Winch Drum Dowel Pin FEA

Alatas Engineering and Design Services (AEDS) delivered a winch drum dowel pin FEA (finite element analysis) for a drilling client located in the UK. The scope of the work involved an FEA assessment study on an existing boom luffing winch of the portside crane manufactured by National Oilwell Varco (NOV).

The client’s NOV National OD 435 crane has a maximum SWL 46.70Te deck lift capacity and a boom working radius of R9.1m and has been installed and commissioned on portside of the client’s Semi-Submersible Platform.

The reason for this crane winch FEA was due to the boom luffing winch suffering one of its Ø5/8″ x 4″ long dowel pins being sheared off during crane operation and was working with the existing two dowel pins instead.

Background for Winch Drum Dowel Pin FEA

During a recent inspection by Chief Engineer, the main boom winch of portside crane and one of the dowel pins installed on the drive side flange had been found as sheared off. This cut was throughout its cross-section at approximately 3″ from cheek plate outside face, which may overload the remaining two dowel pins and their further progression and failure due to shear in the same pattern.

Alatas solution

• Alatas AEDS begin by carrying out some basic calculations considering one load case assuming that the dowel pin material is grade AISI 52100. The calculations show the existing two dowel pins to have sufficient capacity to take the operational shear loads. However, Alatas AEDS proposed an in-depth FEA assessment for different load cases and their combinations to explore dowel pins stress and deformation behaviour to provide to the client.
• Alatas AEDS carry out an extensive structural assessment to assess existing dowel pins’ shear strength and integrity. Our team looked at and main boom winch drum and flanges and, more generally, their capacity of max equivalent (von-Mises) stress and max shear stress along the cross-section of the dowel pins and any deformation under the influence of operational loads as per crane load charts. 
• The boom luffing winch drum and side flanges are assumed to have been manufactured using standard cast Iron with nodular graphite metallurgical structure. These parts are made in an iron-carbon casting material having carbon components present as graphite to material specification GGG-60.
• A finite element stress analysis technique was used to determine the stress distribution in the dowel pins utilized in the boom winch for different loading conditions of rope line pull for the rope location on the drum. The FEA simulation results showed equivalent (von-Mises) stress, max shear stress and shear stress intensity within the permissible/allowable stress limits in the existing two dowel pins. Local stresses occurred near the vicinity of the mating contact faces of drum and drive side flange (which adopts machined holes for interference fit for dowel pins). These stresses were reported considerably within the allowable limit and scoped accordingly for dowel pin itself, over the cross-section and any stress concentration hotspot value with further explanation and were found negligibly small in volume and size. 

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