Fastener inspection of marine crane: Prevent loosening and ensure safe operation

The fasteners (bolts, nuts, pins, etc.) of marine cranes and other equipment are affected by vibration, impact, and corrosion for a long time and are prone to loosening and failure. Here are the key takeaways for efficient inspection and maintenance:

•  Load-bearing structure connection: Offshore crane's base and deck fixing bolts, boom truss node bolts;

•  Connecting moving parts: luffing cylinder pins, slewing rings connecting bolts;

•  Key mechanism installation: hoisting winch base bolts, brake fixing nuts;

•  Exposure to the marine environment: fasteners in the open air (susceptible to salt spray corrosion).

1. Visual judgment

• Observe whether the anti-loosening mark (paint line/color code) is misaligned;
•  Check whether the exposed length of the thread is abnormal (the nut may be withdrawn when loose);
•  Inspect the surface of fasteners for rust, cracks, or deformation.

2. Knock detection: Tap the nut with a copper hammer:

•  Make a crisp sound: the connection is regular;
•  Muffled or shaky sound: may be loose and needs to be further detected with a torque wrench.

3. Torque retightening Torque values according to manufacturer's standard:

•  Re-tighten the suspected loose parts (such as the bolts of the slewing platform) one by one and record the torque value;
•  More 20% of the fasteners must be replaced (the threads may be worn).

4. Non-destructive testing For key parts (such as boom main stress bolts):

•  Use ultrasonic or magnetic particle flaw detection every year to check for internal cracks;
•  Replace the crack at the bottom of the thread immediately, and it is strictly forbidden to continue to use it.
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1. Mechanical anti-loosening

• Install spring washers and stop gaskets;
• Important parts are loosened in series with cotter pins (such as hook pins) or steel wires.

2. Glue bonding and anti-loosening

•  Apply thread locker (medium strength for ordinary bolts, high strength for critical parts);
•  After sizing, reload according to the specified curing time (usually 24 hours).

3. Antiseptic treatment

•  Galvanized or Dacromet coated bolts: salt spray resistance life of more than 5 years;
•  Open-air fasteners are regularly coated with anti-corrosion grease to isolate seawater erosion.

•  Daily inspection: check the fasteners of moving parts before each marine crane's shift;

•  Regular comprehensive inspection: re-tighten the fasteners of the whole deck crane once a quarter;

•  Establish a ledger: record each bolt's torque value, replacement time, and flaw detection results for easy traceability.

•  When the connecting bolts of the boom are found to be loose, stop the offshore crane's operation immediately and set up a warning area.

•  It is forbidden to use worn wrenches (easy to slip and cause an overload of bolts).

•  After severe weather, such as typhoons, all exposed fasteners must be inspected urgently.

Standardized fastener inspections can reduce the risk of ship crane structures falling by up to 80% and are the "basic line of defense" for safety in offshore operations.

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