Common Mistakes by Piping Stress Engineers
A flawless stress analysis certainly deserves the utmost care and attention when it comes to technical input, extensive knowledge, and practical experience. For a new piping engineer, it would be beneficial to read this informative blog post in order to learn about the common mistakes made in the field, which will ultimately help to enhance his or her overall experience and proficiency in performing stress analyses.
1-Missing information about the project
We need information to start a piping stress analysis. Most information is given at the project's beginning according to the plant location's climate, client requests, and process requirements.
A piping stress engineer should collect some information related to the region. This information includes seismic code and conditions, wind conditions in the area, and ambient temperature, and it is crucial to start any project design.
However, you must consult with the project process engineer for each specific piping system. The process engineer's input is not only important but essential to setting up your load cases for the stress analysis. Some of the particular questions must be directed to the process engineer. These are;
What are the operating conditions?
What are the design conditions?
Is it a two-phase flow?
Which valves are closed?
What are the control valve’s working conditions?
What are the PSV’s relief conditions?
Equipment working principles or conditions.
These questions can vary depending on the piping system requirement. The crucial point for both piping stress engineers and piping engineers is this: if you don't consult with the project's process engineer or the project engineer, your design and stress analysis will likely be flawed, resulting in wasted time and effort.
2- Positioning the restraints
Restraints are the most important element for a piping stress engineer to protect the pipe and equipment against internal and external forces. These restraints are stoppers, guides, and flexible supports like snubbers, spring supports, and struts.
A piping engineer should use these elements to prevent the pipe and equipment. While positioning the restraint, it is also essential to check the existing structure’s position, beam, and columns.
For example;
Imagine that you have a long pipe rack and are responsible for designing a long pipe on it. You have to use at least one stopper on the line. The pipe stoppers take huge loads depending on their size, operating temperature, wind, and seismic conditions. These loads are transferred to the steel or pipe rack structure. Therefore, it is important to put the stoppers on the column axes instead of the beams between the columns. The loads may damage the beam and also result in overstressing the line or connecting equipment.
A Wrong Stopper Position
3- Working without a checklist
Another common mistake is not using a checklist during the piping stress analysis. A piping stress engineer has to add lots of information or input into the stress analysis software like Caesar II or AutoPipe. All this information is essential and critical. Any minor change or mistake may lead to incorrect output, potentially resulting in a disaster.
To prevent this, it is very important to use a checklist and add all the information to the checklist. Following the analysis, the input and information in the checklist must be cross-checked.
You can watch the YouTube video attached below about “Stress Engineering’s Checklist” or read the blog post. This is the link.
Piping Stress Engineer's Check List
4- Underestimating the code requirement
International piping codes are standardized guidelines and regulations for the design, installation, and maintenance of piping systems. Some of the most widely recognized international piping codes include:
ASME B31: A series of American Society of Mechanical Engineers (ASME) codes covering various piping systems, including power piping, process piping, and pipeline transportation systems.
API Standards: American Petroleum Institute (API) standards for oil and gas industry piping, including API 5L for line pipe specifications.
ISO Standards: International Organization for Standardization (ISO) codes, such as ISO 6708 for pipe components and ISO 15649 for industrial piping systems.
EN 13480: European Standard for metallic industrial piping.
NFPA 13: National Fire Protection Association standard for the installation of sprinkler systems.
UPC and IPC: Uniform Plumbing Code and International Plumbing Code, widely used in building construction.
These codes ensure safety, reliability, and consistency in piping systems across various industries and applications worldwide.
A piping stress engineer should carefully read the relevant code, especially the stress and support requirements. This is essential for both piping stress and piping engineers. Without reading or understanding the code requirements, you may have to change your design, which will cause rework for you.
This is also valid for the client's specifications.
5- Overdesigning the small bores and non-critical lines
In industrial piping, engineering often focuses on designing critical lines that transport high-temperature, high-pressure fluids or hazardous materials. However, small bore piping (SBP) and non-critical lines, which handle less hazardous fluids or utilities, sometimes face overdesign. While the intent behind overdesign may be to ensure safety and durability, it can lead to inefficiencies, higher costs, and wasted resources.
Understanding Small Bore and Non-Critical Lines
Small Bore Piping (SBP): Piping systems with diameters typically less than 2 inches (50 mm) used for auxiliary services such as instrument connections, drains, vents, and relief systems.
