summary of the second hydrogen cedar safety meeting 24 november 2008 present: j.gulley/ sc-gs,...
TRANSCRIPT
Summary of the second
Hydrogen CEDAR Safety Meeting
24 November 2008
Present: J.Gulley/ SC-GS, A.Sharma/PH-FGSO,
Augusto, Cristina, Lau, Niels
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 2
Reminder:
A first discussion with safety took place on 5 January 2005
See summary on web page of Beam WG
Since then studies concentrated on light detection
The agreed next step is to install a “standard” CEDAR on
the new K12 beam and operate it with Hydrogen at 3.6 bar
absolute pressure
The meeting concentrated on this option only.
Note that the volume of the counter is ~1.1 m3
This corresponds to ~4 m3 of gas at atmospheric pressure
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 3
Entrance and exit windows The material and thickness of the entrance and exit windows (0.4
mm of Al, AFNOR=AZ5GU in the standard CEDAR, for Helium
pressures up to 15 bars) must be discussed with Benoit Delille in
SC/GS. It may well be that the safety factor is gas dependent.
B.Delille explained that the safety factors for a group 1 gas (H2)
are the same as for group 2 gases (e.g. He), but there is a more
stringent quality control on the fabrication, e.g. radiography of
welds.
A risk analysis is needed and EN13445 resp CODAP norms must
be respected. Note that the required thickness goes with Ø2 !
Preliminary ANSYS calculations have been made by
Ans Pardons to compare the windows of a standard CEDAR
counter (for 15 bars of He of N2) with windows for 4 bars of
Hydrogen.
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 4
ANSYS calculations (non-linear) with elastic Aluminium for several cases. A thickness of 0.2mm seems ok. Stress plots are attached.
Not taking into account: Stress from clampingStress from heating
Stress in centre:(stress plots shown from center to 0.9* radius, to not show the stress
concentration due to the clamping)Thickness=0.4mm & pressure= 15 bar: 520MPa
(above plasticity limit of some aluminium grades) 0.2mm & pressure= 3bar: 275 MPa
(heat-treated aluminium grades have yield limits around this value 0.1mm & pressure= 3bar: 430 MPa
(above plasticity limit of some aluminium grades)
Deflection in centre: Thickness= 0.4mm & pressure= 15 bar: 5.4mm
0.2mm & pressure = 3bar: 4mm0.1mm & pressure = 3bar: 5mm
CEDAR WINDOW THICKNESS CALCULATIONS BY A.PARDONS
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Insulating material Polyurethane is admitted in small quantities, whereas polystyrene
is strictly forbidden. The material used in the CEDAR is
polyurethane.
As it is very unlikely that the material specification can be found
back 30 years later, and as the polyurethane has degraded over
the last 30 years anyway, it is strongly suggested to replace the
thermal insulation.
Check with J.Gulley before purchase, supply data sheet.
If this is not done, a sample must be provided to S.Sgobba and
S.Clement in TS/MME for analysis and a fire test.
Check with J.Gulley which fire test is suitable.
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 9
Protection of motors and HV The diaphragm motors, the PMTs and the control unit
below the nose must be enclosed in a Nitrogen
enclosure at slight overpressure.
Inside this enclosure a Hydrogen detector must be
placed (by David Hay in TS/ASE).
No special precaution is needed for the X/Y motors for
the CEDAR alignment with the beam.
The small gap between the exit window and the beam
vacuum will be put under Nitrogen.
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 10
Hydrogen bottles and transport
The Hydrogen bottle will be stored in a gas building outside the cavern.
Gas will be brought to the counter via a stainless tube of minimum diameter 6 mm (André Castel in TS/LEA). The gas pressure will be limited by a safety valve to a maximum of about 4 bars. This valve will be inspected regularly like all pressure valves.
The return tube must be stainless steel as well and of at least 8 mm diameter, to avoid the build up of local gas concentrations. It should be equipped with no-return valves. It should release the gas outside at a sufficient height (about 3 metres above ground level).
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 11
Pressure control
The CEDAR pressure pumps must be Hydrogen rated
(“EX” norm).
Similarly the nearby pumps in the beam vacuum sections
just upstream and downstream. Note that the vacuum
window may be damaged by the Cedar entrance or exit
windows in case they rupture.
Ferdi Hahn in PH/DT can be consulted concerning EX
rated pressure gauges. The Hamilton gauges heat the gas
to 40oC and are not obviously EX-rated.
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 12
Dear Lau,
I send you two links to Vega (our standard) and to Endress and
Hauser (high pression).
You have to choose the ATEX versions for a zone 2 application.
Endress and Hauser can probably do the accuracy you need,
Vega might not be as good (on paper)...
As an alternative you could also consider to build a small reference
pressure volume and measure relative pressure to increase the accuracy.
….
Ferdi
Vega: http://www.vegacontrols.co.uk/products.asp?fixedRangeID=10
Endress Hauser: http://www.uk.endress.com/
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 13
e.g. Endress and Hauser:
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or:
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Leak detection and alarms Two domes shall be installed, one above the nose and control unit
and one above the exit window.
In case all purged Nitrogen enclosures are equipped with H2 detectors,
the domes are probably not necessary.
Both shall be equipped with Hydrogen detectors.
In case of rupture of one of the windows or Hydrogen detection by
one of the detectors, a Level-3 alarm will be sent automatically to
the Fire Brigade.
And the Cedar pumps, motors and PMTs, as well as nearby beam
vacuum pumps will be stopped.
Sector valves will be closed in the nearby beam line vacuum
sectors.
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N2 enclosure
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N2 enclosure (but not R.Malleyran, please…)
H2 detector
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Procedures
Procedures will be made available that describe all
steps in the normal operation of the CEDAR (empty
before filling with Hydrogen, how to vent), as well in
case of e.g. leak detection or window rupture.
This includes the technical intervention, but also whom
to inform and what alarms to send where.
LG, 11-12-2008 Summary of Hydrogen CEDAR Safety meeting 19
Final remark
The safety experts reacted very positively to the fact
that we involved them from the start.
They came to our meeting, as well as to TCC8 and to a
CEDAR in the COMPASS beam line to understand
better.
Many thanks to them!