RACI™ RockShield™

Steel pipes are normally protected by means of appropriate plastic coatings and are bound to remain unaffected by corrosion for as long as their protective coatings remain intact. But protective coatings tend to crack and deteriorate as they come under attack from a number of factors, i.e. the handling of tubes during installation, the movement of large size materials in the ground as it settles, erratic blocks left from demolition work, and the carelessness of operators often digging just too close to buried piping.

As time goes by, due to cracks in the protective coating, the piping will start suffering corrosion problems precisely at the points
where the cracks are. Corrosion will be more severe if piping is laid in soil containing corrosion cells or sulphate-reducing microorganisms,
or in areas with stray currents.

Active Protection (Cathodic Protection)

Another way to counteract piping corrosion, which is often already underway, is to use a type of electric protection referred to as
"cathodic protection".

Cathodic protection will either stop corrosion — if cracks are small and limited in numbers — or slow down the corrosive process — if
cracks are large in numbers or sizeable.
"Cathodic protection" is obtained by giving a more negative potential to the metal structure (cathode) that is in contact with the soil
(aggressive environment). This can be achieved using the following systems:

       

  • Spontaneous current system
  •    

  • Impressed current system
  •    

  • Current drainage system

Generally, cathodic protection is achieved by connecting the metal material to be protected (cathode) with another metal with lower
nobility, which will consequently perform an anodic function (anode) (see Fig. 1).

The above-mentioned systems are always implemented with the aim of lowering the metal-soil potential (referred to the Cu-CuSO4-
reference electrode) to a value of approximately 1.5 v (known as "protection potential").
Piping protection can also be achieved by impressed current supplied by a Cathodic Power Supply.
Beyond certain limits of coating deterioration, however, the supply of current will not produce any result and the only applicable
solution in this case will be to proceed with pipe replacement.

State Of Immunity

This immunity condition can be achieved by applying a good protective coating (with high insulation resistance) and electrical protection,
i.e. cathodic protection, to the metal structure.
The current supplied through cathodic protection will take the metal-soil potential to protection value.

Situation of Gas Networks in the 1960s

In the 1960s a vast number of preliminary underground checks were carried out in order to switch urban gas distribution networks
from manufactured gas to methane. This is how gas distribution companies became aware that the problem of gas dispersion resulting
from the corrosion of coated steel piping buried underground was widespread and likely to increase with time.

This discovery led to immediate action. Electrical parameter inspections became more frequent, and cathodic protection of piping
was intensified. As a result, the resources allocated and the costs incurred for pipe protection increased.

Additional, conspicuous costs had to be incurred to fight the problems caused by "stray currents". The following course of action
was therefore taken:

       

  • any contact between piping and metal structures was to be eliminated;
  •    

  • dispersion was to be localised and repaired.

In the end, the increase in stray currents and the amplification of damage to pipe coatings was identified as the most evident cause
of pipe corrosion.

To solve the situation without recurring to conventional protective methods (laying of pipes in sand beds) it became necessary to
resource an effective solution for the protection of pipe coatings that would meet a number of requirements. The target product
should be made of age-resistant materials, should be easy to install and, above all, reasonably priced.

The more technologically advanced companies started to use "Espansit 3 Rockshield™ Net".

Rockshield™ Net

Owing to the reasons stated above, the "Espansit 3" Rockshield™ Net has become the ultimate solution for the mechanical protection
of coated steel piping.

The Rockshield™ Net is obtained from the extrusion of special blends of high and low density polyethylene with the addition of black
coloured foaming agents.

Its diamond-shaped mesh structure provides superior protection. Its weft allows for maximum absorption of load stress and stress
applied by ground settling.

Once applied, the Rockshield™ Net forms an unfastened tubular structure around the piping. This means the piping is free to move
as a result of thermal expansion, without running the risk of its protective coating being damaged by any sharp materials pressing
against it.

With its strength, the Rockshield™ Net ensures protection from piercing by sharp objects (which are a frequent presence in soils),
squashing and abrasion from other metal structures, and damage from careless digging.

The "Espansit 3" Rockshield™ Net is highly resistant to chemicals and microorganisms found in the subsurface. This means that even
after burial, the net will keep its protective properties unchanged over the years.
When piping is laid in a rocky excavation, or in a stone-rich environment, it is advisable to use the 9mm-thick "Espansit 3" net.