Cast iron pipes used in sewer networks continue to be relevant material. Despite the high competition of plastic, reliable pipelines designed for the long-term service are constructed from cast-iron products. They have both strengths and weaknesses that are worth exploring. Do you agree?
We will talk about which cast-iron pipes for external sewage are ideally suited and which are used exclusively in laying the internal system. In our article, we present the features of marking, describe the types of joints in the assembly of cast-iron communications. Alternatives are also listed.
High Strength Cast Iron Pipe
Design decisions to reduce pig iron in sewer networks are traditionally driven by economic considerations. As for reliability and durability - there are simply no materials equal to a cast-iron pipe.
Products made of ductile iron are widely used in the field of engineering, water supply, water disposal, as well as in the field of gas and oil production.
Image Gallery
Photo from
Cast iron pipes and flange fittings
Cast iron pipes of various diameters
Performance enhancement
Significant disadvantage - heavy pipe weight
Sewerage device for a country house
Pressure sewer collector assembly
Cast Iron Pipe Production Process
Cast iron pipe internal drainage
A significant proportion of this production is made up of cast iron high-strength pipes.
Their operational properties, in comparison with conventional pipes, are supplemented by the following mechanical characteristics:
- high degree of impact strength;
- low yield strength;
- low temporary resistance;
- low coefficient of elongation.
Obtaining such characteristics was achieved through the introduction of spheroidal (or lamellar) graphite into the structure of cast iron.
In other words, the metal structure is saturated with a significant amount of carbon, which in practical terms adds to the final products such properties as:
- wear resistance;
- compressive strength;
- fatigue strength;
- ease of machining;
- good casting qualities.
High-strength cast-iron pipes are mentioned for a reason. The implementation of external sewage projects usually involves the construction of drainage lines from structures with their laying under the thickness of the soil. Such a sewage system is classified by the abbreviation TML.
The operation of sewage lines underground, as a rule, is characterized by increased physical and thermal loads, which are easily handled by high-strength cast-iron pipes. The depth of the laying of sewer pipes in the ground is regulated by building codes.
Pipe classification by design
For sewer cast-iron pipes of the TML classification, there is a conditional division of them into two types according to their functional properties:
- Socketless (SML).
- Bell-shaped (SME).
The first are distinguished by the fact that they are structurally executed as exceptionally smooth elements from beginning to end along the entire length. The second, on the other hand, has a bell slightly widened in diameter at one end.
Pipes made of cast iron, made under the drainage systems of buildings, produce different in design. The most commonly used in practice are socketless and bell-shaped cast-iron pipes
Socketless cast-iron pipes are considered to be the best option for installing outdoor sewage systems that are classified as TML systems. Pipes of the SML type provide more convenience in laying conditions, and allow easy and quick dismantling if necessary.
Both types of pipes are available with a nominal size of inner diameter of 100 mm, while the size of the outer diameter is 110 mm. As a rule, the nominal and any other size of the diameter is indicated by a marking (for example - DN100).
Frequently practiced diameters of cast-iron pipes (bell-shaped and bell-less) are in the range of 100 - 400 mm. In general, this range covers diameters up to 1000 mm. The standard length is 3000 mm.
Socketless pipe made on the basis of plate cast iron and included in the SML classification group, as well as fittings necessary for the full installation of drainage systems
There are also products that belong to other classification groups. For example, SMU classification products are functionally designed for building drainage systems and drainage systems.
There are pipes for the transportation of chemical aggressive media. They are classified by MLK. And cast iron products under the MLB classifier are suitable for drainage systems on roads and bridges.
Features of the design and composition used when casting iron pipes are indicated in the marking:
Image Gallery
Photo from
Ductile iron pipe
Long cast iron products of the PRC
Sewerage construction from the pipes of the Cheka
SML pipes for external and internal lines
How to connect pipes SML and SME?
Cast-iron-free sewer pipes made of cast iron are connected to one another using special tightening fixing devices. These connecting elements consist of a steel tightening collar and an elastic sleeve, which is applied to the joint area.
In practice, two modifications of the steel clamp screed are used - one screw (CE) or two screws (CV). The material of the elastic coupling provides high quality tightness, and the properties of the steel tightening ring exclude the appearance of corrosion.
Metal clamps and couplings, supplemented with elastic inserts, are usually used to connect the socketless cast-iron pipes to each other. There are several modifications of such fasteners
Connecting clamps are used not only for connecting individual pipes in the construction of the pipeline. The same components are used for joints with fittings.
Clamps are manufactured for various mounting diameters and are designed for the entire range of operating pressures. There are modifications of clamps with the effect of sound absorption used in the silent sewer device. Their installation does not require the use of additional sound insulation in the places of passage of pipelines through the ceiling.
Image Gallery
Photo from
Use of clamps and fittings
Sewer system in the basement
Sewer system assembly options
Laying on thermal insulation and between insulation plates
Bell-shaped elements are connected by the principle of inserting a flat end of one pipe into the bell-shaped part of another. The softness of the connection and the tightness, as a rule, is ensured by a rubber ring, which is pressed into the groove on the inner surface of the socket of the cast-iron pipe.
There is also a scheme where the tightness of the connection in the socket (and softness) is achieved by filling the gap between the pipes with sealing material.
The practice of constructing sewage systems based on cast-iron pipes made of cast iron involves the use of one of five connection options (A, B, C, D, D). Four of them with gaskets in the form of rubber rings (5, 6) and one in the form of tarred tow (3)
For bell-shaped elements, the following types of sealing and fixing of joints are characteristic:
- Chasing asbestos cement filler.
