A Description of the Two Manufacturing Methods
Shop Fabricated Piping Systems
Loose Supplied Pipe and Fittings
Advantages and Disadvantages of Each Fabrication Method
Shop Fabricated Pipe Systems:
50 - 90% of all welds can be performed in the shop More economical in the long run; the end user only pays for what he/she gets Shop fabrication is more efficient than field fabrication (by as much as 5 to 1); installation time is greatly reduced Pipe systems can be custom designed and manufactured to customer specifications Shop fabrication labor rates are much more economical than field labor rates With the plain end butt weld system, no couplings nor nipples are required. Fittings and flanges can be mated to each other without couplings. Field welding of long straight runs of piping do not require couplings. This reduces the total number of welds, both shop & field, in the system.
Requires drafting services of either the purchaser or fabricator. Has higher up-front expenses. May require a longer delivery time to the jobsite
Loose Pipe and Fittings:
Advantages:Fewer up-front costs such as layout design, drafting, etc.
In the short run, it is more economical. Has a shorter delivery time to the jobsite. No drafting services required
Disadvantages:In the long run, it is not as economical as shop fabrication. Has a much higher field installation cost. Requires a greater number of field weld kits. Pipe, fittings, and welds are wasted because of the need to purchase extras.
Potential Applications for Each Fabrication Method
Selection Process Guidelines:
Shop fabricated pipe systems greatly reduce the number of welds needed to be performed in the field, thus reducing the amount of field labor involved in the project. Field fabricated jobs require less up-front planning and layout design time.
Installation conditions can often be adverse, thus making field installation timely and expensive. The shop-fabricated system, with its minimal number of field welds, leaves less to chance during field installation of the project.
Shop fabrication is a much more efficient process than field fabrication. Typically three shop welds can be performed in the same time it takes to perform a single field weld. This ratio, of course, is dependent upon a number of factors, however, the high ratio is primarily due to the planning and scheduling behind shop fabrication.
By minimizing the number of field welds, a shop fabricated system requires a much smaller amount of time dedicated to field installation. Thus shorter turnarounds can be achieved and shutdowns can be minimized.