Engineers adhere to ASME/ANSI norms and guidelines. The piping system’s construction helps to ensure that it meets the pressure integrity criteria.
Standards and guidelines help to determine pressure integrity properties and simplify design rules.
The difference between codes and standards is useful for designers who need exact flange specifications and component designs. The following are the most often encountered regulations and standards.
1. Minimum wall flange thickness
2. Permissible materials for construction
3. Allowable work stresses
Thermal expansion, live loads, seismic loads, deadweight, internal pressure, and other external or internal loads all have an impact on structural behavior.
However, the pipe regulations do not provide design guidelines for basic in-line components such as valves and flange fitting components. These types of items are designed using industry standards as a reference.
1. Pressure-integrity standards: The standards assist in setting consistent minimum-performance criteria. Designing and producing components to the same standards will help them work equally.
It is useful to realize that pressure integrity is not synonymous with leakage integrity.
During operation and testing, pressure integrity is one assurance of leak-tightness, but it does not account for the complete risk profile to the structural stability of the pressure boundary or additional stresses.
2. Dimensional standards: The standards define the configuration that aids in controlling the parameters of components. These dimensional standards are primarily designed to verify that similar parts manufactured by different suppliers are physically interchangeable.
Conformity to ASME flange dimension specifications during product manufacturing does not mean that all similar goods will perform equally.
Many distinct ASME standards for piping components have pressure-temperature ratings in their “Reference Codes and Standards” sections.
As per the ASME B16.5, 2017, there are:
a. 16 nonferrous metal groups
b. 10 high-alloy steel material groups
c. 8 Low-alloy steel and carbon material group
You may view the complete lists and tables on ASME B16.5, 2017. (Standard: “Pipe Flanges and Flanged Fittings: NPS ½ through NPS 24 Metric/Inch Standard” .)
Flanges made of any material in the same group can readily carry the same ASME flange pressure class and pressure-temperature rating for nearly any single material group.
The ASME B16.5 standard specifies seven pressure classes for flanges. These include – 2500, 1500, 900, 600, 400 (less prevalent today), 300, and 150. Class 75 is also defined in ASME B16.47 Series B large diameter.
The rating for flanges in terms of pressure-temperature represents all material categories arranged into 44 tables. Every material sub-group or group is represented by a single table that incorporates the ASME B16.5 2017 edition.
Table B2.1 is an adaptation of ASME Standard B16.5 and is representative of the 34 flange rating tables that provide pressure-temperature values for flanges in the 2.1 material group.
The tables below are grouped by pressure class, which may be found at the top. The maximum working temperatures are also displayed along the left margin.
During practice, determining the flange’s rating using ASME B16.5 is rather simple. The following is the recommended three-step process:
a. Determine the maximum temperature and pressure required for the flange.
b. You can choose the material for the flange from the 44 mentioned material categories. Be careful of the qualifying notes on maximum operating temperatures for various materials, which may impact the final material selection.
c. You must reference the appropriate group table of materials. You can begin with the temperature given one increment above the desired maximum working temperature.
Begin with the Class 150 column and work your way to the right until you discover the appropriate pressure rating for the specified temperature, which exceeds or equals the required operating pressure.
The specified column that meets the requirements can determine the appropriate pressure class and the actual pressure-temperature rating of the flange.
ASTM A182 is one of the chrome-based material requirements in Material Group 2.2.
Table B2.2 shows that a Class 600 flange has a rating of 890 psig (6136 kPa gage) at 650°F (343°C).
Table A1.1 Materials Used for ASME B16.5 Flange Construction (Partial Listing)
Table B1.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 1.1 Materials
Table B2.1 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.1 Materials
Table B2.2 Pressure-Temperature Ratings for ASME B16.5 Flanges Made from Material Group 2.2 Materials
