Q1: What diameter range of bolts can typically be tested?

A: High-strength bolts of M12 and above, with lengths ranging from 80mm to 6000mm. Support customizing a larger range of bolts.

Q2: Is the torque of the bolt measured?

A: No, what is measured is the bolt preload force (axial stress). During construction, the conversion of tightening torque into preload force is affected by friction. Measuring the preload force can directly reflect the tightening status of the bolt since friction is affected by many factors, such as lubrication conditions, surface roughness, etc.,

Q3: What are the main principles of measuring equipment?

A: According to the Chinese national standard GB/T 43232–2023 Fasteners – Measurement method of axial stress by ultrasonic, electromagnetic ultrasonic (EMAT) dual-wave technology is used without the need for coupling agent or polishing of the workpiece.

By simultaneously emitting ultrasonic longitudinal waves and transverse waves, and then measuring the flight time of the ultrasonic longitudinal waves and transverse waves, the axial stress (preload) of the bolt is calculated according to the method specified in the national standard GB/T 43232-2023 without the original length of the bolt.

This method makes full use of the linear change of ultrasonic transverse wave sound speed and longitudinal wave sound speed with the change of stress, and measures the bolts of the same specification, length and stress through two modes of waves (transverse wave and longitudinal wave), which technically eliminates the adverse impact of the unknown original length of the bolt on the measurement.

Q4: There is paint on the surface of the bolt. Does it need to be removed before measurement?

A: No removal required. Electromagnetic ultrasonic technology can directly penetrate non-metallic coatings (such as paint, plastics) without polishing or damaging the surface.

Q6: What is the approximate accuracy of dual-wave testing?

A: For bolts from the same batch, the accuracy is usually ±3~5% Full (Full = 75% of the bolt material yield strength). The measurement accuracy is affected by the consistency of the bolt material.

Q5: When measuring bolt preload force using electromagnetic ultrasonic dual waves, are there any environmental factors that need to be considered?

A:  Bolt temperature can affect ultrasonic wave speeds and the interpretation of stress. Temperature should be measured and recorded, and compensation should follow the instrument’s validated procedure. Measurement and reference conditions, including temperature differences or gradients, should be considered when evaluating the result.

Q7: What is the repeat accuracy of long-term monitoring?

A: Through the patented technology “Double Wave Inspection”, the repeat accuracy can reach ±1%Full (Full = 75% bolt material yield strength), ensuring the reliability of long-term monitoring data.

Q8: What do I need to prepare in advance before taking measurements?

A: Parameters such as the clamping length of bolts from the same batch must be provided. It is recommended to use spare bolts to calibrate the longitudinal and transverse wave velocity ratio (R0); if spare bolts are not available, a small number of bolts can be loosened on site for calibration.

Q9: Do I need spare bolts for calibration?

A: Not necessary. The built-in database of the instrument supports calibration-free testing. The measurement results, however, may have overall deviations. Nonetheless, it can still determine the dispersion of the preload force effectively and identify abnormal bolts.

Q10: If no spare bolts are available or no bolts can be loosened on site, can the test still be carried out?

A: You can use the instrument’s own database for testing. The measurement results, however, may have overall deviations. Nonetheless, it can still determine the dispersion of the preload force effectively and identify abnormal bolts.

Q11: What is the difference between measuring bolt preload force and performing ultrasonic flaw detection (including phased array) on bolts?

A: Preload force measurement: quantitative analysis of bolt stress status for preventive maintenance; Ultrasonic flaw detection: Qualitative detection of cracks and other defects, which is a post-event diagnosis. The two techniques are complementary to each other. Preload testing can avoid bolt fatigue defects caused by abnormal stress.

Q12: What are the advantages of bolt preload testing compared to traditional torque (tool) testing?

A: 1) Measurement basis: Ultrasonic measurement evaluates axial stress from ultrasonic data rather than estimating preload from tightening torque. Comparative accuracy depends on calibration, material properties, measurement conditions, and the methods being compared;

2) Long-term tracking: supports preload force change trend analysis and optimizes maintenance cycles;

3) Efficient and safe: single measurement takes less than 30 seconds, no heavy tools required, reducing labor risks;

4) Non-destructive testing: does not damage the bolt structure and is suitable for equipment in service.

Q13: Can the bolt preload force be tested for both bolts tightened by the tension method and bolts tightened by the torque method?

A: Yes. Regardless of the tightening method used, this technology can directly measure the actual preload force of the bolt.

Q14: Approximately how many bolts can be inspected in an 8-hour working day?

A: The inspection time of a single bolt is  typically less than 30 seconds, and approximately 600 inspections can be tested in 8 hours shift (including probe positioning, flange relocation, and data recording).

Q15: Which industries or fields require bolt preload force measurement?

A: Any scenario where high-strength bolts are used for fastening requires preload force measurement. Such as wind turbines, engineering machinery, bridges, steel structures, petrochemicals, rail transit and other fields.

Q16: Can the preload force of a M36, grade 8.8 foundation anchor bolt (length 4800mm) of the wind turbine be measured?

A: Yes. We have successfully tested M33, M39, M42, M48 and other foundation anchor bolts of various specifications.