Steel Pipe Roofing

Interlocking Steel Pipes used in Pipe Roofs are common for excavation involving minimal disruption to major services and roads. We have seen multiple projects in Singapore implemented by Land Transport Authority (LTA) using such methods.


Pipe roof configuration to allow for excavation within the enclosed area.


Typical Interlock for connecting pipes together.


Interlocks welded on the pipes.

The pipes are interlocked together to form a continuous roof which prevents settlement and soil movement during excavation beneath. This process is usually installed using a Mini TBM, like that of a Herrenknecht  as one shown.


AVN TBM – From Manufacturer’s Website

Sizes of these drilling holes range from approximately 600mm to as big as 1500mm.

The challenge in producing steel pipes for such projects is being able to deliver a continuous stretch of pipes (up to 100m) with the accuracy required to ensure ease in driving successive pipes when using TBM.

Mer Lion Metals have won contracts for Thomson Lines (T219, T220 and T225) in 2016 for the supply of such pipes with interlocks. We have done so by using pipes rolled by Three Rolled Bend (TRB) methods to ensure accuracy in pipe dimensions and correct welding techniques to ensure straightness of the interlock throughout the pipes. Spiral welded steel pipes are not ideal for such application as the welding method causes uneven deformation on the pipes during the interlock welding process that would cause tolerances to go beyond the acceptable conditions.

Attention to detail on the interlocks and the pipe dimensions are critical to ensuring the straightness. For pipes, we can control the tolerance of diameter up to 0.5% from the nominal value and wall thickness of up to +/-3% from nominal. In terms of straightness of either the pipes or the interlocks, we have been able to achieve up to 0.2% of length or 3mm over any 1m distance along the length of the pipes. Further to that, since tunneling always comes with space constraints, these pipes are required to be spliced on site. As such, compatibility between pipes in splicing sequence are very important as well. In order to ascertain high compatibility, all pipes are lined up on a levelled platform in the factory and checked prior to delivery to site. We do not only care about delivering high quality pipes to the site, we also consider ways of customizing our pipes to reduce works on site, by adjusting small details during the fabrication of these pipes.


Ts and Plates Welded.


Ts welded throughout the entire drive length.


Plates and Slitting of the pipe.


Welding of the plate onto the pipe.


Laying the entire drive out for measurement testing and accuracy.


Straightness of the slit on the entire drive of the pipes.


Drive length being laid out up to 100m in entire length for measurement of straightness and accuracy.


Aligning pipes for testing and measurement.


Final inspection and checks before shipping out.


By collaborating with our customers, we provide customized solutions such as different length configurations, interlock adjustments, special dimension requirements for the interlocks, fabrication nozzles and other add-on features to the pipes, storage and tailored delivery schedule.


Installation of Nozzle into pipes.


Nozzle samples.

Storage in our stores for delivery.

Storage in our stores for delivery.

Contact us to find out more on how we can assist you on your pipe roofing or interlocking pipe projects.


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