Buried systems pipelines

The resistivity values obtained represent the average resistivity of the soil to a depth equal to the pin spacing. Resistance measurements are typically performed to a depth equal to that of the buried system (pipeline) being evaluated. Typical probe spacing is in increments of 0.5 to 1 m. 

In the early years of industrial development in the United States, many plants buried their outside pipelines. The initial cost for this type of installation is low because no supports are required and the earth provides insulation. However, location and repair of leaks are difficult, and other pipes buried in the same trench may make repairs impossible. Above-ground piping systems in industrial plants have proven to be more economical than buried systems, and, except for major water and gas lines, most in-plant piping systems in new plants are now located above ground or in crawl-space tunnels. 

In that industrial territory along the banks of the Rhine are a number of large chemical plants producing basic chemicals that go into aspirin, food additives, dyes, fertilizers, plastics, and fibers. A dozen of these plants have the distinction of being linked to the world s oldest hydrogen pipeline network, and one of the most extensive a 130-mile system of buried steel pipelines wrapped in bitumen and plastic that traverses cities, crosses the Rhine in two places, and transports more than 10.6 billion cubic feet of... 

As far as corrosion-related bacteria are concerned, in this chapter we will focus on both external and internal corrosion systems of a buried metallic pipeline. 

Davis, P, Burn, S., Moglia, M. Gould, S. 2007. A physical probabilistic model to predict failure rates in buried Wc pipelines. Reliability Engineering and System Safety. 92 1258-1266. 

Corrosion likelihood describes the expected corrosion rates or the expected extent of corrosion effects over a planned useful life [14]. Accurate predictions of corrosion rates are not possible, due to the incomplete knowledge of the parameters of the system and, most of all, to the stochastic nature of local corrosion. Figure 4-3 gives schematic information on the different states of corrosion of extended objects (e.g., buried pipelines) according to the concepts in Ref. 15. The arrows represent the current densities of the anode and cathode partial reactions at a particular instant. It must be assumed that two narrowly separated arrows interchange with each other periodically in such a way that they exist at both fracture locations for the same amount of time. The result is a continuous corrosion attack along the surface. 

A continuous polymer anode system has been developed specifically for the cathodic protection of buried pipelines and tanks. The anode, marketed under the trade name Anodeflex , consists of a continuous stranded copper conductor (6AWG) which is encased in a thick jacket of carbon-loaded polymer, overall diameter 12-5 mm. To prevent unintentional short circuits an insulating braid is sometimes applied to the outer surface of the conductive polymer. 

The anode may be installed in conventional groundbeds or be laid in close proximity to the cathode, e.g. parallel to a pipeline route. The anode may be buried either directly in soil or in carbonaceous backfill. The major applications for this material are tank protection, internal protection, mitigation of poor current distribution and hot spot protection, i.e. to supplement conventional cathodic protection systems and provide increased levels of cathodic protection in areas that exhibit low levels of protection. 

An electric railway or tramway system with an adjacent buried pipeline or cable which may cross the running rails at intervals is illustrated in Fig. 10.35 in which the arrows indicate the general flow of stray currents when one vehicle is in service. Rapid variations of current and potentials will occur as the tram or train moves along the rails. Corrosion will occur at points near the sub-station or near negative feeders where the stray current leaves the buried structure to return to the negative busbar at the sub-station. 

Installation of a Brillouin system is most cost-effective when applied to a new pipeline construction when the trenching is available for inserting the optical fiber cables. If the existing sections of buried pipeline require replacement or repair, then the Brillouin system can also be used selectively in high consequence areas. In general, total system costs will vary for each application. 

Hydrostatic test pressure (TP) shall be limited to the pressure calculated per para. IP-10.7.2. The maximum testing interval shall be 10 years. Inline examination is normally applied to pipelines or buried piping specifically designed for this type of assessment and should be a requirement for piping systems only when the piping is specifically designed for inline examination. 

The concepts are similar for both onshore and subsea pipelines. In the above conceptual picture, it is assumed that the pipeline wall temperature is constant at 39°F. If a line is insulated, hydrate dissociation becomes much more difficult because the insulation that prevented heat loss from the pipe in normal operation will prevent heat influx to the pipe for hydrate dissociation. Alternatively, if the pipe is buried, the pipe wall temperature will be greater than 39°F and the system may be insulated by the ground. 

The Baku-Tbilisi-Ceyhan and the South-Caucasus-Pipeline projects will be arranged in a 22-meter wide construction corridor for two parallel pipelines buried in a 2.2-meter deep trench. This alone illustrates the complexity of facilitating pipeline systems in regards of environmental issues and the complicated morphological mountainous relief. 

Cathodic protection has many applications, e.g. in refineries, power stations, gas, water, and oil utilities on marine structures, e.g. jetties, piers, locks, offshore platforms, pipelines, ships hulls, etc. and on land structures, e.g. buried pipeline, storage tanks, cables, etc. For each use, the cathodic protection system requires careful design, either impressed current, sacrificial anodes, or a combination of both may be chosen. There may also be other protection systems, e.g. paint, the nature of which will affect the design parameters and must be taken into consideration. 

The pipeline is usually buried to a depth of 2 m (6 ft) to minimize freezing concerns. The line should be equipped with extensive redundant instrumentation to ensure complete safety and integrity of the system. 

In this technique, the electrical current is delivered to the structure to be protected from a direct current (dc) power source through an auxiliary electrode. The structure acts as a cathode and the auxiliary electrode becomes the anode in the cell [26, 27]. Figure 8 shows an impressed current system used to protect a pipeline. Both the buried anode(s) and the pipeline are coimected to an electrical rectifier, which supphes direct current to the buried... 

CP is the required method of corrosion control of buried pipelines. The two forms of CP are impressed-current and sacrificial anode systems. Both forms of protection have been in use in industry for quite some time and the industrial personnel are familiar with their installation and operation (NACE Standard RP0169-96). 

A problem of particularly large economic significance is corrosion on buried pipelines, and there are special reasons to worry about the external corrosion. Examples from some communities show that a major part of the water in the public fresh water pipeline system gets lost due to leakage, mainly because of corrosion. 

In NACE 2003, this author presented an algorithm that later became the basis of a software package to predict corrosion of a buried pipeline and especially predict the possibility of MIC. The software was also capable of comparing the changes and modifications applied in the system to see how efficient corrosion mitigation strategies had been. 

FIGURE 4.50 (See color insert.) Subsystems of a buried pipeline as a system (system = pipe, internal subsystems including flnid and lining conditions, external subsystem including the coating and soil conditions). 

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