A discussion of the test procedures of the API 6AV1 standard based on wear prediction simulations

The API Spec 6AV1 standard specifies the design requirements for valves operating in fields with sand production in order to reduce the risk of failure. In one of the validation tests, a valve is cyclically opened and closed under controlled conditions whilst a sand slurry is flowing in the loop. The carrier fluid is water with polymer viscosifiers to increase the viscosity up to about 55 cP. After completion of around 500 opening-closing cycles, high static pressure is applied upstream the valve to check for possible leakage. Objective of this study was to assess whether the occurrence of leakage might be affected by testing parameters that, being not specified by the standard, are decided by the experimenter; among them, particular attention was paid to the pressure and flow conditions during the valve operation. To this aim, numerical simulations were carried out combining different modelling approaches, and analyzing the failure of the valve from the point of view of the damage produced by impact wear. The difficulties inherent in the task of estimating erosion via numerical simulations are further enhanced in this work, since a number of complex case-specific issues had to be faced. First, the movement of the valve stem. Second, the co-existence of laminar and turbulent flow conditions due to the high viscosity of the carrier fluid. Third, the simulation of the valve as part of the entire loop. Fourth, the identification of a suitable indicator of valve leakage. Apart from the interest from a modelling point of view, the obtained results can help to improve the specification test procedures and acceptance criteria in the future.