Bolt Inspection for Wind Power Industry

Background

Bolts are widely used for fastening connections in modern industrial fields, such as bridges, wind power, and high-speed rails. Bolts are prone to various defects, some occurring when being installed, when in service, or during manufacturing. Detecting defects in bolts can help improve machinery and equipment safety and increase these components’ service life.

Bolts for wind power mainly include blade bolts connecting bolts between flanges and blades;? tower bolts, which are high strength bolts used on the wind turbine, etc.

The bolts material is usually carbon steel, with hexagonal shape. The diameter of the nut ranges from 20 - 60mm, and the length ranges from 150-500mm.

The common defects of bolts are mainly cracks. Parts most prone to cracks is generally the root area of 1 to 3 threads near the fastening area of the bolt and nut.

When using conventional ultrasonic technology to detect bolts, we generally use the longitudinal wave normal probe, or longitudinal wave probe with small angle, and put them at the bolt end for inspection. Or we can put a transverse wave probe with large angle at the bolt shank for inspection. However, there are the following problems for this kind of inspection:

• The probe needs to perform different scanning paths. (as the pictures below)
• Because of the limited end surface, different angles of probes are needed for one bolt, bringing low testing efficiency.
• Due to the tight arrangement of threads, multiple A-scan echoes will be generated simultaneously, which is difficult for inspectors to identify defects.

Solutions

Phased array probes features:

• The sound beam of PA probes can be deflected and focused, which improve the testing efficiency.
• With higher sensitivity and SNR, the testing result is more accurate and intuitive, which is easier for defect identification.

We will show you the bolt inspection solutions, with 4 kind of PA probes.?

Solution with Normal PA Probe

Solution with PA Low-profile Probe

Solution with PA Membrane Probe

Used for Phased array testing, the SNR is better than normal PA probes.

Used for 3D real-time TFM imaging, the testing result is more intuitive.

Testing Results Conclusion

• All these three kinds of PA probes (normal PA probe, PA low-profile probe, PA membrane probe) can be used for detecting bolt.
• For? PA low-profile probe, its probe position can be only at the bolt shank,? which is only suitable for testing bolts in new production condition, or bolts that can be completely disassembled and are not in service.
• All these three kinds of PA probes has to be rotated to ensure covering defects located at all angles.
• Due to focusing effect, all these three kinds of PA probes cannot test bolt with a center hole.

Solution with PA Ring Probe

Features:

• As the special focusing effect, PA ring probe is suitable for testing bolts with center holes.
• PA ring probe can cover defects located at all angles in one-time.
• Better sensitivity and SNR.