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Introduction

The materials used for constructing for the transportation of water have evolved over a very long period of time from the most basic ditches and stone channels in the years BC through hollowed out wooden logs to labour intensively constructed large scale brick sewers in Victorian times to the most modern of composite and manmade materials we see today.

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This page shows some of the more common materials seen today by CCTV surveyors during pipe inspections.

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Material Classes

Drainage materials are generally classed into two types, with two additional sub types:

• Modular - sewer conduits that are constructed from small building blocks without any discrete joints, like brick sewers.

• Piped - sewers and drains that are constructed from discrete jointed manufactured pipes:

  • Rigid pipes - pipes that have no capacity to bend when stressed under load, they just break.

  • Flexible Pipes - pipes that can absorb a degree of deformation without any loss of structural integrity because of their design and manufacturing process.

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Modular Sewer Construction

Modular sewers, usually referred to as ‘Brick’ or ‘Masonry’ are constructed using building blocks and mortar and are always rigid, but there is a distinct difference between the materials ‘Brick’ and ‘Masonry’ although the construction methods are basically the same:

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Where there is no option in a material list for tiled constructions, we would use ‘Other’ with a comment. Here, the sewer is constructed from manufactured interlocking clay tile segments creating a smooth internal surface that is hard wearing. If you look in the distance, you can see the design of the tiles where the sewer has failed and there were often two layers of interlocking tile skins in the construction.

Piped Sewer Construction

As written previously, piped sewers are usually sub divided into rigid and flexible groups where there are advantages and disadvantages of both:

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• Lack of flexibility, so any local ground movement cannot be absorbed by the pipe joint, and the pipe simply breaks and cracks either side of the joint which in itself is a large immovable object under the ground.

• Disintegration and loss of seal - when these pipes were laid maybe 100 years ago, society did not have the cleaning products that we have nowadays, most of which are advertised on our TVs as being able to effortlessly remove limescale from our kitchen worktops and bathroom basins. This feature of these products, which we just tip away down the plughole also dissolve away the lime in the mortar joints in the sewers, leading to joint failures and leakage both in and out of the sewer.

Flexible and Rigid Pipes

As mentioned, pipes can be sub divided into flexible and rigid materials. Generally speaking, it is easier to define which pipes are flexible materials, and therefor by deduction, if it is not flexible, it must be rigid.

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As far as the metals are concerned, there are two distinct properties of metals that come into play here - is the material malleable or brittle? These are terms used to describe the properties of the material, and materials like steel are malleable, which means that they will bend under load, even if it is very hard to actually do it, so it is a flexible material. On the other hand, cast iron is rigid. It does not bend, it just breaks, in the same way that concrete and clay do, but again, it is extremely difficult to actually do this in real life.

Clay Pipes (Rigid)

Clay pipes are always rigid have been around for a very long time in sewer construction due to their hard wearing and smooth surface properties. Most clay pipes nowadays are plain ended with plastic jointing collars and neoprene seals whereas older clay pipes were usually socket and spigot pipes with tarred yarn and lime mortar joints.

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The word ‘Vitrified’ means glasslike, so by definition, ‘Vitrified Clay’ has been glazed and has a shiny surface. Not all clay pipes are glazed, in fact most modern clay pipes are not glazed, so the word ‘Vitrified’ should be used carefully. Additionally, ‘Salt Glazed’ clay pipes and Sometimes vitrified clay pipes are not the same thing. 'Salt Glazed pipes are extremely rare but very attractive to look at. These are very old pipes where salt was used in the glazing process to give a white surface to the pipealso referred to as ‘Salt Glazed’ pipes due to the Sodium that is used in the glaze to create the clear glasslike finish.

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Vitrified Clay Products

Notice in all of the three pictures above that the clay has a shiny surface - this is vitrified clay. The last image is not even a sewer pipe at all, it is actually a roof tile, but the material is the same as is used in drains, and the photo nicely shows the glazed finish.

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These are the modern version of clay pipes that have plain ends, plastic collars and are not vitrified. The pipe material has no glazing at all and is just bare clay. Still very hard wearing and great for sewers. Notice the pipes in the 2nd picture that have perforations (or holes) in the sides. These are often seen in surface water drainage systems where the holes are either used to allow water to enter the pipe from the surrounding ground or are used to allow flooded water from the pipe to soak away into the surrounding ground.

