Bottom Plates External Protection
Bottom Plates External Protection
(OP)
Dear Engineers,
For the external protection of the bottom plates of a crude oil above ground fixed dome roof tank against soil corrosion, is it still advised to apply underside painting, whether a CP system has been established or not?
In the past, the popular type was epoxy coal tar, but I heard that it has been abandoned? Is that true? and why?
What other recommended paint generic types to use?
Thanks
For the external protection of the bottom plates of a crude oil above ground fixed dome roof tank against soil corrosion, is it still advised to apply underside painting, whether a CP system has been established or not?
In the past, the popular type was epoxy coal tar, but I heard that it has been abandoned? Is that true? and why?
What other recommended paint generic types to use?
Thanks
RE: Bottom Plates External Protection
Shop-built tanks may be coated on the underside of the bottom, but this is uncommon for field-erected tanks.
Usually, some combination of doing nothing, using cathodic systems, adding corrosion allowance, using pad below the bottom.
RE: Bottom Plates External Protection
Epoxy tar or other paints can be effective for shop erected tanks. In your case, the paint of underside of bottom plates will deteriorate during welding.
I looked to your member profile and internet country domain is (LY).. If this is the case, I will suggest the bitumen sprayed compacted sand or the better asphalt layer.
If you are asking for the existing tank in your other question, i will suggest the use of 100 mm RC spacer to avoid CP also.
RE: Bottom Plates External Protection
Regards
RE: Bottom Plates External Protection
Yes, this topic is related to my previous one.
Actually, our new plates were required with Carboweld 11.
As a more preventive measure, our staff are thinking of using an epoxy glass flake as a top coat for the plates underside, do you think that will be suitable and effective?
Regards,
RE: Bottom Plates External Protection
You can't weld the bottom without disturbing a coating and coating after installation is painfully expensive unless these are small tanks.
Dragging coated plate over the foundation and each other during erection ruins the coating.
Thick coating may reduce your ability to measure thickness during future inspections.
Keep the chime dry with proper drainage, do routine inspection and have a realistic expectation of service life.
Additional measures:
Use 5/16" bottom plates to give yourself additional life.
Use cone up concrete under the bottom with leak detection grooves.
Again, these are my opinions only and remember - you read it on the World's Wild Web.
RE: Bottom Plates External Protection
Coating selection will depend on a number of factors, mainly temperature. For up to 80 deg C, here are a number of example coatings that might be applied (bearing in mind that the coating has to be proven resistant to environments generated by the CP):
High build epoxy, 1500 microns - examples Carboguard 102, Interzone 485, Sigmaline 2500
Glass flake vinyl ester, 3 x 500 microns - example Polyglass VEF
Glass flake epoxy, 2 x 750 microns - example Marathon 1000 XHB
Leave a 50 mm cutback at weld preparations, and your ISO 15257 Level 4 certificated cathodic protection specialist can design a CP system accounting for the bare metal and factoring in other handling and age related degradation.
If CP is decided to be necessary, don't use bitumen sand, or oiled sand, as it will shield the CP: link to Matcor
Steve Jones
Corrosion Management Consultant
www.linkedin.com/in/drstevejones
All answers are personal opinions only and are in no way connected with any employer.
RE: Bottom Plates External Protection
I still don't understand how you achieve anything useful coating the underside of a bottom. If you coat the plates before they are welded, the heat of welding and movement of plates during setup will ruin the coating and corrosion will zoom there. If you coat them after they are welded, well, I don't see that realistically happening unless it is a shop built tank.
Please help me understand!
RE: Bottom Plates External Protection
Steve Jones
Corrosion Management Consultant
www.linkedin.com/in/drstevejones
All answers are personal opinions only and are in no way connected with any employer.
RE: Bottom Plates External Protection
RE: Bottom Plates External Protection
Steve Jones
Corrosion Management Consultant
www.linkedin.com/in/drstevejones
All answers are personal opinions only and are in no way connected with any employer.