Process Safety Improvement of An Ethylene Cargo Ship Loading System

A system for shipping, loading and unloading flammable materials to and from any means of transport involves a high level of hazardousness. When we talk about loading ethylene to a seagoing tanker, the complexity of the situation is much higher.

Improvements made to an existent ethylene loading system to seagoing tankers with the aim of improving its Process Safety conditions are herein discussed.  These facilities, that were designed and erected in the 70’s by making use of the at the time available technology does not comply today with  many of the safe design and mechanical integrity requirements that today govern the design, construction and operation of these flammable loading/unloading terminals. It is worth mentioning that the flammable loading system in question is part of port facilities that are shared with other companies to load and unload seagoing tankers with a diversity of other products, such as LPG, Gasoline, etc., and this contributes to increase the potential of accident occurrence and scaling.

The authors detail the different steps carried out  and tools used by the team in charge of designing the required improvements for updating and revamping the existing facilities to attain a successful  project completion.  One of the first steps was the carrying out of a LOPA analysis of the existing facilities  in order to detect and close the existing gaps between the existing and the desired level of safety conditions. Such analysis enabled to reveal the possibility of occurrence of a loading arm failure with the consequent release of flammable materials and the ensuing fire and explosion with a very high impact potential on the facilities  and  the surrounding area.  The evaluation team assessed the need of studying and improving the existing facilities both from the mechanical and the Safety Instrumented System process control viewpoints.

This paper overviews the studies and improvements that were carried out to enhance the safety conditions of the system.     The 3 km pipeline that connects the pumping station with the loading station and the prevailing temperature and pressure operating conditions ( 30 bar at -104 ° C) dictated strict design conditions to comply with. This required to carry out stress and liquid hammer analyses of the facilities to determine the accurate EBV (Emergency Block Valve) opening and closing timing that the LOPA studies determined that were to be installed.

One of the key points of the improvement was the replacement of the existing loading arm with one provided with an automatic uncoupling and unhooking-up system with mechanical blocks to prevent the occurrence of mechanical breakage with the consequent release of flammable products in case of malfunction or emergency situations that would require that any ship being loaded should immediately be removed from the loading berth facilities.  The project team worked jointly with the loading arm technology supplier in order to determine the exact design characteristics associated with the loading activities and the environmental and tidal conditions to be taken into account to design properly adapted safety systems to  ensure their proper operation in case of extreme conditions.

Another recommendation from the mechanical viewpoint was to replace the existing load arm system with a new one provided with special safety systems, specially designed to operate safely under higher wind loads ( 37 km /hr.) and  fit for the prevailing weather conditions at the area.

In addition, improvements were also designed for the instrumented safety system that involved the inclusion of an approved  Logic Solver  for the SIL level that resulted from the LOPA analysis. 

The paper also includes interesting aspects of the construction characteristics of the project that were introduced to ensure the proper safety conditions of the area. Particular site conditions required that the design team resolved to remove the existing loading arm and install the new one from the sea side by means of a floating crane. As with any project the challenge was to carry out a safe design but also within the budgetary and the strict completion deadline limits that were set forth in order to reduce as much as possible the impact on port facilities operation. Project planning, joint project team work with port authorities, loading station operators, the other local companies that make use of these port facilities were the key factors that guaranteed project completion success.

A distinctive characteristic of this project is the diversity of Process Safety problems that should be simultaneously studied and solved by a multidisciplinary project team in order to enhance the reliability of the existing facilities.

Finally, the authors describe in this paper an actual case study about the integral application of risk analysis methodologies and safe process design, as part of a project  aimed at enhancing existing facilities.