*2.1.10 Influence of service length (SL)*

From the perspective of mechanical equipment maintenance management, object service age (or operating time) and frequency of use are also indicators that affect its risk level. The SL index is related to the service life of the mechanical equipment, the operating environment and working conditions, the frequency of use (continuous operation, interval operation, and temporary use), the past failures, and the maintenance of the mechanical equipment. Therefore, through discussions with field operations and maintenance personnel, it was determined that the SL index of mechanical equipment in petroleum and petrochemical enterprises is divided into four levels, and its scoring standards are shown in **Table 11**.
