Kellog Trunnion allowable stress

[BrendG]

Dear Experts,

As per Kellogg company subject 3810, after calculating loads as for table A with formulas in figures VI-VIII, stresses are calculated as shown in the pape (SB, SPL, ...).

This stresses calculated must be compared with the total allowable stress "S" never over 30ksi.

My question comes because i have seen many places where 1.5Sh is taken as maximum allowed stress for nomal operating case and 2.0Sh for occasional cases.

But as is shown in table B from kellogg method, the stresses calculated should be less than 2.0Sh for normal operating case and 2.4Sh for short time operating.

Anyone could explain me why not using 2.0Sh for OPE and 2.4Sh for OCC?

Thank you

 

[C2it]

The so-called 'Kellogg equation' originated in the 1955 Edition of 'Kellogg design of Piping Systems and has little or nothing to do with The Kellogg Company or KBR of today. It is a simple one line equation that supposes to represent a complex stress field which has been misinterpreted and extended (wrongly) to elbow trunnions over the years. Allowable limits applied are solely the discretion of the company or individual that provides them, and bear no relation to any authorised Code or specification. IMHO the best that can be said is that the 'Kellogg trunnion method' is a comparison to countless similar designs, most of which have survived their design life. This admirable record is in now danger due to use of high yield materials with thin wall piping.

For a far better solution, look at ASME III Article Y-5000 for straight trunnions and the similar work for elbow trunnions found in EPRI report TR-107453.