Discussion on the Calibration Method of Online Pressure Instrument

Pressure instruments are widely used in the measurement of liquid, gas, steam pressure and vacuum in the metallurgical manufacturing industry. Among them, most pressure instruments are used in the production processes such as blast furnace ironmaking, molten steel smelting, slab continuous casting, steel rolling, and the operation activities of raw materials entering and leaving the factory. As special instruments for displaying, adjusting and controlling the process pressure parameters on site, they are both auxiliary technical means and cost accounting means and supervision means for safe operation. Their effectiveness directly affects the increase and decrease of the consumption of raw materials of the enterprise's products, the quality level, and the safety stability.

1. Problem statement

The various processes of super-large metallurgical manufacturing enterprises are continuous connection operations, which often results in many on-site pressure instruments reaching the calibration cycle, but because they cannot stop production, they cannot remove the pressure instruments that need to be inspected from the production line, resulting in the use of such pressure instruments beyond the cycle and losing their effectiveness. Such pressure instruments in use violate the relevant legal control provisions of the "Metrology Law" and the relevant requirements of international standards such as ISO10012 and ISO9001, resulting in the legal loss of control of measuring instruments, and their measurement and detection data also lose the legal authenticity and authority.

At present, most enterprises implement the method of sending on-site pressure instruments for offline inspection (i.e., sending them to professional laboratories inside or outside the enterprise for verification/calibration, generally in the range of 0~100MPa). Due to the inconvenience of disassembly and assembly, and the long time spent on offline verification/calibration, it has a certain impact on production control. In addition, the pressure instruments sent for inspection are verified/calibrated under laboratory standard conditions, which are quite different from the working conditions on site; the inspection/retrieval increases the cost and it is inevitable to bump and vibrate on the way; there is a considerable objective gap between the effectiveness, accuracy and economy of their intended use.

In order to maintain the effectiveness, accuracy and economy of the pressure instruments in use, the calibration of online pressure instruments has become a new issue faced by super-large metallurgical enterprises, and it has been discussed to varying degrees in various metallurgical enterprises.

2. Planning of online calibration of pressure instruments

1. Working principle of pressure instruments

The working principle of pressure instruments is that the elastic deformation of the spring tube under pressure or vacuum causes the displacement of the tube end, and the displacement is amplified by the mechanical transmission mechanism and then transmitted to the indicating device. The measured pressure value or vacuum value indicated by the pointer can be read on the dial engraved with the legal measurement unit.

2. Expected online calibration

⑴ Purpose: Implement online calibration to meet the measurement needs of production processes and reduce the cost of external inspection.
⑵ Calibration instrument range: pressure instruments in use on site of the enterprise.
⑶ Calibration range: 0~100MPa
⑷ Calibration comparison accuracy: 1.5%~1.6%
⑸ Expected goal: To achieve controlled and effective online pressure instruments.
⑹ Types of calibration schemes: a. Ideal calibration comparison; b. Practical calibration comparison.

3. Material preparation

⑴ Special pipe puncher
⑵ Several corresponding controlled and effective standard tables that meet the accuracy and range of on-site pressure instruments.
⑶ Calibration comparison records.

III. Exploration of online calibration comparison schemes

1. Scheme 1: Practical calibration comparison of pressure instruments

⑴ On the same pipeline: Within an appropriate range from the on-site pressure instrument to be calibrated, use a special pipe puncher to lead out the pressure pipeline, and place a stop valve in the middle of the pressure pipeline (the stop valve is in the closed state). Install a pressure transmitter and a controlled and effective standard pressure gauge of the same specification as the instrument to be calibrated at the interface behind the stop valve.
⑵ Slowly open the stop valve to full open, wait for the fluid medium in the pipeline to fully enter the standard meter for a few minutes, and then read the indication values ​​of the two meters respectively.
⑶ Fill in the calibration comparison record.

2. Scheme 2, ideal calibration comparison of pressure instruments Make

a mobile simple "pressure calibration bench".

⑴ On the fluid medium pipeline, close the "stop valve 1" of the field pressure instrument in use (i.e. to be calibrated) (the stop valve is in the closed state).
⑵ Appropriately extend the pressure pipeline after the stop valve.
⑶ Install a tee on the extended pressure pipeline.
⑷ Install the pressure instrument with zero indication in use at the interface of the straight pipe port of the tee.
⑸ Newly install "stop valve 2" at the interface of the T-shaped pipe port of the tee (the stop valve is also in the closed state).
⑹ Connect the pressure "special calibration pipe" after "stop valve 2" to the "special calibration pipe interface" preset on the simple mobile "pressure calibration bench".
⑺ The "pressure calibration bench" is also preset with controlled and effective standard pressure gauges of corresponding models and specifications.
⑻ After checking that there are no omissions, slowly open stop valve 1 and stop valve 2 one by one until they are fully open; after a few minutes, read the indications of the two meters respectively.
⑼ Fill in the calibration comparison record. (end)