# The Influence of Axial Compressive Stress and Internal Pressure on a Pipeline Network: A Review
## 1 Introduction  
The rising demand for raw materials has compelled industries to exploit resources in remote locations [1]. As such, the transportation of fluid substances from such locations is facilitated by pipeline networks which have been well-established as the safest and most cost-effective mode of transportation in the industry [2, 3, 4, 5, 6, 7]. Steel pipelines have been used for decades due to their outstanding structural integrity. Underground steel pipes are regarded as the most efficient transport medium for the long-distance transmission of fluids at high temperatures and pressures [8]. However, depending on the soil conditions, some pipelines are constructed aboveground. As pipelines pass through different terrains, the sophisticated network of pipes is designed to channel fluid in different directions. To achieve this, pipe bends are used at specified locations to alter the flow direction of the flowing fluid.  
The influence of axial compressive stress on a pipe has proven to be the most significant among other external loads [9, 10, 11, 12]. This condition, coupled with pipe corrosion, which is the most common and detrimental problem with steel pipes, results in a significant loss of pipe integrity [11, 12]. Generally, steel pipelines have high yield strengths, leading to high allowable stresses. It is common to utilize pipes with yield strengths as high as 80% of the ultimate tensile strength. Despite the outstanding mechanical properties of steel pipelines, they experience various types of corrosion. The continued usage of these corroded pipes may lead to an overall reduction in the pipeline structural integrity, resulting in reduced failure pressure. In particular, pipe bends are most susceptible to failure, and are often regarded as the weakest link, as they experience unbalanced thrust forces due to the differences in the surface area of the intrados and extrados. The highest stress concentrations generally occur at the affected area's deepest point [13, 14, 15].  
The electrochemical reactions that occur in the presence of electrolytes cause corrosion in pipelines [9]. Since this process is of an electrochemical nature, it also favors the detection and mitigation of the degradation of the pipe wall by current and voltage monitoring, which is associated with the corrosion rate [5]. Both external and internal factors governthe corrosion rate of a pipeline [16]. An increase in the electrolyte concentration, coupled with harsh operating conditions, results in an increased rate of corrosion.  
There are various types of corrosion, such as uniform general corrosion [15; 16], galvanic corrosion [15], pitting corrosion [16], and crevice corrosion [15]. However, in this review, only uniform general corrosion is addressed. Uniform general corrosion is the simplest type of corrosion, where there is a uniform metal loss rate over an exposed surface. Uniform general corrosion is characterized as the metal loss of a region with a length and width exceeding three times the full-wall thickness. Within uniform general corrosion, there are two distinct types of corrosion: single corrosion and multiple interacting corrosion defects.  
For single corrosion defects, pipe failure is said to occur when disruption occurs at the defect region and the pressurized fluid begins to tear or crack through the remaining thin ligament of the pipe. For multiple interacting corrosion defects, the failure occurs when stress and strain disruptions occur on at least one of the corrosion defects. Each corrosion defect imposes its stress and strain disturbances. The regions of expansion of stress and strain disturbances are known as regions of influence of corrosion defects. Overlapping regions of influence due to adjacent interacting corrosion defects may cause a decrease in the failure pressure [17].