In our first article, we introduced the key elements in successful pipe system design – material selection, component design, support design, system stress analysis, and installation. In this article we are going to take a closer look at the first of these elements, i.e. material selection.
Composite Pipe Material Selection: Corrosion Barriers and Criteria
Composite piping systems, like FRP piping and FRP dual laminate piping, are manufactured with a corrosion barrier and a structural laminate. The corrosion barrier provides the chemical resistance needed to protect the structural laminate so that the piping system can perform its intended function. There is a wide range of corrosion barriers commonly used in the Corrosion Industry, everything from just a surfacing veil in a light duty resin system, to corrosion barriers containing multiple layers of surfacing veil and chopped strand mat manufactured using premium grade resins, to those made using fluoropolymer materials. For long term, trouble-free service of your piping system, you need to have a corrosion barrier that will stand up to the challenge of your application. But there can be significant cost differences between the various corrosion barrier configurations. Selecting the right configuration for the application will ensure you get the performance you want without paying for more than you need.
The first step in selecting the right corrosion barrier configuration is accurately defining the environment to which the piping will be exposed. Items that need to be identified are:
- Chemical environment
- Concentrations of chemicals (normal and maximum)
- Process temperatures (normal operating and upset)
It’s important to consider not only the individual chemicals that will be present in the process stream, but also the combinations of chemicals that might be present. The particular combination of chemicals could pose additional corrosion challenges that need to be addressed. It’s also very important to accurately define the temperatures of the process stream as chemical attack can be significantly accelerated at higher temperatures.
With the process conditions properly defined, we can determine whether an FRP corrosion barrier will be suitable for the conditions, or whether it will be necessary to use a thermoplastic corrosion barrier, i.e., a dual laminate piping system.
For most corrosion applications, the standard FRP corrosion barrier is 0.100” – 0.120” (2.5 – 3.0 mm) thick, consisting of 1 or 2 layers of surfacing veil and 2 layers of chopped strand mat. Surfacing veils are usually composed of “C” glass or polyester; both are commonly used and both are resistant to a wide range of process conditions. There are a few applications where one would be preferred over the other such as hydrochloric acid where “C” veil would be preferred, or hydrofluoric acid where polyester would be preferred, but both types of veil have been used successfully in many applications.
Chopped strand mat is either “E” or “ECR” glass. “E” glass has been used successfully in corrosion barriers for over fifty years. “ECR” glass, which is a boron-free form of “E” glass, has been gaining wide acceptance in recent years. “ECR” glass displays improved chemical resistance in some services (particularly acids), and it also displays moderately better mechanical properties. While the “110 mil” corrosion barrier is the most widely used configuration, thicker corrosion barriers, e.g. 0.22” (5.6 mm) are often specified for more aggressive services.
