When working with piping designs there are many variables to consider, specifically when it comes to codes. Two of the most commonly used codes with piping design are ASME B31.1 and ASME B31.3, both serving a specific purpose and designed with different applications in mind. In order to determine which code to use, one must first understand the differences between each code.
What Is ASME B31.1
ASME B31.1, often referred to as the Power Piping Code, is typically used in power generation and industrial plants, and specifically designed for high-pressure boiler systems and steam systems. This code is highly explicit and governs the design, construction, and testing of piping systems associated with boilers and steam plants. Given the extreme pressures and temperatures involved in these systems, ASME B31.1 incorporates stricter safety margins to account for the worst-case scenarios, such as expansion, movement, and stress.
Key Characteristics of ASME B31.1
- High Safety Margins: The code increases safety margins by reducing the allowable stress that can be applied to components. For example, where another system might allow 20,000 lbs. of force, ASME B31.1 might limit it to 15,000 lbs. to ensure added safety.
- Material Use: While it uses similar materials and tables as other piping codes, the stress limits are lower, reflecting the high-pressure, high-temperature environment of boiler systems.
- Strict Requirements: The margin of safety in ASME B31.1 typically ranges from 2 to 2.4, which is higher than
inmany other piping codes.
What Is ASME B31.3
ASME B31.3, known as the Process Piping Code, is designed for medium-temperature process piping, which may still involve steam and reasonable pressures, but not to the extreme levels found in ASME B31.1 systems. This code is often used in commercial and industrial process piping systems, including refineries, chemical plants, textile and paper plants, as well as food and beverage processing facilities.
Key Characteristics of ASME B31.3
- Variable Safety Margins: The safety margins in ASME B31.3 vary between 1.5 and 2, depending on the material and conditions, allowing for more flexibility in design.
- Application Flexibility: ASME B31.3 allows for higher allowable stress for the same materials at the same temperatures compared to ASME B31.1, reflecting its use in less extreme conditions.
- Process Piping Focus: This code is particularly suited for the various piping requirements in chemical and processing plants, where systems might involve a wide range of temperatures and pressures.
The Impact on Piping Design
Safety Margins and Stress Levels
The most significant impact on piping design between these two codes lies in the safety margins. ASME B31.1 demands higher safety factors, which means that piping systems designed under this code must account for greater stress and potential expansion. In contrast, ASME B31.3 allows for higher stress limits, giving engineers more flexibility but also requiring careful consideration of the operational environment.
Case Study: Boiler Feed Water System
A practical example of this difference is in the design of a boiler feed water system. On one side of an isolating valve, the piping system adheres to ASME B31.1, requiring thicker steel for added safety. On the other side, following ASME B31.3, thinner wall steel might be used to reduce costs. However, this can lead to complications in maintenance and repairs, as the system now requires specialized handling due to the differing standards on either side of the valve.
Hydrotesting and Certification
There are also significant differences in how hydrotesting is handled under these codes. ASME B31.1 has stricter requirements for hydrotesting and the associated pipe stress, often requiring specialized certification and training (e.g., R stamp for repairs). ASME B31.3, while still rigorous, generally allows for less stringent testing procedures, reflecting its application in less extreme conditions.
Choosing the Right Code for Your Project
Understanding the differences between ASME B31.1 and ASME B31.3 is crucial for engineers tasked with designing piping systems. The choice between these codes can affect everything from material selection and safety margins to long-term maintenance and operational costs. No matter the piping design need, whether that be for power generating stations or other power piping designs, or process piping needs within a refinery or other processing plant, JBW’s team of engineers can ensure that they choose the right code, balancing safety, efficiency, and cost-effectiveness.
