Woodside Petroleum Pile Reforming Project

Extract from March 1994 Oil and Gas Australia Magazine

The most successful pile reforming method employed by Woodside to reform the Goodwyn piles involved filling the pile tip with iron ore sand to provide a seal and pressurizing the pile with water after first creating a seal at the top. The effect of pressurisation was to inflate the pile in much the same way as a flattened straw can be inflated back to circular shape by blocking one end and blowing into the other.

When Woodside needed a plug for the top of the piles to enable this pressurisation method, they searched the world for suitable technologies and suppliers. At this stage, it was envisaged that the plug would have to be capable of sealing a pile inflation pressure of up to 10 MPa (1500 psi). Over the area of the 2560 ID piles this represents a force of more that 5000 tonnes.

To be self supporting against this sort of load and still provide a guaranteed seal on the inside of a seam welded pile is a very tall order, but Woodside ended up finding a company with the solution right in it’s backyard – AGE Developments Pty Ltd, which is based in Perth.

AGE Developments design and manufacture inflatable packers and when first approached to assist the pile performing project was keen to “have a go”. This first approach, initiated by AGE in conjunction with Dawson Engineering and presented through Heerema McDermott Aust. Pty Ltd (HeereMac), was in fact a packer designed principally as a primary reforming tool, the intention being to lower the packer into the deformed area of the piles and reform the pile directly through packer inflation.

Woodside were sufficiently convinced by the initial scale tests developed to investigate the concept of using an inflatable packer for pile reforming to proceed with a contract to manufacture a full scale packer. This packer was 1570 mm maximum diameter with a six metre effective rubber length and rated for 15 MPa when inflated in the 2560 mm ID piles.

To build this packer, AGE had to develop new design and manufacturing techniques “on-the-run”, to deal with the tremendous scale increase required for manufacturing so large a packer. (Usual high pressure inflatable packers range up to a maximum of 20 inch diameter; large diameters are generally restricted to low pressure applications). After much hard work and persistence, AGE Developments delivered the completed packer for testing in mid July.

Unfortunately, due to a material fault in an ultra-high strength steel casing, this packer failed during testing. Nevertheless, valuable lessons had been learnt and the parties involved determined that these could be applied to production of a successful packer.

In the meantime, Woodside had successfully performed a full scale test of the concept of pile inflation adding impetus to the packer development work in order to implement pile pressurisation for routine reforming. For the original reforming packer, pile pressurisation was to have been a secondary function. Following the successful test the order of importance reversed with pile pressurisation becoming the primary requirement.

A new packer was therefore designed with input from all existing parties plus Woodside’s own engineering staff and Wholohan Grill and Partners. The resulting packer design, built by AGE Developments through a contract with HeereMac, was delivered in mid November having taken less than 12 weeks to manufacture.

The statistics are impressive; 1.83 metre diameter, six metre rubber length, rated for 10 MPa in 2560 ID pile, packer element weight of approximately 23 tonnes. The reinforced rubber element is some 200 mm thick, contains more than eight tonnes of rubber and more than 1000 kilometres of high strength reinforcing wire cables.

Following delivery of this packer, AGE Developments immediately commenced building what is believed to be the largest high pressure inflatable packer ever made. This packer, 1.8 metres in diameter and six metres long with a rated operating pressure of 15 MPa (2000 psi) in a 2560 ID pile, forms an integral part of another tool (the jacked mandrel tool) designed to reform the damaged piles.

The completed tool, which was assembled, successfully tested in Kwinana and subsequently delivered offshore, consists of the AGE packer installed on the outside of a 4000 tonne capacity jack built by Hycom BV of the Netherlands under contract to HeereMac. All up weight is approximately 160 tonnes with the packer contributing around 26 tonnes.

This tool was designed to provide a reforming capacity in three separate ways: as a plug for pile pressurisation; for direct reforming via packer inflation; and for direct reforming via jacking.

In the first instance, the tool is installed in the top of the pile and the packer is inflated to secure it in place. Water is then pumped through the packer to pressurise the pile below the packer plug, thereby reforming the pile hydraulically. The packer inflation pressure must be sufficient to anchor the tool against the force generated by the reforming pressure.

For direct reforming using the packer alone, the tool is inserted into the pile area requiring reforming and simply inflated. As inflation proceeds, the packer pushes the pile and surrounding soil into a circular shape. This method generates enormous reforming loads behind the packer, e.g. at seven MPa total load is approximately 25,000 tonnes but is very localised and requires that the packer can first be inserted into the area that needs reforming.

Where the tool cannot enter the area to be reformed, it is installed immediately above this zone. The packer is inflated to anchor the tool in position and then the jack is stroked out to reform the pile ahead of the packer. Subsequent deflation and retraction allows the packer to be lowered in behind the jack nose and the process may then be repeated as necessary to progressively reform the tip of the pile.

Finally, it must be acknowledged that development of these tools was a team effort from the concept stages through prototype testing, manufacture, final testing and delivery.

The project used the combined talents and resources of the many individuals and corporations. For the most part the work was conducted in an atmosphere appropriate to this team approach and the project benefited and was successful as a result.