GlassReinforced Plastic Bore Casing for Large Diameter and Deep Bores

ReportNo WSAA 12

July 1990

 

SYNOPSIS

 

InWestern Australia mild steel pipe used for bore casing lasts for as little asfour years. On average the collapse pressure strength of steel casing isreduced through corrosion by approximately 10% per year.

 

Productionbores used by the Water Authority of W.A. for Perths water supply range from250 ND by 40 metres deep costing about $40 000 to replace, to 500 ND by 1100metres deep costing about $900 000 to replace.

 

Thealternative materials to mild steel for bores of this size are fibre reinforcedplastics (FRP) and stainless steel. Stainless steel is approximately twice asexpensive to purchase as GRP (glass fibre reinforced plastic) and twice asexpensive to install due to factors such as the equipment required to handlethe weight and the jointing costs.

 

Thejoints on the previously available GRP casing, however, were unreliable andunsafe to use in deeper pressure grouted bores particularly of larger diameter.Many construction failures occurred for which the drilling contractor wasunfairly expected to assume responsibility.

 

Theaim of this project was to improve the reliability and capacity of these borecasing joints to enable the safe use of GRP casing to at least 400 ND and 500metres depth.

 

Althoughat the conclusion of this successful project, development of GRP casing to itsfull potential is not complete, the aims of developing reliability andextending the size and depth range have been met.

 

Tables1 and 2 give the recommended maximum depth ratings for the newly developed GRPcasing joints for pressure grouted bores using the test results fromdevelopment to December 1989.

 

Thecapacities and depths given in Tables 1 and 2 have been calculated using a loadfactor of 1.5.

 

Copiesof the Report are available from WSAA, price $A20. Orders may be placed throughthe Bookshop at www.wsaa.asn.au or by email to info@wsaa.asn.au.