Corrosion in Filter Water Tank 1

[ak1965]

1. A Filter water tank of 18000 m.3 capacity, that is in service for last 20 years seen a sudden faiure of trusses supports.

2. It is fixed roof type tank. Plate material is IS226 M.S.

3. Some corrosion was also seen on trusses. as per design trusses bottom of approx. 200 mm was submerged in the water due to overflow line elvation at that level.

Query:

1. Corrosion marks on adjcent shell plate is very less. is the submerged truss could be the reason of corrosion on truss?

2. if yes, can we plan to reduce the level of overflow nozzle so that maximum water level comes down below truss structure?

3. In general what coould be the other reaosn of failure?

 

[mrfailure]

Be careful of putting the cart before the horse here. Your observation of corrosion marks may be pertinent or may be a red herring. You should not try to force your scenario to fit these facts.

There is not enough information to say anything about why the trusses failed at this point in time. You really need to have someone experienced in failure analysis to evaluate and first determine the failure mode and mechanism; they can then determine whether the corrosion observations are relevant and in what way.

 

[ak1965]

Thanks mrfailure


1. My query is whether a partly submerged truss is worse than a non-submerged truss from corrosion point of view??

2. if we coat the truss members properly will it help to reduce corrosion rates in partly submerged truss?

 

[mrfailure]

1. Submersion will generally increase corrosion rate, with maximum corrosion near the top of the water line due to wetting/drying cycles.

2. Corrosion rate can be slowed or stopped with an appropriate coating.

These comments are generalities of course; you would have to look at specifics related to your system.

 

[bimr]

Probably not a good idea to submerge the roof supports as it will lead to additional corrosion of the supports.

If you have ice in the tank, it may cause the roof to collapse.