[PSUBS-MAILIST] Hull Penetration and Reinforcement

[Jon Wallace <jonw@psubs.org>]

I'm looking for help understanding some specific elements of engineered 
reinforcement requirements for hull penetrations as per ABS, and also 
opening up a discussion of best practices. For reference, I'm looking at 
the ABS Steel Vessel Rules document:

Part 4 - Vessel Systems and Machinery
Chapter 4 - Boilers, Pressure Vessels and Fired Equipment
Section 1 - Appendix 1 – Rules for Design
7 Openings and Reinforcements

First, I have a specific question related to Figure 8 on page 311, 
elements Tn and Trn at the top left of the nozzle. Did they mark the 
illustration incorrectly? The variable Tn is defined as the nozzle wall 
thickness exclusive of corrosion allowance. The variable Trn is defined 
as the required nozzle wall thickness exclusive of corrosion allowance 
for a maximum working pressure. The equations using these elements look 
correct (Tn-Trn) which would complement the idea of calculating the 
amount of reinforcement provided by the thickness of the nozzle above 
that required for the working pressure. However, the illustration for 
Trn appears to show a sliver of metal as the actual difference between 
Tn and Trn, rather than how Trn is defined in the text. Looking at the 
illustration, I would have expected Trn to be shown as the material with 
the "\" lines through it (or the "/" lines in the right segment) rather 
than the sliver of metal it is currently pointing to.

2010 ABS rule 4-4-1A1/7.1 restricts the calculations for penetration 
reinforcement of shells 60in diameter or less, to 1/2 the shell diameter 
but not exceeding 20 inches. For a typical K-sub (36 inch diameter) this 
means the calculations are valid for a conning tower or viewport no 
wider than 18 inches (457mm). The rule states "Reinforcement of larger 
openings is to be submitted for specific approval".

I don't think I've ever seen a conning tower on any PSUB that is 18 
inches or smaller, and most appear to be 22 to 24 inches in diameter. 
For those of you not working off of K-sub plans, what are you using as a 
guide to calculate the thickness of the conning tower and/or 
reinforcement metal? Busby (http://busby.psubs.org) stated in Chapter 5, 
Page 255 (Hull Penetrations) that an ASME standard is to replace 100% of 
the material taken from the hull. If I calculated correctly however, 
Kittredge replaced the K-sub conning tower penetration with about 400% 
of the material taken from the hull (can anyone check my numbers? Hull 
thickness 1/4inch, conning tower ring is 24.5 x .75 x 9 inches).

Have I missed another ABS document that deals with this issue? 
Notwithstanding submission of a design to an ABS surveyor, what is the 
best practice PSUBS be promoting for this issue?

Jon




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