Articles & Case Studies

Technocover solution clinches chamber headroom – as well as improving health and safety and security at Northumbrian Water pumping station

Posted: Monday 15th June 2009

The refurbishment of a pumping station in County Durham is part of Northumbrian Water’s (NW) lot 6 pumping station programme, work designated under its£1.1 billion AMP4 investment.

Introduction

MWHC’s North East Business Unit are framework contractors designated to undertake pumping station refurbishment/new builds under NW’s Lot 6 Framework.

MWHC carried out a full stage 1a design for the refurbishment of this strategic pumping station, undertaking the main design and acting as Principal Contractors. From the design criteria, a fixed contract price was established and agreed with NW.

The replacement of existing access covers to the pump chamber, to improve security and operational health and safety, formed a key element of the work. A traffic light survey by NW highlighted the need, in particular, to address the issue of restricted headroom in the chamber.

As well as bearing onto a rebate within the chamber wall, the support beams to the cover system were located at 1m centres along the 10m chamber length. With numerous beams to negotiate, this effectively gave just 1.8m headroom for personnel.

In addition, the cover assembly, which comprised steel durbar plate with asphalt weatherproofing, was no longer water-tight and the plates were difficult to open and handle.

Option

MWHC looked at the option of raising the chamber walls to get headroom to around 2.1m (door height), but this would have involved major civil’s work, adding significant cost and time to the work programme, as well as exposing this strategic pipeline to the elements.

The other option was to resolve the headroom problem in the design of the replacement access system.

MWHC turned to Technocover for a solution that would maximise as much chamber height as possible whilst meeting other important security and manual handling criteria.

MWHC asked Technocover to look at sitting the new cover and support steel work on the top of the existing chamber wall, at the same time extending the height of the perimeter angle frame to help achieve the extra working height.

The next challenge was to arrive at a beam arrangement that would leave the new-found head space as unimpeded as possible. Technocover adapted the initial design proposal to remove a further two support beams, easing headroom even more.

In contrast to the 10 beams of the previous assembly, Technocover simplified the support system to just four beams. This includes two primary beams spaced 5m apart, with two secondary beams bolted between them, running as close as possible with the two pipe runs, again to give more emphasis on overall space when walking within the chamber.

Removal

As well as addressing headroom issues, the beam configuration also needed to account for operational needs in terms of cover removal.

The cover assembly provides an approx 9.6m by 4.6m (cover) clear opening overall. Cover lids within the assembly are arranged in five distinct runs which can be independently lifted to give strategic access to equipment – valve spindles, pumps - and different areas of the chamber. Covers can also be individually removed.

With the previous durbar plate system, all of the covers (5m long) had to be lifted out to gain access to a single pump. This gave rise to an area some 3m by 5m being subject to falls from height. The new solution allows different banks of covers to be removed in isolation to access specific areas, thereby significantly improving safety.

Four different cover sizes were used to achieve the required clear opening in each bank of covers, making the resolution of the beam configuration all the more impressive.

Two of the covers incorporate a personnel access hatch, designed for single person operation and mounted with a Sentrol contact alarm. They are hinged with automatic safety stays, allowing one person operation within the lifting effort of HSE manual handling regulations. All other covers are equipped with lifting points for safe mechanical removal.

Both hatches have an integral ladder which stows under the cover to provide fall protection. Four valve spindle access points were also provided within the cover system which is engineered for pedestrian loadings of 5kN/m2.

Sloped

The pump chamber is set into sloped ground, meaning that the finished level of the cover at one end is over 1m above the ground.

MWHC had initially designed a perimeter handrail and access steps as indicated in NW’s traffic light survey. Technocover needed to design the handrail supports so that they did not interfere with any proposed cover lifting, but at the same time remaining within the boundaries of NW standard handrail design, including 120mm high kick plate attached to the handrail upstands.

Located on the outskirts of Durham, and therefore relatively close to an urban centre, the site dictated that the covers needed to provide a high level of security.

MWHC specified that the cover solution should broadly comply with LPCB security rating 3 requirements. Among other things, the covers have either internal shoot-bolt locking or, for those designated with external locking, shrouded padlocks and lever-down locking.

A Duragalv hot dip, post-galvanised zinc finish, applied in-house under quality controlled conditions, provides superior durability to meet the 20 years service life.

Installed

As well as carrying out site survey, design and manufacture, Technocover also installed the covers.

Kel Smith, MWHC Project Manager was very impressed with the product and service provided. “Technocover’s technical input, design drawings, site support and installation were excellent.”

Iain Burn, Northumbrian Water Project Manager, said: “Technocover worked with MWHC to deliver a cost-effective, high quality solution which answered the range of health and safety, and security issues associated with the pump chamber covers.

“We have also appreciated the value-adding aspects of Technocover’s service, including installation by their own accredited fitters and quality assured corrosion-proofing carried out on their own post-galvanising facilities.”

In its sub-contractor role, Technocover undertakes all the required risk assessment, method statement and sequence of works documentation covering personnel, procedures and vehicles accessing the site.

With space at the site limited, Technocover’s site service team needed to consider the logistics and health and safety of operating the company’s vehicle- mounted Hiab on site.

MWHC staff removed the existing covers, frames and beams using a 6m long A- Frame, and made good the chamber walls. For safety purposes, MWHC filled the entire open chamber with air bags prior to Technocover arriving and fenced off the working area.

Technocover installed and commissioned the new access system, together with handrails, steps and platform, within three days. MWHC completed the three concrete pads on site to support the platform legs.

Other works at the pumping station have included installation of new MCC with variable speed drives, standby generator and general civil improvement works.




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