API 650 Annex G Aluminum Geodesic Roof 1

[NDT3RICH]

Is an aluminum geodesic roof considered a fixed roof in accordance with API 650 5.10.1?

Background : A new tank is being built in which the wind girder is being used a walkway. Per 5.9.6, a wind girder used as a walkway shall be located between 42" and 48" from the top angle or the top of the shell unless the tank is covered with a fixed roof. Annex G G.1.3.1 states the tank shall be designed as an open top tank and its wind girder shall meet the requirements of 5.9.

 

[JStephen]

I believe the intent of that 42" requirement is just so the shell acts as a guardrail to keep you from falling into the tank, and an aluminum dome roof would serve the same purpose.
Usually, the aluminum dome manufacturers will specify details required for the attachment of the dome, which will normally involve a wind girder just a few inches below the top of the shell.
I suppose it can and is done, but generally, the aluminum-domed roofs I've seen didn't have wind girders used as a walkway, either.

 

[BZ29]

As stated by JStephen. As per API 5.9.5.6, in my opinion as well, lowering of walkway is just for safety purpose of worker in case of open top or external floating roof. And as per 5.9.5.2 in case of lowering the wind girder another curb angle is also required at the top.

Alum. geodesic roof design also seems to include two person load in design as per "G.4.2.3.2 The roof shall be designed to support two concentrated loads 1100 N (250 lbf), each distributed over two
separate 0.1 m2 (1 ft2) areas of any panel.". If that is the case, then it should be considered as fixed roof for placement of wind girder, although for strength calculation of shell it is considered as open top.

 

[IFRs]

Aluminum domed tanks with wind girders large enough to be walkways around the tank, and handrails on the outside of the girder, are a supreme luxury and awesome safety improvement. I am always pleased to work on one of those tanks. It is visually attractive and there is always something to do in the future that benefits from the vision and dedication to safety that such an installation shows. Although lowering the wind girder adds a top angle to the shell, I think it is a better detail than having the wind girder just below the tank top. It allows for good access to foam chambers, dome roof gutters, inspection hatches, improves the ventilation effectiveness of the screens around the dome and provides a safe work location when installing the dome.