Specific Cases

Chemicals in effluents and contaminated ground

Technical note for Vitrified Clay Pipes – number 8 deals with the ability of clay pipes and fittings to resist chemicals in effluents and contaminated ground.

Operational Performance

Clay pipes have long been the preferred option in a broad range of aggressive conditions and can carry all effluents acceptable to sewage treatment plants.

Clay pipes themselves are resistant to most chemicals with the exception of hydrofluoric acid (HF). Any limitation of the system with respect to chemical resistance relates to the flexible joint materials.

In service too, the clay pipe has excellent resistance to abrasion and is unaffected by pipe-cleaning operations, particularly rodding and high-pressure jetting, which may curtail the operational life of other materials. Clay pipes withstand more than 7500 psi of jetting pressure; more than treble many flexible pipe materials.

There are documented instances of rodent damage to flexible pipelines. As a rigid material, clay has no vulnerability to rodent attack.

Various materials are offered by the clay pipe manufacturers. Standard SBR sealing rings are capable of carrying effluent within the pH range 3 to 11 at normal ambient temperatures. Surges of pH outside these limits can be accommodated so long as the line is subsequently flushed with water or aqueous waste within these limits.

Alternative sealing rings are widely available which have a high inherent chemical resistance to a much wider range of chemicals. Nitrile rings are particularly suitable for applications involving oil and petrol type contamination whilst EPDM rings are for more general chemical conditions and applications involving high temperatures and are resistant to damage from effluents and groundwater over the pH range 2-12. Regardless of which seal is used, caution should be exercised if there is to be any discharge of organic solvents, since these will adversely affect the rubber.

In the UK manufacturers’ “sleeve” systems, the sealing ring is housed in a polypropylene coupling socket. This material has a very high order of chemical resistance.

Clay pipes are ideally suited for applications involving contact with contaminated ground. The same considerations with respect to the joint apply but additional precautions sometimes need to be taken. This can be surrounding the line with imported uncontaminated fill and in extreme cases wrapping the pipe joints with a suitable barrier material. In sulphate bearing ground, clay pipes with standard joints are appropriate.

Because clay drainage is able to withstand such aggressive conditions supplemented by special seals as appropriate, it is eminently suitable for use on reclaimed industrial or commercial development sites.

Clay pipes are also the ideal choice for systems prone to septicity and are unaffected by the effects of hydrogen sulphide built up.

The evaluation of effluents and selection of appropriate pipe materials can be complex and difficult. Guidance on the resistance of materials to various chemicals is available in CPDA Technical Note Number 8 and in the table below. It is important that careful consideration is given not only to the constituents and their concentrations, but also to the temperature, rate of discharge and hydraulics of flow.

Further help and advice on the performance of clay pipe systems and their resistance to chemicals found in effluents and groundwaters can be obtained by contacting the Technical Advisory Service of the various UK manufacturers. In extremely aggressive/corrosive environments such as the chemical/process industries, Naylor’s Thermachem pipe – a fully chemically resistant ceramic system – may be required.

A = normally suitable
E = need expert advice, each case to be considered on its own merits
S = specially suitable
Note: It is important to take account of quantities and concentration of all types of chemical likely to be encountered

Earthquake Zones

Reviews of the performance of clay pipe systems in earthquake zones in Asia and the Americas have identified that modern flexibly jointed clay systems have performed well in the face of ground movement. In such zones, the use of shorter length pipes (e.g. 1m) is recommended.

For advice regarding other Specific Cases please contact the technical department of one of the CPDA members.