Pipe Flexibility Analysis
From this study of flexibility analysis it is the design of the supports to the same pipe to allow the displacement of expansion or contraction of the pipe.
- What code is applied to the system.
- Design pressure and temperature conditions.
- The specifications of the material.
- The pipe diameter and the wall thickness of each component of the system.
- The scheme of the system including dimensions and movements at any point.
- Limitations of final reactions on points, such as those established by equipment manufacturers.
Having determined the basis of the problem, the applicable code could establish the minimum safety requirements for the material at the design pressure and temperature conditions. Some codes specify thermal expansion factors and modulus of elasticity for materials commonly used in piping as well as provide formulas for determining stress intensification factors and flexibility factors for system components.
Pipeline flexibility analysis consists of determining whether a line has sufficient capacity to absorb the loads that affect it such as the pipe weight itself, thermal expansion, forces produced by fluid pressure, vibrations, earthquakes, and Others. One of the factors that can increase or decrease the flexibility of a pipe is its geometric configuration.
- Failure of piping or supports due to excessive stress or fatigue.
- Leaks in the joints.
- Failure of nozzles of connected equipment (pressure vessels, pumps, turbines.), by excessive reactions.
In pipes, as well as in other structures, the analysis of the stresses can be carried out with different degrees of precision. At one extreme is the simple comparison with similar arrangements, which have satisfactorily met the requirements of the service; At the other extreme are calculation methods, which involve lengthy and complicated procedures and are relatively expensive for an engineering group. For this reason, it must be ensured that the following requirements are met:
- The range of stresses at any point due to displacements in the system must not exceed the range of allowable stresses established in the section of allowable stresses.
- Reaction forces should not be detrimental to connected media or equipment.
- The pipe movements must be within the established limits.
There are two modalities of flexibility analysis:
The informal flexibility analysis and the formal flexibility analysis.
In this respect, ASME code B31.3 identifies certain conditions, for which formal analysis is not required to confirm the acceptability of the pipe from the point of view of its flexibility. These conditions are:
- The system is similar to one that has worked with a successful record of productive service.
- The system can be judged quickly by comparison with other similar systems previously analyzed.
- The system is of uniform size, has no more than two fixing points without supports or intermediate restrictions.