DEVELOPMENT OF METHODS FOR ASSESSING THE CHEMICAL COMPATIBILITY OF THREAD SEALANTS USED WITH PLASTIC FITTINGS

摘要

Thread sealants have been used to help ensure a leak-tight joint and reduce friction during installation between threaded metal pipe and fittings for over 100 years. Thermoplastic fittings using the same taper thread cannot be assembled as if they were metal due to chemical compatibility and maximum material stress. However these same sealants are often used on a plastic fitting joint. This may be done either because the installer has been trained to use the same sealants on all threaded joints, or because the plastic parts are not fitted properly and are leaking under pressure. Unfortunately, sealants that work well and are compatible with metal pipe threads may contain stress-cracking agents that will cause failure in plastic fitting joints. Because it is unlikely that the industry practice of using thread sealants will change in the foreseeable future, a method is needed to evaluate these products to determine compatibility with existing fittings materials and designs. The current work develops three categories of testing using tensile, flexural, and threaded part configurations. Several variations in each of these methods are attempted, with multiple types of sealants and materials. There is a definite trade-off in test duration and complexity of the test method. The results of this testing program are provided, with analysis of the failure types and recommendations for the development of an ASTM test method.