Hundreds of millions of dollars are spent each year in the United States replacing corroded and failed steel pipe with new steel pipe in process industries. In many of these applications Fiberglass Reinforced Plastic (FRP) pipe would be a better and more cost effective replacement material. However, due to unfamiliarity with FRP, the decision is often made to replace in kind. The successful design and installation of FRP pipe systems requires adherence to established design principles and practices - just as does the successful installation of steel pipe systems. By understanding and applying these principles to FRP, plant operators may benefit from the advantages of FRP through lower installed and life cycle costs. This paper will review some of the most important differences between steel and FRP pipe design and present a case history of a successful steel pipe replacement project.
FRP has been used as a material of construction for industrial pipe systems since the 1950's. FRP competes with carbon steel, rubber lined carbon steel, stainless steels, and alloys. The requirements for metal pipe components and system design are well established and clearly defined in the ASME Pipe Codes - B31.1 Power Piping and 831.3 Process Piping. The requirements for FRP component and system design are also well established however they are not so well defined in the ASME Pipe Codes. This has lead to some resistance from pipe designers to use FRP and in other instances has lead to unsuccessful applications of the material. FRP holds great potential to reduce pipe system costs and to offer significant performance advantages. This paper will review the some of the most important differences between steel and FRP pipe design, reference and describe the ASTM Standards and Specifications most applicable to FRP, and review a successful replacement of steel pipe with FRP.
FRP is much more flexible than steel. Typical elastic modulus of FRP is 1/20th that of steel. This means oscillations in an FRP pipe system will occur more easily than with steel, column type failure is more of an issue in FRP system design, and loads on supports for a given amount of expansion will be much lower in an FRP system. The longitudinal strength of FRP is lower than steel requiring more careful consideration of longitudinal loads. FRP does not yield meaning stress concentrations and point loads must be avoided. The coefficient of thermal expansion for FRP is approximately 2.5 that of steel requiring more allowance for growth. Strength and rigidity drop rapidly as we approach the heat distortion temperature (HOT) of the resin. This typically occurs within 30 degrees Fahrenheit of the resin's HOT. Flange connections in FRP require careful consideration particularly when mating to equipment. FRP pipe and components can be permanently joined in the shop and the field by a variety of methods including bell and spigot adhesive joints and laminated butt joins. These joints involve procedures not normally familiar to welders and pipe filters. These differences in material properties and requirements can be easily accounted for through informed design.