Design Basis: Why is it so crucial to have a well-defined Design basis document for a successful Project
Design Basis: Why is it so crucial to have a well-defined Design basis document for a successful Project Home / Learning We recently finished a project at MECS Engineering that reminded me of the importance of a transparent & well-defined design basis, a topic very close to my heart which I always talk over when I see a gap and hence this article. Before starting any project, a critical and vital element is a well-defined design basis (also called design requirements or basis of design) in addition to a well-defined scope of work (SOW). If not appropriately defined and documented, it results in scope changes, delay in the project timeline, impact on the project budget, and sometimes a total disaster. A concise and complete design basis document makes the basis of a quality design product and a successful project. What is Design Basis? Design basis documents the rationale, criteria, principles, assumptions, and constraints used for detailed engineering and the final design product. It is essentially a set of conditions, requirements, needs of the project & performance criteria, including the legal and code requirements. It applies to an SSC (system, structure, and component) of the complete facility or a modification in the existing facility. This article focuses on the engineering world, although the Design basis importance applies to almost every industry. Various formats are followed by different organizations based on the type of industry. Sometimes it can be an extensive document covering every aspect of the project, from the initiation phase to the installation and commissioning phase, including the commissioning requirements. A caveat, though, is that one should not go into fine details, e.g., detailed calculations, construction details, etc. A project can also fail if the design basis document includes details meant to be part of the detailed engineering. These details are issued as separate documents. If needed, there can be multiple design basis documents, e.g., a separate DB for Piping Design or Structural Design, where specific requirements can be added. U.S. Department of Energy defines Design basis as “Information that identifies the specific functions to be performed by a structure, system, or component of a facility, and the specific values or range of values chosen for controlling parameters as reference bounds of Design. These values may be (1) restraints derived from generally accepted “state of the art” practices for achieving functional goals, or (2) requirements derived from analyses (based on calculations and/or experiments) of the effects of a postulated accident for which a structure, system, or component must meet its functional goals.” What stage Design Basis document should be initiated in project life cycle? The Design Basis document is a dynamic document that can be updated as the project progresses. Typically, it starts at the definition or conceptual / feasibility stage of the project, focusing on the needs and assumptions to meet the project requirements, defining a narrative of the system description like the purpose of the system (or a modification) to meet the specified requirements. The design basis should also address the Constructability, Operability, Maintainability, and Safety (COMS) aspects. It is a crucial part and, if neglected, can even result in the project’s cancellation during the execution stage. I have seen a couple of such cases. Every single component and line in the proposed design should have a thought process supporting it. Most of the requirements, assumptions, and constraints should be captured during the conceptual phase; however, additional details may be needed during the preliminary stage, which should be added when known and the document revised. By the end of the Preliminary engineering phase, the Design Basis document should be rock solid with all required information for the detailed engineering. Any significant change during the detailed engineering phase would impact the project timeline, budget, and sometimes a total disaster. What is covered in the design basis document? Depending on the project’s scope (minor OR major modification OR an entirely new facility), industry type, the design base document varies in detail. Nevertheless, the goal is to have all the required information as described above so that an independent team can deliver a final product without coming back to the author of the Design Basis document for any clarification (Ideal case). Here is a generic partial list of information typically included in the DB. Project Requirements (Project need statement) Scope of the Project Relevant Legislation: Licensing and Registration requirements Applicable Codes and Standards QA requirements Operational conditions and limits (Normal operating conditions, anticipated operational occurrences) Design Parameters and Loads: Pressure, Temperature, Thermal, Seismic, wind, snow, Environmental conditions and requirements Ambient conditions Safety Requirements Human factors requirements Material specifications and factors affecting the material selection e.g., corrosion, erosion, neutron flux in the nuclear facility Interfacing systems: The life expectancy of the installation Assumptions considered in the design Limitations on the Design Constraints: Site access, material selection or material movement, or any such constraint Testing requirements Commissioning requirements (at high level) Additional parameters in specific cases: Certain projects need special attention to the complete cycle of the project to include required design parameters. For example, one project MECS Engineering just completed involved the structural analysis of skid on a container that would be transported to various geographic locations after fabrication. In such cases, you need to include the wind and snow loads for all possible areas and pick the worst-case scenario as the design basis. Include the loads during the skid’s lifting operation, applicable modes of transportation, acceleration values, etc. There are opportunities to optimize the design by limiting the allowable loads in the design basis. e.g., there can be geographic locations where snow and wind loads are excessive, and if you try to cover every site as per the original scope of the project, the structure needed can be super heavy. In those cases, you can put a limit on allowable loads in your design basis and document it as a constraint. A separate design can be prepared to cover the very few locations with excessive loads instead of impacting the
Key Considerations for Optimal Steam Piping Design
