Bursting Diaphragm Testing

Bursting disc inspection mainly conducts scientific testing and analysis on the static actuation pressure testing, burst pressure tolerance testing, cyclic pressure fatigue property testing, negative pressure resistance, sealing performance and leakage rate testing, and material physical and chemical property testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Static actuation pressure testing: This is the most core performance indicator testing of the bursting discs. Through the hydraulic or pneumatic pressure systems, the pressures are slowly and steadily increased and applied to the discs until the discs rupture. The testing aims to precisely determine the designed burst pressures (i.e. the rated burst pressures) of the discs, and verify whether their actual burst pressures are within the specified allowable deviation ranges (usually ±5% or ±10%).

Burst pressure tolerance testing: To ensure the performance consistency of the discs in the same batch, the burst pressure testing needs to be carried out on the sampled or all discs. Through the statistical analysis (such as the calculation of the average values and standard deviations), the dispersion degrees between the actual burst pressures and rated values are evaluated, confirming whether they meet the tolerance requirements in the product standards or purchase specifications. This is the key of ensuring the reliability of the system overpressure protection.

Cyclic pressure fatigue property testing: Simulating the pressure fluctuation conditions borne by the discs during the long-term service. The discs are placed under the cyclic pressures lower than their burst pressures (such as 80%-90% of the designed burst pressures), carrying out the thousands to tens of thousands of pressurization and depressurization cycles. The testing purpose is to evaluate the structural integrity of the discs under the alternating loads, ensuring that they do not fail in advance or leak due to the fatigue before reaching the burst pressures.

Negative pressure (vacuum) resistance testing: Evaluating the resistance capabilities of the bursting discs under the vacuum (negative pressure) working conditions that may be generated in the systems. The discs are installed in the vacuum chambers, the specified negative pressure values are applied and held for a certain time, observing whether the discs have the depression, deformation or reverse rupture. This testing is crucial for preventing the vacuum destruction caused by the misoperations or process fluctuations.

Sealing performance and leakage rate testing: After the disc installation and before the burst, their sealing integrity needs to be verified. Usually using the helium mass spectrometer leak detectors or pressure decay methods, under the testing pressures lower than the actuation pressures (such as 90% of the designed burst pressures), whether there are the micro leaks at the sealing surfaces between the discs and holders as well as in the discs themselves is detected, ensuring their absolute sealing under the normal working pressures.

Material physical and chemical property testing: The basic property verification is carried out on the raw materials used to make the discs (such as the stainless steel, Hastelloy alloys, graphite and composite materials). The testing items include the chemical composition analysis, metallographic structure observation, hardness testing, tensile strengths, yield strengths and elongations, ensuring that the materials themselves meet the design requirements of the corrosion resistance, mechanical strengths and plasticity.

Testing Scope

Forward-acting (tension-type) bursting discs: The domes of this type of discs protrude toward the pressure sources, and undergo the tensile deformation until the rupture under the pressures. The testing emphases are the ductility of their metal materials, precision of the burst pressures, as well as the arch heights and thickness uniformity after the forming. After the burst, they usually produce the petal-shaped fragments, and whether the fragments will cause the blockage or damage to the downstream pipelines needs to be tested.

Reverse-acting (compression-type) bursting discs: The domes of the discs face away from the pressure sources, maintaining the stability through the compressive stresses generated by the system pressures and peripheral clamping, and instantly flip and rupture under the action of the specific devices (such as the knife blades and scores). The testing needs to specially pay attention to their stability (anti-pressure-fluctuation capability), accuracy of the reversal pressures, as well as the sharpness and positioning precision of the blades or scores.

Flat-type (graphite, composite material) bursting discs: Made of the brittle materials, without the pre-formed arches. The testing core is their bending strengths and brittle fracture characteristics. Their thicknesses and internal defects (such as the porosity and cracks) need to be precisely controlled, because the small differences will significantly affect the burst pressures. At the same time, their corrosion resistance and fragment shapes need to be tested.

Scored and non-scored bursting discs: The scored discs guide the rupture paths through the preset weakened lines, realizing the more precise burst pressures and controllable opening areas. The testing needs to precisely measure the depths, widths and shape consistency of the scores. The non-scored type relies on the material uniformity, and the testing focuses more on the performance uniformity of the materials themselves and the stability of the forming processes.

Bursting discs under the different medium working conditions: The testing needs to consider the medium characteristics. For the corrosive media (acids and alkalis), the intergranular corrosion testing and stress corrosion cracking (SCC) testing need to be additionally carried out; for the high-temperature media, the high-temperature burst pressure testing needs to be carried out, evaluating the material strength changes with the temperatures; for the polymerization, crystallization or high-viscosity media, whether the disc surface characteristics are easy to adhere the materials needs to be evaluated.

Bursting disc assemblies with the accessories (such as the liners and protective shields): The testing objects extend to the whole safety relief devices. The sealing properties and strengths of the liners (anti-corrosion and anti-vacuum), the pressure-bearing capabilities and flow areas of the protective shields (anti-fragment), as well as the overall properties after the assembly of the various components and whether the interface dimensions meet the standards need to be verified.

