The Fundamentals of Fiberglass

Standards for fiberglass tanks and piping.

Fiberglass reinforced thermosetting plastic (“fiberglass”) was used as an alternative to protected steel, stainless steel and exotic materials for the first time in 1950. Centrifugal cast fiberglass piping was used in the crude oil production industry to solve corrosion problems that same year. Manufacturers developed national standards and test methods for fiberglass storage and piping systems in the 1960s.

Cured by the system –
What exactly is fiberglass? Fiberglass tanks and piping contain glass fiber reinforcement embedded in cured thermosetting resin. Hence, the term Fiberglass Reinforced Plastic (FRP) describes the fiberglass material system.

This composite structure typically contains additives such as pigments and dyes. By selecting the proper combination of resin, glass fibers, additives and design, the fabricator can create a product that meets the equipment designer’s performance standards. These are based upon the standards listed in this column

Glass fibers –
All fiberglass begins as individual glass filaments drawn from a furnace. Many filaments are formed simultaneously and gathered into a strand, and a surface treating sizing is added to maintain fiber properties. Glass fibers are designed for several purposes including use in acid, alkali and other chemical environments. The mechanical strength of a fiberglass product depends up on the amount, type and arrangement of a glass fiber reinforcement within the material system. This mechanical strength increases proportionally with the amount of glass fiber reinforcement used.

Resins –
The second major component of fiberglass tanks and piping is the resin system. One of the two basic groups of resins is not used with glass fiber reinforcing. Here is a brief description of the difference between the two resin systems:

• Thermoplastics are resins that are normally solid at room temperature, but are softened by heat and will flow under pressure. Typical products include kitchenware, children’s toys, bottles and other common items.

• Thermosetting plastics are resins that undergo an irreversible reaction when cured in the presence of a catalyst. They are insoluble, and cannot be re-melted. There are two generic types of resins used in this process: epoxy and polyester. Epoxy resins are used primarily for the manufacture of small diameter piping. Polyester resins are commonly used for large diameter piping and storage tanks. Polyester resins come in many variations with different properties to resist acids, caustics and high temperatures.

Fiberglass products use only thermosetting resin systems. The resin system is selected on the basis of its chemical, mechanical and thermal properties.

What a glass –
Resistance to corrosion in aggressive environments is one of the primary reasons for using fiberglass tanks or piping. Typical types of corrosion – including galvanic, aerobic, pitting and intergranular corrosion – do not affect fiberglass. While it resists a wide range of chemicals and temperatures, fiberglass requires the right design, fabrication and installation to match the right application. For example, fiberglass may be subject to chemical attack from hydrolysis, oxidation or incompatible solutions (e.g., sulfuric acid, caustics and methanol) unless the proper resinglass matrix is used to provide protection against such an attack.

Today, off-the-shelf and custom fiberglass tanks and piping are used in corrosive environments and high pressure (e.g. 60 psi) process applications. These systems are widely used in virtually inexhaustible applications – chemical, municipal and industrial – for the retail petroleum industry as well as exploration and production of petroleum products.

Setting the standard –
Today, there are a number of nationally recognized standards and specifications for fiberglass tanks and piping. There are separate standards developed for military applications. The following is a list of civilian organizations with published standards and specifications for fiberglass tanks and piping:

• American Petroleum Institute
• American Society of Mechanical Engineers
• American Society for Testing and Materials
• Factory Mutual Research
• National Sanitation Foundation
• UL Underwriters Laboratories Inc. (See sidebar for a list of standards published by these organizations.)

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