Recommend anchor bolts for 12% Soduum Hypochlorite tank

[DWPENGR]

Hello Everyone,
I need to select some type of anchor bolt to attach a polyethylene tank to a concrete foundation inside a secondary containment basin. The tank holds a 12% solution of Sodium Hypochlorite. I plan to paint the secondary containment basin with a Vinyl Ester coating to protect the concrete. I'd like to anchor the tank with bolts that will resist a Sodium Hypochlorite spill. Can I use galvanized steel anchor bolts or SS304 bolts or something else? Any suggestions would be greatly appreciated.

Thanks in advance.

 

[CoryPad]

What would be the duration of hypochlorite contact? If it is short, with comprehensive cleaning, then I think you could use a standard austenitic stainless steel like 304. If it is extended contact (or poor cleaning after a spill), you may need a different alloy system (Ni, Co, etc.).

 

[DWPENGR]

CoreyPad,
Thanks for your reply. Duration is hard to say. The power plant may not fix leaks in the pumps or piping system in a timely manner. At this point in my design, I'd just like to digest all the comments I receive and make an educated best guess.

 

[TVP]

Standard austenitic stainless steels are very susceptible to stress corrosion cracking and pitting when in contact with sodium hypochlorite, even at room temperature with a concentration of 5% (Outokumpu Corrosion Handbook). Even a more highly alloyed grade like 904L is susceptible to pitting. Now, as CoryPad mentioned, if it is not constant immersion, with some cleaning, then perhaps some of these less expensive grades can be used. If not, then you may need to consider a superaustenitic grade like 254SMO or something truly corrosion resistant like titanium or zirconium.

 

[metengr]

You need to take a step back and evaluate risk of exposure to a spill and what impact an anchor bolt failure would cause if a spill occurred and was not cleaned up or neutralized in time. You are not designing these anchor bolts for constant immersion service and if you are this would be overkill in design.

We have various polyethylene sodium hypochlorite storage tanks for bio-treatment of our discharge water at several of our power plants and the tanks are supported by carbon steel supports in a concrete containment. Never had an issue with failure of the legs or even corrosion from exposure to sodium hypochlorite solution. The legs are painted to protect from atmospheric corrosion.

 

[DWPENGR]

metengr,
Thanks for your reply. The tanks you describe sound similar to mine. I have several tanks, ea. 2,500-gal, supported on elevated steel (painted) supports. For now, I plan to use SS 316 anchor bolts (with nuts & washers) to connect the painted steel frame to the foundation. I know that I have potential galvanic action between the SS 316 anchor bolts and the painted base frame so I also plan to install PVC insulating washers between the painted steel base frames & the SS 316 washers. I think that if there is a future spill, the foundation & anchor bolts will still be good. But if the painted steel base frame is damaged, then the plant can easily just purchase another support from the tank Manufacturer.

 

[SteveWag]

Epoxy a threaded fiberglass rod into a drilled hole and use a fiberglass nut and locknut.

Steve

 

[CoryPad]

Your proposed joint is not a good idea. The PVC washers will creep, resulting in preload loss and joint loosening.

If the painted steel frame is suitable for this service, a coated steel fastener also should be suitable. I recommend a resin-bonded PTFE coating for the bolt, which has good chemical and corrosion resistance.

Some potential coatings are Xylan from Whitford and Fluorokote from Metal Coatings Corp.

 

[EdStainless]

I'll second Cory's suggestion of coated steel bolts.
It is a lot easier to spot corrosion on these and repair them than to identify a SS bolt that is about to snap from SCC.

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Plymouth Tube

 

[DWPENGR]

I would like to thank everyone who responded to my post. I have decided to purchase bolts coated with Fluorokote available through a Los Angeles disrtibutor.