What are the common connection methods for KRAH pipe?

Main connection methods

Socket-and-spigot rubber ring connection

Advantages

Reliable sealing performance, adaptable to sewage media characteristics

The rubber sealing ring (made of EPDM) has excellent elasticity and corrosion resistance, tightly fitting the sealing surfaces of the socket and spigot. Under internal pipe water pressure or external soil pressure, the sealing ring is further compressed, enhancing the sealing effect and effectively preventing sewage leakage (especially municipal sewage containing suspended matter and corrosive components).

The sealing ring is highly compatible with HDPE pipe and is not susceptible to seal failure due to material aging. It maintains stable sealing performance over long-term use (typically ≥50 years). Installation is easy and requires minimal construction conditions.

The spigot-and-socket design requires no complex tools. Simply align the spigot with the socket and complete the connection by hoisting or manually pushing (for small and medium diameters). Verify the seal is in place. This makes it suitable for use in narrow trenches, muddy environments, and other locations with limited construction conditions.

Highly corrosion-resistant and with a long maintenance cycle.

The main body of the KRAH pipe is made of HDPE, while the spigot, spigot, and seal are all non-metallic. It is resistant to acids, alkalis, and corrosive media such as sulfides and chloride ions in sewage, and will not rust like metal pipes or metal fittings.

The absence of metal components in the joint eliminates the risk of electrochemical corrosion and reduces the frequency and cost of subsequent maintenance (such as replacing corroded fittings).

Disadvantages

Requires certain installation precision.

If the socket is not inserted deep enough into the socket, the sealing ring is installed crookedly, or the socket or socket is damaged by bumps, the sealing effect will be directly affected and may cause leakage. Due to the heavy weight of some large-diameter KRAH pipes (DN ≥ 1200), precise control of the lifting angle is required during connection, otherwise the sealing ring may be squeezed and deformed.

Not suitable for high-pressure piping systems.

Carat pipes are primarily used in gravity flow sewage and drainage projects (operating pressure is generally ≤ 0.1 MPa). The sealing ability of the spigot-and-socket rubber ring connection decreases with increasing internal pressure. If used in pressure flow pipelines (such as sewage risers), excessive internal pressure may cause the sealing ring to be squeezed out, posing a risk of leakage.

The spigot-and-socket rubber ring connection is the most cost-effective and mainstream connection method for KRAH pipes in municipal sewage and drainage projects. Its core advantages are reliable sealing, easy installation, strong flexibility, and low cost. It is suitable for most gravity flow, small and medium-sized pipes, and relatively stable foundation conditions. However, it should be noted that its weak pullout resistance makes it unsuitable for high-pressure or high-drop environments. If necessary, auxiliary measures such as anti-drop clamps should be used to ensure the long-term safety of the piping system.

Electric Fusion

Advantages

Adaptable in construction and suitable for complex environments

Low space requirements: Electric fusion requires no large-scale docking equipment, only a portable electric fusion welder. It can be operated in confined spaces (such as under urban roads and around buildings) or in areas with shallow burial depths. It is particularly suitable for the complex "construction and maintenance" scenarios of municipal engineering.

High tolerance for pipe roundness: Carat pipes may exhibit slight elliptical deformation during transportation or storage. The flexible design of electric fusion fittings can accommodate a certain degree of roundness deviation, reducing installation difficulties caused by pipe deformation.

Stable Corrosion Resistance: HDPE is inherently acid- and alkali-resistant and corrosion-resistant. Electric fusion does not damage the pipe's anti-corrosion coating, nor does it introduce corrosion risks from metal parts (such as bolts in flange connections) due to the connection method. It is suitable for environments with corrosive media such as acids, alkalis, and grease in municipal sewage. High construction efficiency and minimal ongoing maintenance. The electrofusion jointing process is standardized (clean the surface → install the fittings → weld with electricity). Unlike butt fusion, precise pipe alignment adjustments are not required, making it easy for workers with minimal training to operate. The construction time per joint is short (typically 10-30 minutes, increasing slightly with increasing pipe diameter). The joint quality is consistent, reducing the likelihood of repairs due to joint problems later, thus reducing municipal pipeline operation and maintenance costs.

Disadvantages

High cost and high initial investment. The manufacturing cost of electrofusion fittings (with built-in resistance wire) is significantly higher than that of standard fittings using rubber ring socket joints (especially for large-diameter pipes, where the cost difference can reach 30%-50%). Furthermore, a dedicated electrofusion welding machine (with stable voltage and programmable control) is required. The initial equipment investment is higher than the tools required for rubber ring joints (such as tensioners), which may pose a constraint for municipal projects with limited budgets. Repair is difficult and has a low tolerance for errors.

