Pipe Stress Analysis Services
Pipe stress analysis is a critical component in ensuring the safety and reliability of industrial piping systems. At Dynaflow Research Group, we specialize in addressing the complex challenges associated with pipe stress, from initial design to comprehensive root cause failure analysis.
Our expertise helps reduce the likelihood of failures caused by factors such as insufficient flexibility or transient forces like water hammer. We understand that each system has unique requirements, and our tailored approach ensures that all relevant considerations are addressed.
When failures occur, DRG is equipped to identify the underlying causes and implement strategies to prevent future incidents. This is particularly vital for failures resulting from dynamic effects, which can often be subtle and challenging to diagnose. With years of experience, DRG is a trusted partner for companies facing pipe stress challenges, offering both static and dynamic stress analysis to support new designs and troubleshoot existing systems.
Static stress analysis focuses on evaluating the flexibility of piping systems to ensure compliance with design codes and standards such as ASME B31 and EN13480. This analysis is crucial for maintaining code stresses within allowable limits, considering factors like pipe stress, nozzle loads, flange loads, and support loads.
DRG’s assessments account for various conditions, including buried piping, offshore installations, and cold service environments, which may pose a risk of brittle fracture. Our engineers also incorporate the latest improvements in Stress Intensification Factors (SIFs) and flexibilities for tees and bends, ensuring a comprehensive evaluation of the system’s static integrity.
Dynamic stress analysis is essential when there is a risk of dynamic forces impacting the piping system. These forces can arise from mechanical sources, such as vibrating equipment or seismic activity, or fluid-driven phenomena like pulsations or water hammer.
DRG conducts dynamic analyses to create robust systems capable of withstanding such excitations. This process involves more than simply adding dynamic loads to a static model; it requires careful consideration of factors like support stiffness, gaps, and grid resolution. By addressing these complexities, DRG ensures that your piping system is resilient and reliable under dynamic conditions.
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Pipe Stress Analysis Case Studies
The main objective of a piping flexibility study is to keep code stresses within the allowable limits set by the relevant codes and standards. DRG conducts assessments that conform to industry standard American ASME B31 and European EN13480 for steel and ISO 14692 for FRP (Fiberglass Reinforced Plastic). When required we can also perform the analyses for a wide range of alternative design codes, like RToD Stoomwezen (Dutch code) or PD 8010.
DRG assesses whether the structural integrity of the piping system can be guaranteed. For FRP systems attention is given to specific features like non-standardized material properties, non-tensile joints, and thrust blocks, which do not play a role in steel piping. Please refer to our fiberglass service for more details regarding our fiberglass expertise.
The code stress in the piping system is not the only criterion that should be considered. Loads on supports, nozzles, and flanges are also assessed. Support and nozzle loads will be compared with the provided allowable loads, while the equivalent pressure on the flanges is compared with the pressure rating tables in AMSE B16.5 or EN1092. Fiberglass flanges are verified to conform to the pressure rating of the manufacturer. Special attention will be paid to the support configuration and supporting structure when large loads are unavoidable. When necessary, supports, nozzles, and flanges can be analyzed in more detail using FEA (Finite Element Analysis).
Our engineers are adept at taking special conditions into account. Whether the piping is buried, on an offshore plant or FPSO, or when cold service means that the risk for brittle fracture needs to be evaluated; we will make sure that all the relevant aspects of the analysis are considered.
In the case of a buried piping analysis, DRG verifies the pipe for backfill conditions, settlement conditions, loads at road crossings as well as many other load types. Different solutions exist to solve overstressed conditions and these are chosen in consultation with the client.
The recent ASME B31.3 code improvements on Stress Intensifications Factors (SIFs) and flexibilities for tees and bends as per ASME B31 J (2017) are included in our approach for steel systems. Especially for thin-walled piping these improved SIFs and flexibilities are relevant.
Engineering does not always stop after the static analysis of the piping system. If there is a risk of dynamic loads on the piping, then these should also be considered at the design stage.
Dynamic excitation can be either mechanical, such as direct forcing by vibrating equipment or seismic activity, or fluid-driven such as pulsations or water hammer within the pipe. If excitations are expected, or if vibrations are observed in the field, DRG can be your partner in achieving a robust system, by conducting a dynamic analysis.
A dynamic stress analysis is often an extension of a static analysis. Running a dynamic analysis, however, is not just a case of adding dynamic loads to your static model. Factors such as support stiffness, gaps, and grid resolution have a significant impact on the results.There are three approaches for a dynamic piping analysis.
Option 1: Modal Analysis
A modal analysis is the starting point of a dynamic analysis and can determine the mechanical Eigenfrequencies and -modes of the system. This gives an insight into how susceptible a system is to excitation by dynamic loads.
Option 2: Cycling Loading
When periodic loading is present, for example, a forced excitation by equipment, the possibility of fatigue failure needs to be evaluated. For this analysis, the loads will be applied periodically at a given frequency. It will then be calculated how much a given mechanical resonance frequency will be excited. The resulting code stresses in steel will be checked for conformance with the relevant design fatigue curve such as those in ASME B31.3 section 302.3.5 (d). For fiberglass, cyclic loading affects the allowable stress.
Option 3: Single event worst-case loading
In the case of water hammer/pressure surges, the excitation force is not periodic (i.e. the frequency of events is much lower than the typical Eigenfrequency of piping systems) and instead, the risk to the piping is a large magnitude single event with possible pipe rupture or excessive displacements. In this case, DRG will apply the dynamic loading as a function of time in a time history analysis. The resulting displacement, stress, flange, and nozzle loads will be evaluated against the applicable displacement and occasional load limits.
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Software Solutions For Pipe Stress Analysis
Caesar II
DRG conducts piping flexibility assessments using the software Caesar II from Hexagon. Caesar II is used for both static and dynamic piping analyses. We have a thorough understanding of the software and are also an official Caesar II training provider for Hexagon. Caesar II is considered the industry standard for pipe stress analysis.
ISOtracer
Our in-house developed piping modeling tool ISOtracer combines the modeling of a piping system and allows efficient mark-up, in a single package. By tracing over a series of isometrics a 3-D piping model can be built. Additionally, the isometrics can be efficiently marked up at the same time.
