Buried structures

Backfilling with limestone or other alkahne material is an added step to protect buried structures from microbiological damage. Providing adequate drainage to produce a diy environment both above and below ground in the area of the buried structure will also reduce the risk of this type of damage. 

Saponification Paints are most commonly used to protect steel from corrosion by seawater in marine applications and soil in the case of buried structures. Additional protection is often supplied by the application of cathodic protection to the steel. Any paint coating used in conjunction with cathodic protection must be resistant to the alkali which is produced on the steel at defect sites in the coating. The amount of alkali generated depends on the potential to which the steel is polarized. Some paint binders such as alkyds and vinyl ester are very susceptible to saponification, and should not be used on cathodically protected structures. Cathodic disbondment testing should be undertaken if the relevant information is not available. 

Buried structures bonded into traction system in such a way as to receive impressed-current protection... 

Disadvantages Possible interaction effects on other buried structures (Section 10.6) subject to the availability of a suitable a.c. supply source or other source of d.c. regular electrical maintenance checks and inspection required running costs for electrical supply (usually not very high except in the case of bare marine structures and in power stations where structures are often bare and include bimetallic couples) subject to power shutdowns and failures. 

Graphite, silicon-iron and scrap-steel anodes used for buried structures and landward faces of jetties, wharves, etc. 

Stray-current electrolysis occurring as a result of the application of cathodic protection to a nearby immersed or buried structure is known as cathodic-protection interaction and is described in Section 10.6. 

The corrosion of underground pipes and cables caused by the electrolytic action of stray currents from d.c. electric railway and tramway systems has long been a serious problem. Regulations limiting the maximum potential between tramway rails and neighbouring buried structures and the maximum potential difference between points on the rail systems have been in operation in the UK since 1894 and in Germany since 1910 . 

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. 

Calculation of the amount of stray current entering or leaving a buried structure is a difficult matter, and a solution is usually possible only if the layout of the buried plant is simple. The very complicated cases normally met with in practice are not usually capable of solution, owing to hetero-... 

Catastrophic corrosion damage to buried structures may occasionally occur as a result of earth leakage faults on d.c. equipment or on traction systems using metallic posts to support overhead catenary wires. Care should be taken when making earth potential measurements because of the high potential gradients that may be present. 

The results of these experiments have been considered by the Joint Committee for the Co-ordination of the Cathodic Protection of Buried Structures and, in view of the various types of buried structures concerned and the circumstances in which field tests are conducted, the Committee decided not to amend its provisional recommendation that when cathodic protection is applied to a buried structure the maximum permissible potential change in the positive direction on a nearby pipe or cable should be 20 mV. If there is a history of corrosion on the unprotected installation no detectable positive change in structure/soil potential should be permitted. These criteria of interaction have been adopted in the British Standard Code of Practice for Cathodic Protection . 

A number of methods may be used to reduce the interaction on neighbouring structures. In some circumstances it may be practicable to reduce the current output applied to the protected structure or to resite the ground-bed so that the anode effect on an unprotected pipe or cable is altered as required. The physical separation between the groundbed and nearby buried structures can be increased by installing anodes at the bottom of deep-driven shafts and substantial improvements can be made using this technique. 

If both buried structures have been subject to corrosion damage the best solution may be to install a joint cathodic-protection scheme with sufficient current output to provide adequate protection for both installations. The application of separate cathodic-protection schemes to structures buried... 

Although the geometry of buried structures cannot be altered the groundbed can be placed so that the anode effect and the structure effect on the unprotected structure tend to balance each other. 

If one of the structures to be bonded is the sheath or metallic armouring of an electric supply cable, special precautions will be necessary to ensure that the voltage rise at the bond in the event of an instantaneous earth fault on the power-supply system does not endanger personnel or equipment associated with other buried structures. The bond and any associated current-limiting device should be suitably insulated and of adequate current-carrying capacity. 

Account must also be taken of small alternating currents which may be diverted from the sheath of a power supply cable by a bond connected to nearby buried structures. Such currents may be sustained for long periods and if they are diverted to the sheaths of telecommunication cables noise may be induced in the telephone circuits. 

Recent experience has confirmed that, by adopting the recommendations of the British Standards Institution or similar codes of practice operating in other countries, the likelihood of corrosion damage to buried structures adjacent to cathodically protected installations is negligible. This is because recently installed cathodically protected structures are usually coated with eflicient and durable insulating coverings such as epoxy resins and the protective current applied is consequently small. In many cases the small protective currents that can be applied by means of galvanic anodes is adequate. 

These characteristics cover the general ideal for a pipeline coaling, but obviously modified conditions may impose requirements which are more, or less stringent this of course also applies to other types of buried structures. 

P.V.C. tends to be more conformable to irregularities than polyethylene. Both types have their right and proper application for buried structures. 

Cathodic Protection Rectifier transformer-rectifier arrangement for supplying the direct current which flows between a groundbed and a buried structure which is receiving cathodic protection. 

Continuity Bond electrical connection made to connect together adjacent sections of a buried structure in order to ensure its electrical continuity. 

Structure/Soil Potential potential measured between a buried structure and... 

Buried Structures There has been no dramatic improvement in the protection of buried structures against MIC over the last several decades. Experience has been that coating systems, by themselves, do not provide adequate protection for a buried structure over the years for best results, a properly designed and maintained cathodic protection (CP) systemmust be used in conjunction with a protective coating (regardless of the quality of the coating, as applied) to control... 

Corrosion of buried structures has been blamed on the sulfate-reducing bacteria (SRB) for well over a century. It was easy to blame the SRB for the corrosion as they smelled very bad (rotten egg smell). It is now known that SRB are one component of the MIC communities required to get corrosion of most buried structures. 

Applicability in fine-grained soils around buried structures (tanks, pipes, etc.) may be limited because of soil movement. 

A new insensitive, cast-cured PBX called -135, has been developed in order to meet the requirements of US Navy s Insensitive Munitions Advanced Development Programfor High Explosives (IMAD/HE). PBXIH-135 has enhanced internal blast performance, improved non-vulnerability and penetration survivability characteristics compared with PBXN-109. Thermobaric explosives are required to defeat hard and deeply buried structures. PBXIH-135 thermobaric explosive which not only offers effective blast and thermal effects, but is also extremely insensitive to factors responsible for accidental detonation during transit or storage, may also be used for this purpose. 

The impact of an enhanced surface sensitivity is pictured by probing the polymer structures at different depths. In addition, the possibility of determining buried structures is addressed. Depending on the characteristic structure of the thin film a simulation of the two-dimensional GISAXS pattern is important to determine the influence of structural key parameters. Therefore GISAXS pattern simulations are shown to picture sample induced limiting factors of the detection of large scale structures. 

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