Experimental determination and analysis of effective method for determining appropriate torque used to intall MSAS-valves.
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On behalf of Petroleum Technology Company AS (PTC), an experimental study regarding one of their safety valves has been conducted. The respective safety valve is called a Modular Surface Annulus Safety (MSAS) valve. This valve functions as a primary barrier against dangerous blow-outs from the annulus in an oil and gas-producing well. It is a back check valve, where a piston moves inside a valve housing. In the past there has been some issues regarding what torque values these valves are to be installed with. Too high torque values could lead to insufficient clearance between the moving piston and the valve housing. Insufficient clearance would lead to malfunctioning of the valve, and potential dangerous blow-outs from the well, due to a primary barrier not functioning properly. The goal of this thesis has been to come up with a method for determining the appropriate installation torque that is to be used during installation of such valves. In order to determine the appropriate installation torque there are three things that have to be accounted for. The first is achieving sufficient pre-tensioning of the valve so that the valve does not loosen due to vibrations. The second is to ensure that there is sufficient clearance between the valve housing and piston after installation. The third is to determine whether lubrications are necessary or not. In order to account for these things two different tests have been designed, Torque test 1 and Torque test 2 (TT1 and TT2). The previous tests totaled 118 measurements. In addition to these tests there have been performed finite element analysis (FEA) via SolidWorks Simulations. These tests and simulations are briefly described in the following. TT1 was designed to measure the relationship between applied torque, corresponding axial force and the coefficient of friction between the valve and the VR-profile that it is inserted into. The relationship between the applied torque and corresponding axial force was measured via an electronic load cell. This was possible due to the design of the test setup. The coefficient of friction at different lubrication conditions was possible to calculate due to specially machined test parts, as well as engineering equations from threaded bolt theory. TT2 was designed to measure the radial displacement that takes place in the valve housing when exposed to the installation torque, due to the angled contact surface in front of the valve. The purpose of the test was to calculate the torque that would lead to insufficient clearance between the valve housing and piston at given frictional conditions, calculated from the results from TT1. This test was performed via strain gauges as well as manual measurements via a micrometer. Both of the previous tests were conducted in pit one, in PTC’s workshop. Two different valve housings were studied. A 2.0” valve, and a 2.5” valve, both with Xylan coating and 8 TPI Stub Acme threads.
Master's thesis in Mechanical engineering