Report : Mining Development in South Africa
Product: Stretch and Seal
The South African mining industry is supplied with small bore steel tube and pipe for the chilled water, compressed air and return water pipelines needed to operate underground. Most of the mining operations are unique to southern Africa as they are mostly deep shaft with the deepest approaching 4000M. On investigation, the pipes are either bitumen dipped or galvanized. No thermoset corrosion protective coatings are used. The pipes are either flanged or coupled using Victaulic couplings. The life of a pipe is anywhere between 18 months and 5 years. Corrosion is rampant due to high temperatures underground up to 40 deg Centigrade with continuous fissure water seeping through the rock wall. Below is a pipe section that has been in service for 28 months.
The galvanized pipes are expected to last 36 months, they were replaced some 4 months before the picture was taken. The photograph below gives an idea of being 2800M below the surface. Wall temperatures are 37 Deg C with humidity at 80 %.
Piping supplied to the mines in RSA (between the sizes of 100mm and 200mm) account for 11,000M of new pipe per month. Of the 11,000M, about 35% replaces corroded pipes.
Stretch and Seal Trials
We were granted the option to do trial tests at 4 locations, AngloGold Ashanti (2 separate shafts) in Klerksdorp, Carltonville 1 shaft and Konkola in Zambia.
The tests were done in September 2008 and are still in good working order. The 350nb pipe sprung a leak on the slurry line feeding the concentrators’ and mills.
It must be noted that the erosion on the slurry lines is severe as the rubber lining has already been eroded away. Surface preparation included the removal of the crusted contaminant and the washing of the entire pipe circumference. A wire scrapper was used about the hole in the pipe. The tape was stretched between 200 and 250 percent. After wrapping the tape was left to cure for 3 hours before the pipeline went live. The operating pressure of the line is 5.8 bar and runs intermittently for up to 8 hours per day. The test needed to perform for a period of 3 months for Konkola to approve the tape. The picture below shows the application of Stretch and Seal. Four Layers over the hole and a double layer extending 250mm to each side of the hole.
The results after 6 weeks; no change. Until to date, the seal is still intact.
Second trial on the inlet section of the settlement tanks.
Inlet pressure is 4.8 bars, the coolant is continuously recycled and therefore, a build up of chlorides’ has risen to 12,000 ppm. This seal was wrapped during operation.
At AngloGold Ashanti in Klerksdorp, the S & S taper was used on Fiber Cement piping with a stress crack forming from years of abuse. The pipe was coated in October 2008 and was again inspected in January 2009. The pipe is still in service. From the photograph below, it can be seen that the fissure crack corrosion is the bulk of the miner pipeline problem for the compressed air and return water lines.
The corrosion is not consistent over the full pipe length, but where the fissure cracks in the shaft and levels are. If the life expectancy of a pipe can be doubled by protecting it from the corrosive nature of the dripping ground water.
It is no mean task to achieve a product listing with a mining company and such status is acquired through the following process:
- Perform a 3 month trial with a perfect track record of no failures.
- Obtain 3 section generated orders from 3 separate shafts from the same mine.
- Meet the MSDS (material safety data sheet) minimum needs and fire retardant requirements of the mine.