In order to better understand the challenges faced by Engineering to match the construction schedule, it is worth knowing that the critical path of an oil & gas facilities project is that of its pipework. Piping is indeed by far the most time consuming activity at the job Site. This is due to large number of pipes found in a facility, to the fact that each of them is a made of a collection of individual items, such as straight lengths (limited to 6 or 12 meter in length), elbows, tees, etc. welded to each other, and to the time it takes to make such welds. It takes a full day to one welder to perform a field weld of a 500mm diameter pipe of average thickness (this time is halved for a shop weld performed in the piping pre-fabrication shop, but shop welds account for only 2/3 of the welds).
Reviewing what piping site activities entail helps to precise the demands for engineering:
Piping Site activities start with pre-fabrication, carried out in a workshop, followed by erection at the plant Site.
Piping pre-fabrication activities are dependent on availability of both the construction drawings and materials. Typically, a good progress will only be achieved once 50% of the isometric drawings have been issued for construction and 75% of the materials of all types have been delivered at Site. The latter will require timely of Engineering requisitions, according to the lead time of the various items, which depend on the type, size, material (exotic vs common) etc. For what regards construction drawings, one must bear in mind that the drawings issued by Engineering, the "design" Isometrics, are not directly used for construction but need to be translated into shop drawings, the "shop" Isometrics. This process, called spooling, must be adequately organized, between the Engineer and the Constructor, in order to minimize the time lag. It will typically involve sharing of files – or even the 3D model itself – as well as information on the readiness of such or such lines.
Piping erection will progress satisfactorily once pre-fabrication is around 30% complete and the equipment that the pipe-work connects have been erected. A good productivity will typically be reached once 60% of the equipment will have been erected. Additionally, effective installation of piping will require availability of pipe supports. The latter are very numerous. Their standardization and timely mass production must be properly planned in order to allow concurrent installation with that of the pipe-work.
Copyright ©2011 Dave Brown
