Marine Breakaway Coupling – when you hear the name, what comes to your mind? Well, a Marine Breakaway Coupling refers to a device fitted with a flexible hose pipe, and it parts whenever an axial load or internal pressure surges above a certain fixed value. The couplings have differing designs based on the roles they play in either liquefied gas transfer or oil transfer systems. Marine Breakaway Couplings are often found in onshore (marine) oil terminals making use of flexible hoses, in offshore rig operations and also in offshore marine terminals where there is the utilization of catenary suspended hoses and floating hoses for bulk oil transfers.
The Mechanism of a Marine Breakaway Coupling
Breakaway couplings for use in marine offshore oil terminals are often passive devices since they have a general composition of a unit joined in two halves including a shut-off valve that doesn’t require a control source or external powering to activate them. The valves are locked mechanically in the open position and fail-safe enabling them to close once they are activated. The halves part whenever a load or a surge is applied to it thus initiating the valves to close. With the separation of the unit, liquid flow of the substance on transfer stops and then containment is done on either part of the separated hose, this is in the case of double closure fittings. Breakaway couplings are of two types; Single closure fittings close the upstream end of the separation on the hose while double closure fittings close both the downstream and upstream ends of the hose. You may be wondering what holds the unit together during separation. Break bolts, designed to withstand pressure surges, up to the stipulated calculations, and axial loads, instantly break whenever the loads exceed the limit. Therefore, break bolts hold the units together in function. The material utilized for the manufacture of break bolts is one with a high tensile load breaking predictability and thus are critical for the unit reliability. The break bolts are designed to break only on tensile loads, not shear. Utilization of breakaway couplings is in small bore applications where the couplings use a flap valve. Mounting of the valves within the bore of the unit makes them cause a drop in the pressure of the system because of the restriction in the bore. MBCs that comprise flap valves find use in offshore crude transfer systems.
The purpose of a Marine Breakaway Coupling
Marine Breakaway Couplings are primarily fitted to mitigate the outcomes of a Mooring hawser failure, potential rupture of the loading hoses as a result of a tanker drifting which causes over-stress to the hose, tanker breakout which leads to excessive axial loading on the hose. Another purpose of an MBC is to mitigate surge pressure whose cause is possibly due to loading valves shutting against loading pressure in full flow which has a potential damage to the hose.
When to use a Marine Breakaway Coupling
MBCs are often fitted to protect the weaker components in the system, for instance, the small diameter tail hoses in a floating string. MBCs have a function in surface floating, subsea and catenary hoses. An MBC requirement should be due to a risk assessment of the loading system with the terminal location, product flow rates, product pressures, environmental conditions, limits for operation and configuration in consideration.