Flood Alleviation Schemes Use Steel

Posted on Feb 25, 2014

Flooding is of major concern in the current climate and there are two areas where coated and lined steel pipes can be of strategic importance to both the Environment Agency and Water Authorities.

1. Environment Agency :  The EA has recently procured 1000mm and 1400mm coated and lined steel water pipes for Flood Alleviation schemes in the South East of England. The pipes and fittings formed part of a new pumping station around the tidally affected zones near Dagenham. This is all part of the East London improvement scheme which is set to tackle issues created by the combination of heavy rainfall and high tides. Steel pipe and fittings were coated and lined with Scotchkote 206N as specified by the client.

2. Severn Trent Water : STW completed the installation of a 26km 600mm main running from Strensham WTW near Tewkesbury to Churchdown Reservoir to the east of Gloucester. The new pipeline, installed in two phases, was procured in response to the threat of flooding to the works at Strensham. The Avon runs very close to the site and significant rainfall had caused the banks to burst. Gloucester is supplied by Strensham WTW and at the time this was a critical supply route for potable water to the city. Following the flood risk it was agreed that a new pipeline would be installed to provide a Security of Supply to the city of Gloucester. Coated and lined steel was selected for the scheme, including a 300m+ horizontal directional drill under the Avon. Two key areas of consideration on material selection included :

PN25 rated pipeline.

a. Steel provides a welded solution which removes the requirement for thrust blocks or other joint restraint mechanisms associated with higher working pressures. This provides an environmental, logistical and financial benefit, especially where concrete thrust blocks are considered. 

b. The design of the steel pipe allowed the client to keep the material costs to a minimum. This was achieved by manufacturing with a higher grade of steel combined with a standard wall thickness.

Corrosion Prevention

a. In the areas to the east and south of Gloucester there have been a number of reported incidences  with ductile iron corrosion and bursts. This is mainly due to the aggressive ground conditions to be found in the area coupled with insufficient corrosion protection on the existing pipelines. All metallic pipes are at risk of corrosion and it is only the quality of the corrosion protection that provides a suitable design life for a pipeline.

b. The supplied steel pipes utilised an established and high quality corrosion protection of three layer polyethylene – fusion bonded epoxy, adhesive and heat bonded seamless, extruded polyethylene. Across the welded field joints two layer Canusa heat shrink sleeves were utilised to maintain the external protection.

c. The whloe length of the pipeline has been protected using a cathodic protection system. This can be applied in two ways; as a sacrificial anode or as an impressed current. Both systems protect the pipeline should the mainline coating be damaged at any time during installation or in the future.