Lift Plan for Knockout Box

Relevant Codes and Standards

ASME BTH-1-2011 – Design of Below-The-Hook Lifting Devices

Materials and Components

Structural Steel

Project Brief

The roof on an S02 knockout box began collapsing, indicating a serious degradation of the integrity of the vessel walls and requiring rapid replacement. I/O Design was to estimate the lift weight of the existing vessel including process material buildup, and design lifting provisions that compensate for the reduced vessel integrity as well as the additional weight due to process material buildup.


  • Information on the amount/distribution of process material is minimal (estimate of material depth was provided, but no information on distribution), access to interior of vessel, while in operation, is not possible.
  • Vessel walls have corroded substantially, requiring great care in the attachment of the lifting provisions.
  • Vessel is to remain in service until commencement of lifting operations, production down time must be minimal.


A 3D model was created from the OEM drawings of the vessel, and the volume of potential material buildup was analyzed. Using the specific gravity of the process material, an estimate was made of the actual vessel weight and COG including buildup. Because the information available on the built up material was minimal, I/O Design considered the maximum potential buildup volume, in order to ensure this estimate was conservative. Using this weight, lifting provisions were designed with integrated spreader bars to allow a “four slings to the hook” style lift. These provisions were attached to repads welded to areas of the vessel where the wall was thickest, and could be attached in advance of lifting operations. When lifting operations commenced, the crane LMI indicated that the lift weight was less than I/O Design’s estimate. Lifting operations then proceeded successfully and without incident, minimizing production down time.