9 October 2013 – The structural integrity of a gas pipeline and the assurance that the interior of the pipeline is contaminant-free are the two most critical elements in its construction. For this reason, the 150 kilometre gas pipeline between Sasol’s Secunda and Sasolburg plants required the supply of reliable compressors.
“There are a number of instances where a variety of our normal and high-pressure oil-free compressors have been used for both dewatering and cleaning of pipelines,” Louwrens Erasmus, general manager of Rand-Air, says.
The Sasol pipeline projects extend over three provinces, Mpumalanga, Gauteng and the Free State, and were awarded to a joint venture between WBHO and SPIECAPAG. SPIECAPAG specialises in the delivery of onshore pipelines and facilities such as compression, pumping and metering stations, hydrocarbon storage systems, slurry pipes and water pipe networks. The company has laid over 50,000 kilometres of pipelines covering the five continents.
Benoit Patanchon, plant and logistics manager for the SPIECAPAG/WBHO joint venture selected two Atlas Copco oil-free compressors from Rand-Air, based on the performance of these compressors on a similar project. In addition to the two 24 bar oil-free compressors, the company also hired three 300 to 400 cubic foot per minute (cfm) compressors and one 1,000 cfm compressor at seven bar pressure from Rand-Air.
“The two oil-free Atlas Copco compressors were used for the hydro-testing, cleaning and drying of the pipeline. Oil-free compressors were both a technical and safety requirement on site. We simply could not afford to allow any external contaminants to be introduced into the pipeline, due to the very high cleanliness specification of our client,” Patanchon says.
Apart from the quality considerations, it is critical that no heat is generated inside the pipeline. “Since gas is extremely flammable and volatile, it is important that the internal pipeline environment is carefully controlled to ensure maximised safety levels.” He says that the smaller compressors provided by Rand-Air were used for blasting and pipeline coating and civil works.
Pre-testing of the pipeline was undertaken, using the 1,000 cfm compressor, after the pipeline was laid. This ensured that the pipeline is contaminant-free and that the structural integrity of the pipeline was not compromised. “There is no margin for error, so we needed to ensure that the pipeline is 100% leak-free. Once we were satisfied with the structural integrity, we used the oil-free compressors to push pigs through for cleaning and final drying of the pipeline section.”
The smaller compressors were used for six months by the coating team. Similarly, the larger 1,000 cfm compressor was on site for about six months. The time that the compressors were kept in a specific location was dependent on the length of each section.
“We needed the oil-free compressors for about three to four months. During this time they were pushed to their capacity, as they were required to produce pressures capable of covering distances of up to 25 kilometres.”