Sewer pipe systems: Types, materials and selection

Buried underground, sewer pipes are largely invisible; however, they play a critical role in maintaining public health and protecting the environment. By safely transporting wastewater from homes, industrial facilities and commercial settings to municipal sewage systems and treatment plants, sewer networks prevent water contamination and the spread of diseases.

However, selecting the right sewer for each project is far from simple. Numerous factors, such as site conditions, network capacity, installation considerations, costs and regulatory standards, must be evaluated. This article explores the most common sewer types and materials, including pipe systems for aggressive wastewater, challenging topography, high traffic loads, and/or demanding environmental conditions.

_{What are the types of sewer pipes?}

Sewers are made from various materials, each with its own advantages and disadvantages. However, all underground sewer pipe systems can be grouped into two main categories: gravity and pressure sewers.

• Gravity sewers rely on a natural downhill slope to carry wastewater and do not need external power. Gravity sewer setups typically require more excavation and deeper trenches to achieve the required gradient. Regular access points, such as manholes or inspection chambers, must be planned to meet maintenance needs. Gravity systems are used widely as they offer a long lifespan, low operational costs and a relatively simple design.
• Pressure sewers rely on pumps to transport wastewater; thus, smaller-diameter pipes and shallower trenches can be used. Pressure systems can be installed independently of topography, including in flat and uphill terrain, and are suited for areas where extensive excavation is not possible or feasible. However, such systems require highly resistant components to ensure reliable performance; they also have higher ongoing maintenance costs due to pump operation. Nowadays, smart pumping stations are used to monitor and optimize pressure system performance and promptly address potential issues.
• Hybrid sewage systems can be designed to address specific conditions. For example, pumps may be added in areas with higher elevation or obstacles to connect sections of a gravity sewer system.

_{How to choose the best sewer pipe?}

There is no single best sewer type or material, and the product selection should always be based on project-specific criteria.

_{Hydraulic capacity}

The pipe diameter and laid slope must accommodate expected wastewater volumes and peak flows without surcharging.

Gravity systems are typically installed at ~2% slope; however, lower inclines can be used with larger sewer diameters. If the slope is too flat, wastewater moves too slowly, causing solid waste to settle in the pipe. If the slope is too steep, water flows too quickly, leaving solid waste behind, which can also lead to clogging.

The kind of sewer system also matters:

• Sanitary sewers carry wastewater only (blackwater and greywater); therefore, smaller diameters can be used.
• Combined sewers carry both sewage and stormwater within the same system, requiring higher system capacity and larger pipes to minimize overflow risks. Nowadays, special overflow systems are often added to manage periods of heavy rainfall. 

Pipe systems with smooth interiors and expert hydraulic design ensure optimal performance, minimizing solids settling and blockage risks.

_{Durability and strength requirements}

The system's overall load-bearing capacity must meet project requirements and is determined by numerous factors: pipe material and dimensions, site conditions, load type, and even the jointing and installation method.

• The Nominal Stiffness (SN) rating indicates a plastic pipe's resistance to crushing or deformation under external load. The SN rating is used for gravity systems and is measured in kilonewtons per square meter (kN/m²). A higher number, such as SN 10 or SN 12, means the system is suitable for deeper burial and heavier traffic loads. A lower rating, such as SN 2, indicates suitability for light-load applications, such as home sewer connections or green areas.
• The Standard Dimension Ratio (SDR) rating indicates a plastic pipe's wall thickness relative to its outside diameter and must be considered for pressure systems. A lower figure, such as SDR 11, means a thicker wall and capacity of handling higher internal pressures. A higher SDR means a thinner wall and lower pressure resistance.

_{Corrosion and chemical resistance}

Pipes with high chemical and corrosion resistance are crucial for sewage systems installed in challenging environments — such as industrial sites, areas with high groundwater levels, stray currents, or saline or sulfate-rich soils.

