Scouring and Wear of Elbows
Posted: 04/06/2021 04:14:10 Hits: 11
Pipelines, roads, railways, air and water transportation are the five major transportation. Among them, pipelines have the advantages of large transportation volume, small engineering volume, short transportation distances and low losses, which play an irreplaceable role in petroleum, chemical, metallurgical and other industries. Petroleum pipelines have been working in harsh environments for a long time. The thinning and even cracking of the pipe's wall caused by scouring and wear, fatigue damage, internal defects of materials, chemical corrosion and other factors not only have caused serious economic losses, but also brought great pressure to the environment. From 2002 to 2006, more than 50 perforation accidents of pipelines occurred in the Yaha gas condensate field in Xinjiang Province. It was found that the perforation mainly concentrated at the elbows after investigation. Wear caused by scouring and chemical corrosion were the main reasons for frequent occurrences of failures of pipelines.
In January 2004, an explosion occurred in the heating furnace area of a coking workshop in a refinery and it was found that the cause of the accident was the elbow's material replaced not meeting the requirement in the repair process, which caused the elbow that is in operation to be scoured and worn by solid particles, thus thinning the wall thickness, reducing the pressure bearing capacity and causing an explosion. In 1997, scientific research institutions investigated 42 high-strength steel pipelines and found that quality of welding accounted for 36.74%, quality of pipe fittings accounted for 41.18% and wear caused by scouring accounted for 22.06% in the reasons for 68 accidents in the pipeline.
Although there have been a lot of improvements and innovations in the inspecting equipment and methods of petrochemical pipelines, it is often impossible to accurately determine the location of the most serious thinning in the actual operation process, which brings certain pressure to the safety assessment of the pipeline. Although companies have increased the manpower and material resources for inspection and maintenance, they cannot completely avoid the safety problems of the pipeline system. Accidents such as thinning and perforation of the pipeline caused by corrosion and scouring still occur frequently. Partial corrosion such as pitting corrosion and crevice corrosion often occurs for petrochemical pipelines after analyzing a great number of accidents, and there is certain regularity for the location of occurrence, which are closely related to scouring and wearing of the flow field characteristics of multiphase flow, impurity precipitation and impacts of the pipeline’s pressure fluctuation.
It can be found that the elbow is the most common part with the greatest bearing force, partial thinning and perforation in the entire pipeline by analyzing most failure cases. Relevant studies have pointed out that the wear caused by scouring of the elbow is 50 times higher than that of the straight pipe, as shown in Figure 1.1. Both elbows and straight pipes have obvious wear caused by scouring. It can be found that the wear caused by scouring of the elbow is more serious than that of the straight pipe, and wear of outer walls of the elbow is significantly serious than its inner walls by comparing the two figures.
Figure 1.1 Scouring and thinning of pipelines and elbows
To sum up, the scouring and wearing caused by solid particles has become a major problem in the process of oil transportation, and it has posed a serious threat to people's lives and safety of property. Therefore, in-depth study of the formation mechanism of scouring and wearing of pipelines, accurate prediction of the intensity and distribution of scouring and wearing and exploration of how to reduce the scouring and wearing of pipelines are of important engineering value.
The scorpions and lizards in the sand and shellfish in the silt environment have undergone long-term evolution and formed a surface form that can effectively resist external wear. This provides new thinking to study the scouring and wearing resistance of pipelines. How to improve the scouring and wearing resistance of traditional pipelines and elbows not only is important for manufacturers, but also has important practical application value for reducing economic losses caused by scouring and wearing of pipelines and solving environmental problems caused by leakage of pipelines.
In January 2004, an explosion occurred in the heating furnace area of a coking workshop in a refinery and it was found that the cause of the accident was the elbow's material replaced not meeting the requirement in the repair process, which caused the elbow that is in operation to be scoured and worn by solid particles, thus thinning the wall thickness, reducing the pressure bearing capacity and causing an explosion. In 1997, scientific research institutions investigated 42 high-strength steel pipelines and found that quality of welding accounted for 36.74%, quality of pipe fittings accounted for 41.18% and wear caused by scouring accounted for 22.06% in the reasons for 68 accidents in the pipeline.
Although there have been a lot of improvements and innovations in the inspecting equipment and methods of petrochemical pipelines, it is often impossible to accurately determine the location of the most serious thinning in the actual operation process, which brings certain pressure to the safety assessment of the pipeline. Although companies have increased the manpower and material resources for inspection and maintenance, they cannot completely avoid the safety problems of the pipeline system. Accidents such as thinning and perforation of the pipeline caused by corrosion and scouring still occur frequently. Partial corrosion such as pitting corrosion and crevice corrosion often occurs for petrochemical pipelines after analyzing a great number of accidents, and there is certain regularity for the location of occurrence, which are closely related to scouring and wearing of the flow field characteristics of multiphase flow, impurity precipitation and impacts of the pipeline’s pressure fluctuation.
It can be found that the elbow is the most common part with the greatest bearing force, partial thinning and perforation in the entire pipeline by analyzing most failure cases. Relevant studies have pointed out that the wear caused by scouring of the elbow is 50 times higher than that of the straight pipe, as shown in Figure 1.1. Both elbows and straight pipes have obvious wear caused by scouring. It can be found that the wear caused by scouring of the elbow is more serious than that of the straight pipe, and wear of outer walls of the elbow is significantly serious than its inner walls by comparing the two figures.
Figure 1.1 Scouring and thinning of pipelines and elbows
To sum up, the scouring and wearing caused by solid particles has become a major problem in the process of oil transportation, and it has posed a serious threat to people's lives and safety of property. Therefore, in-depth study of the formation mechanism of scouring and wearing of pipelines, accurate prediction of the intensity and distribution of scouring and wearing and exploration of how to reduce the scouring and wearing of pipelines are of important engineering value.
The scorpions and lizards in the sand and shellfish in the silt environment have undergone long-term evolution and formed a surface form that can effectively resist external wear. This provides new thinking to study the scouring and wearing resistance of pipelines. How to improve the scouring and wearing resistance of traditional pipelines and elbows not only is important for manufacturers, but also has important practical application value for reducing economic losses caused by scouring and wearing of pipelines and solving environmental problems caused by leakage of pipelines.
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