Strange crack in tank
Strange crack in tank
(OP)
Can someone please help me out with this crack? I'd like to know a possible cause and suggested repairs. The crack is longitudinal and is beside a vertical weld in a 30m high 30 yr old precipitation tank. The crack is 3mm deep, and extends from 8mm to 78mm from the weld toe.
The crack is in the tank cylinder, about 1/3 up from the bottom
Thanks,
Richard
The crack is in the tank cylinder, about 1/3 up from the bottom
Thanks,
Richard





RE: Strange crack in tank
What is the material of construction of the tank and the environment it sees, process, temperature, etc.
Was the tank insulated.
RE: Strange crack in tank
Richard
RE: Strange crack in tank
Your second repair option is to extract a small boat sample of the tank wall (containing the crack) and remove the remaining portion of the longitudinal crack by local excavation (grinding). After the boat sample and the remainder of the crack are removed, locally weld restore the excavation and the area where the boat sample was removed, and perform nondestructive testing before and after welding is completed.
RE: Strange crack in tank
I don't know your use, but I associate sodium aluminate with the precipitate from rinsing aluminum after caustic etching. If some NaOH is present, could be a caustic embrittlement issue.
The NACE caustic soda service chart recommends stress relief of carbon steel welds for use with 50% NaOH above 120oF (49oC). As [NaOH] decreases toward 0%, the safe zone (for non-stress relieved CS welds) rises to 180oF (82oC).
Chart is on page 18 in a PowerPoint presentation of D.H. Lister & W.G. Cook, Univ. of New Brunswick:
http://w
RE: Strange crack in tank
More likely to be caustic stress corrosion cracking as identified in the HAZ areas previously.
It is sometimes worth investigating for other welds in the zone of the crack if it appears in a "strange" area. Previous weld repairs may have been carried out on the tank.
RE: Strange crack in tank
Consider posting your question on www.ast-forum.com
I think it's a great forum......
-MJC
RE: Strange crack in tank