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Salt White Glazed Clay

Often Sometimes seen in drains around luxury town houses in the old parts of cities, where the drainage system is extremely old, and are often still working just great. See the white clay work of the drainage channels in this chamber, and even the tiles making up the benching (thanks to Sam Bean for this photo).

Common structural problems with clay pipes usually revolve around cracks, fractures, joints and breaks due to the very nature of the joints and the material itself. If you try to deform a clay pipe by even 5%, then it will not bend, it will fracture and break.

Concrete Pipes (Rigid)

Concrete is usually used for larger diameter sewers from 300mm dia upwards to almost any conceivable size. Concrete pipes can be:

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In a CCTV inspection report, this pipe should be labelled as cast iron with a spray coated lining inserted during manufacture.

Cast Iron Pipes (Rigid)

Cast Iron has been around in drainage pipes as a material for a very long time, and is used both above and below ground.

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In the last photo here, we see a cast iron and a steel pipe side-by-side. We know this because the appearance of the surface of the left pipe.

Mixed Materials

Most global drainage inspection standards offer the CCTV inspector to select the option ‘Mixed’ material from a list. This is where the sewer is made from more than one material and descriptions of the materials should be entered into the inspection remarks field.

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Here, the sides of the culvert are constructed from unit blocks (Regular Course Masonry) and the Crown of the pipe (the top) is built from bricks.

Polyvinyl Chloride PVC (Flexible)

Plastic pipes by their very nature can accept an element of deformation and bending without any loss of their structure, provided that they are well laid in good bedding as defined by the pipe manufacturers. The general rule of thumb with plastic pipes is that they can accept 6% of deformation without any loss of strength. One thing for sure with plastic deformation is that when it is deformed significantly, it loses its colour and turns white - try taking a piece of PVC from any product at home and bending it in half if you can - see the colour disappear from the product along its bend crease.

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Purple PVC Pipe with Socket & Spigot Joints

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Multi-coloured PVC Pipe

Polyethylene Pipe (Flexible)

Polyethylene (or PE) pipes are most commonly seen in highways drainage. They offer greater safe deformation extents than PVC, but there is a still a designed limit to how much they can deform with any loss of structure.

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Polyethylene is often referred to as low, medium and high density (LDPE, MDPE and HDPE). The twin wall pipe you see here are low density polyethylene. High density PE is impossible to tell apart from Polypropylene (below) and looks and feels the same. Only advice from the installer or the designer can help with telling these apart.

Polypropylene Pipes (Flexible)

Polypropylene is a thick-walled plastic that is very smooth and is almost waxy to the touch. It most often comes as plain ended pipes which can be butt-fusion welded together onsite making a watertight and almost seamless joint, notwithstanding welding defects.

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In the last image, we see a very long single length of either Polypropylene or High Density Polyethylene pipe on a pipe coil trailer as would be delivered to site, where the pipe can be dragged straight off the trailer and into the ground by a pipe bursting machine. A great pipe rehabilitation technique where there are no connections in the original sewer.

Pitch Fibre (Flexible)

Pitch Fibre pipe, also known as Orangeburg in the USA after one of the major manufacturers was a manmade pipe popular from the 1950s to the 1970s. It is a processed product containing a mix of fibres (often asbestos) and a pitch tar. The result was a pipe that was cheap to manufacture, easy to handle and install because it was lightweight and was supplied in long lengths (usually 5m) so could be installed quickly.

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Pitch Fibre pipe is not normally seen in pipe over 15omm (6”) diameter in the UK.

Glass Reinforced Plastic (Flexible)

Glass Reinforced Plastic, also commonly known as GRP, FRP (Fibre Reinforced Plastic) or just Fibre Glass is a chemically mixed resin base around a fibre structural matrix. It’s the same stuff that boat hulls and touring caravans are made from amongst other things.

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Circular and Egg-shaped GRP Components

Lined Pipes

As has been mentioned previously, care should always be taken in CCTV inspection reports when recording or observing linings. As we have seen already, it is possible to have pipes manufactured at the factory with a lining already inside it, and it is also possible to insert a new lining into an existing pipe.

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