Introduction
Pressure gauges are metrological instruments used for safety protection, industrial process control, monitoring, and surveillance of pressure. Accurate indication by pressure gauges is critical to the operation of equipment and facilities, so periodic calibration is necessary.
The previous article covered the development of calibration requirements for pressure gauges, hierarchical management, and specific calibration requirements. This installment discusses five related topics: the scope of calibration, personnel qualification requirements, and precautions during use, clarifying practical issues around pressure gauge calibration.
Mandatory Calibration Scope for Pressure Gauges
Notes:
- Measurement of pressure with alarm devices generally refers to electric-contact pressure gauges or remote-transmission pressure gauges. Remote-transmission signals may be current-type, resistance-type, or voltage-type.
- Measurement of pressures for hazardous, toxic, or highly corrosive media typically covers toxic gases such as carbon monoxide, hydrogen sulfide, ammonia, chlorine, vinyl chloride, benzene, hydrogen fluoride, phosgene, and corrosive media such as sulfuric acid, hydrochloric acid, and strong alkalis in chemical plants.
Personnel Qualification Requirements for Pressure Gauge Calibration
Calibration of pressure gauges must be performed by legally authorized metrology verification institutions. Such institutions must operate within their authorized scope, and personnel performing calibration tasks must pass competency assessments.
Before June 8, 2016, personnel performing pressure gauge calibration were required to hold a Metrology Inspector Certificate or a Registered Metrologist Certificate.
Since June 8, 2016, qualification licensing for metrology inspectors was cancelled and merged with the Registered Metrologist system as part of administrative approval reforms. The General Administration of Quality Supervision coordinated revision of the Registered Metrologist system and implemented a transition period. During the transition, personnel conducting pressure gauge calibration no longer needed the Metrology Inspector Certificate.
The qualification requirements for pressure gauge calibration are based on the following national laws, regulations, and departmental rules:
1. Metrology Law of the People’s Republic of China (2018 amendment)
Article 20: Metrology administrative departments at or above county level may, as needed, set up metrology verification institutions or authorize other units to perform mandatory verification and other verification and testing tasks. Personnel executing such verification and testing tasks must pass competence assessments.
2. Implementation Rules for the Metrology Law (2018 amendment)
Article 25: Metrology verification institutions established by metrology administrative departments at or above county level are national legal metrology verification institutions. Their duties include establishing measurement standards, performing value transfer, executing mandatory verification and other legally required verification and testing tasks, drafting technical specifications, providing technical support for metrology supervision, and handling metrology supervision work.
Article 26: Personnel of national legal metrology verification institutions must pass competence assessments.
3. Measures for the Supervision and Administration of Legal Metrology Verification Institutions (State Quality and Technical Supervision Bureau Order No. 15, 2001)
Verification institutions must be assessed and issued a metrology authorization certificate by the national or provincial quality and technical supervision departments and operate within the certificate's authorized scope. Institutions without a valid metrology authorization certificate may not perform corresponding verification work.
4. Measures for the Administration of Metrology Verification Personnel (State Quality Supervision, Inspection and Quarantine Administration Order No. 105, 2007)
Article 4: Personnel engaged in metrology verification activities must meet relevant conditions and be approved by the quality and technical supervision department to obtain metrology inspector qualifications.
Articles 7, 8, and 10 describe application, review timelines, certificate issuance, and a five-year validity period for the metrology inspector certificate. Article 13 states that those holding a Registered Metrologist Certificate issued by provincial or higher quality supervision departments may engage in metrology verification activities.
5. State Council Decision on Cancelling a Batch of Occupational Qualification Licenses and Recognition Matters (State Council 2016 No. 35)
This decision lists occupational qualification licenses and recognition items to be cancelled, including items related to professional technical personnel qualifications.
6. Notice on Follow-up Work after Cancellation of Metrology Inspector Qualification Licensing (2016 No. 1183)
The notice emphasizes careful implementation of the reform merging metrology inspector qualifications into the Registered Metrologist system, strengthened archiving and transitional management of existing metrology inspector records and registered metrologist qualifications, and ensuring continuity of oversight during the transition.
