Re: [PSUBS-MAILIST] Hull Penetration and Reinforcement

On Sat, Apr 3, 2010 at 12:40 PM, Jon Wallace <jonw@psubs.org> wrote:

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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