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Hydro-pneumatic Accumulator / Damper Safety Design
and Use Code
1) The units should be capable of losing the energy they
store by virtue of the gas within them prior to reaching destruct pressure.
The incorporation of a Gas Burst Disc, our designation G.B.D. at the end
of the Part Nbr., is one method of accomplishing this.
2) The units must be manufactured in such a way that both
the tactile and close visual inspection can be made without difficulty at
any place within the units, this enables stress corrosion and pitting to
be detected when units are re-pressure tested annually or as appropriate.
3) The units shall not have less than 3:1 gas vent pressure
to design pressure ratio, so that potential energy storage capability is
lost at a lesser pressure than final failure pressure.
4) Units shall not have less than a 4:1 safety factor,
i.e. burst pressure to design pressure, except when specifically required
to be in accordance with A.S.M.E. B31.3a (pipe fittings), BS5500 or others.
5) Design pressure shall not be less than 10% above maximum
working pressure, to allow for the normal inconsistencies of system pressure
relief valves.
6) There shall be an allowance for corrosion to 10% of
wall thickness, or 3mm if required by user under A.S.M.E. Code for Unfired
Pressure Vessels.
7) Allowance shall be made in the design calculations
for any stress raisers, example screw thread closures, or any that could
be caused by scratching of the bore of the unit, possibly resulting from
malfunction of sliding parts, example pistons without bearing pads.
8) Units shall be type tested to destruction, and 1% or
one off per batch, made from the same material tested in the event of any
engineering change.
9) The work/shop order number shall be recorded on the
material analysis and physical properties certificate of the material used
in the construction.
10) The units shall be designed in such a way that it
is impossible to begin to disassemble them until the pressure has been vented
from within them.
11) The comlete accumulator/damper including all bladder/diaphragm/sealing
members assembly shall be pressurized to 1-1/2 times working pressure before
dispatch/shipment.
12) They shall be made from sufficiently ductile material
to enable the result of any over pressurization to a dangerous level to
result in a measurable retained deformation after they have been depressurized.
13) Any unit of a welded construction shall be pressurized
to twice it’s working pressure where not specifically prohibited by Code
and shall be de-rated by 30% of it’s calculated maximum working pressure
for any cyclic duty exceeding 1,000 p.a.
14) Accumulators/dampers must be designed to retain above
safety factors in the event of gas over pressurization, e.g. due to a local
fire.
15) Every accumulator/damper must be used with a pressure
relief valve so positioned as to make it impossible to isolate the accumulator/damper
from the said relief valve.
16) A bleed valve shall be so positioned in relation to
the accumulator, its non isolatable relief valve, and its isolation valve,
that it is impossible for the bleed valve to be isolated from any pressure
remaining within the accumulator so that in the event of the bleed valve
being opened it cannot fail to empty any remaining pressurized fluid from
the accumulator.
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