Ex-factory withstand pressure and leakage testing is a mandatory quality gate that verifies the structural integrity, sealing performance, and electrical safety of products before they leave the manufacturing plant. This technical guide explains the standard test items, methods, acceptance criteria, and applicable standards (GB/T, ISO, IEC, EN, ASTM, JIS) used by manufacturers and accredited third-party laboratories for routine ex-factory inspection.
Technical Overview
Ex-factory withstand pressure and leakage testing (also called routine or end-of-line pressure and leak inspection) refers to the 100% inspection performed on every production unit before shipment. Unlike type testing, which is carried out on representative samples during product certification, ex-factory testing is a routine production control step designed to catch manufacturing defects such as casting porosity, weld cracks, thin walls, defective seals, misassembled closures, or faulty insulation before the product reaches the customer.
The test has two complementary parts. The withstand pressure (proof strength) portion confirms that the pressure boundary — shell, body, casing, or tank — can hold a pressure above the rated value without rupture, visible deformation, or weeping. The leakage (tightness) portion confirms that seals, seats, gaskets, threads, and joints do not allow the working medium to escape beyond the permissible leak rate. For electrical and electronic products, the same concept applies in the form of a dielectric withstand (electric strength) test combined with a leakage current measurement, typically executed as a routine test under Annex A of GB 4706.1 / IEC 60335-1.
- Verify structural strength at a proof pressure above the maximum allowable working pressure.
- Confirm seat, seal, and joint tightness within a defined leak-rate class.
- Detect workmanship defects that cannot be found by visual or dimensional inspection alone.
- Provide traceable test records supporting conformity assessment, export documentation, and batch release.
Typical governing references include GB/T 13927 and ISO 5208 for industrial valve pressure testing, GB/T 150 for pressure vessels, GB/T 6111 and ISO 1167 for internal pressure resistance of thermoplastic piping, EN series standards for sanitary and building products, ASTM and JIS standards for component-level verification, and GB 4706.1 / IEC 60335-1 for electrical safety routine tests.
Testing Samples
Valves and Pipeline Components
Gate, globe, ball, butterfly, check, safety, and control valves are the most common subjects of ex-factory pressure and leakage testing. Each valve undergoes a shell strength test on the body and a seat tightness test in both flow directions where applicable, in accordance with GB/T 13927 or ISO 5208. Fittings, strainers, expansion joints, and manifolds follow equivalent component standards.
Pipes, Fittings and Plumbing Products
Thermoplastic and metal pipes, elbows, teas, reducers, PPR and PE fittings, faucets, mixing valves, and sanitary tapware are tested for internal pressure resistance and sealing integrity. Sanitary products are typically evaluated against GB 18145 or EN 817, which specify hydrostatic and tightness requirements for inlets, outlets, and diverter seals.
Pressure Vessels, Tanks and Gas Cylinders
Welded pressure vessels, air receiver tanks, accumulators, fire extinguishers, and gas cylinders are subjected to hydrostatic proof pressure tests during manufacture, following the safety technical regulations and GB/T 150 or the relevant cylinder standards. Leak testing of valves and joints on cylinders is performed pneumatically at specified pressures.
Pumps, Compressors and Heat Exchangers
Pump and compressor casings are hydrostatically tested at approximately 1.5 times the maximum allowable working pressure, and mechanical seals or gland packing are checked for excessive leakage during the ex-factory run test. Heat exchanger shells and tube-to-tubesheet joints receive hydrostatic and, where required, tracer-gas leak tests.
Electrical and Electronic Products
For household appliances, motors, power tools, luminaires, and power supplies, the ex-factory inspection consists of a dielectric withstand (electric strength) test, a leakage current measurement, and a protective grounding continuity check, performed as a routine test on the production line per GB 4706.1, GB/T 5171, IEC 60335-1, or the applicable IEC/EN/UL product safety standard.
Testing Items
Depending on the product category, an ex-factory withstand pressure and leakage inspection typically includes the following items:
- Hydrostatic shell or body strength test at a proof pressure, commonly 1.3 to 1.5 times the rated or maximum allowable working pressure.
- Seat and seal tightness test at approximately 1.1 times the nominal pressure, with the leak rate assigned to a defined class from Rate A (no visible leakage) through progressively coarser classes for less critical services.
- Low-pressure pneumatic (air or nitrogen) tightness test, often at 0.6 MPa for gas service components.
- Leak rate quantification by pressure decay, bubble counting, or tracer gas methods for products with quantitative leakage limits.
- Dielectric withstand voltage test between live parts and accessible conductive parts, typically applied for 1 second at a routine-test voltage defined by the product safety standard.
- Leakage current measurement at rated voltage and frequency, with limits depending on insulation class and product type.
- Supporting checks such as insulation resistance, grounding continuity, visual surface examination, and verification of nameplate pressure ratings.
Testing Methods
Hydrostatic Strength Test
The component is filled with clean water (with corrosion inhibitor where required), fully degassed, and pressurized to the specified proof pressure using a calibrated hand pump or power pump. The pressure is held for a standard-defined duration, commonly 15 to 300 seconds for valves depending on nominal size, and longer for vessels. The item passes if there is no visible leakage, no weeping through the pressure boundary, and no permanent deformation. Water is preferred for high pressures because it stores far less hazardous energy than compressed gas.
