My last two articles on flange leakage explain the basic theory behind flange leakage checking and methods for performing flange leakage checking using the pressure equivalent method. In this article, I will explain the steps taken to perform a flange leakage check using Caesar II by the ASME Sec VIII method.
Background of ASME Sec VIII Flange Leakage Checking
ASME Sec VIII flange leakage method is performed when the flange analysis using the pressure equivalent method shows failure in Caesar II. The pressure equivalent method is believed to be highly conservative and does not provide the actual results. In most situations, the pressure equivalent flange leakage checking shows failure even with very less axial force and bending moments. It is, therefore, a standard engineering practice to perform the ASME Sec VIII method for those flanges where the pressure equivalent method shows failure.
ASME Sec VIII flange leakage checking method is widely accepted in industries and frequently used to qualify the flanges where the pressure equivalent method shows a failure.
Inputs for ASME Sec VIII Flange Leakage Checking
The following codes and standards are required for data input in the Caesar II flange leakage spreadsheet while performing the ASME Sec VIII method.
- ASME B 16.5/ASME B 16.47- Latest Edition (For Flange Data)
- ASME B 16.20- Latest Edition (For Gasket Data)
- Piping Material Specification (For Flange, Bolt and Gasket Materials and types)
Steps for ASME Sec VIII Flange Checking Method in Caesar II
The basic steps involved in performing ASME Sec VIII flange leakage checking are mentioned below:
- After performing static analysis click the “Analysis” and then click “Flanges” in CAESAR II as shown below.
- Provide a file name and select the proper Flange Type in the section as mentioned in the PMS. Input the flange parameters in the consistent unit as per the used UNIT FIL as shown below:
- Press the key “Ctrl+F” to select the concerning Size and Rating. Few data will automatically be filled from the Caesar II database. However, it is good practice to confirm the data from the governing code.
- Flange Class is the flange pressure rating and is required for checking the P-T Rating of Equivalent Pressure.
- Flange Grade: Select Material Group No. as per ASME B 16.5 Table 1A list of material specifications. The following table can be used as a reference:
- Refer to the applicable flange code ASME 16.5 or ASME B 16.47 and update automatically filled flange data. Take special care while inputting for ‘Small End Hub Thickness’& ‘Large End Hub Thickness’. ‘Small End Hub Thickness ’ must be equal to the Pipe Thickness. Large End Hub Thickness must be equal to (X-B) where X is Hub Diameter and B Flange ID.
- Enter hub Length h=(Y-tf) where Y is length through Hub and tf is flange thickness.
- Now it is the turn to enter the Bolts and gasket parameters. Take parameters from ASME B 16.20 or ASME B 16.21 as shown below:
- Check Bolt Circle Diameter, Number of Bolts and Bolt Diameter, suggested by CAESAR II in reference with ASME B 16.47, 16.5.
- Correctly input for Gasket information in conjunction with ASME B 16.20 or 16.21 as applicable.
For Effective Gasket Modulus, press Shift+? Key and then follow “High End” in Help statement. Leak Pressure Ratio m, Gasket Seating Stress y shall be in accordance with ASME SECTION VIII Div.1. Values for Caesar II help can be taken by pressing Shift+? or by pressing the F1 key keeping the cursor on the relevant box.
- For Nubbin Width in the right side, Leave blank for Welding Neck Type and input Ring joint width as per the ring no. as described on ASME B 16.20 Table 3 TYPE R RING GASKET DIMENSIONS AND TOLERANCES for ring type joint.
- Facing Sketch/ Facing Column can be inputted as follows mentioned below:
- Now input the material data as shown below:
- Select the material of Flange and bolt, and Input design temperature.
- Flange Allowable & Bolt Allowable at design and ambient temp can be taken from the CAESAR II database for particular flange and bolt material.
Flange Modulus of Elasticity shall be taken from table C-6 of ASME B-31.3.which is given in millions of psi convert it to consistent unit
- Use 1.0 for Flange Allowable Stress Multiplier and 2.0 for Bolt Allowable Stress Multiplier. Use project-specific data if available.
- Now Input Design Pressure, Axial Force, Bending Moment from Static analysis of the Caesar file as shown below:
- Now run the analysis to study the output results. Normally If safety Factor is less than one then joint failure is predicted and in output this is shown by a * mark.
- If the output result shows failure then try to reduce the bending moment or axial force and reanalyze. If that is not possible check if the flange rating can be increased.
Sometimes, the flanges are seen to be failing is seating stresses. In such scenario, try to get actual gasket seating stress data from vendor and enter into the spreadsheet. Normally with reduced gasket seating stress value seating failure can be avoided.