Energy engineering

29 August 2008

Bechtel used a J&R gantry to install four water pumps

Bechtel used a J&R gantry to install four water pumps

The initial plan was to install the pumps which weighed 95 kips (42.4 tonnes) with a 600 US ton (536 tonne) hydraulic crane.

However, the mob/demob cost alone was calculated to be in excess of US$200,000. In addition, the pumps were to be delivered over a relatively long period of time, adding a further $400,000 to the rental of crane.

An alternative plan was needed, so Bechtel decided to use the J&R gantry already on site for the offloading of the turbines and generators to be set up on the walls of the pump house.

Fortunately, the wall was 4 feet (1.2m) wide, the same width as the track of the gantry. The pumps were 43 feet (13m) tall and the height of the gantry, with the dead section extended, was only 39 feet, 7 inches (12.1m) to the bottom of the header beams. The pumps set into a pit that was 10 feet (3m) deep. At the bottom of the pit was an opening for each of the four pumps to be installed, so that each pump sat 8 feet (2.4m) below the pit floor.

There were two other problems, one of them being that the pump needed to be rotated 90 degrees after being upended; the other was that the pumps had to be lowered into the hole deeper than the gantry would go down, even if the dead section was retracted.

The first challenge was solved using a J&R Power rotator, rented from Bechtel. It worked in two ways.

1. It allowed the load to be rotated exactly to where the pump needed to be for setting on anchor bolts.

2. The power rotator also allowed the load to be lifted high enough to clear the floor of the pit by 1 foot (0.3m). The power rotator setting on top of the header beams raised the entire lift by 3 feet (0.9m).

Two 30 ton (tonne) chainfalls were used to lower the pump 18 feet (5.5 m) once it was over each of the four holes. The pumps were picked up on one end with the gantry in a lowered position. The other end of the pump was then picked up with a Terex Demag AC 120-1 hydraulic crane. The gantry then travelled on the tracks over the open pit with the AC 120-1 swinging and booming up and down to get the end of the load to the edge of the pit.

At this point the gantry lifted the pump to its maximum height and was put into travel mode, rather than hoist mode, and walked back towards the crane as it lowered the pump into the pit. When the pump was fully erected, the crane slacked off and the rigging was disconnected.

The job was completed 26 February 2008.
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