Testing Methods

Hydraulic burst testing method: The most commonly used method with the high precision, especially suitable for the high burst pressure occasions. The water or oil is used as the pressurizing medium, and through the high-pressure pumps and precision pressure transducers/transmitters, the pressures are increased at the constant rates (usually not exceeding 0.1 MPa/s) until the disc burst, recording the peak pressures. This method has the small medium compressibility, stable pressure control and good data repeatability, and is the standard method of obtaining the reference burst pressures.

Pneumatic burst testing method: The nitrogen, air and other gases are used as the pressurizing media. Suitable for the disc testing with the low pressures or the cleanliness requirements for the media. Because the gases are compressible, the energy accumulation exists during the pressurization process, and the pressure release at the burst moment is more intense. During the testing, the special attention needs to be paid to the safety protection. This method is also commonly used for the leakage testing and fatigue testing.

Fatigue life testing method: The dedicated pressure cycling testing machines are used to apply the periodic pressure loads to the discs. By setting the pressure upper limits (usually 80%-95% of the burst pressures), pressure lower limits, cycling frequencies and total numbers of cycles, the long-term service conditions are simulated. After the testing, the visual inspection and non-destructive testing (such as the penetrant testing) need to be carried out on the non-burst discs, to find the micro cracks or deformations.

Non-destructive testing (NDT) methods: Evaluating the qualities of the discs under the premise of not destroying them. Including: the ultrasonic thickness measurement (checking the thickness uniformity); liquid penetrant testing (PT, checking the surface open defects); eddy current testing (suitable for the conductive materials, checking the near-surface defects); X-ray imaging (checking the internal structures, welding defects and score shapes). These methods are often used for the quality control during the production processes and the finished product sampling inspection.

Dimension and morphology testing methods: The precision measuring tools such as the micrometers and laser thickness gauges are used to measure the thicknesses at the various points of the discs; the three-dimensional coordinate measuring machines (CMM) or optical projectors are used to measure the key geometric parameters such as the outer diameters, arch heights and score dimensions; the surface roughness testers are used to detect the finish of the sealing surfaces, ensuring the installation sealing.

Environmental simulation testing method: The burst or property testing is carried out under the specific environmental conditions. Including: the testing in the high/low temperature environmental chambers, evaluating the effects of the temperatures on the burst pressures; the property testing after the immersion in the corrosive media, evaluating the corrosion resistance; the vibration table testing, evaluating the stability of the discs under the transportation or working vibration environments.

Testing Standards

Domestic Standards:

1. GB/T 567, Bursting disc safety devices

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

International Standards:

1. ISO 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices

2. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Burst pressure testing machine: The core testing equipment, divided into the hydraulic and pneumatic types. The main components include: the high-pressure pumps or air compressor sources, precision boosters, high-pressure-resistant testing chambers, high-precision pressure transducers (precision usually better than 0.25% FS), high-speed data acquisition systems (used to capture the pressure peaks at the burst moments) and safety protective shields. The modern testing machines integrate the automatic control and data recording software, realizing the automation of the testing processes.

Pressure cycling fatigue testing machine: The equipment specially used to simulate the pressure fluctuation working conditions. With the precise pressure closed-loop control capabilities, the long-time stable cycling can be carried out according to the preset waveforms (such as the sine waves and square waves) and parameters. The equipment is equipped with the cycle counters and automatic shutdown functions, and usually integrates the leakage monitoring modules, which can monitor the sealing states in real time during the testing process.

High-precision measuring instruments: Including the digital micrometers and laser micrometers (for the thickness measurement, with the resolutions reaching 0.001mm); optical projectors or image measuring instruments (for the non-contact measurement of the two-dimensional profile dimensions and score shapes); coordinate measuring machines (CMM, used to obtain the precise data of the complex three-dimensional morphologies of the discs).

Non-destructive testing (NDT) equipment: Ultrasonic thickness gauges (with the micro-diameter probes, used for the thickness measurement of the small sizes or curved surfaces); eddy current testing instruments (equipped with the dedicated probes, used for the surface/near-surface defect testing of the conductive materials); liquid penetrant testing kits (including the cleaners, penetrants and developers); for the high-end applications or composite materials, the industrial CT (computed tomography) may be used for the three-dimensional analysis of the internal structures.

Leakage testing equipment: The helium mass spectrometer leak detectors are the most sensitive equipment (reaching the order of 10-9 Pa·m³/s), detecting the extremely tiny leaks through the vacuum or sniffer modes. The pressure decay leak detectors calculate the leakage rates by monitoring the pressure changes in the sealed chambers, with the relatively simple and direct methods, suitable for the fast inspection at the production sites.

Material physical and chemical property testing equipment: The universal material testing machines (used for the tensile and compression testing, obtaining the mechanical properties such as the strengths and elongations of the materials); metallographic microscopes and sample preparation equipment (used to observe the material micro-structures); hardness testers (Rockwell and Vickers hardness testers, used to test the material hardnesses); spectroscopic analysers or chemical composition analysers (used to verify whether the raw material compositions meet the standards).