ANSI ratings are a set of standards created by the American National Standards Institute to designate the pressure-temperature ratings of pipe flanges. Traditionally, valves that have flanges connected are described with ANSI Class ratings. The ANSI ratings of flanges for strainers, valves, or fittings help ensure that the right flange is used, given the type of material and the maximum temperature and pressure to which it will be exposed. In its denotation, ANSI Class is followed by a number, including Class 150, 300, 400, 600, 900, 1500, and 2500.
Origin of the ANSI Class Rating
The American National Standards Institute (ANSI) is a nonprofit organization that oversees the standards of various products, processes, services, systems, and personnel in the U.S. They work to promote the facilitation of accepted standards to safeguard the integrity of products, as well as the public, and to keep the competition of businesses and manufacturers fair.
When it comes to the standards set for flanges, the American National Standard is documented in ASME B16.5-2017: Pipe Flanges and Flanged Fittings by the American Society of Mechanical Engineers (ASME). The standard for flanges involves pressure-temperature ratings, dimensions, tolerances, materials, marking, testing, and methods of designating openings. This standard has been in existence since 1920, when ANSI was new.
Since that time, there have been numerous modifications and updates that led to the current B16.5 document, which was released in 1988.
What is an ANSI Class Rating?
The ANSI Class rating of a flange is defined as the maximum amount of pressure that the flange can withstand at increasing temperatures. There are seven primary pressure classes for flanges. They are 150, 300, 400, 600, 900, 1500, and 2500. You may see the terms class, pressure rating, lbs., or #, referring to the rating of flanges. These terms are used interchangeably, and all refer to the same concept of the pressure-temperature performance of flanges, or other parts like fittings and valves.
Temperature Ratings and Pressure Ratings
The various materials that are used for piping (stainless steel, alloy, steel, carbon steel, etc.) all have different properties, mechanically and chemically. That means that depending on the specific material, how they handle stress at different temperatures will vary. For that reason, the ASME established the maximum allowable stress value of a material at a specific temperature. These maximums are documented in ASME B31.3. This temperature rating is used to calculate how thick the walls of the pipes, flanges, and fittings have to be to withstand the stress due to pressure.
The pressure rating, like the temperature rating, denotes the maximum operating pressure that the flange or other equipment can handle in relation to the working temperature. As the temperatures rise, the maximum pressure goes down.
Let’s consider some examples:
Example #1: Two flanges have the same bore size and are made of the same material. However, they have two different pressure ratings (one is class 300, and the other is class 600). The flange with the lower rating (class 300) will be lighter and smaller than the flange with the higher rating (class 600).
Example #2: Let’s take a look at one class 300 flange made of carbon steel. At a temperature of 500 degrees Fahrenheit, the flange can withstand pressure of 605 PSI, while at 700 degrees F, can only withstand 530 PSI.
ANSI Class vs. PSI
There are many piping system parts that have ratings that are expressed in pressure per square inch, or PSI. However, the parts that are associated with flanged connections are traditionally expressed in ANSI classes. Because of this, there is sometimes confusion when people are considering which flange is best for a specific project. It’s easy to get confused because the class rating is also called an ANSI class pressure rating. But the class rating for a flange involves knowing the material it is made of, the maximum working temperature, and the maximum operating pressure it has to withstand. The PSI is simply the amount of pressure used in the calculation of the class rating. That means that the ASNI class rating and the PSI will not usually be the same number, because the ANSI class rating also depends upon the material and the maximum working temperature.
In other words, a class 300 flange doesn’t have a 300 PSI rating. The rating it has will vary depending on both what it’s made of and how high a temperature it needs to withstand. Common y strainer materials include stainless steel, carbon steel, cast iron, bronze, brass, PVC, and CPVC. Charts based on information from the American National Standard can be found online that detail the pressure and temperatures that different classes of flanges can withstand. For example, The Engineering Tool Box has charts for Steel Pipe Flanges and Carbon Steel Flanges, which show the temperatures these flanges can withstand based on their PSI and ANSI class ratings.
Finding the Right ANSI Class for Y Strainer Flanges
When looking for the right ANSI class for pipeline strainers or other type of flanges, it’s important that you know the maximum temperatures and pressures that it needs to hold up to. Once you have that information, and what type of material it needs to be, you can find charts online that will show you which class rating will work for your job.
Using the right ANSI class rated flange is essential to making your piping system work efficiently and safely. The above information should help you understand what you need to know, and why you need to know it, when you are deciding on the flange class that is right for your job.