Don't forget

8 January, 2010

After years of heavy use, sewers, drainage pipes, drains, manholes, chambers and other water and waste water retaining storage assets can become corroded and weakened. If they are not maintained it can lead to collapses, blockages and costly repairs. Such disruptions are frequently linked to badly maintained water and waste water assets.

A major enemy in sewers is Hydrogen Sulphide (H2s) which attacks concrete and mortar above the liquid level in pipes and chambers causing it to deteriorate and fail. H2s which naturally occurs within sewer silts, for example, can severely corrode both pipes and chambers actually eating into the concrete and mortar above the liquid flow levels.

When this problem is combined with production effluent it can be a recipe for disaster if allowed to continue unmonitored. The chemical cocktail within the effluent has a similar effect below the liquid level as the H2s does above, thus placing the entire system at risk. Therefore, it remains essential that all foul water or other aggressive waste transfer systems remain both functional and isolated (sealed). Infiltration of ground or surface water, for example, can lead to additional costs by increasing the volume of waste being treated. Exfiltration of waste liquid products can lead to environmental incidents if the waste finds its way into a water course, resulting in heavy fines from the Environment Agency for pollution.

To minimise any potential disruptions, it is important that water and waste water assets are inspected and effectively maintained on a regular basis. Monitoring and maintaining assets need not be costly when carried out in a proactive rather than reactive manner.

The need to investigate

Cleaning and inspection are the first steps that need to be taken in ascertaining the condition of any water or waste water asset. This can usually be carried out remotely using specialist CCTV and high pressure water jetting equipment. Suitably trained and experienced personnel need to be employed to view the resultant survey recordings and decide what, if any, actions may be required.

Methods

There are two main methods used for rehabilitating, renovating or repairing systems - man entry and non-man entry.

Man entry systems are carried out by operatives physically entering the assets to carry out the rehabilitation. Many man entry systems are identified as being type I linings.

A type I lining is where the lining and the existing sewer combine to act as a rigid composite section. To do this, a bond is required between the lining and the existing sewer. Examples of the materials used in type I linings are ferrocement, gunite, glass reinforced plastic and glass reinforced cement.

Some of these techniques are based upon the use of pre-cast components which then rely upon a grout around the annulus to transfer load between the new lining and the existing structure. This can have a significant disadvantage in sections of sewer where the existing structure varies in cross sectional area, meanders or both - not uncommon in older brick or stone built culverts.

Techniques such as in-situ ferrocement lining, from Ferro Monk, can offer a number of advantages. For example, the system is designed around a pre-cast invert, designed to be handled and grouted into position in order that it can normally accommodate dry weather flows. This can negate the need for expensive over pumping installations. The rest of the installation is carried out in-situ, with layers of mesh and sprayed ferrocement being applied and finished to the required thickness.

Non-man entry methods, often called ‘no dig technology’ or ‘trenchless technology’, are technically known as type II linings. This methodology employs remote techniques and equipment to carry out the necessary rehabilitations, renovations or repairs, carried out in most instances using existing accesses such as manholes.

Type II linings differ in that the lining is designed into a structural pipe within its own right and does not require a bond with the existing sewer.

A commonly used method is cured in place pipe lining (CIPP), a technique for full or part length, manhole to manhole relining of pipes and culverts. It uses resin impregnated polyester felt lining tubes to create a new pipe within the old, bridging gaps and holes in damaged pipes and sealing cracks. Even lateral connections can be reconnected into the newly lined pipes by using state of the art remotely controlled robotic cutting equipment.

Many systems are based upon the use of an epoxy impregnated medium, such as glass fibre matting, which is wrapped around an inflatable packer. The system is introduced into the sewer, positioned at the point of repair (allowing sufficient overlap into the defect-free host) and the packer inflated, pushing the patch against the pipe. Following cure, the packer is deflated and recovered for reuse.

Summary

Maintenance of water and waste water assets need not be costly if dealt with in both a timely and correct manner, however, it is essential to seek the advice from a specialist company. Identifying problems early can prevent major, often expensive disruption to business. Proactive planned inspections can be the key. Reactive action can often be too late when the unexpected flooding, pollution, collapse and stoppage of production has already happened.

Source: Energy Management