Patent AU-2015101342-A4 (AU)
Title: Tensa load limiting bails
Inventor: MARKWELL DERICK GEORGE
IPC: E21B19/06
Filed: 2015-09-18
Granted: 2015-10-29
Abstract: TENSA LOAD LIMITING BAILS During well completion, well intervention, well testing or workover operations from a floating rig, safe operation can be compromised by failure of the rig's heave compensation system. This can cause catastrophic damage to the rig, equipment and personnel especially when the rig is connected to the seabed with hydrocarbons in the system. The TENSA Load Limiting Bails (LLB) work as an independent safety mechanism in cases when the rig's heave compensator fails. The LLB is normally fully retracted and will not affect the normal functionality of the rig's compensator. It will automatically extend when its preload tension is exceeded. The LLB are normally configured in a pair but they can be used individually in other applications. During normal operation, the LLB is maintained fully retracted by pressurized nitrogen. The LLB starts extending only when the load is higher than the load due to the precharge pressure (activation load). By increasing or decreasing the precharge pressure the initial activation load at which the bail arm extends is adjustable. The maximum LLB load is normally limited to 1.25 times the Safe working loads (SWL). However, this maximum load can be changed by adjusting the relief setting of the pressure relief valves. There is an extension range (normally about 25% of total LLB stroke length) where the LLB will extend without relieving any nitrogen precharge. It will then retract and remain at the initial load setting after the overload scenario is passed. This is known as the Full Recovery Range (FRR). It can be stroked further up to the full stroke of the LLB and the load will remain approximately constant at the maximum set load based on the pressure relief setting. When extension beyond the FRR is utilized, a small amount of the internal nitrogen precharge is relieved and the preload will be slightly less when the LLB is fully retracted. The Load Limiting Bails (LLB) in accordance with this invention comprises of gas/ hydraulic cylinder with built-in or external accumulators, adjustable/ fixed gas pressure relief valves for limiting the maximum pressure/ load, one or more damping check valves in the cylinder to provide damping on recoil and detachable end connections at each end for the bail. These end connections are typically in the form of API standard Elevator Links but the LLB has the option to be configured with alternative end connections such as hooks or padeyes to suit different applications. The TENSA LLB has the following features: * Automatically returns to retracted position once the overload condition has passed. * No replacement parts are required once activation has occurred. (eg shear pins) * No connecting hoses. Each bail arm is a standalone system. * Robust and easy to handle. The unit can be laid directly on the deck in any orientation. * Activation load can easily be adjusted by changing the initial pre-charge pressure * Direct replacement of the existing rig conventional elevator links. * Does not affect the normal operation of the existing rig compensator. * Bail arm ends are replaceable and alternative end attachments can be provided (eg lifting padeyes) B\ SECTION A-A