Each field assignment has its unique criteria due to site situation such as lack of lifting, access constraint, and concurrent activities at site as well as structural fabrication tolerance. As such, unconventional thinking and versatility are very important attributes needed from experience insitu machining specialist. During the Covid 19 pandemic period, a repeat assignment for machining a fire pump foundation on-board a FPSO was completed using a different approach due to limited rigging and lifting support available in the yard.
GD&T of the job required to achieve a flatness surface runout of not more than 0.2mm for each foundation pad and within 1mm for all the 10 pads. Total of five pads, each 1.2m apart, were welded on a support beam over a length of 11metres. There are total two support beams, parallel and 2m apart from each other on the deck of the vessel.
Previously, a standard portable linear milling machine was setup 3 times to complete the machining with the aid of laser alignment equipment.
To adapt with site situation, our field service team went back to drawing board for alternative solutions after knowing our client’s constraint.From the discussion, the team decided to utilize 2 units of linear milling machine and incorporate additional foundation frame. The foundation frames were placed and tack welded between the landing pads as shown in photo 1.
The cross beam of the milling machines were installed with over hanged to accommodate 2 milling spindles at each ends as shown in photo 2 below.
Even though the design, modification and setup required extra preparation as compared to previous deployment, the modified approach needed minimum lifting and riggings during the machining process which eliminated long waiting time at site. The work scope was completed well within the committed duration even though the team had a slower start as compared to previous assignment.