Pipelines are accounted to be the safest means of mass good transportation. They are used particularly for transportation of liquids and gases. While mentioning the safety of pipelines, it is important to differentiate between the safety of supply for the consumers who are dependent on pipelines on one hand, and the safety (in sense of personal safety, protection of environment and goods) from potential dangers to personnel and environment which can be caused by these pipelines on the other hand (Table 1.3-1):
Safety of supply for the gas pipelines which serves the energy delivery to the public is very important, since numerous industrial operations and households are very strongly dependent on gas as energy medium. This strong dependency is attributed to the fact that storage of gas at the consumer is not taken into consideration so that the shortfall of a gas pipeline can cause momentary difficulties of energy supply to the consumer.
In case of pipelines for transportation of crude oil and petroleum products the situation is similar, even though it is not noticeable directly by the individual consumer. Therefore, the safe and continuous supply of the raw products to the refineries connected through a crude oil pipeline is vitally important, since the stockpiling is sufficient only for few days. Should the supply fail beyond this short period of time, it would cause standstill in the operation of the concerned refineries, and combined with this circumstance it would result consequently in high costs and possibly in the supply difficulties for consumers of the refinery products. Therefore, the supply safety is basically reflecting the question of availability with the target to operate the pipeline plants with downtime periods and shortfalls as short as possible. In contrary to this, for the consideration of safety in sense of personnel and environmental protection, it is of vital importance to eliminate or restrict the dangers associated with the operation of pipelines as much as possible or to an acceptable level.
In case of pipelines that transport dangerous liquids, the potential endangering of persons (employer and third parties) is caused primarily by the fire and explosion risks and toxicity of the transported fluids as the case may be. Additional endangering comes, for instance for every pressurized container through mechanical impacts which can cause damage such as line rupture. In comparison to high pressure gas pipelines, this danger is lower in case of a liquid pipelines due to lower compressibility of the transportation fluids. This result will be underlined by the fact that the liquid pipelines cannot suffer large crack lengths due to high velocity of pressure relief waves, which is possible in case of gas pipelines by all means.
Significant importance comes to the protection of water as an important safety consideration of pipelines that transport of crude oil and petroleum products, which is underlined by particular strong legislation in this area. The safety related technical requirements as being derived from this aspect are thus understandable, if the potential threat and the possible impact of damages are imagined. Finally, the protection of the environment is to be mentioned as a safety target plainly, which takes into account the protection of the transportation routes, as being crossed numerously by other pipelines due to their long dimensions or on account of running parallel to other pipelines. Against the background of the specified safety targets, the considerations related to their realisation are reflected through definition of technical requirements for pipelines as regards to their condition, operation method and maintenance. This shall keep the risk of damage as low as possible (primary safety target). On the other hand, in case of damage (which cannot be eliminated entirely) it shall be detected by proper methodologies and thus positioned in order to keep the impacts at lowest level by the applied measures and to prevent the damages (secondary safety target). This would restrict the damage extent as much as possible (Table 1.3-2).
Since the pipelines feature high throughputs (in case of large pipelines several thousands m3 per hour) the neccesity of fast leak or damage detection and positioning as well as effective damage prevention in case of line failure (break) becomes particularly apparent due to possible damage extent despite the very low probability of damage occurrence. The most significant factors through which the safety of pipelines will be determined are as follows:
- Plant conditions
- Operation method
- Maintenance
- External influences (e.g. corrosion, external strains) and
- Interference of third parties
Most relevant for the primary safety of the pipelines is the technical condition of the entire plant system, which stems from the design, planning, construction realisation and the equipment selection. The operation procedure as being time dependent and an important influence factor particularly for the safety of pipelines shall be defined in such a way that the load assumptions (e.g. allowable operating pressure) shall be not exceeded also by consideration of operation failure. Despite the multiple strong developed automation in pipeline operation the operation staff has a big responsibility and important function particularly in case of large and branched pipelines. The maintenance, which comprises the supervision, repair and inspection measures, shall preserve the nominal condition of the pipeline plant inclusive of the safety technology related components. These provisions must be based first on the equipment which is necessary for the safe pipeline operation, and secondly they shall stretch on the pressurized pipeline body itself. In addition to the operating parameters such as internal pressure and internal corrosion (if applicable) which shall be taken into consideration, it is also important to consider the external influences on the pipeline (which is laid mostly underground) such as external corrosion or additional strains imposed as consequence of earth movements in mining affected areas. Finally, the third party interferences are important as they may have an adverse influence on the safety of pipelines.
Note: This article has been published on www.piping-world.com with permission from the author Dr. Orhan Degermenci.