Articles

All You Need to Know about Flange Leakage in Piping Systems

by Engineering Geek Expert in industrial engineering including piping,
Whether it is an oil refinery, power plant, chemical processing facility, or any industrial plant, pipe leaks are a nightmare. The material leakage from the faulty piping system can be poisonous and potentially deadly. The flange connects pipes, valves, pumps and other components using bolted connections & gaskets to form a piping system. 

Flange leakage is a severe problem in the piping system as it has tremendous potential to prove extremely hazardous. This article provides you insights about common causes of flange leakage and methods to perform flange leakage check.

Possible Causes for Flange Leaks

  • Improper installation in bolt up procedure or confined operation conditions near the flange can make some bolts extra loose while over-tightening the others. It eventually can crush the gasket and cause service leaks.
  • Inappropriate flange alignment during face parallelism causes uneven gasket compression, local crushing and subsequent flange leakages.
  • If a gasket is installed off-center compared to the flange faces, it will be unevenly compressed, making the joint prone to leakage.
  • Dirt, pipe scale, scratches, protrusions, weld spatter on gasket seating surfaces and warped seating surfaces provide leakage paths.
  • Excessive vibration levels can loosen flange bolts, which causes flange leakage.
  • Excessive forces and bending moments at the flange location can loosen the bolting or distort the flanges and lead to leaks.
  • The selection of the wrong gasket size or material during installation can cause corrosion or blowout damages, which results in leakages.

The leakage problems need to be identified during the design stage to avoid/ reduce leakage possibility during operation. Flange leakage is a function of the relative stiffness of gasket, flange and bolting in the piping system. 

ASME B16.5 is a construction code for designing new flanges. It doesn’t account for the external bending moment in the pipe. It leads to a wire drawing effect on the flange’s mating surface. The process piping flanges are designed following ASME BPV Section VIII of Division 1, appendix 2, using allowable stress and temperature limits of ASME B 31.3.

Criteria for Flange Analysis

The rules for when flange leakage checking is required should be specified in the ITB (Invitation To Bid) documents or project specs. 

Analysis Methodology

The flange leakage calculations can be performed in many different ways. But the three widely used methods for checking flange leakages are as follows:

1. Equivalent Pressure Method (Based on ASME B 16.5 pressure temperature table)

This method converts piping axial forces (F) and bending moments (M) into equivalent pressure (Pe) on the flange using the following equations.

Pe1=4F/ΠG^2 [Equivalent Pressure for Axial Force]Pe2=16M/ΠG^3 [Equivalent Pressure for Bending Moment]
G = diameter of gasket load reaction

Now consider adding these two equivalent pressures with pipe design pressure (Pd) to find total force (Pt=Pd+Pe1+Pe2).  And, enter the ASME B 16.5 pressure-temperature value rating table associated with flange material. 

If Pt is less than the provided pressure on the rating table following the associated temperature, then the flange will not leak. 

2. ASME VIII-1 Appendix 2 Method:

This method calculates flange stresses, including longitudinal hub stress, radial flange stress and tangential flange stress based on provided equations/formulas. The calculated stresses are then compared with allowable stresses defined in BPVC Code Sec VIII Div 1 Appendix 2, Clause 2-8.

3. ASME NC-3658.3 Calculation Method:

In this method, the flanges are assessed using the ASME BPVC Section III Subsection NC-3658.3 method. The determined flange moments are then compared to some limited values as calculated from code equations. 

Conclusion

Every organization has different criteria on which flanges need to be checked during the design phase. Consider using widely accepted CAESAR-II software for piping flexibility analysis of a piping system.

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About Engineering Geek Junior   Expert in industrial engineering including piping,

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Joined APSense since, November 20th, 2019, From Seattle, United States.

Created on Sep 3rd 2020 06:48. Viewed 241 times.

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