Table of content
Introduction
There are two series of flanges in the pipeline industry: A series and B series. What is the difference between these two series of flanges? What are the characteristics of its two series? How to make a choice? With these questions in mind, let’s read this article to understand A series and B series flanges.
What Are Series A and Series B Flanges?
A-series flanges: lighter weight, smaller screw hole diameter. This series of flanges can be appropriately reduced in size and weight within the range that meets production standards.
B-series flanges: heavy in weight, with larger screw hole diameters. This series of flanges is relatively old and has a larger volume.
Both series of flanges are produced according to different international standards.
Why Do We Have Two Series of Flanges?
According to the development of the industry, two series of flanges have been derived.
- A-series: With a heavier weight, it is suitable for more compact and economical pipeline series. This series of flanges saves material costs and is easier to install.
- B-series: It is an older standard, previously API 605. This series of flanges is relatively heavy and is now commonly used in the oil and gas pipeline industry.
Main Differences Between Series A and Series B Flanges
1. Difference in size and weight
A-series: Smaller in size, lighter in weight, and easier to install and operate.
B series: Larger in size, heavier in weight, and more difficult to install than A series.
2. Bolt hole diameter
A series: The bolt hole diameter is relatively small. This means that the bolt is closer to the center, which can reduce the overall size of the flange.
B series: The bolt hole diameter is relatively large. Due to the larger overall flange size.
3. Pressure level
Both use pressure ratings under ASME standards, such as class 150, 300, 600, 900, 1500, etc.
A series: Under the same standard and pressure level, A series can withstand lower pressure than B series.
4. Application
A series: commonly used in modern pipeline systems. For industries where weight, cost, and pressure levels are not particularly high, it is sufficient for application. It can also be used in some power plants and marine projects.
B series: commonly used in some old-fashioned or ultra heavy pipeline projects. It is more commonly used in some old-fashioned systems, so B-series flanges also need to be selected for replacement.
Series A vs Series B Flanges: Quick Comparison Table
| Feature | Series A Flanges | Series B Flanges |
|---|---|---|
| Standard | ASME B16.47 Series A | ASME B16.47 Series B (old API 605) |
| Size & Weight | Smaller, lighter | Larger, heavier |
| Bolt Circle | Smaller diameter | Larger diameter |
| Pressure Handling | Higher external load capacity | Lower compared to Series A |
| Applications | Modern systems, new projects | Legacy systems, refineries, replacements |
| Cost | More economical (less material) | More expensive due to size/weight |
| Use Today | Preferred choice in new installations | Mainly for compatibility with old systems |
Flange Selection: Which One Should You Choose?
For some newly laid pipelines, A-series flanges are usually used. This type is more economical and efficient.
For the replacement of flanges in some old pipeline equipment, the B-series method may also be needed to match it.
Summary
A-series flanges: lightweight, small size, and higher strength per unit weight. It is a commonly used series in the current system and has been widely promoted and used.
B-series flanges: heavier and larger in size, but in order to be compatible with old equipment, B-series flanges still need to be used for replacement.
But both types of flanges are produced in accordance with ASME standards.
So for newly built pipelines, choose A-series flanges, and for replacing old equipment, choose B-series.
