Magnetic particle flaw detector

1. Overview

The CDX series portable magnetic particle flaw detectors are developed on the basis of the magnetic flux leakage (MFL) testing principle for ferromagnetic materials and can be put into service directly in the field. During inspection, a magnetizing field is applied to the ferromagnetic workpiece. When discontinuities such as cracks, inclusions, porosity, or laminations occur on or near the surface of the workpiece, a leakage field is formed at the affected area, where magnetic particles accumulate and produce magnetically visible indications. The inspector can then determine the location, length, and morphology of the defect. The three models each have a distinct positioning: the HS-CDX-200 is a combined AC/DC unit capable of detecting both surface and near-surface defects; the HS-CDX-300 is a lightweight AC unit mainly used for batch screening of welds in the field; and the HS-CDX-500 is an AC unit with adjustable magnetizing current and built-in demagnetization, suitable for precision components whose residual magnetism must be controlled after inspection. The complete unit can be fitted with four interchangeable probes — A, D, E, and O: the A horseshoe probe is designed for fillet welds; the D electromagnetic yoke with adjustable pole spacing is suitable for flat and curved workpieces; the E crossed rotating-field probe is designed for welds and can reveal both transverse and longitudinal cracks in a single scan; and the O ring coil provides circumferential magnetization for small rotational parts such as shafts and bolts. The products are therefore widely used in special equipment, steel structure engineering, machinery manufacturing, rail transit, and petrochemical and power industries, serving in-service inspection and outbound quality control duties.

2. Main Technical Specifications

3. Applicable Industries and Application Scenarios

3.1 Pressure Vessels and Pressure Piping (boilers, petrochemical storage tanks, pressure piping)

3.1.1 In-service Periodic Inspection of Butt Welds on Large Crude Oil Storage Tank Walls (recommended model: HS-CDX-200)

Scenario background:

Large vertical crude oil storage tanks have long service lives. Corrosion by the medium, pressure cycling, and temperature fluctuation combine to readily initiate fatigue cracks and corrosion cracking in the butt welds and T-joints of the tank wall. In accordance with the relevant special equipment codes, a storage tank must undergo a comprehensive periodic inspection every 6–12 years, of which magnetic particle inspection of surface and near-surface weld defects is a mandatory item. Being large in volume, storage tanks cannot be transported to a workshop, so inspection must be carried out inside the tank with portable equipment. In addition to surface-opening cracks, defects formed during welding, such as incomplete penetration and inclusions, often lurk in the shallow (near-surface) layers of the tank wall welds, which are difficult to detect reliably with AC magnetization alone. This scenario therefore employs the combined AC/DC HS-CDX-200 magnetic particle flaw detector.

Equipment application process:

Before the operation begins, safety preparations are completed first: the tank is ventilated and gas-tested and confirmed to pass, and working scaffolding is then erected. The weld inspection area is subsequently pretreated by grinding to remove paint, rust, and mill scale from the weld surface until a metallic luster is exposed, and surface oil is cleaned. Black aqueous magnetic particle suspension and an A1-type test piece are prepared, and a sensitivity check is performed with the test piece on one side of the weld to be inspected, confirming that both the magnetization system and the suspension system of the equipment are in normal condition. The E-type crossed yoke probe is used as the main probe to scan the weld surface in AC magnetization mode, identifying transverse and longitudinal surface cracks; at locations suspected of subsurface defects, the mode is switched to DC magnetization, leveraging the stronger penetration of the DC field to inspect near-surface inclusions, lack of fusion, and similar defects in the weld. During magnetization, the suspension is sprayed synchronously while the magnetic indications are observed, and defect locations are marked and photographed immediately for records. Because the HS-CDX-200 has no built-in demagnetization, the area must be demagnetized with an external demagnetizer after each weld inspection to prevent residual magnetism from attracting dust to the workpiece. Throughout the process, the ambient temperature, magnetization parameters, and defect locations and lengths are recorded to form the nondestructive testing (NDT) report. The entire tank wall weld is inspected in a staged manner, with the corner regions of the T-joints and the bottom large fillet welds prioritized for scanning with the A horseshoe probe. Once any nonconforming defect is confirmed, it is immediately marked for subsequent grinding, re-inspection, and repair. After all inspections, the inspection records and imaging data are compiled and submitted to the special equipment inspection authority for archiving as the basis for tank safety assessment. In a single inspection of this scenario, a single wall weld can extend for hundreds of meters, and the dual AC/DC modes of the HS-CDX-200 meet the standard's requirements for near-surface defect detection, aligning with the special equipment inspection codes.