Pneumatic Tightness Test
For gas-service components and as a complementary check, air or nitrogen is applied at lower test pressures, typically a factor of 1.1 times the rated pressure with an upper safety cap. Sealing surfaces, joints, and connections are examined with a soap solution, or the outlet side is monitored for bubble formation or pressure rise. Strict barricading and energy-control precautions apply because compressed gas stores significant energy.
Immersion Bubble and Pressure-Decay Testing
In the immersion method, the pressurized part is submerged in a water tank and any continuous stream of bubbles reveals a leak path; this simple visual method reliably detects leaks on the order of 10⁻⁵ Pa·m³/s. In automated pressure-decay testing, the part is pressurized, isolated, and the pressure drop over a fixed time is compared against a calibrated tolerance, with temperature compensation applied. Differential-pressure (dual-channel) instruments improve sensitivity for high-volume production lines.
Helium Mass Spectrometry Leak Detection
Products with demanding sealing requirements, such as refrigeration circuits, vacuum devices, and hazardous-media components, are tested with a helium tracer gas using either vacuum-chamber or sniffing probes. This method detects leak rates down to the 10⁻⁹ Pa·m³/s range and is used when the acceptance limit is expressed quantitatively rather than as "no visible leakage".
Dielectric Withstand and Leakage Current Tests
For electrical products, a routine electric strength test applies a high voltage — commonly in the range of 1.0 to 1.5 kV for 1 second for basic insulation of Class I appliances, or higher for reinforced insulation — between energized parts and accessible metal parts. The instrument monitors for breakdown and trip current. Leakage current is then measured with the appliance at rated voltage, using the standardized human-body impedance network, and compared against the class-dependent limit, commonly 0.25 to 3.5 mA. These tests implement the routine test requirements of GB 4706.1 / IEC 60335-1 Annex A and equivalent UL and EN standards.
Records, Instrumentation and Traceability
All test equipment — pressure gauges, transducers, high-voltage testers, and current meters — must be calibrated and traceable to national metrology standards. Each tested unit should have a recorded test pressure, medium, hold duration, result, operator identity, and date, enabling complete ex-factory traceability for audits, export inspection, and any future failure investigation. Where independent confirmation is required, accredited third-party laboratories can perform witnessed testing, verification sampling, or conformity reporting.
Applications
Ex-factory withstand pressure and leakage testing is applied across virtually every industry that manufactures pressure-bearing or electrically powered products:
- Oil and gas, petrochemical, and power generation — valves, fittings, vessels, and piping assemblies prior to installation.
- Building services, HVAC, water supply, and firefighting — sprinkler components, pumps, water meters, taps, and manifold systems.
- Automotive and transportation — fuel and brake components, radiators, air-conditioning loops, and tanks.
- Household appliances and consumer electrics — production-line electric strength and leakage current testing for cookers, water heaters, motors, and power tools.
- Medical and specialty gas systems — regulators, cylinders, and fittings requiring quantitative leak-rate verification.
- Export trade — routine ex-factory results, together with reports from accredited third-party laboratories, support customs documentation, buyer acceptance, and certification audits.
FAQ
What is the difference between a type test and an ex-factory test?
A type test is a comprehensive evaluation of a product design, performed once or periodically on representative samples at an accredited laboratory. An ex-factory test is a simplified routine inspection applied to every unit on the production line before shipment, focusing on the critical safety characteristics of strength and tightness.
What test pressures are typically used?
For valve shells and most pressure boundaries, the hydrostatic proof pressure is commonly 1.5 times the maximum allowable working pressure, while seat and seal tightness tests are performed at approximately 1.1 times the rated pressure. The exact factor is always defined by the applicable GB/T, ISO, EN, ASTM, or JIS product standard.
Why is water used for strength tests and air for tightness tests?
Water is nearly incompressible, so a failure during a high-pressure strength test releases very little stored energy, making it inherently safer. Compressed air or nitrogen is convenient and sensitive for detecting small leaks at low pressure, which is why it is generally limited to tightness verification with strict safety controls.
How are leakage results judged?
Metallic valves are graded against the leak-rate classes of GB/T 13927 / ISO 5208, ranging from no visible leakage for critical services to coarser, quantitatively defined rates for low-hazard media. Other products are judged by a pass/fail pressure-decay tolerance, a bubble-free hold period, or a maximum leak rate in Pa·m³/s specified by the design standard.
Are electrical withstand and leakage current tests part of ex-factory inspection?
Yes. For electrical products, the terms refer to the dielectric withstand voltage test and the leakage current measurement, which are mandatory routine tests under GB 4706.1 and IEC 60335-1. They are performed on 100% of units to verify insulation integrity and user protection before shipment.
Can testing be outsourced or independently verified?
Manufacturers normally perform ex-factory tests with their own calibrated equipment. Buyers, regulators, or certification bodies may additionally commission witnessed testing, sampling verification, or full report issuance through accredited third-party laboratories to confirm the reliability of in-house results.