Test Method for Evaluation of the Resistance of Fiberglass Rods to Combined Mechanical and Chemical Stress

A flexural stress test for determining failure time of fiberglass rods in acid or other stress cracking ing agents has been developed. It differs from the CIGRE test in having two support points instead of one. This results in a 6" length of uniform stress in the rod between support points, and freedom from contact stress and concentration effects. Stress levels can be set readily and precisely over a wide range. Failure times of most rods stressed to ca. 25 ksi (ca. 20% of ultimate strength) averaged 3-5 days in lN nitric acid, including two coated rods. Another coated rod did not fail in over 30 days and is clearly superior to all the other rods from five manufacturers. Most rods failed by cracking transversely across the rod cross-section, as observed in service. The failure times at 56.7 ksi for air, water and acid on uncoated rods were as follows: over 30 days, 1 day and less than 10 minutes, respectively. While much less severe than acid, water is a stress cracking agent. The test is a simple, inexpensive means of evaluating rods for resistance to fracture under the combined effect of stress and acid.