In chemical plants, pharmaceutical workshops, and new energy material production lines stand rows of metal containers shaped like giant thermos flasks — reaction kettles. Inside them, chemical reactions proceed under high temperature and high pressure.

How to ensure these pressure vessels are completely airtight before put into service and prevent any leakage of toxic, flammable or high-value gases?

The solution lies in a critical procedure: air tightness test before factory delivery.

 1. Pressure Drop Method (Pressure Holding Method): The Most Classic and Intuitive Pressure Test It is the most fundamental and widely adopted method, working on the same principle as inflating a bicycle tire and leaving it standing for inspection. Operation steps: Seal the reaction kettle completely, fill it with clean and dry compressed air or nitrogen, and raise the pressure to the specified test pressure (generally 1.05–1.1 times the design pressure or working pressure). Then close all valves and keep the system in a static state for a certain period (such as 30 minutes or several hours). Judgment criteria: Adopt high-precision pressure gauges to monitor the pressure drop within the standing period. If the pressure drop is lower than the standard allowable limit (strict calculation formulas are specified in relevant standards), the equipment is deemed qualified. A noticeable pressure drop indicates existing leakage points. Advantages and limitations: This method is simple to operate and low in cost, which can effectively judge whether leakage exists. However, just like a clinical thermometer that only tells you a fever occurs, it cannot accurately locate specific leakage positions, and it is not sensitive enough to detect micro leakage.

 2. Bubble Method (Leak Detection Liquid Method): Giving Leak Points a "Bubble Bath" This intuitive method is adopted when the pressure drop method indicates potential abnormalities, or for detailed inspection of key components. Operation steps: Maintain a certain positive pressure inside the reaction kettle, then carefully brush or spray special leak detection liquid (usually low-surface-tension, high-foaming soapy water or professional reagents) on all potential leakage positions, including welds, flange connections, valve stems, mechanical seal seats and other key areas. Judgment criteria: Observe the coated surfaces. Once leakage occurs, escaping gas will pass through the liquid layer and form continuous and stable bubbles, which accurately mark the leakage points. The position where bubbles appear is exactly where the defect is located. Advantages and limitations: It features simple operation and enables direct positioning of leakage points, facilitating subsequent maintenance and repair. Nevertheless, it requires high responsibility of inspectors to ensure full coverage of testing areas. In addition, it may fail to produce visible bubbles for ultra-fine micro-leakage with an extremely low leakage rate.

3. Helium Mass Spectrometer Leak Detection: The Highestprecision "Molecular Detective" As the current gold standard for high-end and high-standard industries such as semiconductors, aerospace and high-end pharmaceutical production, this method boasts extreme precision, capable of detecting tiny leaks as small as billions of times the size of a pinhole. Operation process: It has two mainstream working modes. First, sniffer probe mode: Fill the reaction kettle with helium at a set concentration. Inspectors scan suspicious external areas with a handheld sniffer probe. Once trace helium is sucked in, the instrument triggers an immediate alarm and pinpoints the leak location. Second, vacuum hood mode: Evacuate the reaction kettle to a vacuum state, then spray helium over the outer surface with a helium spray gun. If any leakage exists, helium will penetrate into the kettle and be captured and identified by the detection instrument. Why helium is adopted: Helium is an inert gas with superior properties — safe, non-toxic, low molecular weight, and extremely low content in ambient air. It easily passes through micro-pores and is rarely interfered with by external factors, making it an ideal tracer gas. Advantages and limitations: It delivers ultra-high sensitivity, quantitative leakage rate measurement and accurate leak positioning. However, the supporting equipment is costly, and the operation is sophisticated. It demands strict environmental conditions and professional operators, so it is generally applied only in the most stringent working scenarios.

A standardized pre-delivery air tightness test is never a simple inflation check, but a standardized, strictly regulated procedure in full compliance with industry specifications:

1. Preliminary preparation Ensure all welding and assembly work of the reaction kettle is completed and inspected qualified. Clean the internal cavity, remove or isolate components unable to withstand test pressure (such as certain instruments), and install blanking plates.

2. Selection of test methods and media Determine the test pressure, pressure holding duration, acceptance criteria and the most suitable detection method in accordance with design drawings, technical agreements and national standards (e.g., TSG 21 Supervision Regulation on Safety Technology for Stationary Pressure Vessels). Prioritize safe media such as air or nitrogen. Direct testing with oxygen or flammable gases is strictly prohibited.

3. Gradual pressure boosting and real-time monitoring Increase pressure slowly in stages. Maintain pressure for a short period at each stage, and proceed with further pressurization only after confirming no abnormalities. Safety protection measures must be implemented throughout the whole process.

4. Test implementation and result judgment Carry out detection in strict accordance with the selected method and record all test data. Any unqualified leakage shall be marked and repaired. A full set of repeated tests is required after rework until full compliance is achieved. 5. Documentation and quality accountability All test procedures, data and results shall be compiled into official reports, signed and confirmed by responsible personnel, and permanently filed together with equipment archives to realize full quality traceability.

The air tightness test of reaction kettles before delivery is an invisible quality defense line built with precision instruments and rigorous procedures. Though conducted prior to product delivery, it serves as the most fundamental and critical link in the entire chemical production safety chain. This line of defense safeguards not only the integrity of equipment, but also corporate property, employee safety and environmental protection.