A quick cure for lining large diameter mains

Yorkshire Water has embarked upon one of the UK’s biggest large diameter mains

pipe relining operations using the latest polyurethane (PU) quick cure lining

process. Nearly 8kms of water main from the Langsett treatment works in Sheffield,

northern England will be renovated in the $1.7M capital project.

The 33″dia Sheffield main provides 300,000 homes and business in the north

of the city with water and delivers just over 7ML/day. Contractors John Kennedy

(Civil Engineering) Ltd of Manchester lined the main in 100 metre sections,

isolating each section by digging down to the main and removing a short length

of pipe to allow access, before carrying out the work and then piecing the pipe

back up. Around 80 of these excavations were made during the project.

Yorkshire Water’s project manager, Richard Long said, ‘This a very significant

capital works scheme for us. Having proved in our field tests that the quick

cure lining scheme works effectively in large diameter pipes, this is our first

major scheme where it is being used. Other water companies are evaluating this

new technology but we think this is one of the country’s biggest capital schemes

actually using it.’

Section 19 of the UK Water Act, which requires the guaranteed provision of

potable water, has led to water companies concentrating their efforts on improving

the legacy of Victorian cast iron mains which impart predominantly iron and

manganese into the water. The manganese, which is deposited in the mains, emanates

from the raw water and is as a result of historical water treatment processes

which couldn’t remove it. These have since been superseded. The iron is a product

of corrosion of the cast iron mains themselves. Three possible solutions to

this are: clean the pipe; completely replace sections of pipe; or scrape and

reline.

In the first option, pipes are cleaned by forcing a foam swab along the pipe,

normally using water pressure. This is only used, however, if the pipe is already

lined.

Pipes are replaced if they have perished to such an extent that scraping could

make them fragile. To test the integrity of a pipe a section is removed, shotblasted,

and then the thickness of the remaining metal is measured.

In the case of the Sheffield main, the 100-year old pipes had been constructed

from 2″ (5 cm) thick cast iron, making the main an ideal candidate for

the scrape and reline process using the quick cure technology. Drag scraping

was used on each isolated section to remove encrusted matter by a 2 ft dia cylinder

armed with backwards-facing spring-loaded metal teeth scraping the inside of

the pipe clean.

Next, the trailer-mounted lining rig, comprising tanks containing the polyurethane

materials held at the correct temperature by heaters, mixes the lining material

and applies it centrifugally via its spinning head to the inside of the main.

It is dragged along by a winch, leaving a uniform 1.5 mm thickness of polyurethane.

Measurement devices monitor the correct speed of delivery of the material to

the spinning head. Finally, a camera checks the quality of the lining.

Richard Long said, ‘Traditional epoxy resin lining methods can mean consumers

are without water for up to 36 hours. The mains section has to be cut into,

scraped, lined, left for 16 hours then checked by camera before reconnection

can take place. This timescale can be unacceptable to business, hospitals, schools

and other essential users of water as well as to domestic

consumers.

‘Also, arranging alternative supplies can be expensive and slows down progress.

Using the new method in the Sheffield scheme has significantly speeded up the

completion of the project.’

Although the new quick cure material is more expensive, savings obtained by

the rapid cure time mean that overall relining costs are no higher than the

costs of traditional pipe lining and with increasing use, the cost of the new

material is likely to drop. However, with the Sheffield scheme, the alternative

to PU lining was MDPE sliplining due to epoxy resin being unsuitable for such

a large diameter pipe and as such this technique represents a significantly

cost saving.