- Installation of a sealing cuff.
- Installation of a self-sealing ring.
- Use of bolt-on union flange.
- The use of a thorn tenon.
The method of fixing the pipe joint using hot and cold welding is also practiced, but it is used extremely rarely. This is explained by the complexity of cast iron welding technology. In addition, for the welding of cast iron, specialists, professional welding tools and expensive nickel-based electrodes are required.
The article, which details all the arguments and discusses the characteristics of various types, will familiarize you with the features of choosing pipes for the construction of an internal sewer system.
Features of the structure and application
The main feature of cast-iron pipes from the TML classifier group is its purpose for installation underground under a depth of 0.8 to 6 meters. Created specifically as elements of external TML systems, the pipes are characterized by an increased degree of strength and corrosion protection.
The operational parameters of the compressive resistance allow sewer lines to be laid without fear of damage, for example, under a roadway with heavy weight loads. But during installation, it is required to comply with DIN EN 877, 1610, GOST standards, which provide for the creation of an appropriate supporting foundation and floors.
The structure of a modern socketless pipe made of cast iron consists of a two-layer internal coating with epoxy resin (1), an external coating with epoxy varnish (2), a working layer of cast iron with lamellar or spheroidal graphite (3), a protective coating with zinc (4)
Among the features of high-strength cast-iron pipes, the presence of an effective coating (external and internal), including on shaped parts, should also be highlighted. The coating is carried out with the introduction of zinc and epoxy resins, which ensures high reliability of corrosion protection even in pronouncedly aggressive environments.
These pipes can be successfully used for laying in soils with high pH (0-10). The inner lacquered epoxy coating of cast iron sewer pipes has a smooth (sliding) structure, which minimizes the drag coefficient during the movement of effluents.
The structure of modern cast iron pipe TML:
- Coating with a modified epoxy resin in two layers (layer thickness 120 μm).
- Protective coating with epoxy varnish (layer thickness 60 μm).
- High carbon cast iron base layer.
- Protective coating with zinc powder (spray density 130 g / m2).
The standard pipe length (3000 mm) can be easily shortened to the required size if necessary, for example, with an electric pipe cutter. When trimming a cast-iron pipe, it is necessary to ensure an accurate even cut. This approach guarantees the reliability of sealing during the assembly of sewage lines.
In addition, the edges of the cut, as a rule, are painted with special paint and coated with insulation tape type Pro-Cut. For aggressive environments, special seals are used. These measures further increase and negate the risks of leaks.
In this way, a connecting unit is created on the edge of the cut-off cast-iron pipe when a Pro-Cut insulation tape is used as a protective and sealing element.
The list of features of cast-iron sewer pipes is impressive. Compared to the same polymer products, which are rapidly gaining popularity due to their low cost, cast iron products have many advantages.
A fire-iron and high temperatures are not afraid of a cast iron, while plastic pipes soften already at T = 100º, and at higher temperatures they begin to deform and can melt.
Cast iron pipelines are characterized by low noise during the operation of the system and do not require the installation of expansion joints for expansion. They can be laid in the thickness of concrete without fear of rupture from compression / expansion of materials.
Thus, the acquisition costs will very soon be offset by the economical use of cast iron pipes. Their application does not require the creation of fire and noise insulation, the overhaul period is several times higher than the same period for plastic communications. The duration of operation is not limited even to a 100-year period.
Pre-insulated products
The cast iron products of the TML classifier complement the products, which are pre-insulated cast iron pipes. Such modifications are successfully applied in environmental conditions with low temperature values.
In fact, these are the same socketless or bell-shaped pipes of high strength (1), additionally coated with technological layers (2, 3, 4) of thermal insulation.
A variant of a socketless cast-iron pipe, supplemented by a thermal insulation element. Products in this design are called "pre-insulated pipes." They are designed for use in low ambient temperatures.
As an effective heat insulator, thermosetting foam (3) or a similar material with a dense structure and incombustibility properties of the A2 class is used. The heat insulator is closed by a casing of sheet galvanized steel (4). The thickness of the casing sheet is at least 1 mm. The casing is fixed with clamps (2), also made of galvanized steel.
Pre-insulated cast iron pipes are designed for operation in humidity conditions up to 75%. Insulation prevents condensation at low and critically low temperatures. There are modifications with the introduction of a heating cable directly into the structure of the heat insulator.
Reasons to replace cast iron with polymers
What is the reason for the growing popularity of polymer products, which seek to replace cast iron?
As it turns out, the main reasons are:
- risks of cast iron corrosion from damage by stray currents of electromagnetic fields;
- lack of additional protection of the inner walls of the pipes from aggressive environments;
- the rigidity of the products, positively affecting a single pipe, but provoking a shift in the total soil loads to the joints at a pipeline assembled from a dozen or more pipes;
- technical difficulties that inevitably arise during the repair process or in case of the creation of new communication inserts.
Polymer pipes are much more often than cast iron pipes used to create autonomous sewage systems in private homes.
You will learn about which pipes are best used in the construction of the outer part of the sewer system in a suburban area from the next article devoted to this difficult issue.
Some useful tips about choosing pipes will be useful for creating DIY sewage systems:
Meanwhile, polymer products are inferior in technical and operational terms to products made of cast iron. They have significantly more disadvantages compared to cast-iron sewer pipes.
It is convenient and rational to use polymers in domestic sewage systems, but for serious external communications it is reasonable to use cast iron from any point of view.
Do you have useful information on the device of external sewage made of cast-iron pipes? Want to talk about how you built the system on your site? Please write comments in the block below, post a photo on the topic of the article, ask questions.