"UG" simply means underground -- pipe designed to be buried below ground level -- and Class 51 (sometimes written SABS791 Class 51) is a common specification for underground sewer and drain pipe in South Africa. It is a different system to the pressure-class pipe (Class 6/9/16) used above ground or for water supply.
What makes sewer and drain pipe different
Underground sewer and drain pipe carries waste water and effluent by gravity rather than pressure, similar in principle to stormwater drainage but built to the relevant sewer specification and buried below the surface. It needs to handle ground loading from the soil and anything above it (driveways, foundations, vehicle traffic in some cases), not just the water pressure inside the pipe. See our UG Class 51 sewer and drain fittings.
Solvent weld joints
Many UG sewer and drain fittings use a solvent weld joint, where a solvent cement is applied to the pipe and socket before assembly. This creates a permanent, fused joint rather than a mechanical or push-fit connection. Solvent welding needs clean, dry surfaces and the correct cement for the pipe material to form a reliable, leak-free joint -- rushing or skipping steps here is one of the most common causes of underground leaks later.
Why burial depth and bedding matter
Underground pipe needs proper bedding (typically a layer of sand or fine, compacted material beneath and around the pipe) and adequate cover depth so it is protected from surface loads and ground movement. Skipping proper bedding is a common cause of pipe damage long after installation is complete, even when the pipe and fittings themselves were correctly specified.
When to use UG Class 51
UG Class 51 fittings are typically specified for residential and light commercial sewer connections, stormwater mains below driveways or paving, and similar non-pressure underground applications where a robust, buried pipe system is required.
Planning an underground drainage or sewer connection? Talk to our team or message us on WhatsApp with your layout and we will help you confirm what you need.