Originally posted 2017-06-21 15:16:08.
Calibration is a process of setting a device to indicate a signal according to a specified value already created in it. In any engineering activity calibration play a lot of role in ensuring that error is minimized while carrying out any engineering job. Imagine when a pressure gauge is indicating 50psi in a gas flow line when the actual pressure in the pipeline is 150psi, such situation will lead to unexpected blowout and be bursting of the facilities on the site even without any emergency indication, for that reason calibration of our reading, indicating, regulating and measuring instruments becomes very vital in the field of engineering.
These days many firms has been spending lots of their money in ensuring that all their equipment are properly calibrated from time to time to avoid unexpected casualty and damage to their plants.
It can be noted no equipment is expected to be at its full efficiency as of when installed after operating for months and years, the theory of material lifespan has it that every material in a particular function will experience fatigue along its lifespan, and this is among the reason our reading instruments such as dial gauges will develop minor errors in reading after being used for years. The same goes to valves which has some of its parts getting stiffed and hence not flexible enough to respond to pressure changes after being in use for years. Therefore, companies find it necessary to have all of these equipment calibrated from time to time.
Calibration of valves had been a longtime practice in the engineering servicing companies, it is a special job category in the oil and gas industries which is usually contracted to companies specialized for that purpose. We shall be discussing how the calibration of valves is carried out by most of these companies.
The process of calibrating a valve can be tedious when the deviation in the valve is very high, this factor can be caused due to longtime the valve spent after the previous calibration before bringing it for the recent calibration, in other words when valves calibration schedules are spaced so long such as a year or more than a month, it could lead to high deviation in the valve functions thereby making the calibration more serious or hard when compared to valves with short time interval of calibration like six months and less.
The imagine above reveals the set up for valve calibration, below are details of the set up arrangement;
A fabricated stand having attachments for fixing of hydraulic jack hose and the fixing of valve at the top, the structure is so arranged that it can be stable even at high pressure impact. Below the structure there is an attachment of a pressure gauge, and pressure release valve attached opposite the position of the two hose.
The working principle of the set up lies on the pressure input and response from the set up. The upper part of the hose delivers pressure from the hydraulic jack into the structure the pressure input is done continuously until the pressure gauge reading has reached a particular point where the valve springs makes a pop sound, the sound shows that at the pressure reading at that moment is what can trigger the valve to indicate or perform its function. Therefore, the moment such occurs the pressure reading will be taken and that reading will be used to compare to the already established standard of the valve operating pressure, when difference exists then the valve needs calibration if not no calibration is needed.
When there is need for calibration in the setup, the pressure will first be removed from the whole set up through the small pressure relieve valve by the side of the hose connectors by turning the valve and making the fluid in the system to return back to the hydraulic jack. After that, the valve will be loosed and serviced by cleaning and washing of its parts and fixing it back, when subjected to another test, the long screw which controls the spring tension will be used to adjust the valve to respond to any required pressure as indicated by the pressure gauge below the setup, this process is usually carried with full concentration and calculation.