Safety through accuracy
A significant number of failures in plants have been observed throughout history.
One example is the Flixborough disaster caused by a failure to pay attention to the structural analysis of the piping system. In place of a reactor, a bypass line was connected. The flexibility analysis of piping with already installed expansion bellows was not performed using the appropriate structural analysis checks, resulting in a leak and disaster.
To avoid a situation like Flixborough, organizations need an industry-leading solution to aid them in accurate, efficient pipe stress analysis. CAESAR II® helps engineers determine thermal effects, thermal/forced cycles/vibrations and other considerations that are crucial to the design of a piping system.
Piping that appears to be accurately built based on its initial pressure design and supporting construction will behave very differently under temperatures with vibrational working effects; this aspect is critical when considering the system's final workability. A rigid/stiff piping system cannot accommodate even minor thermal expansion displacements which can result in massive thermal expansion stresses and leaks. In company-speak, that’s a lot of money wasted on re-work or cleanup.
Information and insight
Piping codes such as ASME B31.1 and B31.3 focus on these characteristics and continue to evolve to improve safety by presenting new stress calculation methodologies and determining the allowable stresses for such failure conditions. Codes are updated in response to new materials, learnings, feedback and industry experiences. In CAESAR II's most recent release, version 13, eight such new piping code editions are now available to apply and use.
A material's allowable yield stress decreases as it warms up, which is a well-known fact. Similarly, as temperature rises, the allowable sustained stresses of a material decrease.
At this high temperature, the allowable expansion stress range may exceed the allowable yield stress of the material. Pipes that have been compressed previously must overcome this before entering tension. This is known as elastic shakedown, and it occurs in the compression to tension range and keeps stresses within the elastic limits of the material, enables it to provide more allowable than yield.
Sustained and occasional stress are examples of primary stress. As the deflection increases, so does the stress. Secondary thermal expansion stresses, on the other hand, are reduced when expansion deflection is allowed to grow without applying constraints or supports.
The piping codes such as ASME B31.1 & B31.3 specifies different allowable limits for these various types of stresses. All these stresses must be within the code's allowable limits.
Possible outcomes and risk
Excessive flexibility can be detrimental. It requires more material, space, and maintenance, and it is susceptible to vibration. Such piping has a lower natural frequency and can easily resonate with any source of vibration, whether it is external, such as rotating equipment, or internal, such as pressure pulses. Such excessive flexibility may result in piping having a shorter life than intended, resulting in potential breakdown, downtime, injury and additional repair costs.
So much is dependent on the combination of specifications and environmental conditions in and around piping. Using these insights to examine any piping system helps predict failure and aid in the construction of safe, efficient projects.
CAESAR II takes all these inputs into account and calculates pipe stresses, which are then compared to the allowable to determine failure. The recent direct integration of ASME B31J Stress Intensification Factors (SIFs) & Tees helps to apply the flexibility associated with it in the piping system. The solution offers a comprehensive solution for piping stress and flexibility analysis in all environments, including buried, onshore, offshore, and subsea. The programme is easy to understand and use, making it ideal for users who require a quick start-up and confidence in their safety code calculations.
CAESAR II is the market leader and most respected software for meeting code design requirements. Its new updates include the most recent piping code editions, as well as B31J, and a plethora of different input fields that can accommodate a wide range of design requirements. It has a user-friendly load case editor and comprehensive, user-friendly reporting.
Register for Reducing Risk with Essential ASME Code Updates in CAESAR II and learn how you can create safe, easy-to-maintain, and cost-effective piping designs!
About the author
Prior to joining Hexagon, Suhas Darokar has over 17 years of experience in the field of Piping Stress/Flexibility Analysis in EPC companies as an End User of CAESAR II®. He holds a master's and bachelor's degree in Mechanical Engineering. He joined Hexagon's Asset Lifecycle Intelligence division in 2020 as an SME and Principal Software Lead for CAESAR II development. He worked on CAESAR II development v13, which included the implementation of B31J and eight new piping code editions, and he uses his experience in technical support to help resolve customer queries. He resides in India.
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