The U.S. Coast Guard recently conducted a marine casualty investigation into an uncontrolled release of isobutane from a 2-inch cargo tank pipe aboard a pressure barge certificated to carry flammable cargoes. The direct cause of the incident was traced to the failure of the studs of a ball valve installed on a cargo tank’s gauging pipe which sheared off and caused the ball valve to separate from the cargo pipe. The affected ball valve, manufactured by Ohio Valve Company, was supplied with four body studs for securing the manifold valve block to the valve body and stamped in a manner indicating compliance with American Society for Testing and Materials (ASTM) standard A193 Grade B8M (316 Stainless Steel). These body studs were purchased by Ohio Valve Company from Jian Huang Enterprise Co., Ltd.

Metallurgical testing revealed that the studs were composed of non-conforming steel not meeting ASTM A193 Grade B8M, making them more vulnerable to stress corrosion cracking and premature failure. The use of this non-conforming steel in a marine and chemical environment, combined with tensile stress levels exceeding the material’s rated strength, led to the failure of the studs.

A similar failure occurred in April 2025 which also resulted in an uncontrolled release of isobutane onboard a different pressure barge. In this incident, the same Class 300 2-inch ball valve model was involved, and metallurgical testing again confirmed the use of non-conforming studs as the cause of the incident.

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