Flange Leakage Evaluation based on NC 3658.3 Method method using Caesar II

This is the last post on the topic Flange Leakage Evaluation using Caesar II. I had already published 3 more posts on flange leakage checking. Click here to visit those. In this section I will describe the methods of flange leakage evaluation by NC 3658.3 method using Caesar II.
NC 3658.3 Method for flange leakage evaluation can only be applied if the following two conditions are met:
  1. Flanges, bolts and Gaskets used are designed based on as specified in ASME B 16.5a and
  2. Boting material must have a allowable stress value at 100°F(38°C) >=20000 psi (138 MPa) (High Strength Bolting)
Governing Equation: 
By NC 3658.3 method the generated external moment (Mfs) is limited to a value as provided by the below mentioned equation:
Mfs<=3125(Sy/36000)C X Ab     (in U.S. Unit)
Here Sy=Yield strength of flange material at temperature
and Ab= Bolt area
The ratio of Sy/36000 has to be taken less than unity.
So it is obvious from the above equation that we have to enter the bolt area and yield strength as input into Caesar II Spreadsheet.
Evaluation steps followed in Caesar II:
  •  Select Flange Node(From/To/Both) and Calculation Type(NC-3658.3) as shown in Fig. 1.
  • Input Bolt circle diameter from ASME B 16.5.
  • Input Yield Strengths at temperature from ASME BPVC code Section II Part D Table Y1.
  • Calculate the Bolt Area (Ab) as shown below and input in required place:
Bolt area, Ab is the total cross-sectional area of the bolts at the root of thread or section of least diameter under stress.
Calculate the bolt area as mentioned below :
Droot = D1bsc – 2*0.21650635P &
D1bsc  = Dbsc – 2*h
Droot = Root diameter of bolt
Dbsc = Basic major (nominal) dia of bolt (as per ASME B1.1, para 8.3)
D1bsc = Basic Minor diameter (as per ASME B1.1, para 8.3)
h = Height of thread (as per ASME B1.1, Table 5)
P = Pitch of Bolt (as per ASME B1.1, Table 1)
Root Area of bolt (Ab) = n x (pi/4* Droot* Droot)                            Where n = No. of bolts
Fig.1: Input Spreadsheet from Caesar II for flange leakage check by NC 3658.3 method
  • Now go to the Load Case Option Editor (Fig.2) and select flange analysis temperature based on operating/design conditions and click the Run button for analysis.
  • Select the Load Case(s) for which Flange Leakage Check has to be performed and see the results. If the ratio of Flange Stresses to Allowable Stress is less than 100 % (See Fig. 2), Then the flange is within allowable limit and should not produce leakage. If it is more than 100%, Then try to reduce moments at the flange by re-analysis of the system and recheck using the above method.
Fig.2: A typical Caesar II flange leakage analysis report

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

10 thoughts on “Flange Leakage Evaluation based on NC 3658.3 Method method using Caesar II

    1. Criteria should be based on ITB document..I dont feel it will defer from hot lines…In short you can check/ investigate for leakage possibilities in the following cases:
      1. On control valves
      2. On PSv connections
      3. On other connections where leakage can cause serious harm to mankind

      Roughly you can check all locations where bending stress near to flanges are more than 4000 psi.

      1. Dear Anup,

        Kindly share your whatsup number for asking more Stress related questions?

        Guys, I am creating Whatsup Group for Stress Analysis member ?

        Please share your phone number to my what’s up number +91-99678-12330

  1. hello sir in flange leakage evaluation method NC 3658.3 in result if ratio is more than 100% how to change the moments explain in detail 

    rizhwan md

  2. Dear Sir,
    I come from the middle east region which is not a very seismic prone zone. I am performing flange leakage using the NC method. I wanted to enquire if flange leakage needed to be performed for the wind and seismic cases as well??

    1. Flange leakage is normally not checked for wind and seismic cases. However if your client says to do so you don’t have other option.

  3. Hi Good Evening Every Body,
    I have Query Regarding NC 3658.3 Result, I notice that in some cases when i am checking flange leakage for higher flange size in output of flange leakage area of bolt (AB sq mm) is showing ***** Value in SI units. if you run same file in US unit than AB sq Inch value is there. so My Query is why it happen.

Leave a Reply

Your email address will not be published. Required fields are marked *


Recent Content

Subscribe For Latest Updates

Signup for our newsletter and get notified when we publish new articles for free!