Electrofusion joints are permanent connections. If quality issues arise (such as incomplete penetration or over-melting), they cannot be disassembled and reinstalled like rubber ring joints. Instead, the damaged area must be cut and re-welded, which not only increases material loss but also potentially prolongs the construction period (especially when repairing backfilled pipes, which require a larger excavation area).

Limited applicability to large-diameter pipes

For large-diameter KRAH pipes (DN1200 and above), the manufacturing difficulty and cost of electric fusion fittings increase dramatically. Furthermore, welding requires longer heating times, which can lead to unstable joint quality due to uneven heat dissipation. Therefore, in large-diameter municipal sewage pipes, electric fusion joints are typically used only in specialized locations (such as bends and diameter changes), while main pipes are more often connected using butt fusion or rubber ring joints.

In municipal sewage and drainage pipes, the core advantages of KRAH pipe electric fusion joints are leak resistance, high strength, and adaptability to complex construction spaces. They are particularly suitable for applications with stringent sealing requirements (such as crossing water source protection areas and residential areas) or in confined working environments. However, their high cost and difficulty in repair limit their application in large-diameter pipes or projects with limited budgets. In actual projects, it is often combined with methods such as rubber ring sockets and hot melt butt fusion, taking into account pipe diameter, construction conditions, and cost budget.

Throttling Socket Connection

Advantages

Easy installation and low equipment dependence

The connection process is primarily manual or mechanically assisted. No specialized welding equipment is required, requiring only simple tools such as rubber ring lubricant and a tightening tool. This makes it easier to perform in the field or in emergency repair situations where power is scarce. The simple operation process allows workers to quickly master the process, making it suitable for municipal projects with tight deadlines.

High tolerance for pipe diameter deviations

Carat pipes may deform slightly during transportation or storage. The socket structure of the throttling connection (such as the elastic rubber ring) can accommodate a certain degree of pipe diameter deviation or ovality, reducing installation difficulties caused by insufficient pipe dimensional accuracy. It is particularly suitable for the rapid installation of small and medium-diameter pipes (DN300-DN800). High Repair Flexibility

If a connection leaks or is damaged, it can be repaired by replacing the rubber ring or adjusting the socket depth, eliminating the need to cut the pipe. This makes it easier to maintain than the "one-time melting" method of electrofusion, making it suitable for local repairs during later maintenance of municipal pipelines.

Disadvantages

Weak sealing and a higher risk of leakage. A throttling connection relies on mechanical fit (such as compression sealing with a rubber ring) rather than molecular fusion, resulting in a physical gap at the connection. When the pipeline is affected by foundation settlement, soil displacement, or temperature fluctuations, the socket may become slightly loose, causing the rubber ring seal to fail, leading to sewage leakage (polluting the surrounding environment) or external water infiltration (increasing pipeline load). This poses a significant risk to the environmental protection requirements (leakage prevention) of municipal sewage pipelines.

Low connection strength and limited load-bearing capacity

A throttling connection primarily relies on friction and the elasticity of the rubber ring to secure the pipe and fitting. The pipe and fitting do not form a single integral structure, resulting in significantly lower axial tensile strength and radial shear strength than an electrofusion connection. In areas where municipal pipes are buried deep, subject to complex ground loads (such as heavy vehicle overrun), or with significant foundation settlement, joints are prone to loosening, disconnection, and even pipe misalignment, compromising drainage safety.

Construction quality is significantly affected by human factors.

Operational details such as the rubber ring's installation position, socket depth, and pipe cleanliness directly impact connection quality. Improper handling (e.g., the rubber ring not fully seated in the groove, or mud and sand introduced during socket insertion) can easily lead to poor initial sealing. Furthermore, later visual inspection (such as pressure testing of electrofusion joints) is difficult to assess joint quality, leading to significant hidden risks.

The core advantages of the KRAH tube throttling connection lie in its low cost, simple construction, and flexible maintenance. It is suitable for small and medium-diameter municipal drainage pipes with low sealing requirements and simple loads (such as residential branch lines and temporary drainage). However, its drawbacks, including poor sealing, low strength, and high flow resistance, make it difficult to meet the environmental protection (leakage prevention) and structural safety (load resistance) requirements of municipal trunk sewage pipelines. In actual projects, throttling connections are usually used as a low-cost alternative. The project's requirements for sealing and strength must be strictly evaluated to avoid a surge in subsequent operation and maintenance costs due to initial cost savings.