Review of rigging attachments to the equipment being lifted have prevented lift failures. When planning major crane lifts we are very careful about confirming the crane foundation, rigging stability/capacity, and crane capacity. Are we taking enough time to analyze the points of attachment for the rigging? Becht Engineering Heavy Lift Division says “NO”. Our experience is that reviews of rigging points of attachment have identified critical flaws that may have resulted in dropped loads.
In industry today, the load/vessel designers typically design the lifting lugs and trunnions at the same time. It is our experience that the owners of the equipment and the crane contractors are assuming these devices are properly designed and rated. It is a common practice that the crane contractor assumes responsibility for rigging above the points of attachment.
Generally, the consensus is that trunnions and lift lugs are designed by others and they should be right. That has not been our experience. Becht performs a thorough analysis of the points of attachment as part of our engineered lift plan reviews. Our team reviews the design calculations to include the device and the structure it is mounted on, such as a vessel shell or skirt. In addition, we run a finite element analysis (FEA) model to confirm the stresses are with an allowable range.
Becht reviews have disclosed numerous issues with trunnions, lifting lugs and the loads they are attached to. One such issue was where the pipe used for the trunnion hub, was overstressed. According to our FEA the pipe would have severely deformed, possibly causing damage to the rigging gear. Becht engineers designed stiffener brackets that were installed inside the trunnion hub resolving the issue.
In another case, when lift link plates were used, the diameter of the link plate was smaller than the diameter of the trunnion. This resulted in point loading of the link plates that they were not designed for. Both diameters matched on the lift plan drawings but the lift contractor did not physically measure to confirm. When the lift started, there was a loud popping sound and the lift was stopped. Fortunately, the problem did not result in a load drop but could have been catastrophic.
Don’t Assume Anything!! Check, Re-Check And Check Again
Structural problems with a load or vessel are often encountered. Especially when upending a very long load. In one case, Becht discovered the tower skirt would have deformed due to the stresses imposed by the tailing lugs. Becht made a recommendation to install stiffener beams inside the skirt to prevent any deformation. The beams are shown in the photo below.
Special consideration should be given to demolition lifts. A thorough investigation must be done to assure the material you are mounting the device to is not overstressed. The integrity of the material should be confirmed. Occasionally we find the vessel shell is overstressed due to deterioration or thinning. In that case, adding a re-pad plate is a common solution. Another solution may include inserting a lifting pipe or beam though the vessel with stiffeners or re-pad plates attached to the shell.
Lifting Lugs require similar checks as trunnions. The main difference is that they must be designed and installed considering specific loading angles. The lug could see a transverse force at the start of the lift, an oblique force as the load is upended followed by an axial force when the load is vertical. Lateral loading is unacceptable but must be considered as an impact factor.
The same codes apply to lifting lugs as for trunnions. See ASME BTH-1 and ASME B30.20.The 1,500-ton lifting lug in the photo below had to be tested to 1,800 tons. ASME allows these devices to be rated at 80% of the test load.
In conclusion, don’t take it for granted that the points of attachment are properly designed to perform to capacity during the lift. The points of attachment may be of sufficient capacity but could damage your load. Take the time to verify the design and assure they meet ASME Code. This blog does not include every consideration but instead is intended to inspire creative thinking and prompt a pro-active approach to design and use of these devices. If you don’t have the engineering skill sets in house, Becht Engineering would be pleased to provide a thorough analysis.
Becht Prevents Problems
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Joseph (Joe) Collins is the Heavy Lift Division Manager for Becht Engineering Co., Inc. He is providing Consulting and Design Services for Lifting and Transport of process equipment, machinery, chemical, refining and nuclear vessels and components.His duties include consulting to clients using the world’s largest cranes and super heavy lift projects.
Mr. Collins has over 45-years’ experience in the heavy lift industry. He served as Commissioner and later as Vice President for the National Commission for the Certification of Crane Operators (NCCCO). Joe also served as a member of the Cranes and Derrick Advisory Committee (C-DAC) to OSHA, which wrote and delivered the initial draft of the new OSHA Crane Safety Standard. In January 2011, Engineering News Record magazine honored Joe as one of the “Top 25 Newsmakers” for his work with C-DAC.
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