Durability and Reliability of Electro-Mechanical Relays for Oil and Gas

Electro-mechanical relays (EMRs) are widely used in variety of manufacturing industries including oil and gas. One of their applications in the oil and gas industry is in the design of downhole logging wireline and measurement-while-drilling/logging-while-drilling (MWD/LWD) instruments such as magnetic resonance instruments, formation testing instruments, cement bond tools, etc. EMRs are mainly electrically operated switches that multiplex high-powered circuits using a low-power signal. Typically, EMRs consist of one or two wire coils wrapped around magnetic cores, a movable armature, and a set of contact(s) that reside inside a sealed vacuum compartment. The structural durability and reliability of EMRs has been the subject of research for many years, and these characteristics are considered a prime reliability concerns in the oil and gas industry. Their poor reliability has been documented by their several inherent failure modes, e.g., limited life expectancy due to shock, vibration, temperature and moisture, thermal stresses caused by soldering, contact wear, contact bouncing, and contact arcing/welding. This paper presents results from a reliability study and an engineering assessment to determine the applicability and functionality of EMRs in electromagnetic-acoustic sensors. The discussion includes steps to improve and minimize the risk.