06 Calibration Requirements for Pressure Gauges Used on Special Equipment
Standards relating to special equipment do not impose unique requirements on the pressure gauges used, other than requiring compliance with relevant national metrology regulations and standards. Therefore, hierarchical management, calibration cycles, and mandatory verification ranges for pressure gauges used on special equipment should follow the general provisions on pressure gauge classification, calibration, and mandatory verification described above.
1. Fixed Pressure Vessels
Technical Supervision Regulation for Fixed Pressure Vessels, TSG 21-2016:
9.2.1.2 Pressure gauge verification: Verification and maintenance of pressure gauges shall comply with relevant national metrology regulations. Pressure gauges must be verified before installation, a red line indicating the working pressure shall be marked on the dial, and the next verification date shall be noted. Pressure gauges shall be sealed with lead after verification.
2. Mobile Pressure Vessels
Technical Supervision Regulation for Mobile Pressure Vessels, TSG R0005-2011:
9.1 Safety accessory periodic inspection: Periodic inspection of safety accessories shall follow the Rules for Periodic Inspection of Pressure Vessels and relevant safety technical specifications.
3. Pressure Gauges on Industrial Pipelines
Pressure Pipeline Safety Technical Supervision Regulation—Industrial Pipelines, TSG D0001-2009:
Article 151: Accuracy class, range, and installation position of pipeline pressure gauges, thermometers, and other instruments shall meet relevant safety technical specifications and standards.
Rules for Periodic Inspection of Pressure Pipelines, TSG D7005-2018:
2.4.2.10 Safety accessories and instrument inspection: (4) Check whether pressure gauges are within their verification validity period (applies where verification is required).
4. Boiler Pressure Gauges
Boiler Safety Technical Code, TSG 11-2020:
5.2.3 Pressure gauge calibration: Pressure gauges shall be calibrated periodically. A red line indicating working pressure shall be marked on the dial and the next inspection date noted. Pressure gauges shall be sealed with lead after calibration.
07 Precautions When Using Pressure Gauges
Selection of pressure gauges should be based on the operating environment, measured medium, required accuracy, and range, and must comply with applicable national and industry standards and specifications.
01 Pressure Gauge Type Selection
- For harsh environments with strong atmospheric corrosion, heavy dust, or frequent liquid spray, choose appropriate housing materials and protection ratings based on environmental conditions.
- For general media measurement:
- For pressure between -40 kPa and +40 kPa, diaphragm box gauges are recommended.
- For pressures above +40 kPa, Bourdon tube gauges or bellows gauges are generally used.
- For pressures between -100 kPa and 2400 kPa, vacuum pressure gauges should be used.
- For pressures between -100 kPa and 0 kPa, Bourdon tube vacuum gauges are appropriate.
- For mildly corrosive media such as diluted nitric acid or acetic acid, use stainless steel pressure gauges or stainless steel diaphragm gauges.
- For strongly corrosive media, media with solid particles, or viscous liquids such as dilute hydrochloric acid, hydrochloric gas, and heavy oil, use diaphragm or isolating diaphragm gauges; materials must be selected according to the measured medium.
- For crystalline, scab-forming, or high-viscosity media, use flange-type isolating diaphragm gauges.
- In mechanically vibrating environments, use vibration-resistant pressure gauges.
- In flammable or explosive environments where electrical contact signals are required, use explosion-proof electric-contact pressure gauges that meet the installation area's explosion protection requirements.
- For gauges measuring high or medium pressures or highly corrosive media, choose gauges with overpressure relief features in the housing.
- Gauges for special media such as oxygen, hydrogen, and acetylene must be special-purpose gauges and should have the medium name and color warning marks on the dial. Oxygen gauges must be marked with a red "NO OIL" label or a standardized no-oil symbol; oil is strictly prohibited.
