Pipeline mechanical damage

The cathodic protection of pipelines is best monitored by an intensive measurement technique according to Section 3.7, by an off potential survey eveiy 3 years and by remote monitoring of pipe/soil potentials. After installation of parallel pipelines, it can be ascertained by intensive measurements whether new damage of the pipe coating has occurred. These measurements provide evidence of possible external actions that can cause mechanical damage. 

The integrity of pipelines depends upon conect design, including materials selection, support and protection from mechanical damage. Depending upon tlie gas, routine inspection and maintenance may be supplemented by the provision of gas detection and alarm systems. Other considerations are exemplified by the safety-related controls on the transportation of domestic gas via pipeline systems summarized in Table 15.17. 

Compressed air lines are very susceptible to a combustion gciienition e.xplosion, fueled by oil or cliar on tlie pipe walls. E.xplosions in pipelines c ui cause considerable damage. Pipelines witliin wliich gas, vapor, or dust explosions can occur must be designed to have sufficient mechanical streiigtli to withstand pressure or stress beyond tliat required by the application. 

In the special case of pipelines operating at relatively high temperatures such as for the transmission of heavy fuel oil at up to 85°C, heat insulation and electrical insulation are provided by up to 50 mm of foam-expanded polyurethane. As a further insurance against penetration of water, and to prevent mechanical damage, outer coatings of polyethylene (5 mm), butyl laminate tape (0-8 mm) or coal-tar enamel reinforced with glass fibre (2-5 mm) have been used. 

The pipelines used to convey compressed air or nitrogen must be designed to carry pressure. Low-pressure flexible PVC tubing is not suitable. Where the gases are carried for long distances, solid metal lines with takeoff junctions should be provided. Flexible lines should be kept clear of heated ovens and open flames. Kinks and other mechanical damage should be avoided, and when it occurs it should be immediately repaired. 

Winding of the outer layer protecting the anticorrosion insulation against mechanical damage during transportation and installation of the pipeline. This layer is made of a sufficiently thick PE film (0.5 mm), which is the adhesive coat carrier. 

Impressed current anodes must be corrosion resistant and otherwise durable in the environment in which they are used. They must have low consumption rates when coimected to a CP source. All materials used for impressed current anodes are cathodic (more noble) than steel. High silicon cast iron (Fe-0.95C-0.75Mn-14.5Si-4.5Cr) is used for onshore CP applications and in other locations where abrasion resistance and other mechanical damage considerations are important [1]. Graphite anodes are extensively used for onshore pipeline CP applications in which they can be buried in multiple-anode ground beds. However, graphite must be stored and handled carefully because of its brittle nature. 

Recommended for low levels of corrosion and mechanical damage. Armor Plate is monolithic in nature and can be applied to various pipe configurations under different enviromnental conditions such as high temperatures or pressures, below-freezing temperatures and on irregular pipeline surfaces. 

Metal loss tools are used to detect defects that have resulted in wall thinning in a pipeline. They can discriminate to some extent between manufacturing defects, corrosion defects and mechanical damage. There are two main typ>es of tools ... 

The situation in oil industry in the Russian Federation at the moment can be described as critical. It is especially urgent for oil transporting pipelines. More than 70% of pipelines are 15-35 years old. 550 thousand kilometers of pipelines are high risk constrictions [Materials, p. 284]. Aging of oil fields results in higher chemical activity of oil and sewage, which causes intense corrosion of pipes and increased numbers of accidental leaks of oil. Low quality of pipes and construction works and mechanical damage also lead to oil spills. 

An external defect suspected to have been caused by mechanical damage from a backhoe loader during a pipeline installation was found after an ILI inspection for a main 32-in. gas transmission line supplying gas from Sumatra to Java Island in Indonesia (Figure 6.7). 

Composite repairs have been utilized in onshore transmission pipelines for the past decade. These repairs are used on pipe sections that have been weakened due to corrosion and mechanical damage. A survey conducted by the US Department of Transportation showed that the overaU costs can be reduced by 24% using composite repair instead of welded pipe sleeves. Compared to replacement of the whole defective pipe section, the cost has been redueed by approximately 73% (RSPA, 2000). 

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