Section VIII division 1 and it's application to the design of a polar boss for a ASME Section X tank

[gstrcomp]

Hi All,

I'm trying to understand how Section VIII division 1 applies to metallic parts that are being incorporated into a fiber reinforced composite tank that's being designed to Section X rules. I'm specifically looking at Class 1 FRC tanks. It's stated in Section X that the design of all metallic parts must adhere to Section VIII division 1 rules. In particular I'm trying to understand what design rules I have to follow to design a metallic polar boss that's incorporated into the FRC tank. My review of Section VIII division 1 gives me no guidance and any specific design procedures to follow for a polar boss. Since the geometry of the polar boss is complicated does it mean I can use Section VIII division 2 design procedures (FEA) to meet division 1 requirements? Also since Class 1 tanks are qualified by testing and there is no standard design practice, is it possible the same applies to the metallic components?

Any help or guidance would be appreciated.

Thanks

 

[racookpe1978]

What pressure, temperature, fluid, service, and safety factors?

 

[doct9960]

gstrcomp,

Can you attach a sketch or picture of the polar boss?

Even if you say that the "geometry of the polar boss is complicated", there might be applicable rules in ASME Section VIII, Division 1.

If there are no Code rules, then U-2(g) applies. In this case, FEA or proof testing may be performed. Please check with your Authorized Inspector before proceeding with the design.

 

[gr2vessels]

I am not very familiar with the topic, but very keen to learn myself.
Please refer to the link below:

http://www.transoceangas.com/Development_Plan.htm

Cheers,
gr2vessels

 

[doct9960]

The link from gr2vessels gave a clear description of polar bosses.

Found some section views of those polar bosses...

http://hexagonlincoln.com/products/tuffshell-hydrogen-fuel-tanks/

http://hexagonlincoln.com/products/tuffshell-cng-fuel-tanks/

http://www.qtww.com/assets/u/WebsitePresentationApril2013.pdf

(page 8)

http://s86546.gridserver.com/wp-content/uploads/2010/06/InspectionGuidelines.pdf

(page 5)

I don't think there are ASME Section VIII, Div. 1 rules for metallic polar bosses.

 

[gstrcomp]

Thank you everyone for responding to my question. I appreciate the links and information everyone provided.
To answer racookpe1978, the service pressure is 1350 psi with a safety factor of 5, so a burst pressure of 6750 psi. Not sure if that helps.

In terms of a sketch of the polar boss, it's simply a boss and a radially extending flange section with sealing features that allow the liner material to lock into. Nonetheless, I don't see any guidance in Section VIII Division 1 on how to design this part. It seems as doct9960 said that U-2(g) rules apply. If that's the case and I can use FEA to analyze the part, I assume I need to follow the Division 2 design methodology.

If anyone has more information please let me know.

 

[racookpe1978]

I think you have two different concerns: They don't really overlap each other either.

1st is the strength of the metal boss itself against burst pressure. Same as a all-metal tank at that same pressure and temperature.

Second is the blow-off pressure: How to keep the boss from getting blown off (separated from) the tank wall. Strength of the wraps of plastic/kevlar around the boss, shear and burst strength of the tapes and their glue that attach the boss to the tank wall, and adhesion of the tape over the metal to the composite tank. If the wrapping tape fails, or if the plastic and glue (epoxies) attaching those wraps to the metal separate, the boss separates and the tank fails - even if neither the tank wall nor the metal boss fails separately.