This study presents the results of a static stress analysis conducted on a compressor and the exit area of a compression station.
Analysis
A static stress model was developed using the CAESAR II pipe stress software package. The model encompassed the entire system, starting from the suction headers at the beginning of the plant and ending at the exit. The boundaries of the model were defined by the cooler connecting lines, terminating a few meters beyond the aboveground valve and silencer.
The model primarily consisted of underground piping, with some sections of aboveground piping. Soil mechanics were represented in the model using bilinear springs, accounting for axial, horizontal, and vertical directions. The spring stiffness and maximum load-bearing capacities were based on soil data provided by the client, specific to the soil type at the compression project site. The soil mechanics were modeled according to the NEN3650-1 standard.
Results
The analysis revealed that the stresses within the compressor model for each load case were below the allowable values as per the ASME B31.3 code. The compressor nozzles were evaluated according to the API 617 code, with three different checks performed to ensure compliance. In all cases, the nozzle loads remained below the allowable limits. This reduction in stress levels was anticipated to prevent the occurrence of future fatigue cracks.
To maintain the vertical sustained reaction forces on the compressor nozzles within acceptable limits, a spring support was installed just before the connection to the compressor nozzle. Additionally, underground cooler lines placed in non-compacted soil were supported by several underground supports, depending on the length of each cooler line. These supports were essential to reduce the loads on the flange connection to the aboveground valve or silencer to acceptable levels, as well as to alleviate the load on the support inside the compressor building.