3.1.2 Periodic Inspection of Butt Welds on Chemical High-pressure Piping (recommended model: HS-CDX-200)

Scenario background:

High-pressure piping in chemical plants transports media that are high-temperature, high-pressure, and corrosive. Subject to long-term pressure cycling and medium erosion, the weld zones readily initiate fatigue cracks, and once propagated, such cracks may lead to serious safety incidents such as medium leakage or even explosion. In accordance with the relevant codes for periodic inspection of pressure piping, magnetic particle inspection must be performed on pipe welds. Pipes are mostly arranged between pipe-rack supports in confined spaces where stationary inspection machines cannot be positioned, so portable equipment must be used. Moreover, in addition to surface cracks, the heat-affected zones of pipe weld joints often harbor shallow near-surface defects. Since AC magnetic particle inspection can only reveal cracks open to the surface, subsurface defects may be missed; the HS-CDX-200 is therefore selected.

Equipment application process:

Before inspection, the target pipe weld area is isolated, process pressure is released, the temperature is lowered, and operational safety is confirmed. Within a 50mm range on each side of the weld to be inspected, rust and paint are removed by grinding and surface oil is cleaned. The HS-CDX-200 is verified with an A1 test piece to ensure the magnetization system sensitivity meets requirements. Butt welds on straight pipe sections are scanned by the E crossed yoke probe in AC magnetization mode to quickly identify transverse and longitudinal surface cracks; at stress-concentrated pipe sections such as elbows and tees, the mode is switched to DC magnetization to inspect near-surface defects in the heat-affected zone with the deeper field penetration. During magnetization, the probe moves at a uniform speed while black aqueous magnetic particle suspension is sprayed synchronously, and the indications are observed to distinguish false indications from true defects. When a suspicious indication is found, it is verified by repeated magnetization, and the defect coordinates, length, and morphology are recorded. After inspection, an external demagnetizer is used to eliminate residual magnetism in the pipe welds, preventing the pipe from attracting iron filings that could affect subsequent operation. All nonconforming defect locations are marked and the construction unit is notified for repair; after the repair is completed, the HS-CDX-200 is used to re-inspect and confirm that the defects have indeed been eliminated. The inspection images and original records are compiled, archived, and submitted to the special equipment inspection authority for review as the inspection credential for continued service of the pipe section. Because the pipe-rack site offers limited working space, the portable body and quick probe changeover of the HS-CDX-200 cover straight pipes, elbows, tees, and other weld configurations, satisfying all requirements of in-service chemical piping inspection.

3.2 Steel Structure Engineering (plant steel structures, bridges, space frames)

3.2.1 On-site Weld Inspection of Long-span Steel Bridges (recommended model: HS-CDX-300)

Scenario background:

Highway and railway steel box girder bridges are subject to long-term alternating vehicle loads and wind and rain erosion, and the butt welds between box girder plates and the fillet welds of stiffening plates are prone to fatigue cracking. Both the final acceptance inspection and the periodic safety assessment of bridges require magnetic particle inspection of the welds. Bridge members are large fixed structures that cannot be dismantled and transported back to a workshop; inspection can only be performed at height in the field, imposing extremely high demands on equipment weight and portability. The inspection targets in this scenario are primarily surface-opening fatigue cracks, with no mandatory requirement for near-surface defect detection. The HS-CDX-300 lightweight AC magnetic particle flaw detector, weighing only 6kg, is well suited to the working conditions of overhead suspended platforms and is widely used in steel bridge inspection.

Equipment application process:

