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Offshore Oil and Gas - Load Testing of Pedestal Cranes

written by: Willie Scott • edited by: Lamar Stonecypher • updated: 2/11/2010

Offshore installations are serviced by their pedestal cranes. These cranes must be load tested to SOLAS regulations, and this can be carried out at the offshore construction yard using SWL and Proof Load test weights. On completion of a successful load-test a Load-test Certificate is issued.

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    Introduction

    This is another article in the series on Load Testing Offshore Lifting Equipment.

    The majority of offshore pedestal crane manufacturers have their own procedures for load testing once the crane has been installed on the deck, and these will have been approved by the Current Offshore Regulations (SOLAS) and the yard Certification Authority. (Lloyd’s or DNV)

    The procedure that follows is one that I used to test a pair of offshore pedestal cranes on the deck of a jack-up gas platform built here in the North of Scotland before I retired in 2000.

    Please note that this is only a guideline to explain how the cranes are tested, and not to be used as a procedure, as the regulations may well have changed by now.

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    Pedestal Crane Construction and Installation

    The pedestal section of the crane is of hollow round section and flanged at each end. The bottom flange is welded to the plate girder support on the lower deck of the platform, and the top flange drilled to suit the slew-ring which comes with the top half of the crane.

    The pedestal passes down through several deck supporting plate girders to which it is fully circumference welded, as well as being welded to stiffeners all welds being subject to NDT and a report given to the engineer, along with a survey of the crane pedestals verticality.

    Once the top half of the crane arrives it is fitted to the pedestal by the vendor engineers, the ring bolts hydraulically torqued and the wire ropes reeved from the drum through the sheaves.

    The diesel engine and hydraulics are commissioned and the crane overload systems tested, including the winch drum brakes. It is then handed over to yard construction for load-testing, which in my day we used the maximum weight at the maximum jib reach and, the maximum weight at the minimum jib reach. These weights and distances were calculated from the manufacturers O & M Manual.

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    Procedure for Testing Offshore Pedestal Cranes

    The proof load test weight as stipulated by the SOLAS Regulations for pedestal cranes is attached and lifted clear of the deck as the crane jib is boomed out to maximum reach. It is then slewed as far as possible in a clockwise direction, then in an anticlockwise direction and the weight removed.

    The jib is then boomed into the shortest reach and the stipulated test weight for this radius attached. It is rotated as before, clockwise and anticlockwise and the weight removed.

    During these operations the winch drum brakes are operated and seen to be working satisfactorily.

    All this is witnessed by the yard Certification Authority and the engineer, usually from the crane cab (gets a bit crowded at times)

    All the attachment welds are subjected to post-test NDT and the pedestal is post-test surveyed for verticality. These reports are given to the engineer in charge.

    Once all the reports are scrutinized by all parties a load test certificate is issued. This enables the yard rigging department to utilize the crane for the rest of the construction phase, the client is usually agreeable to this as it gives the crane a good running in period, any adjustments being made much cheaper onshore than offshore in the North Sea.

    The crane load test certification is sent offshore at sailaway….

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    Pedestal Crane Drawing

    Pedestal Crane Load-Test