How To Select The Right Carbon Steel Flanges

Elite Piping Manufacture is one of the world’s leading carbon steel flanges manufacturers. Are you looking for the right carbon steel flanges for your project? This article will teach us how to select the right carbon steel flanges.

According To Carbon Steel Flange Standard

There are two main carbon steel flange standard systems in the world. One is the European flange standard system represented by the EU EN standard (nominal pressure level is expressed in PN), and the other is the American flange standard system represented by the US ASME (nominal pressure level is expressed in Class).

In addition, there is the Japanese JIS standard system (nominal pressure level is expressed in K). The latter is not commonly used, and today, we mainly discuss the European and American flange standard systems.

The EU EN carbon steel flange standard system consists of two systems: one is EN1092-1 based on the original DIN (German standard), NF (French standard), and BS (British standard), and the other is EN1759-1 based on ASMEB16.5. The European standard flange system discussed in China often refers to the flange standard system of EN1092-1, and this article is also the case.

EN1092-1 includes 7 grades of nominal pressure of PN2.5, PN6, PN10, PN16, PN25, PN40, and PN100, with a nominal size of DN10-DN4000.

The American standard ASME flange standard system mainly comprises two standards, ASMEB16.5 and ASMEB16.47. ASMEB16.5’s caliber range is DN600 and below, and ASMEB16.47 includes two series, A and B, which are used in occasions above DN600. Among them, ASMEB16.47A was developed on the basis of MSS SP-44, and ASMEB16.47B was developed on the basis of API605.

It should be noted that the A and B series of ASMEB16.47A (corresponding to HG20623A/SH3406-2013 large diameter A) and ASMEB16.47B (corresponding to HG20623B/SH3406-2013 large diameter B) are the distinction of external dimensions such as matching dimensions, which are two concepts with the imperial and metric outer diameters of the flange pipe end.

Matching Size And Pipe Size

The matching size of flange refers to the number of bolts, bolt diameter, sealing surface width, sealing surface height and other dimensions of the flange. Only when these dimensions of the two flanges are completely consistent can the flanges be accurately connected and sealed reliably. Obviously, flanges of different standard series and different pressure levels are basically unable to be matched (exceptions are not excluded, but the scope of exceptions is very small, and it is generally not done in engineering).

Nominal Pressure Level Of

Carbon Steel Flanges

The nominal pressure level is a grouping of flange strength. Flanges of different materials and different nominal pressure levels have different maximum non-impact working pressures allowed at specific temperatures. This is the concept of temperature and pressure ratings.

For European standard flanges, the HG20592 standard is commonly used in China. In its 97 standard, the pressure levels are N0.25, PN0.6, PN1.0, PN1.6, PN2.5, PN4.0, and PN10.0. Since the pressure level is dimensionless, it is indeed related to MPa. In the 09 standard, the pressure level has become associated with Bar, which is PN2.5, PN6, PN10, PN16, PN25, PN40, and PN100, a total of 7 levels.

For the 09 standard, the maximum allowable working pressure of European standard flanges of specific materials at different working temperatures can be calculated by the following formula: p (bar) = (PN value X design strength) / 225.

The design strength is obtained according to the following values: a When the working temperature is lower than the creep temperature of the material, the yield strength of the material is taken. b At the creep temperature, 1.5 times the allowable stress of the material is taken. c When the design strength of the material is higher than 225MPa, 225MPa is taken.

For American standard flanges, one commonly used standard in China is the HG20615/HG20623A/B standard. In its 97 standards, the pressure levels are PN2.0, PN5.0, PN11.0, PN15.0, PN26.0, and PN42.0. In the 09 standard, the pressure level becomes consistent with the ASME standards, which are CLass150, CLass300, CLass600, CLass900, CLass1500, and CLass2500. For the 09 standard, the maximum working pressure allowed at different working temperatures for American standard flanges of specific materials can be calculated by the following formula: p (bar) = (Class value X10X design allowable stress) / 8750. For this formula, when CLass150, substitute 115.

The design allowable stress (MPa) is obtained according to the following values: 60% (carbon steel and low alloy steel) or 70% (stainless steel) of the material yield strength at room temperature or set temperature. b 1.25 times of 25% of the tensile strength at room or set temperature. c The allowable stress value is determined by the long-term strength at high temperatures. And p cannot exceed the maximum working pressure limit determined according to the use experience.

We often use PNXX to indicate their nominal pressure level for European standard flanges. Since PNXX is a dimensionless unit, we generally do not follow PNXX with bar (HG20592-09) or MPa (HG20592-97).

For the American standard flange, HG20592-97, PN2.0, PN5.0, PN11.0, PN15.0, PN26.0, and PN42.0 were used to indicate its pressure level. In the 09 version of the HG20615/HG20623 standard, only CLass (abbreviated as CL) XX was used to indicate its pressure level.

Writing it as 150 is not standard for carbon steel flanges. When selecting any nominal pressure level for any flange, the flange material must be clear. Check the flange standard and review its temperature and pressure ratings. Of course, you can calculate the temperature and pressure ratings yourself using the above method.

European And American Carbon Steel Flange Standard

First, the matching sizes are different, and second, the outer diameters of the pipes may be the same or different. Can CL150 flanges be used in PN2.5, PN6, PN10, and PN16 applications? You need to check the corresponding carbon steel flange standards to see if the specific temperature and pressure ratings (the maximum operating pressure allowed for flanges of specific materials at operating temperatures) meet the requirements. However, they are unlikely to be paired with PN2.5, PN6, PN10, and PN16 flanges. See the specific standards.

How To Mark Carbon Steel Flanges

At least, you should indicate the following: pressure rating, material, sealing surface type, pipe outer diameter, and wall thickness. Of course, for flat welding flanges/socket flanges, you do not need to indicate the pipe wall thickness.