Sewers transporting industrial wastewater must also be particularly resistant, as the solids may contain acids, salts, solvents, sulfur compounds and other substances that can rapidly corrode pipes. Sewage systems handling hot water are generally more vulnerable to degradation, as oxidants are more active at higher temperatures.

Plastic and vitrified clay pipes are highly chemically resistant. Materials like concrete or cast iron may require linings.

_{Site and installation factors}

Soil type, topography, and groundwater levels dictate flexibility requirements for sewer pipes and trench depth. For example, heavier, more brittle materials such as clay or cast iron may not be suitable for unstable, shifting soils, and HDPE systems are preferred in such areas.

Furthermore, the weight, length and flexibility of pipes, as well as their joint type, affect handling and overall installation time, which directly impacts labor costs.

_{Regulatory compliance}

Sewage systems must meet strict requirements to withstand expected loads and mechanical damage and ensure safe wastewater disposal. Such requirements may be defined at international, national or regional levels.

• The European standard EN ISO 11173:2017 specifies testing methods for external impacts on thermoplastic pipes, which are critical for assessing their overall resilience, especially under harsh conditions.
• Some countries have local standards or quality marks. For example, the Nordic Poly Mark system is used in Denmark, Finland, Norway and Sweden to certify plastic pipe systems for low-temperature climates.
• Area-specific plumbing codes and requirements may apply to projects in sensitive locations, such as valuable ecosystems, historic landmarks, critical infrastructure sites or hazardous-material zones.

_{Cost and lifecycle economics}

While it can be tempting to select the cheapest material, upfront costs should be carefully weighed against expected long-term expenses for maintenance and repairs. Wastewater solutions that offer a long service life and low maintenance requirements are usually more economical and sustainable in the long run. When installed correctly, quality sewer pipes should serve up to 100 years, requiring minimal maintenance.

The environmental footprint of sewer pipe systems can vary a lot and must be assessed by evaluating all lifecycle stages.

• An Environmental Product Declaration (EPD) is an objective, third-party verified document that provides transparent, comparable information about the environmental impact of products across their entire lifecycle — from raw material extraction to disposal. EPDs allow for comparisons between products with similar functions, enabling informed, sustainable purchasing decisions.

_{Common issues with sewer pipes}

Sewage systems from all materials can face a range of challenges that can impact their performance and lifespan.

Blockages are a common issue in underground plumbing systems. Older pipes with rough interior surfaces, such as cast iron or concrete, are more prone to scale and debris accumulation, which can restrict wastewater flow and cause backups. Clogging risks are also higher in sewage lines with a limited slope. In most extreme cases, so-called 'fatbergs' may form — large masses of solid waste creating dense obstructions that are costly to remove and increase the risk of overflows and contamination. Modern pipe systems have smooth interiors for optimized hydraulic performance, helping minimize the risk of blockages and reducing inspection and maintenance needs.

Cracks, fractures and leaking joints can result from factors such as ground settlement, heavy loads, or installation errors like insufficient bedding. Selecting a sewer pipe system certified to withstand the relevant mechanical loads and environmental conditions is crucial for uncompromised system performance — just like relying on experienced underground plumbing professionals.

Corrosion is a common issue affecting older sewage lines, for example, unlined cast iron pipes. As pipes corrode and deteriorate, cracks form over time, resulting in leaks and eventual system failure. Corrosion cannot be reversed; therefore, replacing or repairing damaged sections is necessary.

Pipe sagging or misalignments can occur in areas with shifting soils or poor bedding. Sagging slows wastewater movement through the system and increases clogging risks. In worst-case scenarios, joint separation may occur, leading to leaks. While minor sagging can sometimes be fixed with relining, replacing and/or rebedding affected sections is usually necessary.

Tree root intrusion — over time, roots can penetrate small cracks or joints in older sewage lines, especially if they are made from brittle materials like clay or cast iron, causing significant damage or even pipe failure. However, tree roots typically do not break intact pipes and are not a major issue with modern sewer systems.

