Piping in Tight Quarters: Special Design Challenges for Waterworks Plant Yard Piping

Designing new yard piping at existing waterworks plants can be very challenging, especially at already congested sites. There are always several issues associated with existing piping, including the actual location of all old utility lines, which can be helped by the use of Subsurface Utility Engineering that uses nondestructive geophysical investigation techniques. Connecting to and constructing very near existing lines can also be a challenge. Multiple pipeline crossings can result in several conditions that must be given attention, but a detailed sequence of construction can help minimize disruptions and plant shutdowns. Alignment issues include proper separation between water and wastewater lines, designing for future repairs and expansions, keeping utilities in defined corridors, and minimizing the number of fittings. Piping systems must be designed with the appropriate linings, coatings, pipe materials, pressure classes, beddings, joints, corrosion protection, and testing requirements. Designers must stay abreast of the new materials in the market in order to properly analyze alternate systems. Depth of cover plays a very large part in design, as does seismic considerations, and the need for thrust restraint and flexibility at connections to buildings. A critical step in the design is specifying the proper pressure testing procedures, for which a few alternatives are discussed. Good record drawings are a must, as is a design that is cost-effective, since yard piping is so much more expensive per unit of length than equivalent linear pipelines.