Study of potential leakage on several stressed fittings for hydrogen pressures up to 700 bar

1
Study of potentialleakage on severalstressed
fittingsfor hydrogen pressuresup to 700 bar
ICHS4 2011 September, San Francisco
D Houssin-Agbomson1, D Jamois2, Ch Proust2, J
Daubech2, S Ruban1, S Jallais1 sidonie.ruban_at_airl
iquide.com
1 Air Liquide, Centre de Recherche
Claude-Delorme, 78350 Les Loges-en-Josas,
France 2 INERIS, 60550 Verneuil-en-Halatte,
France
2
Content

• Context
• Tested configurations
• Experimental device
• Results
• Conclusions and perspectives

3
I. Context
4
Study description

• Context
• Several H2 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
• H2 systems analysis by fault tree
• Scope fittings
• Identification of leak causes and means of
  mitigation
• Tests for leaks
• INERIS test bench H2, up to 700 bar, on double
  ring tube fittings and threaded ring fittings

5
II. Tested configurations
Studied fittings Stress configurations
6
Studied fittings

• Based on a preliminary study of potentially
  leaking elements, four kinds of commercial
  fittings usually employed on H2 energy-based
  systems were chosen and tested

6-mm double ring tube fitting
Medium-pressuredouble ring tube fitting
Threaded ring tube fitting
Fittings External tube size Maximum working pressure recommended by the constructor
Swagelok double ring tube fitting(316 SS) 6 mm 420 bar
Rotarex double ring tube fitting(316 SS) 6 mm 420 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
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 cm3.s-1 at 20 bar for
  tightening by hand of the fitting
• Experimental conditions of the present study
• H2, 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,22-23
October 2008, Hamburg, Germany
8
Stress configurations (2/2)

• Details of the tested configurations

Stresses Normal 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
Static stresses Assembly-dismantling cycles lt 20 cycles, for high pressure fittings (double and threaded ring tube fittings) 50 cycles
Static stresses Under-tightening 1 1/4 turn, for 6 mm double ring tube fitting 1 turn
Static stresses Under-tightening 1 1/4 turn, for 1/2 double ring tube fitting 3/4 turnand 1 turn
Static stresses Under-tightening 80 N.m with silicone grease on conical sealing surfaces, for 9/16 threaded ring tube fitting 60 N.m with silicone grease
Static stresses Over-tightening 1 1/4 turn, for 6 mm double ring tube fitting 1 1/2 turn
Static stresses Thermal effects 60 to -20C Crimping at 100C and leakage testat 30C
Dynamic stresses Counter-clockwise rotation 0 turn 1/8 turn compared to initial position
Dynamic stresses Flexion 0 10 from fitting initial axis
Dynamic stresses Traction 0 N 320 Nin fitting axis direction
9
III. Experimental device
Main test bench "Dynamic stress" module
10
Main test bench

• A simple but accurate AND safe test bench
• Characterization of H2 high pressure leaks
• Gas for tests H2
• Pressure range up to 700 bar
• Sensitivity flow rate higher than 10-2 cm3.s-1
• Main equipment
• A H2 compressor
• High pressure reservoirs
• Pneumatic valves
• Accurate pressure transducers
• Thermocouples

Climatic enclosure
Climatic enclosure with device for tests
Scheme of the main test bench
11
Module for "dynamic stress"

• 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

• "Dynamic" module
• Main equipment a pneumatic jack (up to 320 N)
• Inserted inside the climatic enclosure of the
  main test bench

12
IV. Results
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 10-2 cm3.s-1

Fitting 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 bar 0.05 cm3.s-1
Maximator threaded ring tube fitting 9/16 Under-tightening with silicone grease60 N.m instead of 80 N.m 700 bar 4.3 cm3.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
  cm3.s-1 for the "0.1 mm-200 bar" hypothesis),
• It would be detected by normal control procedures
  particularly for these types of stresses

Leak visualisation in water

• The other stress scenarii did not exhibit
  detectable leakage given experimental
  installation sensitivity

14
V. Conclusions and perspectives
15
Conclusions

• A specific experimental installation was designed
  and set-up by INERIS in order to study potential
  leakages on fittings commonly used in H2 existing
  systems
• This test bench enables
• to accurately quantify, when existing, leakages
  with a flow rate above 10-2 cm3.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 H2 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 cm3.s-1 for the Swagelok 1/2
  medium-pressure double ring tube fitting after 50
  cycles of assembly-dismantling
• 4.3 cm3.s-1 for a 25 under-tightening of the
  Maximator 9/16 threaded ring tube fitting
• ? A good reliability of the fittings used in
  H2-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
  cm3.s-1 would be required

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
  H2-based systems

17
Thanks foryour attention
ICHS4 2011 September, San Francisco
Study of potential leakage on several stressed
fittingsfor hydrogen pressures up to 700 bar
sidonie.ruban_at_airliquide.com