Gregory S Charney looks at how proper padding of pipelines can protect against damage from rock impingement and cut the cost of repairs.
Most pipelines whether gas, water or sewer, have a tendency to move or hammer as product moves through the carrier. This movement, in conjunction with an improperly padded pipeline, can result in rock impingement. This is when a sharp rock come in contact with the pipe which can cause the protective coating to be damaged resulting in premature corrosion or can cause the pipeline to rupture.
When considering all the cost and effort that goes into planning a major pipeline project and the costs of repairing anomalies, I found myself wondering how the action in (pictured top right) was allowed to happen. The picture clearly shows the pipe has some rock shield taped around the pipe but it was left short and the pipe was then placed on sharp rocks. This project had a respectable Contractor and ample inspection but this section of pipe was covered up without further attention.
When a contractor encounters rock on an underground construction project, the product being installed must be properly padded and thus protected during the installation and backfill process.
The US Office of Pipeline Safety keeps statistics on pipeline related accidents in three categories, Hazardous Liquid Pipelines, Natural Gas, and Distribution Pipelines & Natural Gas Transmission Pipelines. These incidents were caused by corrosion, operator error, material failure and third party are shown in the table below.
In another study issued by NACE titled United States Cost of Corrosion Study, it was estimated the cost of corrosion (internal and external) would be as much as US$56billion over the next few years for petroleum, drinking water and sewer pipelines along with electrical lines. A few simple steps can be taken to insure proper padding installation and protection of pipelines in rocky conditions which will insure the maximum life expectancy of the pipe. First, rock shield has its limits including operator placement (but can be used). Secondly, the bottom of an excavated ditch should have sand bags, dirt berms or foam breakers placed every ±15feet for the pipe to rest on and suspend approximately six inch's above the rocky bottom. Finally, an appropriate screening/padding technology should be used to insure a good 6–12-in of material
1-3/4-in minus is placed to completely encapsulate the pipeline before backfill operations begin.
A little extra care at this stage of construction will go along ways to insuring safety, the maximum life expectancy of the pipeline and thus perform profitably for years to come for the owner.
Gregory S Charney is with Ozzie’s Pipeline Padder Inc, Phoenix, AZ, USA. www.ozzies.com"