The instruments on the oil and gas recovery device are the eyes for operational judgment: readings of temperature, pressure difference, liquid level, and concentration all depend on them. If the instruments are inaccurate, the operators will see false data, and their judgments will deviate accordingly - things that should be defrosted are not defrosted, things that should be inspected are not inspected, and problems are exposed only when they affect the equipment. Instrument calibration addresses this issue: it ensures that the readings of each instrument are reliable and can be traced. Calibration is not a burden; it is a small investment to ensure accurate judgments, and with proper arrangement, it does not take up much man-hour.
Which instruments need to be calibrated
The tables involved in judgment and statistics that are subject to verification include: temperature tables for each section, pressure difference tables at the inlet and outlet of the heat exchanger, liquid level gauges for the condensate tank, recovery quantity meters, as well as pressure and concentration switches related to safety interlocks. Tables that are only displayed on the panel and do not participate in judgment can have their frequency reduced, but they cannot be ignored. It is recommended to create an instrument ledger first: record the location, range, accuracy level, installation date, and last verification date for each instrument. Only after the ledger is established can a verification plan be arranged, and any missed verifications can be directly identified from the ledger.
How to determine the verification cycle
Calibration periods are not one-size-fits-all: safety interlock devices should be strictly calibrated according to relevant requirements; pressure difference and temperature devices should be calibrated based on the operational characteristics of the device - pressure difference gauges involved in defrosting criteria affect operational decisions, and it is recommended to calibrate them every six months; auxiliary display gauges not involved in decision-making can also be calibrated annually. Gauges for measuring and recovering liquid volume involve reconciliation, and it is advisable to calibrate them concurrently with the measurement of solvent input volume, ensuring consistency between the two to align the recovery rate accounts. For newly installed instruments, calibration should be appropriately intensified in the first year of operation, and the regular calibration period should be determined after understanding the drift rate.
How to perform verification
On-site verification does not require all items to be sent for inspection: temperature can be compared using a portable thermometer, and pressure difference can be compared using a handheld calibrator. If the deviation is within the allowable range, it should be recorded and the device can continue to be used. If the deviation exceeds the allowable range, the device should be replaced or calibrated. Meters involving safety interlocks should be sent to qualified institutions for verification. After the interlock setting value is verified, a linkage test should be conducted to confirm the effectiveness of the action. The verification record should include: meter number, verification method, deviation value, conclusion, and next verification date. Each meter should have one page, and the records should be bound into a volume by device.
How to manage records
| Instrument category | Suggested periodicity | verification method |
|---|---|---|
| thermometer | Half a year to one year | Comparison of portable thermometers |
| differential pressure gauge | half a year | Handheld calibrator comparison |
| level gauge | a year | Actual liquid level comparison |
| Recycling meter | Same cycle as feeding and metering | Compare or submit for inspection |
| Safety interlock table | According to relevant requirements | Inspection and linkage test |
| Auxiliary display table | a year | On-site comparison |
The value of verification records lies in the trend: if the deviation direction remains consistent and increases for two consecutive times for the same gauge, it indicates that the gauge is drifting. Even if it does not exceed the tolerance, it is recommended to replace it in advance. If a gauge frequently exceeds the tolerance, check the installation location - instruments in locations with high vibration and high temperature have a short lifespan. It is more cost-effective to change the location than to repeatedly replace the gauge. Records are archived annually and stored for the same lifespan as the equipment archives. They are handed over along with the archives during the transfer.
Steps of organizational verification
- Establish an instrument ledger, registering the location, measurement range, and last calibration date for each instrument;
- Determine the calibration cycle based on instrument categories and participation levels, and formulate an annual plan;
- Conduct on-site comparison and verification, adjust or replace instruments that exceed tolerances;
- After submitting safety interlocking devices for inspection, conduct linkage tests for confirmation;
- Verify and archive each record on a separate page, marking the date of the next verification;
- Adjust the cycle or installation location of individual instruments based on the recorded trends.
Frequently Asked Questions
Should we still calibrate the instrument even if it appears to be functioning normally?
Yes. Many drifts are slow, and the displayed values appear normal precisely because there is no reference. Regular comparison with a standard instrument is the only way to confirm the credibility of the readings. The earlier the drift is detected, the smaller the cost of misjudgment.
Can the device still operate during the verification period?
Most meters can be calibrated with their positions verified without stopping the device; if they need to be removed for inspection, they should be scheduled during maintenance windows, or replaced with spare meters, to avoid blind spots in operational judgment.
How long should the verification records be kept for?
The lifespan of the equipment archives is the same as that of the equipment itself. Safety interlock records should be kept in accordance with relevant requirements, while operation judgment records should be retained until the instrument is no longer in use, so that trend analysis can have continuous data to refer to.
This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd. The company provides design and manufacturing, skid-mounted customization, installation and commissioning, as well as after-sales operation and maintenance services for three-time oil and gas recovery equipment to gas stations and oil depots. If you need on-site inspection or scheme configuration, please feel free to contact us for discussion.