API ADVISORY 6- API 6B excepted 2

[cak4Engg]

Hi all,

Why are API-6B flanges excepted from API-advisory 6(Design and Development Exclusion under the API Monogram Program), while 6BX flanges are excluded?.
since the 6B flanges are excepted from advisory, what all calculations are necessary to clear API Audit.
is through-thickness (neck thickness) verfication sufficient?
As the dimensions for the flanges are given in the code itself I don't understand why we have to redesign the flange?

CaK

 

[jmec87]

Hi CaK,

This is a good question. To calculate the stresses in a flange, the pressure, loads, and many dimensions are required, including the flange hub diameter and hub length. The reason that 6B flanges are excepted from Advisory 6 (and thus need design) is because API 6A only specifies the flange hub diameter as a reference dimension (it is not required to be met) and does not specify the hub length. This means that a 6B flange could be manufactured that meets all the required dimensions from 6A but has excessive stresses due to a hub that is too small. Therefore, design (calculations, FEA, etc.) is necessary to verify the 6B flange design. Because the 6BX flange dimensions in 6A include the hub diameter and length as normative (required) dimensions, all dimensions required for flange stress calculations are specified in 6A for 6BX flanges, and therefore 6BX flanges do not require design.

API does not specify which calculations are necessary, but it does specify the methods in API 6A Section 4.3. Note that API 6A Section 4.3.1.1 (which has the design method requirements for flanges) does not include any actual requirements, but only has a statement about how the flanges were designed. This means that there are no applicable 6A requirements for how you perform the flange design. However, your design process should be in accordance with your quality management system, which has to meet API Q1 if your company has an API Monogram license. I recommend performing flange calculations per API 6A 4.3.3.2 (ASME Method) and ASME BPVC 2004 with 2005 and 2006 Addenda Section VIII Div 2 Appendix 3 (the 2004 edition with 2005 and 2006 addenda is specified in 6A for calculations per 4.3.3.2).

 

[cak4Engg]

Hi jmec87,

Thank you so much for such a detailed response.
Further, say if we are following exactly the dimensions (including reference dimensions) provided in API-6A for 6B flanges, do we have to do a design?
If we have to do a design, I understand that we have to perform the complete flange design calculation as ASME Sec VIII Div-2 of 4.16 (DESIGN RULES FOR FLANGED JOINTS)or FEA of the flange. The weld neck thickness verification of flange won't be sufficient, right?

Cak

 

[jmec87]

Hi Cak,

Even if you follow all the dimensions (including reference dimensions) for 6B flanges, you still have to do a design, because the hub length is not specified at all (reference or normative) in API 6A, and this is an important factor in the flange stress.

How you perform the design analysis (calculations per ASME BPVC Sec VIII Div 2, FEA, or something else) is up to you. I recommend following the flange design requirements of ASME BPVC Sec VIII Div 2 (either 2004 with 2005 and 2006 addenda due to this being reference in 6A 4.3.3.2 or the most recent edition), as this is a proven and recognized methodology. However, as far as compliance to API 6A is concerned, there are no requirements for how you have to analyse the flange design.

 

[sarathmeetme]

Thanks for the clarification on advisary 6 exception of 6B flange.
If we possess API 6A monogram & Q1 (with no exclusions), should we required to prepare & maintain the evidence of design for 6BX flanges for every manufacture?

 

[prasenjith]

Note: 6bx 6b combination adaptor flange require design calculation(monogrammed)

 

[KevinNZ]

This thread raises more questions than answers.

Clause 4.1.1 says the flanges have already been designed by API. It does not say they have to be designed again.

Hub diameter X is a reference dimension (Table 49) but the code does not define what this means.

API 6B say the flange dimensions shall comply with the tables. If calculations show these dimensions do not work then what?

For 6B flange hub diameter X is given. Then can it be assumed if the hub length is very long then X is adequate and no design calculation is required?

Do you have to design a Welding Neck (WN) line-pipe or threaded flange? These do have a hub length. (Can we assume hub diameter X is the same as integral flanges)