Non-Critical Lines: Piping systems not subject to extreme temperatures, high pressures, or hazardous service. Examples include utility lines for water, air, or steam condensate.
These systems are important to overall plant operation but don't demand the same level of engineering rigor as critical lines.
Reasons for Overdesign
Copy-Pasting Critical Design Practices: Engineers may apply conservative design philosophies meant for critical lines to small bore and non-critical systems, leading to unnecessary materials, supports, and analysis.
Excessive Stress Analysis: Complex stress analysis is often applied even though mechanical loads and stresses on SBP are typically minimal. These lines experience much smaller forces than large bore, high-temperature, or high-pressure systems.
Over-Engineered Pipe Supports: Non-critical and small bore piping requires simpler support due to lower weight and mechanical stresses. Over-designing supports adds unnecessary complexity and cost.
Material Selection Beyond Requirements: Using high-specification materials designed for corrosive or high-temperature service may be unnecessary for lines carrying non-hazardous fluids at low pressures.
Consequences of Overdesigning
Overdesigning small bore and non-critical lines leads to several negative outcomes:
Increased Project Costs: Over-engineering requires unnecessary materials, redundant stress analysis, and excessive pipe supports, driving up both material and labor costs.
Complex Fabrication and Installation: Excessive engineering of piping and supports complicates fabrication and installation, leading to slower execution times and more resources spent on systems that don't demand such attention.
Longer Lead Times: Overdesign often increases time required for procurement of materials and components, fabrication, and construction. These added complexities can delay overall project schedules.
Maintenance Burden: Overdesigned systems, especially with redundant supports and complex layouts, become difficult to maintain. Unnecessary components or high-end materials can also increase future repair or replacement costs.
Avoiding Overdesign in Small Bore and Non-Critical Lines
A practical approach to design can help avoid overdesign pitfalls while maintaining system safety, integrity, and reliability:
Adopt a Fit-for-Purpose Mentality: Design small bore and non-critical piping systems based on actual operational requirements. Resist applying the same design parameters used for critical lines, which results in overspending without added value.
Simplify Stress Analysis: For SBP, minimal stress analysis is often sufficient. These systems rarely experience large forces found in critical lines. Thermal expansion, vibration, and mechanical loads are usually minimal in these small diameter, short-span pipes.
Use Standardized Pipe Supports: Support small bore piping with lighter, more cost-effective brackets and clamps. Use standard support configurations to avoid unnecessary complexity and cost. For non-critical lines, simplify pipe supports to focus on essential factors like preventing sagging or excessive vibration.
Select Materials Appropriately: Choose materials based on actual service conditions. For example, carbon steel or lower grades of stainless steel may suffice for utility services, instead of corrosion-resistant alloys used in critical or corrosive environments.
Reduce Excessive Documentation: Simplify engineering deliverables like isometric drawings, support plans, and material takeoffs for non-critical lines. Over-detailed documentation can unnecessarily complicate installation, leading to slower progress and higher costs.
Benefits of Avoiding Overdesign
Applying design principles suited to small bore and non-critical lines offers several benefits:
Cost Reduction: Focusing on pragmatic, appropriate designs reduces material costs, labor costs, and overall project expenditure.
Efficiency in Fabrication and Installation: Simplified designs allow for faster fabrication, delivery, and installation, which can shorten overall project schedules and free up resources.
Improved Resource Allocation: Instead of over-designing non-critical systems, engineering teams can concentrate their efforts on critical systems where failure risks are higher and more stringent safety requirements are necessary.
Easier Maintenance: Simplified systems are easier to maintain and modify, reducing downtime and costs associated with repairs and retrofits.
Conclusion
Overdesigning small bore and non-critical piping lines can significantly inflate project costs and complexity without providing proportional safety or operational benefits. To prevent this, engineers must apply a fit-for-purpose design approach, focusing on simplifying stress analysis, material selection, and support strategies. By doing so, engineering teams can ensure effective resource allocation, optimized project schedules, and easily maintainable operational systems.
Avoiding overdesign, especially in less critical systems, leads to more cost-effective, streamlined projects that still meet safety, durability, and performance requirements.
Common Mistakes by Piping Stress Engineers
