Pipe stress analysis is a testing method that examines a piping system’s behavior under different loading situations.
As such, it’s able to analyze how the material responds to pressure, temperatures, fluid and supports, thus helping engineers:Observe the pipe’s flexibility and stiffness Determine values such as maximum stresses, forces, displacements and restraints Monitor the limits of stress in piping components and their correspondence to applicable standards
Decide on the right support systems to ensure their loads and movements are correct and safe avoiding unsuitable materials that do not support the necessary loads and pressures Notice potential disengagements from support structures and pipes Foresee how mechanical vibrations, seismic loads or acoustic vibrations might influence pipe operations Guarantee pipes are leak-proof to prevent leakage Select appropriate materials that meet strength and durability requirements All in all, the main reason to perform pipe stress analysis is to guarantee maximum safety wherever pipe systems are installed, so that pipe failures can be minimized. The right pipe analysis can also extend the pipe’s life cycle and ensure the quality and integrity of the transported product.
Main types of piping stresses?
Certain pressure, temperature and vibration conditions, as well as occasional loads, all have an impact on pipe systems. As such, the main piping stresses can be divided in 5 categories:Hoop stress: a type of uniform pressure applied internally or externally, it can have an impact on the pipe’s diameter and wall thickness.
Axial stress: caused by factors such as thermal or pressure expansions, as well as applied forces that result in the pipe’s restrained axial growth. As different materials react differently to this type of stress, pipe stress analysis remains crucial to detect this issue.
Bending stress: it originates by certain body forces that can be concentrated (such as those related to valves) or occasional (such as the ones created by atmospheric forces, including seismic movements or extreme wind events). Bending stress can also be detected as forced displacements that are generated by the growth of other equipment and piping that ultimately impacts the analyzed pipe.
Torsional stress: caused by body forces that bring about rotational moments around the pipe axis.
Fatigue stress: this is created by the combination of continuous stresses that may impact certain pipe systems.
Additionally, it’s also important to understand the three categories of loads that influence pipe stress:Primary or sustained stresses, which account for 55% of the standard allowable stress following ASME standards Displacement stresses, which should be kept between 80% to 90% of allowed ASME requirements and can be reduced by adding flexibility to the piping systemOccasional stresses, originated by one-time events (typically related to seismic movements, extreme wind events or relief-thrust loads). ASME codes allow for certain increases in the event of these stresses, including allowing a 15% increase if the event lasts less than 8 hours and less than 800 hours per year (wind-related) and a 20% increase if the event lasts less than 1 hour and less than 80 hours per year (seismic movements and relief thrust).
How to perform a pipe stress analysis?
When is pipe stress analysis recommendedOperating temperatures are 150F or higher Pipe or line sizes are 4’ or above.
When rotating equipment is considered, the analysis should take care when line size is 2 ½” and above If pressure vessels are connected, analysis are performed when line size is 6″ and above Cryogenic pipe systems and those carrying hazardous chemicals must be subject to pipe stress analysis When the system is complex (branches are multiple) When a lack of flexibility is detected When the pipe is subject to vibrations (for instance, when suction or discharging operations occur) If the plant is in an area of high seismic activity.
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