The purpose of the shear joint is to enable the Blowout Preventer (BOP) shear rams to sever the upper completion string as a means of contingency emergency disconnection of the rig from the well. If there were problems in disconnecting the emergency disconnect latch on the Subsea Test Tree (SSTT) and the situation dictated an immediate departure from the well was necessary, the shear rams above the SSTT would be used to sever the shear joint, parting the upper completion string in the BOP stack. The Lower Marine Riser Package (LMRP) could then be disconnected from the BOP stack.
The shear joint is interfaced with the SSTT at the lower end, and the retainer valve at the upper end. It is positioned within the BOP stack to enable it to be severed by the shear rams, as described above.
Externally, the shear joint will have a profile suitable for installation within the internal profile of the BOP stack. Hydraulic fluid should be conducted to the lower SSTT functions and Tubing Hanger Running Tool (THRT) / Through Casing Resistivity Tools (TCRT) functions via synthetic hoses spanning the shear joint upper and lower flanges.
Internally, the shear joint should have a bore suitable to enable the passage of wireline/coiled tubing tools and equipment. All internal bore transitions are to be tapered so as not to interfere with or snag the wireline tools and tree equipment.
The structural integrity of the shear joint will be suitable to be sheared by the BOP shear rams in emergency situations. The material from which the shear joint is made should be suitable for the duty required, and the fluids with which it may come into contact. The wall thickness of the shear joint should be suitable to withstand the combinations of internal and external loading possible under all conditions expected during handling and installation activities, including both normal and contingency operations.
An analysis of the specific BOPs shear capability should be performed in conjunction with the design of the shear joint. A shear test, using a sample of identical geometry, material, and material hardness, complete with attendant synthetic hoses on the outside diameter of the sample, should be performed to verify the design suitability.