Rotary Union Stop Jumps Causing Crane Boom to Oscillate
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Type:  Lessons Learned

Publisher:  Washington River Protection Solutions, Hanford Site (WRPS)

Date: 

Topics:  Engineering, Operations, Construction/Project Management, Hoisting and Rigging

SUMMARY
Carefully monitor crane lifts of low weight items to avoid significantly exceeding the estimated lift force, which could prevent sudden release due to stuck equipment being lifted. Monitoring of lift force by the crane operator of the Load Monitoring Indicator is important to prevent sudden release from stuck items being lifted especially for low weight loads. Materials subject to removal by crane that are in a moist environment need to be either lubricated to prevent corrosion build up or made from non-corrosive metal to prevent exceeding estimated lift force during lifting.

DISCUSSION
Execution of a planned crane lift on a rotary union stop for a tank farm containment box resulted in a sudden release and the rotary union stop jumping a few feet as the friction of the parts let go, causing the crane boom to oscillate. This type of condition could have resulted in serious injury to personnel.

ANALYSIS
The rotary union stop was made of carbon steel material and with humidity caused rusting. Contacting surfaces were rusted together, causing it to stick. Carbon steel was used as it was the material on hand. It was not anticipated that moisture would accumulate and cause rusting, as it had previously been used without issue.

The crane operator performing the lift was watching the spotter and did not view the Load Monitoring Indicator when the lifting force increased well beyond lifting parameters for removal of the rotary union stop. Crane and Rigging management identified during an "Opportunity for Improvement" session that crane operators need to monitor the Load Monitoring Indicator, especially for light loads, when indications are that the object being lifted shows no sign of movement within the expected lifting force.

RECOMMENDATIONS - to prevent recurrence

- When undertaking crane lifts, operators need to be sensitive to the force being exerted by the crane and the estimated force required to lift the object and when it appears to be higher than the force required for lifting, stop and review the Load Monitoring Indicator. This is especially important for small force lifts (e.g. around 150 lbs.).

- During design, Engineering should consider objects in the design that will be lifted which could corrode in wet and damp environments and weld together such that the lifting force required for crane removal is much higher than the weight of the item being lifted.

- Consider application of a lubricant to mitigate corrosion or selection of corrosive resistant steels within design considerations.

REFERENCES
WRPS-PER-2012-2146; RPP-OE-5244 "Operability Evaluation of the Rotary Union Load Path"

CONTACTS
Allan Erhart (509)373-7739; Allan_F_Erhart@rl.gov
^WRPS Lessons Learned

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