Color coding for dedicated gauges:
- Oxygen: sky blue
- Hydrogen: dark green
- Acetylene: white
- Fuel gases: red
- Chlorine: brown
- Ammonia: yellow
Special material requirements:
- Gauges and gaskets for acetylene must not use copper alloys with copper content over 70%, or components made of silver, mercury, zinc, cadmium, or their alloys, because acetylene can form explosive compounds such as copper acetylide or silver acetylide.
- Dry copper acetylide can detonate from slight friction.
- Pure chlorine is not corrosive, but chlorine containing water will react to form HCl and chloride ions; therefore, general pressure gauges cannot be used for chlorine containing water. Chlorine-specific gauges are typically either diaphragm gauges with PTFE-lined wetted cavities (e.g., 316L+PTFE diaphragm body, Ta+PTFE diaphragm), or direct-type gauges with Hastelloy C wetted parts, though the latter is costly.
- Ammonia gauges must be special types and must not have components made of copper or copper alloys; gauge connectors, Bourdon tubes, bellows, and measuring parts must not be made of copper.
- Sulfur-resistant gauges are made from specialty stainless steels with sulfur resistance, suitable for H2S-containing media.
02 Accuracy Class Selection
1. General-purpose gauges, diaphragm box gauges, and diaphragm gauges should use accuracy classes of 1.6 or 2.5.
2. Precision gauges should use accuracy classes of 0.4, 0.25, or 0.16.
03 Case Size Selection
Common dial diameters are 60 mm, 100 mm, and 150 mm; precision gauges typically have dials of 150 mm or larger.
- Gauges installed on pipelines and equipment should preferably use a 100 mm dial.
- For locations with low illumination, high mounting positions, or where readings are difficult to observe, a 150 mm or 200 mm dial is recommended.
- For pneumatic instrument lines and auxiliary equipment, a 60 mm dial is appropriate.
04 Range Selection
- For stable pressures, the normal operating pressure should be within one-third to two-thirds of the instrument upper range value.
- For pulsating pressures (such as pump, compressor, or fan outlets), normal operating pressure should be within one-third to one-half of the instrument upper range value.
- For medium to high pressures (>4 MPa), normal operating pressure should not exceed one-half of the instrument upper range value.
05 Management Requirements for Pressure Gauges on Special Equipment
- Mark a red line on the dial indicating the working pressure and note the next verification date.
- Seal gauges with lead after calibration/verification.
- Install a three-way cock or needle valve between the gauge and the pressure vessel; the valve must have an open/closed mark and locking device, and no other fittings or piping for other uses may be connected.
08 Enforcement for Illegal Use of Pressure Gauges
As measuring instruments, using mandatory or non-mandatory pressure gauges without timely calibration, or continuing to use gauges that fail verification, constitutes illegal behavior. Relevant legal provisions include:
1. Penalty Rules for Metrology Violations (2015 amendment)
Article 12: Penalties for using measuring instruments in violation of metrology laws and regulations:
(2) For mandatory verification instruments, failure to apply for verification or continued use beyond the verification period will result in an order to stop use and a fine of up to RMB 500; continued use after failing verification may result in an order to stop use and a fine of up to RMB 1,000.
(3) For non-mandatory instruments that are not periodically self-verified or verified by an authorized institution, an order to stop use and a fine of up to RMB 200 may be imposed; continued use after failing verification may result in an order to stop use and a fine of up to RMB 500.
2. Metrology Law of the People’s Republic of China (2018 amendment)
Article 25: For measuring instruments within the mandatory verification scope, failure to apply for verification as required or continued use after failing verification will result in an order to stop use and possible fines.
3. Implementation Rules for the Metrology Law (2018 amendment)
Article 43: For measuring instruments within the mandatory verification scope that have not applied for verification as required, measuring instruments outside the mandatory scope that have not been periodically self-verified or sent for verification, or instruments continued in use after failing verification, an order to stop use and a fine of up to RMB 1,000 may be imposed.
Pressure gauges must be calibrated and verified periodically in accordance with applicable laws and regulations, and organizations should establish clear management procedures to avoid ambiguity. Proper calibration practice and management improve the rigor and consistency of metrology verification and control.
