1. What is a salt spray test?

Its basic principle is: a salt solution containing (5%±0.1%) sodium chloride and with a neutral pH is sprayed into a mist using a spray device, allowing it to settle evenly on the sample surface. Changes in the sample are observed under specific temperature (e.g., 35℃), humidity, and time conditions to evaluate its corrosion resistance.

2. Why must gas meters undergo salt spray testing?

As a metering instrument used for extended periods (usually exceeding 10 years) outdoors or in complex environments, the corrosion resistance of gas meters is crucial:

(1) Safety Requirements: Corrosion can lead to perforation of the gas meter casing, failure of threaded connections, jamming of internal mechanical structures, or short circuits in electrical components, causing gas leaks and serious safety accidents.

(2) Metering Accuracy: Corrosion of internal precision mechanical components (such as diaphragms, connecting rods, and valves) or circuit boards directly affects the accuracy of the gas meter, leading to trade disputes or energy waste.

(3) Long-Term Reliability: Gas meters are typically unmaintained after installation and need to maintain stable operation throughout their entire lifespan. Salt spray testing simulates the long-term corrosion of harsh environments (such as coastal areas or areas where de-icing agents are applied in winter) and is an important means of verifying their lifespan.

(4) Regulatory and Standard Compliance: Authoritative domestic and international standards for gas meters (such as Chinese National Standard GB/T and EU Standard EN) clearly stipulate that salt spray testing is a mandatory item in type testing.

3. Standards for Salt Spray Testing of Gas Meters Salt spray testing of gas meters is not conducted arbitrarily but strictly follows relevant national standards. In China, the main standard is: GB/T 6968-2019 "Diaphragm Gas Meters," which is the core national standard for gas meters in China.

It clearly stipulates the requirements, methods, and acceptance criteria for the "salt spray test" of gas meters.

Other common reference standards (potentially applicable to parts or export products):

GB/T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test" (equivalent to international standard ISO 9227), ASTM B117 (American Society for Testing and Materials standard), etc.

4. Brief Introduction to the Test Procedure

Taking GB/T 6968-2019 as an example, the typical salt spray test procedure for gas meters is as follows:

(1) Pretreatment: Clean the gas meter sample thoroughly to remove surface oil and dust.

If the sample has cuts, protect them with an appropriate covering layer to assess the corrosion resistance of the cuts.

(2) Initial Inspection: Inspect the appearance of the sample to ensure there are no initial defects and record its condition.

(3) Sample Placement: Place the gas meter in its normal operating condition (or at the specific angle specified in the standard) inside the salt spray chamber. A certain distance should be maintained between samples to ensure that the salt spray can freely settle on all exposed surfaces.

(4) Test Conditions:

Solution: (5±0.1)% sodium chloride solution, pH value between 6.5 and 7.2.

Instrument Temperature: (35±2)℃.

Collection Rate: 1.0~2.0 ml of salt solution per hour over an area of ​​80 cm².

Test Time: Typically 48 or 96 hours. The specific time depends on the standard requirements and product grade. For critical equipment such as gas meters, a 96-hour (4-day) test is more common and has stricter requirements.

(5) Post-treatment:

After the test, remove the sample from the salt spray chamber and allow it to air dry indoors for 0.5~1 hour.

Then gently rinse with clean running water at a temperature not exceeding 40℃ to remove any residual salt deposits on the surface.

Dry immediately with a hairdryer.

(6) Recovery: Place the sample under standard atmospheric conditions (e.g., temperature 23±2℃, humidity 50%±5%) for 1~2 hours to allow it to stabilize.

5. Result Evaluation and Acceptance Criteria

After testing, a comprehensive inspection and evaluation of the gas meter is required:

(1) Visual Inspection:

Main Surfaces (e.g., front of the casing): No traces of substrate corrosion should be present. Slight, inconspicuous discoloration is permissible.

Secondary Surfaces (e.g., sides, back, bottom): Slight rust is permissible, but there should be no bubbles, peeling, or severe rust spots.

(2) Functional Markings (e.g., nameplates, text, symbols): Must be clearly legible and not blurred by corrosion.

(3) Functional and Performance Testing:

• Air Tightness Test: The gas meter must pass an air tightness test to ensure no leakage. This is the most critical safety requirement and a disqualifying factor.

• Metering Performance Test: After testing, the gas meter's indication error should still be within the maximum permissible error range specified in national standards (usually ±1.5% or ±3%).

• Electrical Safety (if applicable): For smart gas meters, their electrical strength and insulation resistance must still meet the standards.

In summary, a qualified gas meter, after passing the salt spray test, must not only appear to have no major problems, but more importantly, it must ensure structural integrity, reliable sealing, and accurate metering.

Conclusion: The salt spray test is a crucial quality checkpoint in the production and certification process of gas meters. By accelerating the simulation of environmental corrosion over years or even decades, it exposes potential defects in materials and protective processes in a short period, thus ensuring that the gas meters ultimately delivered to users are safe, reliable, and durable. For gas meter manufacturers, passing the rigorous salt spray test is a direct reflection of their product competitiveness.