Materials of Sewer

Brick • Used particularly for large diameter

sewers

• Advantage-

– Can be constructed to any required shape and size

• Disadvantage-

– higher cost

– Slow work progress

– Larger space requirement

• Cement concrete or stone invert

• To prevent ground water infiltration:

– plaster outside surface with mortar using sulphate resistant cement

– inside surface mortar + high alumina cement (IS 6452) or polyurea coating.

Concrete • Advantages

– Relative ease with which required strength may be provided

– Wide range of pipe sizes

– Rapid trench backfill

• Disadvantages

– crown corrosion by sulphide gas

– mid depth water line corrosion by sulphate

– outside deterioration by sulphate from soil water

Precast concrete • Commonly used for branch and main sewers

• Two types

– Non-pressure pipes

• used for gravity flow (sewers running partially full)

• Plain (I.D. 80mm-450mm; thickness: 25mm-35mm) (NP1)

• Reinforced (I.D. 80mm-2600mm; thickness: 25mm-215mm) (NP2, NP3 & NP4)

– Pressure pipes (P1, P2 & P3)

• used for force mains, submerged outfalls, inverted siphons and for gravity sewers where absolute water-tight joints are required.

• Reinforced (I.D. 80mm-1200mm; thickness: 25mm-120mm)

• Length : 2-3m

• These pipes have plain ends or spigot and socket ends.

Cast-in-situ Reinforced Concrete

• constructed where they are more economical

• when non-standard sections are required

• when a special shape is required

• when the headroom and working space are limited.

Stoneware or Vitrified Clay • normally available in lengths of 90 cm

• Skilled labour required for caulking the joints with yarn soaked in cement mortar and packing in the spigot and socket joints

• Classes

– AA: 100% hydraulic testing of pipes to be carried out in manufacturing stage

– A: 5% of the pipes to be tested by following IS 651

• Resistant to most acids and to erosion due to grit and high velocities

• A minimum crushing strength of 1,600 kg/m is adopted for all sizes

• Special bedding or concrete cradling required to improve field supportive strength

Asbestos Cement • usually used in sizes ranging from 80 mm to 1000 mm

in diameter

• Advantages

– Non corrosiveness to most natural soil conditions,

– freedom from electrolytic corrosion,

– good flow characteristics,

– light weight,

– ease in cutting, drilling, threading and fitting with specials,

– allowance of greater deflection up to 12 degrees with mechanical joints,

– ease of handling,

– tight joints and

– quick laying and backfilling are to be considered

• Disadvantages

– subject to corrosion by acids, highly septic sewage and by highly acidic or high sulphate soils

– Cannot stand high super imposed loads and may be broken easily

Cast Iron • Available in diameters from 80 mm to 1050 mm

and are covered with protective coatings

• supplied in 3.66 m and 5.5 m lengths

• A variety of joints are available including socket, spigot, and flanged joints.

• Classified as LA, A and B according to their thickness. Class LA pipes have been taken as the basis for evolving the series of pipes.

• Application: Cast iron pipes with a variety of jointing methods are used for pressure sewers, sewers above ground surface, submerged outfalls, piping in sewage treatment plants and occasionally on gravity sewers where absolutely water-tight joints are essential or where special considerations require their use.

• Advantage: long laying lengths with tight joints, ability when properly designed to withstand relatively high internal pressure and external loads and corrosion resistance in most natural soils.

• Disadvantage:

– corrosion by acids or highly septic sewage and acidic soils

– the amount of deflection allowed should not normally exceed 2.5 degrees for lead caulked joints.

• Inside coating shall be by Cement mortar and outer coating shall be coal tar

Steel • Pressure sewer mains, under water river

crossings, bridge crossings, necessary connections for pumping stations, self-supporting spans, railway crossing and penstocks are some of the situations where steel pipes are preferred

• Advantages

– withstand internal pressure, impact load and vibrations much better than CI pipe.

– more ductile and withstand water hammer better.

• Disadvantage

– cannot withstand high external load

– main is likely to collapse when it is subjected to negative pressure

– susceptible to various types of corrosion

• Inside coating by high alumina cement mortar or polyurea and outside by epoxy.

• Steel pipes shall conform to IS 3589. Electrically welded steel pipes of 200 mm to 2,000 mm diameter should conform to IS 5822.

Ductile Iron Pipes • made by a metallurgical process, which involves

the addition of magnesium into molten iron of low sulphur content.

