» FAQ
Questions and answers about Bell Hydromatics
Q 1: What is the largest size of a
tank that can be erected using jacks?
A: Our jacking equipment is applicable for the following
largest size of tanks according to data available : a)Largest in diameter :
92 meters. b)Largest in height: 64 meters. c)Largest in weight : 1900 tons
These, however, are not limiting figures.
Q 2: Whether tanks with column
supported roof be erected using jacks?
A: Tanks with column supported roof can be safely erected
with the help of jacking equipment, by fixing 1 or 2 jacks on each column.
The column will be erected in fragments of the same height like the shell
plates.
Q 3: What is the type of hydraulic
oil required?
A: General purpose hydraulic oil from MOBIL or other
reputed manufacturer can be applied. Although hydraulic oil of 68 viscosity
is widely used for most conditions, the viscosity of oil shall be
recommended based on ambient temperature at site.
Q 4: What is the ambient
temperature range in which jacks can be used?
A: The jacking equipment can be used in the temperature
range of – 10 degrees Celsius to + 50 degrees Celsius.
Q 5: Can floating roof tanks be
erected using jacks?
A: Floating roof tanks can be erected using jacking
equipment through creating the deck in the clear space provided inside the
tank and placing the pontoons after erection of shell.
Q 6: Can the powerpack be placed
outside the tank?
A: The powerpack can be put inside or outside the tank.
If the powerpack is placed outside the tank, the main hydraulic hose line is
brought inside the tank through the gap provided through spacer beams or
through the manhole.
Q 7: How do personnel enter inside
the tank when the jacking system is used?
A: Spacer beams of around 300 to 400 mm height are
offered around the periphery of the tank on the tank bottom plate. The shell
plates are placed on these spacer beams. Personnel can enter into and out of
the tank through the gap given by these spacer beams.
Q 8: What is maximum safe wind
speed at which a tank can be lifted using jacks?
A: While the safe wind speed large depends on parameters
like weight, height of tank, diameter, number of jacks in use, the number of
jacks is determined so, as to make lifting safe at 23.5 m/s (strong gale
wind), in general.
Q 9: Can the jacks be placed
outside the tank?
A: For repairs of tank bottom plate or foundation, the
jacks has to be placed outside the tank. In this case, appropriate temporary
support arrangement is to be done to support the trestles and stay pipes,
such that the load is distributed to the ground evenly.
Q 10: Can we use a combination of
12 ton and 25 ton jacks in the same tank?
A: 12 and 25 ton jacks should not be applied together in
a single tank. For any one tank, jacks of the same rated capacity can be
used.
Q 11: What is the life period of
the jacks?
A: The jacks are of sturdy design and construction. If
periodic maintenance is done as per our recommendation and the equipment is
not subject to corrosive environment, the expected life of the equipment can
be considered upto 10 years.
Q 12: What is the maximum width or
height of shell plates that can be erected with the jacking system?
A: The standard jacking equipment can be used for minimum
shell plate width (height) of 1400 mm and maximum of 2500 mm. In case of
shell plates that have width (height) of 3000 mm or more, jacking equipment,
these can be supplied against specific requirements.
Q 13: During the construction of a
tank using jacks, is it possible for air to get accumulated inside the tank
and lift the tank off the ground?
A: It is recommended to have one or two openings in the
roof by not fixing one or two roof plates till the shell is completely
erected, for air to pass through.
Q 14: What if a hose bursts or oil
seal ruptures during lifting?
A: The jack is a fail-safe device. Even in the event of
hydraulic seal, the mechanical grip jaws resists the jack from moving
downwards and will hold the jack at the same position on the trestle rod. In
case of a hose rupture while at the time of lifting, it should be stopped
and the hose replaced. The jacks do not slip downwards with the load even if
the hose bursts.
Q 15: Is it possible for the tank
to fall down during lifting or when held by the jacks?
