Technology
Do Screwpiles Corrode
Yes, all steel corrodes. Understanding the corrosion mechanisms correctly and engineering screwpiles in accordance with the elements is a critical part of the design phase.
Engineering addresses corrosion in one of two ways:
- Allow for a predetermined rate of corrosion in line with the structure's design life and the environment.
- Apply appropriate surface corrosion protection to the steel to limit the corrosion rate.
Either option provides for management of the issue, the most appropriate usually comes down to economics.
The use of steel underground is not new as millions of kilometres of steel pipe has been buried over many years throughout the world successfully providing vital foundation solutions and utility services. Over the years this, combined with countless other applications and testing procedures, has provided the scientific and engineering community with a comprehensive database of information for determining an acceptable industry standard for steel corrosion both above and below the ground.
Corrosion occurs when oxygen, moisture and dissolved salts attack the iron molecules in the steel. When any one of these elements is not present, the corrosion process is dramatically reduced to a point where sectional steel loss due to corrosion is minimal. Underground, typically >2.0m, there is little or no oxygen present therefore corrosion rates are dramatically reduced unless non-typical chemical components are present.
It is important to note that concrete piles rely on steel reinforcement and adequate concrete cover for strength and determines its performance and durability. These components are exposed to the same corrosion as steel piles and are similarly affected depending on these conditions.
Certain screwpile applications call for exposure to ambient or marine conditions as a part of the screwpile shaft will be used as the pier element of the foundation. The pier section is exposed to changing conditions of oxygen and water levels as is the connection interface between the pier element and the structure. As a result these components need protection from the exposed elements.
Protection is offered in the form of hot-dip galvanising, two-pac urathane epoxy coatings or Denso-Wrap tar tapes. All are very effective when used in appropriate applications.
For more detailed information download the 'Steel underground, how long will it last?' file available on this page.
