Problems related to flat-bottom tank appearance

[STEVE LIU]

Hi everyone,
I have a question. I’ve noticed that many flat-bottom tanks have black lines after being painted.
I’m curious about how these occur. Are they caused by the welds (Welded joint )? If so, what is the reason?

 

[LittleInch]

Do you mean the vertical lines?

I strongly suspect these are where they are drain holes in the roof edge and this is where the water drops down, discolours the tank and allows some moss or organism to grow.

 

[STEVE LIU]

Hi everyone,
I have a question. I’ve noticed that many flat-bottom tanks have black lines after being painted.
I’m curious about how these occur. Are they caused by the welds (Welded joint )? If so, what is the reason?

Yes , I mean the black

Do you mean the vertical lines?

I strongly suspect these are where they are drain holes in the roof edge and this is where the water drops down, discolours the tank and allows some moss or organism to

Do you mean the vertical lines?

I strongly suspect these are where they are drain holes in the roof edge and this is where the water drops down, discolours the tank and allows some moss or organism to grow.

Yes, I was referring to the black vertical lines. it was just painted a little over a month ago, so seeing these evenly spaced black lines makes me curious about where they came from.

 

[LittleInch]

Rain.

 

[JStephen]

So far as I know, it is pollution that gets washed off the tank roof and makes the stains like that. I remember this issue coming up years ago as well.
Theoretically, a tank is perfectly symmetrical and rain will run off uniformly all around. In reality, there will be minor highs, lows, laps, etc. in the roof plate, so rain tends to run in specific spots more.

 

[LittleInch]

It's difficult to see from the photo but I think if you look close up you'll find that there are gaps in the weld or in the metal itself of that top ring girder.

Water then drop down through it and down the side of the tank.

See if you can get a close up view from the top of the tank.