Before formal operations, safety briefing for work at height is conducted, the platform or scaffolding is erected, and fall-protection measures are implemented. The weld area to be inspected is ground to remove the anticorrosion coating, rust, and spatter, exposing the base metal surface, and oil is cleaned with a cleaning agent. Black aqueous magnetic particle suspension and A1 sensitivity test pieces are prepared, and the test piece is attached to the base metal for sensitivity verification to confirm that the HS-CDX-300 magnetization state is normal. For the long butt welds of box girders, the E-type crossed rotating-field probe is selected — this probe generates a rotating field in a single scan, detecting both transverse and longitudinal cracks and thereby significantly improving the efficiency of long weld inspection. The operator holds the HS-CDX-300 main unit and moves the probe along the weld at a uniform speed maintained at 2–3mm/s while spraying the suspension synchronously, observing the magnetic indications when lighting conditions are suitable; for the fillet welds of stiffening plates and diaphragms, the A horseshoe probe is used instead, focusing on the fillet weld root — a stress-concentrated location and a high-incidence area for fatigue cracks. During inspection, each defect found is photographed, located, and its length recorded one by one. The HS-CDX-300 has no built-in demagnetization, but steel bridges generally impose no strict requirements on residual magnetism, so additional demagnetization is generally unnecessary. The entire box girder is inspected in stages, with welds in high-stress areas such as near the supports and at midspan prioritized. After all inspections, the complete defect records are compiled and an NDT report is issued as reference material for bridge final acceptance or health assessment. Because of the load limits at height, the lightweight HS-CDX-300 can be carried and operated by a single person and, paired with the E crossed yoke, significantly shortens the inspection time for long welds, making it suitable for large-scale surface screening of steel structure welds.

3.2.2 Weld Inspection of Lattice Columns and Space Frames in Large Plants (recommended model: HS-CDX-300)

Scenario background:

Large industrial plants and exhibition centers mostly adopt steel lattice columns and spatial space-frame structures, in which a considerable number of intersecting pipe welds and fillet welds exist between members, and welding defects such as surface cracks and porosity are relatively likely to occur during welding. After installation, steel structure plants must undergo inspection acceptance, and older plants must be inspected periodically to identify fatigue cracks generated during service. Because space-frame members are widely distributed with numerous inspection points, the on-site inspection workload is large, while the inspection requirement is mainly for surface-opening cracks, without the need to detect deep near-surface defects. The HS-CDX-300's lightweight body, ease of use, and convenient probe assembly and disassembly make it capable of rapid multi-point screening.

Equipment application process:

Before entering the site for inspection, mobile scaffolding is erected, and the intersecting weld surfaces of the space-frame members are processed one by one by grinding to remove the antirust paint, weld slag, and mill scale, restoring a clean weld surface. The sensitivity of the HS-CDX-300 is then verified with an A1 test piece, and inspection begins once the magnetization effect is confirmed to pass. For round pipe intersecting welds, the E crossed yoke probe is preferred and scanned around the weld to quickly identify transverse and longitudinal surface cracks; at the fillet weld locations of the members, the A horseshoe probe is used to detect weld-root cracks. The probe moves at a uniform speed while the suspension is sprayed synchronously, and the indications are observed to distinguish false indications from true defects. Suspected defects are confirmed by repeated magnetization, and their locations are marked with their dimensions recorded. Because the inspection points across a plant space frame are widely dispersed, the lightweight HS-CDX-300 enables inspectors to move quickly between different members, and the simple probe changeover notably improves multi-point inspection efficiency. After all members are inspected, the inspection records are compiled into a steel structure NDT report as the final acceptance documentation for the project. Space-frame inspection aims only to identify surface welding cracks, and with the high sensitivity of AC magnetization and simple routine maintenance, the HS-CDX-300 can complete on-site inspection of numerous, widely distributed members quickly.

3.3 Machinery Manufacturing (outgoing inspection of precision parts such as shafts, gears, and fasteners)

3.3.1 Outgoing Inspection of Precision Parts Such as Pins and Gears for Construction Machinery (recommended model: HS-CDX-500)

Scenario background:

Excavator pins and transmission gears used in construction machinery are important load-bearing parts subjected to alternating loads. During forging, heat treatment, and grinding, they readily develop quenching cracks, grinding cracks, and forging cracks, so magnetic particle inspection must be performed before these parts leave the factory to detect surface defects. If residual magnetism remains after inspection, subsequent machining and cutting stages will attract iron filings, scratching the machined surface and affecting assembly accuracy; the demagnetization step therefore cannot be omitted. The HS-CDX-500 combines continuously adjustable magnetizing current and built-in demagnetization, requiring no additional external demagnetization equipment, and is suitable for inspecting precision machined parts.

