Hazard Operability Evaluation Study for High Capacity Mixers Used in Solid Propellant Processing

Solid propellant motors are used as stage/booster motors in all the Indian Space Research Organization (ISRO) launch vehicles. The quantities of solid propellant used ranges from 100 to 400 t for Small Satellite Launch Vehicle (SSLV), Polar Satellite Launch Vehicle (PSLV), Geosynchronous Satellite Launch Vehicle (GSLV) Mk-II and Launch Vehicle Mark (LVM)-3launch vehicles. Solid propellant and its raw materials are highly sensitive to shock, impact, friction and electrostatic discharge which can lead to fire and explosion. The propellant mixing is one of the critical steps of propellant processing operations in manufacturing of solid propellant rocket motor. Propellant mixing involves independent feeding of raw materials and mixing them in a vertical planetary mixer to obtain homogenous slurry for segment casting. In order to cater the increased production, high capacity mixer was indigenously designed and developed. The systems were automated in high capacity mixer to have reliable and uninterrupted process control with minimum/zero manual intervention. This automation enhances the safety of the working personnel involved in the process operation of high capacity mixer. However, due to multifold increase in quantity of solid propellant mixing, the hazard potential/risk involved also has increased multifold. While developing a new system, we should look beyond the happy flow scenarios to identify “hazards” and find out their causes, consequences and prevention strategies. Two disciplines i.e. reliability engineering and safety engineering were involved for carrying out this task. In order to mitigate the high risk involved in design and commissioning phase, Hazard Operability Study (HAZOP) has been carried out to evaluate the hazards associated and efficacy of the inbuilt safety mechanisms in the high capacity mixer. This study was carried out in various steps like dividing the system and circuits into nodes; defining the design intent for each node; identifying the meaningful deviations from design intent based on process parameters and guidewords; recognizing possible causes of deviations; examining the potential consequences; checking the adequacy of available safeguards and recommending the additional actions to enhance safety and operability (Hazard and operability studies—Application guide, in CEI IEC 61882, International Electro Technical Commission, 2001 [1]). The study was performed with reference to a set of piping and instrumentation diagrams (PIDs) of vertical mixer systems and all the nodes of relevant PIDs were analyzed thoroughly. The HAZOP study recommendations were implemented for mitigating the hazards, its consequences and to improve the safe operability of propellant mixing. This includes improvements in standard operating procedures, interlocks, alarms and in a few cases, addition of flow components. This paper details how Hazard Operability Study (HAZOP) was very vital for evaluation and mitigation of hazards of high capacity vertical mixer used in solid propellant processing.