Our jacking equipment has been used 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.
Tanks with column supported roof can be safely erected using jacking equipment, by fixing 1 or 2 jacks on each column. The column will be erected in fragments of the same height as that of the shell plates.
General purpose hydraulic oil from MOBIL or other reputed manufacturer can be used. Although hydraulic oil of 68 viscosity is largely used for most conditions, the viscosity of oil shall be recommended based on ambient temperature at site.
The jacking equipment can be used in the temperature range of - 10 degrees Celsius to + 50 degrees Celsius.
Floating roof tanks can be erected using jacking equipment by fabricating the deck in the clear space available inside the tank and placing the pontoons after erection of shell.
The powerpack can be placed 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 by spacer beams or through the manhole.
Spacer beams of about 300 to 400 mm height are provided 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 provided by these spacer beams.
While the safe wind speed large depends on parameters such as diameter, weight, height of tank, 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.
For repairs to tank bottom plate or foundation, the jacks are placed outside the tank. In this case, appropriate temporary support arrangement is to be made to support the trestles and stay pipes, such that the load is distributed to the ground evenly.
12 and 25 ton jacks should not be used simultaneously in one tank. For any one tank, jacks of the same rated capacity shall be used.
The jacks are of robust design and construction. If periodic maintenance is carried out as per our recommendation and the equipment is not subject to corrosive environment, the expected life of the equipment can be safely considered as 10 years.
The standard jacking equipment can be used for minimum shell plate width (height) of 1400 mm and maximum of 2500 mm. For shell plates having width (height) of 3000 mm or more, jacking equipment can be supplied against specific requirements.
It is advisable to have one or two openings in the roof by not fixing one or two roof plates till the shell is fully erected, for air to pass through.
The jack is a fail-safe device. Even in the event of hydraulic seal, the mechanical grip jaws prevent the jack from moving downwards and will hold the jack at the same position on the trestle rod. In case of a hose rupture during lifting, lifting should be stopped and the hose replaced. The jacks do not slip downwards with the load even if the hose bursts.
Each jack has two pairs of case hardened grip jaws made of special grade of steel. At any given point of time, either one of the pairs is engaged or locked. During 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.
There is some differential lifting depending 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 cause for concern due to the oil cushion effect.
Normally, after the lifting is done, immediately the next shell plate is put in placed and welded to the previous shell plate, thereby releasing the load from the jacks. It is not advisable 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 guy ropes.
In case during lifting, the powerpack fails due to any reason, the pressure in the hydraulic line is maintained and the jacks remain stationary in the semi-lifted position.
In the event of uneven lifting, which at any time can be to the maximum extent of the stroke length of the jack, which is 100 mm, individual jacks can be shut off using a stop cock valve to make any adjustments during lifting.
All roof plates except one or two plates (or more if the diameter is more than 24 mtrs) can be fixed before the erection of jacking equipment, provided 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 top 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.
The minimum thickness of shell plate than can be used for jacking method is 6 mm. However, additional precaution as advised in our instruction manual shall be taken while 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.
The time taken for one lift of 100 mm is approx. 5 minutes. Therefore for 2500 mm, 25 such lifts are required, which would take approx. 125 minutes. However, as practically observed, the lifting duration required to lift 2500 mm for large diameter tanks ranges from 4 to 6 hours.
The stroke length of the jack is 100 mm.
There is no cause for concern till the oil temperature is less than 70 degrees celcius. In case it exceeds this figure, lifting should be stopped and the oil allowed to cool down before resuming lifting. If there is abnormally fast heating of the oil, please contact our Technical support.
Shipment time would vary from 6 weeks to 10 weeks (plus transit time) depending upon quantity and capacity of jacking equipment.
Automatic girth welding is commonly used with the jacking method. The outside welding is completed and inside tack welding is done before lifting. Inside full welding is done after lifting such that the welding level is above the height of the trestles.
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, depending upon the type of jacking equipment selected
b) The maximum wind load on the trestles.
c) The maximum distance between the lifting points in the shell with regard to the stability of shell.
d) The normal maximum distance between the trestles is 3 mtrs.