ASTM D3681-12 Standard Test Method for Chemical Resistance of Fiberglass (Glass Fiber-Reinforced Thermoset Resin) Tubing in Bent Condition

The standard "ASTM D3681-12 Standard Test Method for Chemical Resistance of Fiberglass (Glass Fiber-Reinforced Thermosetting Resin) Tubing in the Bent Condition" developed by the American Society for Testing and Materials (ASTM) describes a test method for determining the chemical resistance properties of fiberglass tubing in the bent condition for diameters of 102 mm and larger. The basis herein is both fiberglass tubing reinforced with glass fiber-reinforced thermosetting resin tubing (RTRP) and glass fiber-reinforced polymer mortar tubing (RPMP). For the purposes of this standard, polymer does not include natural polymers.

Unless otherwise noted, definitions are in accordance with “ASTM D883-22 Standard Terminology for Plastics” and abbreviations are in accordance with “ASTM D1600-18 Standard Terminology for Abbreviated Terms for Plastics”. In addition, for the purposes of this standard, the following terms and definitions apply:

The terminal point is the passage of liquid through the pipe wall unless otherwise specified. The failure mode can be catastrophic, characterized by an abrupt fracture of the pipe wall in the area of greatest stress parallel to the axis of the pipe, with the fiber reinforcement breaking cleanly at the edge of the fracture. Visual evidence of surface wear or pitting may or may not be present.
Fiberglass tubing is a tubular product containing glass fiber reinforcements embedded in or surrounded by a cured thermosetting resin. The composite structure may include aggregate, granular or platelet fillers, thixotropic agents, pigments or dyes. Thermoplastic or thermoset primers or coatings may be included.
Reinforced polymer mortar pipe (RPMP) is fiberglass pipe containing aggregate.
Reinforced thermosetting resin pipe (RTRP) is fiberglass pipe that contains no aggregates.
Stress corrosion is damage that occurs when the pipe wall is exposed to a corrosive environment for a period of time while under tension.

This test method consists of exposing the inside of at least 18 pipe specimens to an abrasive test solution while the pipe is held in a deflected condition at different induced initial ring bending stress levels continuously and measuring the time to failure for each stress level. Test temperatures are obtained by testing in a temperature controlled air environment.

The long-term resistance of the pipe to the test solution is obtained by extrapolating the log-log linear regression line for the initial strain level and time to 50 years. Log-log linear regression analysis of the test data is considered a conservative approach and represents standard industry practice.

This test method evaluates the effect of a chemical medium on a pipe while it is in a deflected condition. It has been found that the effects of chemical media can be accelerated by the stress caused by deflection. This information is useful and necessary for the design and application of buried fiberglass pipes. Pipes of the same diameter but different wall thicknesses develop different stresses with the same deflection. Also, pipes with the same wall thickness but different structures forming the wall can develop different stresses with the same deflection.

During testing, a suitable parallel plate apparatus is used to maintain a constant deflection in the pipe. To obtain uniform strain along the pipe, 6 mm thick elastomeric pads are used between the parallel plate (channel) surfaces and the pipe annulus. Elastomeric pads with Shore A15 to 70 hardness have been used successfully.

When determining the initial strain by Procedure B is required, foil-type, single-element strain gauges suitable for strain levels up to 1,50 percent strain and a length appropriate to the diameter of the pipe are required. An example of the apparatus required is shown in the figure provided in the standard. Strain gauges in lengths of 6 and 13 mm have been found to be effective for pipe diameters of 305 to 610 mm. For recommendations on gauge lengths for other pipe diameters, the strain gauge manufacturer should be consulted.

Test specimens shall be ring sections taken from a randomly selected sample of pipe from a normal production run. The minimum length of test specimens shall be one nominal pipe diameter or 300 mm plus/minus 5 percent, whichever is less.

The standard test temperature should be 23 degrees plus/minus 2 degrees.

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