacturer. Therefore the end-user is responsible for the conformity assessment of the PED, and also responsible for the sound engineering practices. 19

20 The above mentioned is the assessment of conformity according the PED. This case is about safety of people so I asked for a second opinion at a Dutch NOBO called Energy Consult located in Ede at the Herzstraat 14. The consulted person was J.J. Rodenhuis and he agreed fully with above mentioned reasoning and conclusion. Ing. H.G. Rutgers Senior Consultant Tutorial Opleiding & Advies Beltstraat AA Enschede Tel: +31-(0) Mob: h.rutgers@tutorial.nl 20

21 7.4 Contents of the PED modules Module A A1 B B1 C1 D D1 E E1 F G H H1 Description Manufacturers attend to internal manufacturing control, themselves producing and storing the documentation. The authorized body not involved. Manufacturers attend to internal manufacturing control, themselves producing and storing the documentation. The authorized body monitors the final verification through unannounced visits. Manufacturers draw up the technical documentation and provide samples. The authorized body examines the technical documentation and undertakes the necessary testing of the samples and issues an EEC type testing certificate. The manufacturer draws up the technical documentation. The authorized body examines the technical documentation and issues an EEC construction testing certificate. Manufacturers ensure that production conforms to the specifications of the type approval. The authorized body monitors the final verification through unannounced visits. Manufacturers use a documented quality assurance system that covers production, final inspection and testing. The authorized body audits, approves and monitors the quality assurance system. As D but manufacturers must also draw up and file technical documentation for the equipment. Manufacturers use a documented quality assurance system that covers final inspection and testing. The authorized body audits, approves and monitors the quality assurance system. As E but manufacturers must also draw up and file technical documentation for the equipment. Manufacturers ensure that production conforms to the specifications of the type approval or the construction testing certificate. The authorized body inspects each product. The authorized body issues a certificate of conformity. The manufacturer draws up and submits the technical documentation. The authorized body examines the technical documentation, manufacture and each individual product. The authorized body issues a certificate of conformity. Manufacturers use a documented quality assurance system that covers construction, production, final inspection and testing. As H but manufacturers must also apply for construction approval from the same authorized body that monitors the quality assurance system. 21