Cathodic Protection

8 August, 2018

When Your Protection Fails….

Not that kind of protection! We’re talking about cathodic protection of fuel pipes and tanks.

Decommissioning and replacing defunct cathodic protection ground beds requires an element of precision and brute force. Our first job is usually locating the existing beds. This can be no small task on a 30 hectare oil terminal site! The redundant beds were installed over 30 years ago and records are sparse.

We used radio detection methods to accurately locate the old redundant vertical ground beds to the required accuracy of +/-50mm. We need to be that accurate in order to successfully overdrill the beds.
Unusually, on our most recent project, our client asked us to drill through the connecting cables rather than removing them. The cables were isolated by a field engineer prior to us starting work and all our works were carried out under a permit to dig.
To overdrill the existing beds we brought in a shell and auger rig, drilling 350mm boreholes to 5m depth. This effectively decommissioned the existing redundant ground beds to make way for the new ones. With the first stage of the project complete, we are now back on site with our Comacchio rotary rig drilling much deeper boreholes in which we will be installing new anodes. Updates to follow.

6 July, 2018

Cathodic Protection

Drilling large diameter boreholes at a brownfield site to install anodes for a cathodic protection system requires a rather eclectic combination of skills.

Working in a tight space, to a detailed specification, we achieved an anode installation through a complex sequence of geological strata. Clean drilling techniques required us to install an environmental seal through surficial gravels and 30m into underlying clay. We then extended the boreholes through 20m of Thanet sands and 10m of flinty chalk. To complete the anode installation we then tremmied sacrificial coke contact media into the borehole’s response zone with the remainder of the boreholes being grouted back to the surface with bentonite.

Our team consisted of drillers, environmental engineers, mud technicians and cathodic protection engineers, all working together on a busy site to ensure the client got the installation required whilst working within the Environment Agency guidelines. The anodes will now ensure the pipelines are protected for the next 100 years.

If you’d like to know more or if you have an installation requiring cathodic protection be installed then please contact Angus Gale – 01296739433

17 February, 201617 February, 2016

When Horizontal Just Won’t Do

A prominent pipeline client came to us with a problem. A ‘positive’ problem that is. A section of their pipeline runs underground next to a railway line. The railway’s overhead high voltage power lines were causing an amplified positive electrode potential in the ground, which in turn was leading to increased corrosion of their pipeline. In these cases, cathodic protection is the usual solution.

A typical cathodic protection system would comprise a series of shallow earthing rods installed at regular intervals along the pipeline. However, this requires access for maintenance in the future to the entire pipeline. But these pipelines run for hundreds of miles through agricultural land, some of which is only accessible during certain periods of the year. The solution was to design a single anode string capable of achieving the required negative electrode potential in a vertical design. Thus saving on space, maintenance and cost

The client’s senior cathodic protection engineer approached us to see if we could drill a 75m deep borehole and undertake the (negative) anode installation. We took the challenge and set about devising a safe method for installing a multi core anode string weighing more than 300kg! The borehole was installed through 18m of gravel into underlying mudstone. Just to complicate matters further, our environmental appraisal identified a potential risk of penetrating into a sandstone aquifer beneath the mudstone. To mitigate these risks and achieve the required potential we had to install a vent pipe to the base of the borehole, a tonne of coke, gravel and a bentonite seal at the top of the mudstone to ensure the underlying aquifer was protected.

Exactly how we did all this is our secret but needless to say it involved a large rig, and unusually for us, a lot of “negativity” ………….But happy pipeline equals happy client – now that’s positive.