Sand probes are used on flowlines where erosion due to flowing conditions may be experienced. Under these conditions the probe will erode with the passage of sand nd actuate the sensor.
When properly placed in the flowline, the number of sand probe sensor failures can be valuable in helping to determine the erosion wear on the flowline. Therefore, the number and date of occurrence of sand probe failures should be carefully documented. One rule of thumb is to schedule for a wall thickness test (e.g., x-rays) after four sand probe failures.
Sand probes should be inserted in a straight run of pipe at least ten (10) feet downstream of the well choke or any other change in piping direction. The pipe downstream of the probe should also be straight for another four feet. Probes should be selected for the line size of the flowline and should be purchased with 1/2 NPT connections. Figure 1700-5 shows a typical sand probe sensor.
When erosion causes failure of the probe, the flowline pressure enters the sand probe sensor and the internal piston shifts upwards. The supply or instrument port is blocked, and the holding circuit pressure is vented, thus triggering a wellhead shutdown.
The manual handle of the sand probe will give an instant indication that the sand probe has tripped. This manual handle may also be used to manually test the wellhead control system.