• The ductile iron pipes are usually provided with cement mortar lining at the factory by centrifugal process to ensure a uniform thickness throughout its length

• available in the range of 80 mm to 1000 mm diameter, in lengths of 5.5 to 6 m

• Advantages

– excellent properties of machinability,

– impact resistance,

– high wear and tear resistance,

– high tensile strength and ductility and

– corrosion resistance.

– strong, both inner and outer surfaces are smooth,

– These pipes are approximately 30 % lighter than conventional cast iron pipes

Non-Metallic Non-Concrete Synthetic Material Pipes

UPVC Pipe (unplasticized polyvinylchloride )

• Advantages

– resistance to corrosion,

– light weight for transportation,

– toughness, rigidity,

– economical in laying, jointing, and maintenance and

– easy to fabricate

• IS 15328 deals with non-pressure unplasticized polyvinylchloride (PVC) for use in underground sewerage system. IS 9271 deals with the unplasticized polyvinyl chloride (UPVC) single wall corrugated pipes for drainage.

High Density Polyethylene (HDPE) Pipes

• Advantages – Offer smooth interior

surfaces and

– relatively higher resistance to corrosion

– they are available in solid wall

– When laid in straight gradients without humps or depressions, they can easily offer longer life cycle

• joints are usually fusion welded or flange jointed depending on straight runs or fittings

Structured Wall Piping

• These pipes can be manufactured in PVC-U, PP and PE as per EN 13476-3 / IS 16098

• These pipes are either double walled or ribbed walled

• The Type B pipes are generally known as Double Walled Corrugated (DWC) pipes.

• In India, DWC pipes are produced in sizes 75 mm ID to 1,000 mm ID with a standard length of 6 m for easy transportation and handling and to reduce the number of joints required.

Glass Fibre Reinforced Plastic Pipes (GRP)

• widely used in countries where corrosion resistant pipes are required at reasonable costs

• GRP can be used as a lining material for conventional pipes which are subject to corrosion.

• Fibre glass can resist external and internal corrosion whether the corrosion mechanism is galvanic or chemical in nature.

Fibre Glass Reinforced Plastic Pipes (FRP) • FRP is a matrix or composite of

glass fibre, polyester resin and filters.

• These pipes possess better strength, durability, high tensile strength, low density and are highly corrosion resistant.

• Fibre-glass pressure pipes are manufactured in diameters up to 2,400 mm and length up to 18 m.

Pitch Fibre Pipes • These are pitch impregnated fibre pipes

• Advantages

– light in weight

– Durable

– pipes can be easily jointed in any weather condition as internally tapered couplings join the pipes without the use of jointing compound

– flexible,

– resistant to heat, freezing and thawing and earth currents, which cause electrolytic action.

– unaffected by acids and other chemicals, water softeners, sewer gases, oils and greases and laundry detergents.

– can be cut to required length on the site

• Application

– septic tanks and house connection to sewers, farm drainage, down pipes, storm drains, industrial waste drainage

• Available sizes: 50 to 225 mm nominal diameter and length varying from 1.5 to 3.5 m

• Disadvantage

– susceptible to the delamination of their inner surface (blistering)

– susceptible to collapse under applied loading sooner than other pipes

Sewer material and corresponding standard specification

Material Standard specification Code

Brick (Inside plaster with mortar using high alumina cement )

IS 6452

Concrete

Pre-cast concrete (Non-Pressure pipes) IS 458

Cast in-situ reinforced concrete (Concrete ) IS 456

Stoneware or vitrified clay (hydraulic testing) IS 651

Asbestos cement IS 6908

Cast Iron IS 1536 (spun pipe) and IS 1537 (vertically cast pipe)

Steel IS 3589

DI pipes IS 8329 (centrifugally cast DI pipes); manufactured

with ISO 9002 accreditation ; IS 9523 (DI fittings);

UPVC IS 15328 ( Non-pressurized); IS 9271 (single walled corrugated pipe for drainage)

HDPE IS 14333

Structured wall pipe EN 13476-3 / IS 16098

GRP IS 14402

FRP -

Pitch Fibre Pipe IS 11925

Crown corrosion

With gradual deposition of organic and inorganic matter at the bottom of the sewer, the flow of sewage in lower layers become stale leading to anaerobic conditions favourable for Sulphate Reducing Bacteria which converts sulphate to H2S as shown. Thiobacillus thioxidans convert H2S to H2SO4. The suphuric acid deposited at the crown of sewer reacts with concrete and forms CaSO4. Which falls down as droplets making the crown of sewer uneven and thinner. This phenomenon is known as crown corrosion.