ONLY MILLIMETRES BETWEEN YOU AND FAILURE

Screw piles are made of steel, so good quality welds are very important! These connections/splices are very small (literally measuring in millimeters!) and so to the untrained eye – it could be easy to overlook it’s importance.

This is why systems and processes must be followed. So before a screw pile is put in the ground it’s good to understand some of the background to avoid issues later.

DESIGN
Our inhouse screw pile designers specify the weld size in accordance with AS/NZ 3404. We could probably write a blog on this alone, but won’t for now. However, while it is designed to meet the loads now, it also needs to be designed for the lifetime of the pile.

FABRICATION
Seldom are we installing a “one-size-fits-all” pile when onsite. A good screw pile designer/installer will optimize the pipe and helix sizes to the individual loads. Therefore the fabricator must ensure they weld on the correct helix arrangement (thickness and diameter), to the correct pipe (thickness and diameter), with the correct weld size in accordance with the correct weld procedure.  Furthermore, the welder must be ticketed and experience always helps.

Once the welds are completed they must also be checked by a third-party weld inspector. Sometimes this may be visual, but it may also require NDT or ultrasonic testing.

INSTALLATION
The site team must act as the last line of defense with pile inspections before installation. Main Contractors should see a Foreman or Site Engineer bending over a delivery of screw piles – and see them check the helix weld. To do this accurately they should be using a weld fillet gauge to confirm that both the Throat Thickness and Leg Length of the fillet meet the pile order (ultimately the pile design).

THE PROCESS
In New Zealand we have a Producer Statement process. (PS1 to PS4), such that:
- The PS1 would say the weld was designed properly.
- The PS2 independent peer reviewer should check this detail.
- The PS3 is the onsite team checking this detail was received, and then installed.
- The PS4 is the pile designer seeing the site records, and doing the final sign off.

So with a proper process that is rigorously adhered to – then having only millimeters between you and failure isn’t such a big deal.  This is why experience and education play a key part in selecting a reputable screw piling contractor.