internal coatings,potable water tanks

britcan...

A few questions to clarify the tank construction...

Was this tank made "per" a drawing with "spec requirements" [MIl, MS, AS, Etc]... or just a drawing [with notes]?

What alloy/temper is the tank construction??

What welding process was used?? What NDI process??

Please confirm that the finish-welded tank interior was passivated ... if so, per what spec??

Are the interior surfaces completely "smooth"... or are there "bits" of weld-thru [flash or other sharp edges] and/or possible "open" metal seams??? IE: inspection [by borescope] of interior show any significant roughness or fluid-traps???


Regards, Wil Taylor

Thank you for the response

The tank is welded in accordance with Learjet specs LES 1026 and LES 1014 to a specification control dwg.

The material is 304 stainless annealed per AMS 5513. The NDT tests are called in the welding process(s)

The tank is passivated per LES 1323 and ASTMA967 then cleaned in accordance with ASTM A380 using distilled water.
Upon completion of the cleaning there is a water purity test per ISO 14951-10.

The tank is then hot air dried and sealed "to prevent moisture buildup"

The interior is fairly smooth although Visual evaluation shows several areas of open seams where interior baffles meet the tank walls with welded areas (weld -thrus) at intervals along the baffle's length


regards

Britcan

You could make your own spray nozzle, say a "J" shaped extension for the sprayer you normally would use for priming. Something you could feed into the hole, go half-way down, and spray a narrow, tall pattern. Rotate the nozzle 360°. You might need to cut open a prototype to see how well the process works. It would also aid in the certification to have done so.

___ <in
__ / __________ top of tank
\ | |
\J |
/ spray |
/ |
/____________|



Steven Fahey, CET
"Simplicate, and add more lightness" - Bill Stout

I suggest britcan repost this question under the "steel coatings engineering" and/or "corrosion engineering" forums, they have many readers that will provide knowledgable responses.

My input is this:
1. The most important aspect of any coating application is SURFACE PREPARATION. Your design, from the very start, hinders surface preparation and it is doubtful you'll get good performance from an epoxy in this application (for example, the small, mostly closed tank; a smooth passivated CRES surface, both work against good performance of coating systems).
2. Many epoxy paint companies have epoxy coatings the meet NSF requirements for potable water applications.
3. If the container is CRES 304, annealed and passivated, WHY PAINT IT?