At ground level and just below in lighting columns there is an environment rich in moisture, chlorides and oxygen, an environment which promotes the corrosion of steel structures.
The high stress zone for street lighting columns is also at ground level, consequently, any loss of metal thickness in this region can significantly reduce the strength of the column and can, in extreme instances, lead to collapse. 
Unfortunately, this corrosion can be just below ground level and impossible to see without expensive excavation. Out testing method uses the ColcheK™ system, a specialised non-destructive inspection tool for the detection and estimation of this corrosive damage by checking this critical zone without having to excavate or prepare the column in any way.
ColcheK™ uses low frequency electromagnetic technology that is non-contacting and does not emit or use any hazardous radiation. The system compares the wall thickness of the column at and below ground level with the thickness at about 150mm above ground level, and area where there is unlikely to be any major corrosion damage, and if it does exist, can be seen clearly.
Indeed we carry out a visual inspection of the column as part of our testing routine.
By recording the percentage loss of thickness and by visual inspection of the entire column, our test results will ascertain the risk category, life expectancy and retest period of each column. This will eliminate the need for costly replacement of compliant stock, whilst ensuring dangerous columns are highlighted immediately. Each column is graded as follows:-