A: Each jack has two pairs of case hardened grip jaws
fabricated using top grade of steel. At any point of time, either one of the
pairs is engaged or locked. While lifting both the pairs are in "locked"
position. In this position, the jack can move only upwards. Therefore, the
tank cannot fall down when held by the jacks.
Q 16: Will all jacks lift evenly
or will there be some difference in the lifting time of all the jacks in one
tank?
A: There is some differential lifting that depends on the
path used by the oil in the hydraulic line to reach the jacks. Some jacks
may lift before others, however this is not a reason for concern, due to the
oil cushion effect.
Q 17: How long can the tank be
left in lifted position, i.e., when the load is on the jacks?
A: Normally, after the lifting is done, immediately the
next shell plate is put in place and welded to the previous shell plate,
hence, releasing the load from the jacks. It is not recommendable to keep
the jacks loaded for more than the time required to place the next shell
course in position and welding. In case heavy winds are expected during this
period, the tank should be tied with the ropes.
Q 18: Will tank come down if the
powerpack fails during lifting?
A: In case during lifting, the powerpack fails because of
any reason, the pressure in the hydraulic line is maintained and the jacks
stay stationary in the semi-lifted position.
Q 19: If the lifting is uneven,
can the jacks be used to correct the tilt, if any?
A: In the event of uneven lifting that at any time can be
to the maximum extent of the stroke length of the jacks, which is 100 mm,
individual jacks can be closed using a stop cock valve to do any adjustments
during lifting.
Q 20: Should the roof plates be
fixed before the erection of jacking equipment?
A: All the roof plates except one or two plates (or more
if the diameter is more than 24 meters) can be installed before the erection
of jacking equipment, offered the height of the top shell is more than the
length of the trestle. In case the height of the top shell is lesser than
the length of the trestle, then the highest two courses shall be erected
before fixing the trestles, or alternatively, the annular roof plates can be
fixed after the top shell is jacked up.
Q 21: What is the minimum
thickness of shell plates suitable for jack-up method?
A: The minimum thickness of shell plate than can be
applied for jacking method is 6 mm. However, additional precaution as
recommended in our instruction manual shall be taken during the jacking up
of 6 mm thick plates to avoid buckling of 6 mm plates. For plate of 8 mm and
more thickness, additional patch plate or curved angle are not required.
Q 22: What is the time taken for
lifting a tank up by 2.5 mtrs.?
A: The time taken for one lift of 100 mm is approx. 5
minutes. Therefore for 2500 mm, 25 such lifts are needed that would take
approx. 125 minutes. However, as practically observed, the lifting duration
needed to lift 2500 mm for huge diameter tank ranges from 4 to 6 hours.
Q 23: What is the stroke per lift?
A: The stroke length of the jack is 100 mm.
Q 24: What if the oil is getting
heated up?
A: There is no reason for concern till the oil
temperature is less than 70 degrees celcius. If it exceeds this figure,
lifting should be stopped and the oil will cool down before resuming
lifting. If there is abnormally fast heating of the oil, please contact our
Technical support.
Q 25: What is the shipment time
required for jacks?
A: Shipment time would vary from 6 weeks to 10 weeks
(plus transit time), it depends upon quantity and capacity of jacking
equipment.
Q 26: Whether automatic girth
welding machine can be used when the tank is being constructed using jacking
system ?
A: Automatic girth welding is commonly used with the
jacking method. The outer welding is completed and inside tack welding is
done before lifting. Full welding is done inside, after lifting such that
the welding level is above the height of the trestles.
Q 27: How to determine the number
of jacks to be used for a particular tank?
A: The number of trestle required for a tank is settled
by: a) The maximum weight of the tank, the vertical load is max 8, 12 or 25
ton per trestle, which depends upon the kind of jacking equipment selected.
b) The maximum wind load on the trestles. c) The maximum distance between
the lifting points in the shell in regard to the stability of shell. d) The
normal maximum distance among the trestles is 3 mtrs.