Equipment application process:

Before inspection, parts are surface-cleaned to remove cutting fluid, oil, and mill scale and kept dry and clean. The HS-CDX-500 is then connected to a 220V power supply, and the equipment sensitivity is verified with an A1 test piece. The magnetizing current is then adjusted according to the part dimensions and material, with the output field continuously regulated via an SCR to suit pins and gears of different specifications. For short pins and bolt-type parts, the O ring coil is used for circumferential magnetization to detect axial cracks; the D electromagnetic yoke with adjustable pole spacing is used at gear end faces and tooth roots, where the tooth root is a high-incidence stress-concentrated area with grinding cracks as the key detection target. During magnetization, black aqueous magnetic particle suspension is sprayed, indications are observed, defects are marked, and their dimensions are recorded. After inspection, the built-in demagnetization function of the HS-CDX-500 is directly activated to demagnetize the workpieces, and a gaussmeter is then used to re-measure the residual magnetism to ensure it complies with the technical requirements of the drawings, preventing residual magnetism from continuing to attract iron filings. Parts with nonconforming defects are isolated separately, and rejected parts are repaired or scrapped, while conforming parts proceed to the next machining operation. After each batch inspection, the magnetizing current parameters, inspection quantity, and defect statistics are recorded item by item, and the outbound NDT report is issued accordingly. The continuously adjustable magnetizing current enables the HS-CDX-500 to suit precision parts of various specifications; with the demagnetization capability integrated in the unit, no external demagnetization device is required, making it highly suitable for small-batch precision component inspection in machining workshops and resolving the difficulty of residual magnetism control for precision parts.

3.3.2 Outgoing Quality Inspection of High-strength Bolts for Lifting Equipment (recommended model: HS-CDX-500)

Scenario background:

High-strength bolts used in lifting machinery and wind power equipment withstand significant tensile and alternating loads, and surface cracks readily occur during forging, thread rolling, and heat treatment. If a bolt fractures, it may cause a major incident such as a crane collapse. As high-strength bolts are safety-critical components, each one (100%) must undergo magnetic particle inspection before leaving the factory; residual magnetic fields left after inspection will attract metal chips, causing wear during thread assembly, so demagnetization treatment cannot be omitted. The HS-CDX-500 provides both adjustable magnetizing current and built-in demagnetization, making it well suited to batch bolt inspection operations.

Equipment application process:

The high-strength bolts to be inspected are first cleaned to remove surface antirust oil and metal chips, then dried. The HS-CDX-500 is powered on, and the inspection system sensitivity is checked with an A1 test piece. The magnetizing current of the HS-CDX-500 is adjusted according to the bolt diameter specification, and the O ring coil probe is used to circumferentially magnetize the bolts, identifying axial cracks in the shank and threaded section; the head is inspected with the D adjustable electromagnetic yoke probe to check for forging cracks at the fillet radius. During magnetization, the suspension is sprayed and the indications are observed to identify crack defects. After inspection, the built-in demagnetization function is activated to demagnetize the bolts, and a gaussmeter is used to re-measure the residual magnetism to confirm that all residual magnetism indicators comply with the outgoing specifications. Bolts judged nonconforming are isolated and stored by category and no longer enter the assembly process, while conforming products are packaged and warehoused. During same-batch operations, the magnetization parameters and defect quantities are fully recorded, and corresponding inspection certificates are delivered to the customer together with the products. Thanks to the continuously adjustable magnetizing current, the HS-CDX-500 covers high-strength bolts of all specifications from M16 to M64; with demagnetization integrated into the main unit and consequently fewer auxiliary devices, it is well suited for use at the quality inspection stations of component plants.

4. Customization on Request and OEM

4.1 Customization Services

Probe customization: extended-length E crossed yokes, D probes with special pole spacing, dedicated horseshoe A probes for irregular workpieces, and large-diameter ring O coils are available; integrated fluorescent-black light probes are also within the customizable scope for use with fluorescent magnetic particle inspection.

Power supply customization: a lithium-battery wireless power module can be added to form a field-operation version for environments without mains power; a low-voltage safe power supply version can also be provided on request.

Function customization: defect photographing and storage modules, Bluetooth data transmission, and digital recording modules can be added; audible and visual alarms, or digital modules for displaying the current and lifting-force values, can also be installed.

Housing and protection customization: the protection rating can be upgraded with waterproof and dustproof housings, and explosion-proof structural design can be provided to meet the requirements for use in chemical hazardous areas.

Complete package customization: magnetic particle suspension, test pieces, test blocks, tool boxes, demagnetizers, and black lights can be bundled together to form a complete package supply solution.

4.2 OEM Manufacturing Services

Full-machine OEM label production can be undertaken, customized according to the customer-provided brand logo, product nameplate, packaging, and instructions. OEM is available in two modes — bare units and complete equipment sets — and customers may specify the technical parameters themselves, with the factory inspection report delivered together with each machine. Batch supply capability is available to support the supply of complete equipment for project tendering, adjusting the equipment technical specifications in accordance with the tender technical clauses and providing original-equipment qualification documents.