_{Advantages of modern sewer pipe materials}

Choosing high-quality sewer pipe materials is vital for the longevity and reliability of external sewage systems. While historically concrete, clay and cast iron pipes were commonly used in wastewater networks, plumbers today increasingly favor modern materials, such as PVC, PP, HDPE or ABS, due to their long service life, lighter weight, excellent hydraulic properties and corrosion resistance.

Pipelife offers an extensive range of plastic sewage line solutions built to last, meeting the highest standards for modern underground infrastructure networks.

_{Pipe materials for pressure sewers}

HDPE pipes dominate modern pressure sewers, offering an optimal cost-performance ratio and a service life of at least 100 years. HDPE sewers are flexible and can withstand ground movement; they also have excellent chemical resistance. These systems handle surge pressures and extreme temperatures well, and their seamless, welded joints are virtually leak-proof.

• PE 80 and PE 100 pipes are the most common choice for modern pressure sewer systems.
• For particularly challenging applications, such as trenchless sliplining or pipe bursting, coated PE 100-RC systems are often used, as they offer additional protection against point loads and crack growth. 

_{Pipe materials for gravity sewer systems}

Gravity sewer lines can be made from various materials: from iron, clay and concrete to modern thermoplastic materials, such as PVC, PP and PE.

_{PVC pipes: Secure sealing in all weathers}

PVC is among the most popular materials for sewage lines. Compared to other types of plastic, PVC has lower carbon content and can have lower environmental footprint, especially if the raw material is produced with renewable energy (low-carbon PVC).

PVC pipes are lightweight, stiff and exhibit low thermal expansion. Their push-to-fit joints offer speedy installation, which is particularly valuable when working in harsh winter conditions.

• Pipelife's PVC Compact and Coex pipes stand out due to their innovative sewer-lock gasket technology. The design prevents groundwater infiltration and sewage exfiltration, which is essential in areas with high groundwater levels. The sewer-lock gaskets reduce the time and effort required to connect pipes while also minimizing the risk of displacement or damage during assembly. The Compact pipes have high ring stiffness and are available in SN 8 and SN 12 kN/m² classes, making them suitable for areas with heavy mechanical loads, including roads, parking lots and industrial zones. 
• For eco-conscious investments, Pipelife also offers pipes made from bio-attributed PVC based on a mass-balance concept. Manufactured from timber waste, the bio-attributed raw material reduces greenhouse gas emissions by more than 90% compared to conventionally produced PVC.

_{PP sewer pipes: A versatile solution for sewage and drainage}

Due to their durability, high tensile strength and resistance to chemicals and temperatures, polypropylene (PP) pipes are an excellent choice for wastewater systems. With push-to-fit jointing systems available, they are quick and easy to install and offer a service life of up to 100 years.

• PP pipe systems from pure polypropylene without mineral additives are lightweight yet highly resistant to chemical, biological and abrasive wear. They have smooth inner and outer surfaces, helping reduce debris accumulation, and they can be used as both sewer and drain pipes in a variety of applications, providing efficient drainage solutions for residential, commercial, and infrastructure projects. Pipelife’s PP systems are available in SN 8, SN 10, SN 12 and SN 16 kN/m² variants to be tailored to different ground conditions and load requirements.

_{Multi-layer PP pipes: Extra protection for demanding conditions}

Multi-layer PP systems have enhanced technical properties, making them suitable for demanding conditions, such as low cover depth, groundwater impacts and subzero installation temperatures.

• Pipelife's PP Master is a highly durable three-layer polypropylene pipe system meeting leading industry standards. Each layer serves a specific function: the hard outer layer is highly abrasion and impact-resistant; the core layer ensures excellent ring stiffness and longitudinal rigidity; the light-colored, ultra-smooth inner layer offers superior flow properties and facilitates camera inspections. The pipe’s sophisticated socket with a stabilization ring and increased sealing zone prevents accidental disconnection and leaks, ensuring safe and simple handling. PP Master is available in SN 10, SN 12, and SN 16 kN/m² classes.

