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Fiberglass Tubing Sheet Review

Fiberglass (also called glass-reinforced plastic, GRP, glass-fiber reinforced plastic, or GFRP), is a glass fiber reinforced polymer made into selected structural and other shapes.

Fiberglass is a lightweight, strong, and exhibits high capabtibility characteristics. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are less costly. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes.

An individual structural glass fiber is both stiff and strong in tension and compression along its axis. Although it might be assumed that the fiber is weak in compression, it is actually only the long aspect ratio of the fiber which makes it seem so; i.e., because a typical fiber is long and narrow, it buckles easily. On the other hand, the glass fiber is weak in shear loading. Therefore if a collection of fibers can be arranged or manufactured in a preferred direction within a material, and if the fibers can be prevented from buckling in compression, then that material will become structurally strong in that direction.

Furthermore, by incorporating multiple layers of fiber on top of one another, with each layer oriented in various preferred directions, the stiffness and strength properties of the overall material can be controlled in an efficient manner. In the case of fiberglass, it is the plastic matrix which permanently constrains the structural glass fibers to directions chosen by the designer. With chopped strand mat, this directionality is essentially an entire two dimensional plane; with woven fabrics or unidirectional layers, directionality of stiffness and strength can be more precisely controlled within the plane.

A fiberglass component is typically of a thin "shell" construction, sometimes filled on the inside with structural materials, as in the case of surfboards foam may be used. The component may be of nearly arbitrary shape, limited only by the complexity and tolerances of the mold used for manufacturing the shell.

Fiberglass materials are available with a variety of different compositions. This allows for additional design flexibility to meet performance criteria. All fiberglass reinforcement begins as individual filaments of glass drawn from a furnace of molten glass. Many filaments are formed simultaneously and are gathered into a "strand." A surface treatment (sizing) is added to maintain fiber integrity, establish compatibility with resin, and ease further processing by improving consolidation and wet strength. Sizing can also affect resin chemistry and laminate properties.

The three general types of fiber as-built orientation include:

  • Unidirectional. The greatest strength is in the direction of the fibers. Up to 80 percent reinforcement content by weight is possible.
  • Bidirectional. Some of the fibers are positioned at an angle to the rest of the fibers as with helical filament winding and woven fabrics. This provides different strength levels governed by the fiber quantity in each direction of fiber orientation. A combination of continuous and chopped fibers is also used to provide designed directional strength.
  • Multidirectional (isotropic). This arrangement provides nearly equal, although generally lower, strength and modulus in all directions. From 10 percent to 50 percent reinforcement content, by weight, can be obtained with multidirectional materials such as chopped roving or chopped strand mat.

Common uses of fiberglass include boats, piping, tubing, automobiles, baths, hot tubs, water tanks, roofing, pipes, cladding, casts and external door skins.

Fiberglass Tubing - fiberglass tubing and pipe is produced using two basic processes: filament winding and centrifugal casting. Each of the processes produces a pipe with characteristics that while unique, and which may be advantageous for some applications, will meet the performance requirements of AWWA Standard C950.

Manufacturing Fiberglass Tubing and Pipe:

Filament winding is the process of impregnating glass fiber reinforcement with resin, then applying the wetted fibers onto a mandrel in a prescribed pattern. Fillers, if used, are added during the winding process. Chopped glass roving's may be used as supplemental reinforcement. Repeated application of wetted fibers, with or without filler, results in a multi layered structural wall construction of the required thickness. After curing, the pipe may undergo one or more auxiliary operations such as joint preparation. The inside diameter (ID) of the finished pipe is fixed by the mandrel outside diameter (OD). The OD of the finished pipe is variable and is determined by the pipe wall thickness.

The concepts of the filament winding process are illustrated in Figure 1. Within the broad definition of filament winding there are several methods used including reciprocal, continuous, multiple mandrel, and ring and oscillating mandrel, each of which is described briefly.

Figure 1
Reprinted with permission from Fiberglass Pipe Handbook, Fiberglass Pipe Institute, New York, N. Y.

In one type of continuous process, the tube or pipe is made on one or more mandrels, which move past stations that apply fiberglass tapes preimpregnated with resin or glass fiber and resin. The winding angles are controlled through a combination of longitudinal mandrel speed, mandrel rotation (if used), or the rotation of planetary glass application stations. Once started, these methods produce tubes and pipe continuously, stopping only to replenish or change material components.

A second type of continuous process is the continuous advancing mandrel, which is composed of a continuous steel band supported by beams, which forms a cylindrically shaped mandrel. The beams rotate, friction pulls the band around, and roller bearings allow the band to move longitudinally so that the entire mandrel continuously moves in a spiral path toward the end of the machine. Raw materials (continuous fibers, chopped fibers, resin, and aggregate fillers) are fed to the mandrel from overhead. Release films and surfacing materials are applied from rolls adjacent to the mandrel. After curing, a synchronized saw unit cuts the pipe to proper length. This method is illustrate

Multiple Mandrel Method
In this method, a single materials application system applies wetted glass reinforcement simultaneously to two or more mandrels. When the winding operation finishes, the mandrels are indexed to a new position for curing while another set of mandrels is wound

Material Specific gravity Tensile strength MPa (ksi) Compressive strength MPa (ksi)

Material Specific Gravity Tensile strength MPa (ksi) Compressive strength MPa (ksi)
Polyester resin (unreinforced) 1.28 55 (7.98) 140 (20.3)
Polyester and Chopped Strand Mat Laminate 30% E-glass 1.41 100 (14.5) 150 (21.8)
Polyester and Woven Rovings Laminate 45% E-glass 1.59 250 (36.3) 150 (21.8)
Polyester and Satin Weave Cloth Laminate 55% E-glass 1.71 300 (43.5) 250 (36.3)
Polyester and Continuous Rovings Laminate 70% E-glass 1.89 800 (116) 350 (50.8)
E-Glass Epoxy composite 1.98 1,770 (257)  
S-Glass Epoxy composite 1.95 2,358 (342)  

Industry Related Fiberglass Specifications:

  • Fiberglass RTR Pipe Fittings for Non pressure Applications - ASTM D 3840
  • ASTM D 3839, Underground Installation of Fiberglass Pipe
  • Machine Made "Fiberglass" (Glass-Fiber-Reinforced Thermosetting Resin) Flanges ASTM D 4024
  • Contact Molded Fiberglass RTR Flanges ASTM D 5421
  • Low Pressure Fiberglass Line Pipe API 15LR
  • Filament-Wound Fiberglass RTR Pipe ASTM D 2996
  • Fiberglass RTR Pressure Pipe ASTM D 3517
  • Fiberglass RTR Sewer and Industrial Pressure Pipe ASTM D 3754
  • Threads for Fiberglass RTR Pipe (60 deg stub) ASTM D 1694
  • Fiberglass RTR Pipe Joints Using Flexible Elastomeric Seals ASTM D 4161

Note: The term fiberglass RTR takes the place of the ASTM designation fiberglass (glass-fiber-reinforced thermosetting resin).

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