At PPSL District Heating, we understand that the success of a district heating network depends not only on the design and materials, but also on the quality of installation -especially when it comes to welding. When steel pre-insulated pipes are installed outdoors in trenches, choosing the right welding method is essential to ensure long-term performance, safety and durability.
From years of hands-on experience, we’ve found that gas welding (for pipes up to 200mm) and arc welding (for pipes 100mm and above) provide the most reliable, efficient and site-appropriate solutions. Here’s why these methods are our go-to choices and why they’re trusted across the industry.
Gas welding, often using oxy-acetylene, continues to be the most effective approach for thin-walled pipes up to 200mm, particularly for diameters under 100mm. One of the main advantages is that it applies lower heat, which significantly reduces the risk of burn-through – something that can be a serious issue with more intense welding methods in exposed environments.
Another reason gas welding is well suited to trench work is its portability. Equipment is lightweight, easy to deploy and doesn’t require a constant external power supply, making it ideal for challenging site conditions. And when handled by skilled welders, gas welding delivers strong, clean welds with excellent fusion and durability.
As pipe diameter increases, so do the physical stresses placed on the network. For pipes 100mm and above, arc welding (specifically manual metal arc (MMA) welding) offers the strength and penetration required to maintain the structural integrity of the system.
Arc welding also performs better in unpredictable outdoor conditions. Unlike methods such as MIG or TIG, it’s less affected by wind or moisture, making it more forgiving in open trenches where perfect weather and working conditions are rarely guaranteed. It’s a tough, site-resilient technique that delivers consistently reliable results even when the environment doesn’t cooperate.
While MIG and TIG welding techniques can produce high-quality results in controlled environments, they come with limitations in the field. Both rely heavily on shielding gases, which can be disrupted by wind leading to weak welds or porosity. They also require stable power and clean surfaces and tend to involve more complex setup procedures, all of which can slow progress in fast-paced, high-pressure trench installations.
In short, these methods are better suited for workshops than muddy, open-air trenches.
At PPSL, quality assurance doesn’t stop at good welds. It is backed up by robust inspection. For all welds over 65mm, we utilise Phased Array Ultrasonic Testing (PAUT) when required or specified. This advanced non-destructive testing method allows us to detect defects with high accuracy, giving real-time feedback and detailed imaging that supports long-term safety and accountability.
PAUT offers peace of mind, ensuring each weld meets the highest standards for reliability and compliance.
When it comes to welding steel pre-insulated pipes in outdoor trench environments, experience shows that practicality, durability and precision matter most. Gas welding and arc welding deliver on all three fronts. By combining these methods with rigorous testing and a commitment to quality, PPSL ensures each project we undertake is built to stand the test of time.
If you’d like to know more about our welding expertise or how we support high-performing district heating networks, get in touch with the PPSL team. We’re always happy to share our experience and expertise.
