Study of potential leakage on several stressed fittings for hydrogen pressures up to 700 bar D Houssin-Agbomson 1, D Jamois 2, Ch Proust 2, J Daubech 2, S Ruban 1, S Jallais 1 ICHS4 – 2011 September, San Francisco 1 Air Liquide, Centre de Recherche Claude-Delorme, Les Loges-en-Josas, France 2 INERIS, Verneuil-en-Halatte, France

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 2 I. Context II. Tested configurations III. Experimental device IV. Results V. Conclusions and perspectives Content

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 3 I. Context

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 4 Context Several H 2 applications developed in "Hydrogène Horizon Energie" (H2E) project Define "predictable" and "accidental" leaks and be able to assess consequences in order to: Design natural ventilation to avoid any dangerous accumulation of “predictable” leaks Prove that an "important" leak (potentially inducing an explosion) has a very low probability Objectives Quantify "small" leaks which are probable Contribute to assess the probability of "important" leaks Means H 2 systems analysis by fault tree Scope: fittings Identification of leak causes and means of mitigation Tests for leaks INERIS test bench: H 2, up to 700 bar, on double ring tube fittings and threaded ring fittings Study description

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 5 II. Tested configurations Studied fittings Stress configurations

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 6 Studied fittings Based on a preliminary study of potentially leaking elements, four kinds of commercial fittings usually employed on H 2 energy-based systems were chosen and tested Fittings External tube size Maximum working pressure recommended by the constructor Swagelok ® double ring tube fitting (316 SS) 6 mm420 bar Rotarex ® double ring tube fitting (316 SS) 6 mm420 bar Swagelok ® medium-pressure double ring tube fitting (316 SS) 1/2’’1035 bar Maximator ® threaded ring tube fitting (316 SS) 9/16’’1500 bar Double ring Nut Body Nut Body Threaded ring 6-mm double ring tube fittingMedium-pressure double ring tube fitting Threaded ring tube fitting

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 7 Stress configurations (1/2) Existing literature Few results in open literature Conditions already studied (1) Moderate pressures  up to 35 bar Mainly 1/4'' pipe fittings Main result leak flow rate of 800 cm 3.s -1 at 20 bar for tightening by hand of the fitting Experimental conditions of the present study H 2, up to 700 bar Test matrix considered as maximal stress in real-life conditions of a hydrogen-based application Fatigue conditions tested beyond constructor tests and recommendations for users Stress configurations Two kinds of stresses stresses applied at atmospheric pressure (« static tests »): assembly/dismantling cycles / tightening / "thermal effects" stresses applied when the fitting were under pressure (dynamic tests) : rotation / flexion / traction (1) Gentilhomme, O., Tkatschenko, I., Joncquet, G., Anselmet, F., Outcomes from the French National Project DRIVE, Proceedings of the Seventh International Conference and Trade Fair on Hydrogen and Fuel Cell Technologies, October 2008, Hamburg, Germany

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 8 StressesNormal conditions of use Tested stress level considered as maximum in situation Static stresses Assembly- dismantling cycles Around 20 cycles, for 6 mm double ring tube fitting 100 cycles < 20 cycles, for high pressure fittings (double and threaded ring tube fittings) 50 cycles Under- tightening 1 1/4 turn, for 6 mm double ring tube fitting1 turn 1 1/4 turn, for 1/2’’ double ring tube fitting 3/4 turn and 1 turn 80 N.m with silicone grease on conical sealing surfaces, for 9/16’’ threaded ring tube fitting 60 N.m with silicone grease Over- tightening 1 1/4 turn, for 6 mm double ring tube fitting1 1/2 turn Thermal effects +60 to -20°C Crimping at 100°C and leakage test at 30°C Dynamic stresses Counter- clockwise rotation 0 turn 1/8 turn compared to initial position Flexion0° 10° from fitting initial axis Traction0 N 320 N in fitting axis direction Stress configurations (2/2) Details of the tested configurations

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 9 III. Experimental device Main test bench "Dynamic stress" module

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 10 A simple but accurate AND safe test bench… Characterization of H 2 high pressure leaks Gas for tests: H 2 Pressure range: up to 700 bar Sensitivity: flow rate higher than cm 3.s -1 Main equipment A H 2 compressor High pressure reservoirs Pneumatic valves Accurate pressure transducers Thermocouples Climatic enclosure Climatic enclosure with device for tests Scheme of the main test bench Main test bench

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 11 Characteristics Module set-up in order to apply stress on pressurized fittings thanks to a pneumatic jack Pressure range: up to 700 bar Tested "dynamic" stresses Flexion Rotation Traction Only applied on 6-mm tube fitting Module for "dynamic stress" "Dynamic" module Main equipment: a pneumatic jack (up to 320 N) Inserted inside the climatic enclosure of the main test bench

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 12 IV. Results

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 13 Results of the study Only two test configurations showed small leakages  leak flow rates experimentally determined appear close to the threshold sensitivity value of cm 3.s -1 These values are very low compared to the flow rates usually considered for risk analyses of potentially hazardous systems (i.e. around 900 cm 3.s -1 for the "0.1 mm-200 bar" hypothesis), It would be detected by normal control procedures particularly for these types of stresses Fitting External tube size Tested stress Pressure conditions Measured leakage rate Swagelok medium- pressure double ring tube fitting 1/2’’ After 50 assembly-dismantling cycles 700 bar0.05 cm 3.s -1 Maximator threaded ring tube fitting 9/16’’ Under-tightening with silicone grease: 60 N.m instead of 80 N.m 700 bar4.3 cm 3.s -1 The other stress scenarii did not exhibit detectable leakage given experimental installation sensitivity Leak visualisation in water

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 14 V. Conclusions and perspectives

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 15 Conclusions A specific experimental installation was designed and set-up by INERIS in order to study potential leakages on fittings commonly used in H 2 existing systems This test bench enables –to accurately quantify, when existing, leakages with a flow rate above cm 3.s -1 –to carry out the tests with hydrogen in safe conditions –to reach test pressures up to 700 bar –to apply stresses on fittings under H 2 pressure (i.e. “dynamic stresses”) Very few scenarios gave rise to quantifiable leaks (given test bench detectable thresholds) Only two stress configurations showed measurable but low leak flow rates compared to values usually employed for risk assessment –0.05 cm 3.s -1 for the Swagelok ® 1/2’’ medium-pressure double ring tube fitting after 50 cycles of assembly-dismantling –4.3 cm 3.s -1 for a 25% under-tightening of the Maximator ® 9/16’’ threaded ring tube fitting  A good reliability of the fittings used in H 2 -energy based systems is shown  For hydrogen systems considered for the H2E project, the present leakage rates are much too low to produce an accumulation of a flammable atmosphere; a leakage rate of a few tens of cm 3.s -1 would be required A different conclusion may be given for other types of confinement

H 2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 16 Perspectives This study is a first step and several other tests can be considered –Determining the critical stress levels which give rise to significant leaks –Testing other stresses (e.g. vibration effects) –Combining different types of stress (e.g. under-tightening and traction) –Testing other potentially leaking elements of H 2 -based systems

ICHS4 – 2011 September, San Francisco Study of potential leakage on several stressed fittings for hydrogen pressures up to 700 bar Thanks for your attention