Corrosion

[SSood]

Hi Guys

We are experiencing some corrosion issue on a
Storage Tank (dia 36m / ht 16m) as described,
A) BOTTOM PLATES :
• Severe, localised corrosion on A36 steel plate
• size of ~10mm circular (>20 spots)
• almost corrode through the thickness of bottom plate (thk ~6mm) over period of 3mth
• bottom plates were new & coated with solvent free epoxy (SA 2.5 + 600micron of paint)
• tank was filled with Sea Water for hydrotest & floatation test (2 separate events of 2wks & 4wks respectively)

B) SHELL PLATES :
• circumferential corrosions, apparently formed during hold points of Internal Floater’s floatation test
• shell plates MS ; Internal Floater GRP mat’l with S/S HMT seals
• shell plates were old (ISO-8501 grade D) & coated also with solvent free epoxy (SA 2.5 + 600micron of paint)

What could be the possible reason?

Regards
Sood

 

[bimr]

What is being stored in the tank?

 

[SSood]

None is stored. Only Sea Water for hydrotest & floatation test was used during the time of test.

 

[bimr]

Many questions could be asked.

Sea water is quite corrosive. Many things could have gone wrong:

1. Is the coating resistant to sea water?
2. Was the tank rinsed after the test?
3. Typical to do a 1 day hydrostatic test. Are you saying that you did a 2 week test?
4. Was the coating applied in accordance with the coating manufacturer's requirements (temperature, humidity, et al)?