_{Corrugated sewer pipe systems: Solution for high-traffic areas}

Corrugated sewer pipes feature a ribbed exterior and generally have a smooth interior. They are more flexible compared to smooth gravity sewers, which can be advantageous in certain installation scenarios, such as areas with unstable soils.

• Pipelife’s Pragma corrugated pipes are made from high-quality polypropylene block copolymer (PP-B) and designed for the most demanding applications year-round. These pipes feature a lightweight structural design with a smooth inner wall and a corrugated outer wall with a trapezoidal profile, ensuring exceptional impact resistance. The corrugated design provides excellent load-bearing capacity, making the Pragma system suited for heavily trafficked areas, including national roads, highways and airports. Pragma pipes are rated at SN 8, SN 10, SN 12 and SN 16 kN/m².

_{Can sewer pipes be made from recycled materials?}

Recycled plastics, such as PVC and PE, can be used in manufacturing sewer pipes for non-pressure applications. Furthermore, pipes with recycled content must meet the same application-specific performance and safety standards as those made from virgin materials but have a considerably lower environmental footprint.

• Pipelife Bulgaria manufactures Ecocorr sewage and drain pipes from 100% recycled PE, exceeding SN 4 class requirements. These lightweight corrugated pipes are favored for home wastewater systems, private road junctions, green areas and other lighter-load applications.
• Pipelife's Quantum PVC pipes contain a mid-layer from 100% recycled material. Their tri-extrusion manufacturing process ensures exceptional longitudinal and ring stiffness (SN 12 and SN 16 kN/m²), delivering uncompromised performance in highly demanding applications.

_{Sewer manholes and chambers}

Manholes and inspection chambers enable inspection, cleaning, ventilation and repairs of sewer lines. Due to their versatile design, they also serve as line junctions and help regulate wastewater flow by managing changes in elevation or direction. During heavy rain, manholes and chambers can temporarily hold extra water, reducing overflow risks.

• Manholes are larger-diameter chambers designed for human entry when maintenance or repairs are needed.
• Inspection chambers are smaller and enable rodding and camera inspections.

Pipelife PRO sewage manholes and chambers, made from PP-B thermoplastic material, are engineered to meet the highest durability and performance standards. These systems are safe to use in various soil and groundwater conditions. They withstand extreme temperature fluctuations while exhibiting outstanding impact resistance as per EN 13598 and EN ISO 13263 standards.

Even after 50 years of operation under a 5-meter water column pressure, base deformation remains significantly below the standard requirements, ensuring uncompromised sewage system functionality. Pipelife PRO manholes and chambers maintain their tightness under both overpressure (0.5 bar) and under pressure (-0.3 bar).

The modular design and a wide range of configurations of PRO manholes and chambers support seamless connections with pipes ranging from 110 mm to 400 mm in diameter, making the system versatile for both new installations and the rehabilitation of existing networks. 

_{Building reliable underground infrastructure}

Robust wastewater systems are fundamental to safeguarding public health, supporting sustainable urban development and protecting the environment. 

Understanding the common issues and strengths of different sewer pipe types is crucial for selecting the best system for each project — whether installing new sewage lines or replacing outdated ones. By choosing high-quality materials and working with professional contractors and plumbers, municipalities and property owners can count on the long-term reliability and efficiency of their wastewater networks.

Pipelife has developed a range of sewage solutions that offer durability, efficiency and reliable performance, even in the most demanding conditions. Across Europe, these features have made Pipelife's solutions a trusted choice for wastewater infrastructure projects. 

Note: Pipelife's infrastructure systems are sold in most European markets. For detailed information about the specific product systems available in your region, please contact your local Pipelife country organization.