NAI TECHNICAL REPORT
Safety Matters: Welded Chain and Wire Rope and Inspection
Wire Rope Inspection
All wire ropes in service should be inspected visually on a daily basis. A visual inspection consists of observing all ropes which will be used during the day’s operations. These visual observations are important in discovering any damage to the rope. When inspecting the rope, make sure to look for:
· Kinks - are a permanent distortion in the rope. Kinks are caused when the rope cannot rotate about its axis to release the torque.
· Strand Nicking - is when a single or many strands are removed from the rope. This is caused by the small strands of the rope rubbing against each other during extended or normal operation.
· Metal Fatigue - is a weak spot in the wire rope resulting from being bent back and forth at a single point. This is caused by the small strands of the rope rubbing against each other during normal operation.
· Fatigue Breaks - are breaks in the individual wire. They are usually square and in the crown of the strands. This is caused when wire rope is subjected to repetitive bending over a drum, wobbly wheel or roller, tight grooves, or poor end terminations.
· Bird Caging - is when the wire rope strands are forcibly untwisted and become spread outwards. This causes the strands of rope to protrude in the form of a birdcage. This is a result of mistreatment such as sudden stops, being wound too tight on a drum or being pulled through tight sheaves.
· High Stranding - a condition caused by kinking in which rope strands become loosened and lie higher on the rope than other strands. This is caused when the stands are overloaded, crushed or flattened.
Inspections should be carried out by a person who has learned through special training or practical experience what to look for and who knows how to judge the importance of any abnormal conditions they may discover. It is the inspector's responsibility to obtain and follow the proper inspection criteria for each application inspected.
Click here for a Hoist Inspection Checklist
Second Quarter 2010
All welded chains and wire ropes should be thoroughly inspected at regular intervals. The longer it has been in service or the more severe the service, the more frequently it should be inspected. Be sure to maintain records of each inspection. Following are proper testing procedures:
Welded Chain Inspection
All chains should be inspected visually on a daily basis for gouges, nicks, weld spatter, corrosion, and distorted links.
· The chain should be slackened and the adjacent links moved to one side to inspect for wear at the contact points. If there is wear or if stretching is suspected, the chain should be measured according to the hoist manufacturer's instructions. If instructions are not available, the process should continue as follows:
· An unworn, unstretched length of the chain should be selected (e.g., at the slack end).
· The chain should be suspended vertically under tension, and using a caliper-type gauge, the outside length of any convenient number of link (approximately 12 to 24 inches overall) should be measured.
· The same number of links in the used sections should be measured; the percentage increase in length should be calculated.
· Chain should not be rusted or brown. If the crane is in a corrosive atmosphere, be sure to oil it often.
· The hoist should be tested under load in lifting and lowering directions and the operation of the chain and sprockets should be observed. The chain should feed smoothly into and away from the sprockets.
· If the chain binds, jumps, or is noisy, it should be checked first to ensure that it is clean and properly lubricated. If the trouble persists, the chain and mating parts should be inspected for wear, distortion, or other damage. The chain should then be slackened and the adjacent links moved to one side to inspect for wear at the contact points.