History of Corrosion Composites
Corrosion Market Overview
Since the introduction of commercial composites in the late 1940’s, the use of composites in a broad range of applications has increased at a steady pace. This is particularly true for the use of fiberglass reinforced plastics (FRP) in corrosive environments. The inherent corrosion resistance of polyester / vinyl ester resin based composites has driven the use of these materials in a wide range of products, such as: tanks, pipes, ducting, chemical plant equipment, wastewater treatment equipment, and many other products.
Composites have replaced many traditional materials and provided users with longer lasting equipment. In some case composites have replaced very exotic materials, providing similar service life at a much lower cost. The long-term use of composites under harsh conditions has created a history of successful field experience for these products. The development of construction standards and work practices has created the basis for the proliferation of composite applications in corrosive service.
Corrosion-resistant composites account for about 11-15% of the total composites market and generate an estimated three billion dollar in annual sales.
1950s – The Infancy of the Composites Industry
The initial development of polyester / glass fiber composites in the 1930s led to the commercialization of production products over the following twenty year period. 1953 was a critical year in the history of the composites industry: the first composites-bodied Corvette was produced; the first composite sport fishing yacht was created by Hatteras Yachts; and the first high performance industrial corrosion resins were developed by Atlas Chemical and Hooker Chemical Companies. These corrosion-resistant resins employed bisphenol fumarate and chlorendic anhydride resin chemistries. Subsequently, isophthalic resin chemistry was developed which became the mainstay of corrosion-resistant resins and is in widespread use today.
The opportunities for corrosion resistance afforded by bisphenol fumarate and chlorendic anhydride based resins were quickly recognized by the pulp and paper and the chemical process industries, which were the first industries to use this new material in the construction of process equipment.
In the early years, FRP was not considered an “engineered material” because very little was known about the properties of the materials and structures. Creative entrepreneurs and inventors developed new applications through experimentation and trial and error. At this point, formal standards governing the construction of FRP products did not exist.
1960s – The Potential of Composites is Realized
In the 1960s, improved polyester resin formulations and the introduction of synthetic fiber surface veils, used in combination with C-veil, enhanced the performance of the corrosion barrier. Plant engineers adapted existing civil and mechanical engineering methods to the design of FRP equipment, which became known as “Design by Rules.” Because reinforced plastics were not well understood, the application of traditional engineering concepts to composites led engineers to use steel structure design criteria for FRP structures. The traditional engineering methods applied to FRP resulted in the use of steel-bolted connections and metal-like specifications for laminate designs. This steel-like design approach was the root of some notable early failures of FRP products.
Because of inherently different physical properties, it became apparent that metallic structures and composites structures required different design criteria. Steel has uniform properties in all directions and is called an isotropic material. Composites have varying properties in different directions (because of the orientation of its reinforcing fibers) and is known as an anisotropic material. The misapplication of isotropic design methods to anisotropic materials resulted in issues that would define the next stage in the evolution of FRP Technology in the decade to follow.
The first underground gasoline storage tank, using corrosion-resistant isophthalic polyester resin , was introduced at the 1961 SPI Conference in Chicago by the Amoco Division of Standard Oil. From 1961 to 1965, Shell Oil and Owens Corning Fiberglas (OCF) continued this research, producing the first commercial line of large FRP underground storage tanks. By the late 1960s, OCF had extended this program to include large-diameter FRP sewer pipe.
The first FRP manufacturing standard (ASTM C-581) was published in 1965 and defined the construction of hand lay-up laminates. The former “trial and error” work practices that characterized early FRP production was advanced in 1969 with the publication of NBS PS 15-69. This standard established the conservative 10:1 design safety factor in FRP structures that is primarily used today.
1970s – Rapid Growth of Composites
Shell Chemical developed vinyl ester resin chemistry for its internal use in the construction of process equipment for its own plants. Vinyl ester resin offered enhanced corrosion resistance, improved mechanical properties, and high fracture toughness compared to previous resin systems. This new chemistry opened a wider range of applications for composites. Dow Chemical similarly developed vinyl ester formulations for their own chemical plants to use. They subsequently marketed this line of resins that became widely used across the industry.
The “Design by Rules” engineering method continued to be the primary means of specifying composites. However, the forward-looking aerospace industry began the development of fracture mechanics in metals. While the computational mathematics was not easily applied to anisotropic composites, the analytical methods were developing. During this period, engineers began to realize that the cracking mechanism in composites was different than in metals. While there was little application of the new science of fracture mechanics to composites, the standard 10:1 design safety factor provided enough cushion to allow continued growth of the applications.
Standards continued to develop that formalized the design and construction of corrosion-resistant composites. These included: ASTM D-3299 for filament wound tanks; American Water Works C-950 for wastewater applications; and SPI/MTI Quality Assurance Report RTP Corrosion-Resistant Equipment.
The Filament winding process advanced during this decade with the development of the hoop-wind method, which was originally developed for large-diameter aerospace components. The practice of applying fiber at a 55º winding angle produces equal strain in the hoop (transverse) and axial (length) directions of pressure pipe and vessels. This was one of the first major engineering achievements in applying the anisotropic properties of FRP composites to solve a specific engineering problem – matching the shell membrane stiffness in the axial and hoop directions to resist stresses in each direction. This method would become further sophisticated in the years to come.
The use of composites in industrial applications became widespread in the 1970s, and a proliferation of companies entered the composites arena.
1980s – The Engineering Community Begins to Focus on Composites
The advent of desktop computers and stress analysis software provided designers with computational tools formerly only available to large corporations or government agencies. The use of finite element analysis (FEA), even in its early basic form, generated advancements in composites design. Engineers began work to develop better equipment specifications, based more on descriptive specifications than the well-established performance specifications used in steel equipment.
The ASME RTP-1 Committee was formed in 1981 and began work on what was to become the seminal design standard for FRP tanks. This document, Reinforced Thermoset Plastic Corrosion-Resistant Equipment, was first published by the American Society of Mechanical Engineers in 1989.
During the same period, aerospace computer programs were adapted for lamination design analysis of corrosion equipment. This, along with finite element analysis, represented another major advancement in the development of FRP Technology. Many corrosion product molders began hiring engineers experienced in advanced materials mechanics, the theory of elasticity, and orthotropic material behavior.
At the end of the decade, Amoco unearthed a 25-year-old underground gasoline storage tank to determine its condition. The tank proved to be in very sound condition, providing field validation of underground storage tank performance, and was placed back into service.
1990s – Break-Through Years for Composites Design & Applications
The 1990s were a culmination of a number of developing technologies and engineering methods applied to FRP. Engineers began applying the results of R&D to new designs, and the use of lamination analysis became widespread. The corrosion industry had accumulated thirty to forty years of experience and case histories to build a positive performance record. Design criteria became better defined, allowing safety factors to be reduced and allowing fabricators to avoid having to over-build structures. The use of non-destructive testing, such as acoustic emissions analysis, provided validation tools that increased buyer confidence in FRP products.
2000s – Composites Becomes a Standard Engineering Material
Following the advances of the previous decade, FRP became accepted as a standard construction material by engineers and end users. The availability and exchange of information provided by the Internet allowed engineers to create design specifications quickly and to access large amounts of data. The use of specialized reinforcements, such as carbon fiber, ECR glass, stitched fabrics, and 3-D fabrics, coupled with modern design capabilities, has extended the range of applications for FRP.