Key Considerations for Optimal Steam Piping Design Home / Learning Steam piping design is a paramount consideration engineers and designers working in industries such as Power, Oil and Gas, Petrochemicals, refineries, and other process industry. Steam piping serves as the vital system that transports steam from steam generators, commonly known as boilers, to different points of usage.Depending on the specific application, the steam can be either saturated or superheated, operating under extremely high temperatures and pressures. To ensure both the safety and efficiency of steam piping systems, strict adherence to industry codes and standards is imperative. In this comprehensive article, we will explore the key aspects of steam piping design, including code requirements. Code Requirements for Steam Piping Design The two most common codes for the design and construction of steam piping systems are ASME B31.1 – Power Piping and ASME B31.3 – Process Piping. B31.1 applies to steam piping systems in power plants, while B31.3 covers piping in chemical, petroleum, pharmaceutical, and other process industries. These codes outline the minimum requirements for material selection, design, fabrication, inspection, and testing to ensure safety and reliability. Selecting the Right Piping Materials Choosing the appropriate materials for steam piping is crucial due to the extreme conditions that steam systems operate under. The most common materials used are carbon steel, stainless steel, and alloy steel. These materials offer excellent resistance to high temperatures and pressure. For higher-temperature applications, consider materials such as chrome-molybdenum alloys. Factors Influencing Material Selection: Temperature and Pressure: Steam piping systems can operate at varying temperatures and pressures. Material selection should consider the maximum and minimum temperatures the system will experience, as well as the pressure levels it will handle. Strength and Toughness: The material must possess sufficient mechanical strength to handle the stresses generated by high pressures and temperature differentials. Toughness is important to prevent brittle fractures under sudden temperature changes.Thermal Expansion: Steam piping materials should have compatible thermal expansion properties to prevent issues related to differential expansion and contraction.Also Read: A comprehensive guide to pressure vessel design: Ensuring Safety and Reliability Common Piping Materials for Steam Piping Design Carbon Steel (ASTM A106/A53): Carbon steel is widely used in steam piping due to its affordability, high strength, and thermal conductivity. It’s suitable for lower temperature and pressure applications. However, it’s susceptible to corrosion in the presence of moisture and aggressive substances in the steam.Stainless Steel (ASTM A312/A358): Stainless steel offers excellent corrosion resistance and strength, making it suitable for a wide range of steam applications. Types 304 and 316 are commonly used in steam piping systems.Alloy Steel (ASTM A335): Alloy steels, such as chrome-molybdenum alloys (e.g., P11, P22), offer enhanced resistance to high-temperature and high-pressure conditions. They are commonly used in superheated steam applications.Duplex and Super Duplex Stainless Steel: These materials combine high corrosion resistance with strength, making them suitable for aggressive environments or applications with both high pressure and temperature.Nickel Alloys: Nickel-based alloys, like Inconel and Monel, are used in extreme conditions involving high temperatures and aggressive media. They’re suitable for specialized applications in industries like petrochemicals. Applicable Codes for Material Selection: When selecting piping materials, it’s important to consult industry codes and standards that provide guidance on material specifications, properties, and limitations. For instance:ASME B31.1 and ASME B31.3 codes provide guidelines for material selection based on factors like temperature and pressure ratings and ASTM standards provide detailed specifications for various piping materials, helping engineers choose suitable materials based on the application’s requirements. Sizing and Layout of Steam Piping Design Sizing and layout are critical aspects of steam piping design that directly impact the efficiency, performance, and safety of the entire system. Properly sizing the pipes and arranging them in an optimal layout ensures efficient steam distribution, minimizes pressure drop, and reduces the risk of operational issues such as water hammer, condensate accumulation, excessive pressure drop, steam trapping, steam quality, and leakage of steam. The optimum design also helps in the following important points related to sizing and layout: Sizing of Steam Piping: Steam Flow Rate: Determining the steam flow rate is the first step in sizing steam pipes. This involves understanding the amount of steam required for the process and accounting for any potential variations. Pressure Requirements: Consider the desired pressure at the point of use. Pipe sizing should accommodate the pressure drop due to friction and elevation changes, ensuring that the required pressure is maintained.Velocity: Steam velocity within the pipes should be maintained within acceptable limits. Very high velocities can lead to erosion, while low velocities may cause condensation and reduced efficiency.Pipe Diameter: The calculated steam flow rate and pressure drop help determine the appropriate pipe diameter. Smaller pipes can result in excessive pressure drop, while oversized pipes lead to condensation and reduced efficiency.Sizing Standards: Industry codes and standards, such as ASME B31.1 and B31.3, provide guidelines for pipe sizing based on factors like flow rate, pressure, and material. The layout of Steam Piping design: Routing and Accessibility: The layout should allow for easy access for maintenance and repairs. Proper routing prevents obstruction and minimizes the need for complex maneuvers around the piping. Pressure Drop Minimization: Arrange pipes to minimize pressure drop, especially in long runs. Consider gradual inclines and declines to prevent pockets where condensate can accumulate. Expansion and Flexibility: Account for thermal expansion and contraction. Properly placed expansion joints and loops accommodate these movements without stressing the piping or causing misalignments. Drainage: Incorporate proper drainage points to allow condensate to be efficiently removed from the system. Improper drainage can lead to reduced heat transfer and potential water hammer issues. Branching and Manifolds: Design branching and manifold systems that ensure uniform steam distribution to different points of use. Avoid abrupt changes in pipe diameter that can cause turbulence. Supports and Hangers: Install supports and hangers at appropriate intervals to prevent excessive stress on the pipes. This maintains the integrity of the system and prevents sagging. Isolation and Valves: Include isolation valves for maintenance purposes, allowing sections of the system to be shut off without