5. Installation and Commissioning Procedures

5.1 Installation Steps

Unpacking inspection: after unpacking, verify the main unit model, probes, power cable, accessories, and certificate of conformity, and check the main unit housing and cables for damage.

Probe assembly: select from the A/D/E/O probes as required by the inspection, align the probe connector with the main unit interface, tighten it, and confirm that the connection is secure.

Power connection: confirm that the site supplies AC220V and that the ground wire is reliably grounded, then connect the power cable to the main unit power socket.

Accessory preparation: prepare the magnetic particle suspension and test pieces, together with brushes, spray bottles, sandpaper, cleaning agents, and other consumables, and prepare the recording forms.

5.2 Commissioning Procedure

Pre-power-on check: first confirm that the main unit power switch is in the OFF position, then check the cables for damage or short circuit.

Power-on: close the power switch and observe whether the main unit indicator lights illuminate normally.

Sensitivity verification: take a clean ferromagnetic test block, attach an A1 test piece, position the probe, turn on magnetization, and spray the suspension; observe whether the magnetic indication of the artificial defect on the test piece is clearly discernible, thereby confirming that the equipment sensitivity meets the standard requirements.

Parameter setting: the HS-CDX-200 is switched between the AC and DC modes as required; the HS-CDX-300 has a fixed AC output and requires no additional setting; for the HS-CDX-500, the magnetizing current is adjusted to an appropriate level.

Trial magnetization: perform trial magnetization on a defect-free area of the workpiece to be inspected, confirming that the probe lifting force and the field are stable, with no abnormal noise or overheating.

Demagnetization test (HS-CDX-500 only): after magnetizing the test block, activate the built-in demagnetization, then measure the residual magnetism with a gaussmeter to verify that the demagnetization function is genuinely effective.

Formal inspection: only after the above verification passes may workpiece inspection proceed.

5.3 Post-operation Wrap-up

Turn off the power and unplug the power cable, remove the probes, clean the magnetic particles adhering to the probe surfaces, and finally store the equipment and probes together in the protective tool box.

6. Common Troubleshooting and Solutions

Important note: do not disassemble the main unit yourself if an internal circuit fault occurs; contact the manufacturer's after-sales service for repair.

7. Equipment Maintenance Advantages

Modular design for convenient maintenance: the main unit and the probes adopt a separated modular structure. As independent consumable parts, probes can be replaced individually when damaged, without returning the whole machine to the factory, significantly reducing downtime; the circuit interfaces are standardized for good accessory compatibility, and all CDX-series probes are interchangeable, thereby reducing spare-part procurement costs.

Low failure rate and long service life: the equipment employs mature SCR circuitry with strong adaptability to voltage fluctuations, and all core components are industrial-grade devices; the housing is made of high-strength engineering plastic with impact resistance, adapting to harsh on-site environments such as construction sites, the field, and work at height; with proper maintenance, the service life of the complete unit can reach 8–10 years.

Low maintenance cost: routine maintenance only requires cleaning the probe pole faces and the power cable, and the maintenance procedure is not complex; the only consumable parts are the probes, power cable, and fuses, all at low spare-part prices, with no costly periodic maintenance expenses.

High common interchangeability: the four probe types A/D/E/O are fully interchangeable across the three models HS-CDX-200/300/500, so a unit only needs one set of probes to rotate between multiple main units, effectively controlling package procurement costs.

Complete support services: the manufacturer provides free operation training and conducts remote technical guidance from time to time; the equipment can undergo annual calibration with a calibration certificate issued, satisfying the requirements of special equipment inspection, project acceptance, and internal audit systems.

Good protective performance: the main unit is equipped with overcurrent, overtemperature, and leakage protection and shuts down automatically upon misoperation, protecting both the equipment and the operator and reducing the risk of equipment damage caused by misoperation.

8. Safety Precautions

The equipment must be reliably grounded, and insulating protective equipment must be worn during operation; leakage protection must be strengthened when working in humid environments.

Do not insert or remove probes while the equipment is powered, to avoid arcing at the interface that could damage the equipment.

Do not use this equipment in flammable or explosive gas environments (except the YC permanent-magnet models).

Maintain ventilation during inspection operations to avoid inhaling the magnetic particle suspension mist.

The equipment must not be subjected to heavy pressure or dropping, and a dedicated protective case should be used during transport.