Several factors causing deformation of orifice flowmeter

Orifice flowmeters often deform during use, which can cause the instrument to not measure accurately. Deformed orifices are often large-caliber orifice flowmeters, and the temperature of the measured medium is high, such as superheated steam, and the orifice thickness is relatively thin. The throttling device for taking pressure in the annular chamber.

Since the temperature is low when we manufacture the orifice plate and the annular chamber, which is generally room temperature, and the temperature is high during actual use, their geometric dimensions have changed significantly. Since the material of the annular chamber is generally carbon steel, the linear expansion coefficient is generally 11×10-6℃-1, and the material of the orifice plate is 304 stainless steel, the linear expansion coefficient is generally 16×10-6℃-1, so the difference in expansion coefficient is 5×10-6℃-1. When the throttling device is put into use, it comes into contact with the high-temperature fluid, and the orifice plate and the annular chamber expand accordingly. The increment of the outer diameter expansion of the orifice plate is larger than the increment of the inner diameter expansion of the corresponding part of the annular chamber. Therefore, when we manufacture the orifice plate, we must leave enough expansion gap between the orifice plate and the annular chamber through calculation.

So who is the culprit for the deformation of the orifice flowmeter? Today, after on-site inspections and field research and analysis, the staff of Jet Instruments found clues related to it. One thing is certain, that is, the deformation of the orifice plate is due to the disappearance of the gap between the outer diameter of the orifice plate and the annular chamber after thermal expansion. When the orifice plate continues to expand, it cannot expand in the direction of the outer diameter, so under the action of the differential pressure on both sides of the orifice plate, the outlet side is deformed.

The first point is related to the weather. The throttling device originally had no leakage. Due to the extremely cold weather and the strong northwest wind, the positive and negative annular chambers leaked.

The second point is related to the poor insulation of the throttling device. The throttling device with good insulation did not leak.

The third point is related to the leakage at the junction of the positive and negative annular chambers. It was impossible to eliminate the leakage by tightening the bolts, so the throttling device was removed and the sealing gasket was replaced, and then the orifice plate was found to be deformed.

When designing and calculating the throttling device, the gap between the outer diameter of the orifice plate and the annular chamber is large enough, assuming that the temperature of the orifice plate and the annular chamber is the same, but in fact it is impossible. The orifice plate is surrounded by the annular chamber and is provided with heat by the high-temperature fluid, so the temperature is high and it is fully expanded. The inner circle of the annular chamber is in contact with the fluid, but the outer circle is in contact with the atmosphere. In addition, factors such as "poor insulation", "extremely cold weather", and "strong northwest wind" cause its temperature to drop very low, resulting in insufficient reserved gaps and causing deformation of the orifice plate.

In addition, the deformation of the orifice plate is closely related to the leakage at the positive and negative annular chambers. If the leakage is not caused by damage to the sealing gasket, it is because the deformation of the orifice plate causes the gap between the positive and negative annular chambers to increase, and a gap between the sealing gasket and the annular chamber causes leakage.