Bolt Spacing in Flange Design for Lethal Service as per ASME Sec-VIII Div-1 Clause 2-5 & 2-6 1

[ashaykadam]

I have observed following conflict regarding Bolt Spacing & Bolt Correction Factor in Flange Design for Lethal Service as per ASME Sec-VIII Div-1 App-2, Clause 2-5 & 2-6.

As per App-2, Clause 2-5 (d),
"For vessels in lethal service or when specified by the user or his designated agent, the maximum bolt spacing shall not exceed the value calculated in accordance with eq. (3)."

As per App-2, Clause 2-6,
"For vessels in lethal service or when specified by the user or his designated agent, the “Bolt Spacing Correction” shall be applied in calculating the flange stress in 2-7, 2-13(c), and 2-13(d)."

Now I have 4 questions as follows:

1. When as per App-2, Clause 2-5 (d), the maximum bolt spacing is restricted for Lethal Service then why again in Clause 2-6 requirement of “Bolt Spacing Correction” is made applicable?

2. Does it mean that “Bolt Spacing Correction” need to be applied for Lethal Service even though the Bolt spacing is less than the maximum bolt spacing as per Clause 2-5 (d).

3. If answer of 2nd question is “YES” then, please clarify below:
The value of “Bolt Spacing Correction” is Bsc = SQRT [Bs/(2*a+1)] where “Bs” is actual Bolt Spacing.
In case for Lethal Service if value of “Bs” is less than (2*a+1) then whether the value of “Bolt Spacing Correction” is acceptable as less than 1? or it should be minimum 1?

4. Is requirement for consideration of “Bolt Spacing Correction” applicable for all flanges (irrespective of Lethal Service) where Bolt Spacing exceeds (2*a+1)?



Ashay Kadam
Manager
Mechanical Department

Uhde India Private Limited
Mumbai, India.

 

[SnTMan]

ashaykadam, there does appear to be an inconsistancy regarding the Bsc and BSCF. Before these requirements were added to Apx 2 it was customarily done as follows. If bolt spacing exceed the maximum Bsc then the BSCF was calculated and applied. If Bsc was not exceeded, the BSCF was taken as equal to one. It was never taken as less than one.

Point of little interest: Both TEMA and Taylor Forge #502 had requirements for Bsc and BSCF. They each differed slightly. The Apx 2 requirements are a combination of the two.

Regards,

Mike