Stress Calculation of Pipeline Lowering Into Trench
How can we prove the strength of the pipeline to be lowered in a channel trench?
We are explaining the calculation method based on the beam deflection method. Of course, there are some other alternative calculations. But in this blog, we will delve into this beam deflection method. You can compare this calculation with the other to double-check.
There are three steps of pipeline lowering calculation.
1- Calculation of Spacing Between The Site Booms
2- Checking The Line During Initial Lifting
3- Checking The Line During Lowering Into The Trench
Before proceeding, it is essential to list the inputs. Therefore, we need to gather some information from the site. This information includes the pipeline location of the trench, the size of the trench, the pipe's elevation, and the site boom's position. Please refer to the figure provided to understand the required site information better.
Figure-1 Pipeline Lifting Operation Section View (Trench Detail)
Trench Information Table
In addition to the trench information, we should gather all the information about the pipe itself, including its material, thickness, production type, coating, and weight. The list below includes all the required details on the pipeline.
List of the Pipeline Specification
1-Side Boom Spacing Check
We should define a safety factor. Generally, the safety factor is accepted as 1,25. You can increase the factor, but it will impact the cost.
To calculate the safe site boom spacing, use the following equations.
Equation-1 (Min. Sagging between two side booms considering the total weight of the pipe)
2- Checking The Line During The Initial Lifting
Deflection Check
The first thing to do is calculate the moment of inertia.
Using the beam deflection calculation equations, you can calculate the actual sagging. However, estimating the allowable limit using the equations below is essential.
For beams larger than 7 meters (L > 7m), another allowable sagging formula is L/500. It is advisable to verify against this limitation for additional confirmation.
When comparing the allowable deflection with the actual deflection, the actual deflection must be less than the permissible deflection.
Figure-2 Pipeline Sagging During Lifting
Moment Check
General beam equations can be used to check the moment. The section modulus is needed to complete the calculation.
When comparing the maximum allowable moment with the maximum bending moment, the maximum bending moment (Mb) must be less than the maximum permissible bending moment (Mba)!
3- Checking The Line During Lowering into the Trench
The last but essential check is the pipeline when lowered into the trench. The bending radius will be maximum while the pipeline is lowered into the trench. During the positioning and laying process, the pipe will bend in double curvature in the horizontal and vertical planes.
The Hypotenuse Distance is the distance between the trench channel and the skid. It also represents the pipeline's actual deflection.
The allowable deflection must be less than the actual deflection; HP should be less than Sa!
In conclusion, precise calculations for lowering pipelines into trenches are crucial for the success and safety of construction projects. Engineers must consider soil type, trench depth, pipeline material, and equipment capabilities to ensure accurate and efficient installation. These calculations prevent costly errors and delays and support environmental sustainability and public safety. With advancements in technology and ongoing refinement of engineering practices, the process continues to evolve, driving innovation and improving outcomes in civil engineering. The meticulous calculation of pipeline lowering is the foundation for successful infrastructure projects.
You can download the XL file below, which includes an example.
