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,

Study of potentialStudy of potentialleakage on severalleakage on several

stressed fittingsstressed fittingsfor hydrogen pressuresfor hydrogen pressures

up to 700 barup to 700 bar

D Houssin-Agbomson1, D Jamois2, Ch Proust2, J Daubech2, S Ruban1, S Jallais1

[email protected]

ICHS4 – 2011 September, San Francisco

1 Air Liquide, Centre de Recherche Claude-Delorme, 78350 Les Loges-en-Josas, France2 INERIS, 60550 Verneuil-en-Halatte, France

H2 potential leakage on stressed fittings – ICHS4, 2011, San Francisco 2

I. ContextII. Tested configurationsIII. Experimental deviceIV. ResultsV. Conclusions and perspectives

ContentContent


I. ContextI. Context


ContextSeveral 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

ObjectivesQuantify "small" leaks which are probable

Contribute to assess the probability of "important" leaks

MeansH2 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

Mobixane2.5 kW

CommPac-500500 W

Container NRJ5 kW

CommPac-50002.5 - 5 kW

Study description


II. Tested configurationsII. Tested configurations

Studied fittingsStress configurations


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

FittingsExternal tube

sizeMaximum 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

Double ring

NutBody

Nut

Body

Threaded ring

6-mm double ring tube fitting Medium-pressuredouble ring tube fitting

Threaded ring tube fitting


Stress configurations (1/2)

Existing literatureFew 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 studyH2, 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


Stresses Normal conditions of useTested stress level

considered as maximum in situation

Static stressesAssembly-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 fitting 1 turn

1 1/4 turn, for 1/2’’ double ring tube fitting3/4 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 fitting 1 1/2 turn

Thermal effects

+60 to -20°CCrimping at 100°C and

leakage testat 30°C

Dynamic stresses

Counter-clockwise rotation

0 turn1/8 turn compared to

initial position

Flexion 0°10° from fitting initial

axis

Traction 0 N320 N

in fitting axis direction

Stress configurations (2/2)

Details of the tested configurations


III. Experimental deviceIII. Experimental device

Main test bench"Dynamic stress" module


A simple but accurate AND safe test bench…Characterization of H2 high pressure leaks

Gas for tests: H2

Pressure range: up to 700 barSensitivity: flow rate higher than 10-2 cm3.s-1

Main equipmentA H2 compressorHigh pressure reservoirsPneumatic valvesAccurate pressure transducersThermocouples

Climatic enclosure

Climatic enclosure with device for testsScheme of the main test bench

PPP PPP

H2

Compression stationup to 700 bar

1 m3-climatic enclosure

Pressuretransducer

2.4 L-reservoir

30 L-reservoir

Tested fitting

Pneumaticvalve

200 barH2 storage

Evacuation

V1

V2

V3

30 L-reservoir

2.4 L-reservoir

30 L-reservoir

2.4 L-reservoir

Main test bench


Characteristics Module set-up in order to apply stress on pressurized fittings thanks to a pneumatic jackPressure range: up to 700 barTested "dynamic" stresses

• Flexion• Rotation• Traction

Only applied on 6-mm tube fitting

Module for "dynamic stress"

Flexion Rotation Traction

θ°


θ°

Jack

Jack

Testedfitting

Testedfitting

Jack

Testedfitting


Jack

Jack

Testedfitting

Testedfitting

Jack

Testedfitting


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


IV. ResultsIV. Results


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

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

FittingExternal tube size

Tested stressPressure

conditionsMeasured

leakage rate

Swagelok medium-pressure double ring tube fitting

1/2’’After 50 assembly-dismantling

cycles700 bar 0.05 cm3.s-1

Maximator threaded ring tube fitting

9/16’’Under-tightening with silicone

grease:60 N.m instead of 80 N.m

700 bar 4.3 cm3.s-1

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

Leak visualisation in water


V. Conclusions and perspectivesV. Conclusions and perspectives


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 requiredA different conclusion may be given for other types of confinement


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

[email protected]

ICHS4 – 2011 September, San Francisco

Study of potential leakage on several stressed fittingsStudy of potential leakage on several stressed fittingsfor hydrogen pressures up to 700 barfor hydrogen pressures up to 700 bar

Thanks foryour attention

Documents

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,