Caustic Soda Storage Tank Inspection 2

[Bluecat46]

Can any one help regarding recommended general guidelines for inspecting Mild Steel Caustic Soda Storage Tanks?

I have looked at the Dow website, but are there any national/Internationally recognised guidelines?

Thanks

Bluecat46

 

[fegenbush]

I would look into API 510 or API 653. Those are recognized inspection standards that carry weight in US industries. Additionally, DuPont standards may be of interest to you as well.

 

[Duwe6]

Several of the API Recommedded Practices "RP's" specifically recommend Magnetic Particle testing - MT - due to the known issue of Caustic Stress Corrosion Cracking. Any API-653 certified Inspector is knowledgable on this damage mechanism.

Depending on the time since last Internal Inspx, temperature of product, and strength of solution, you need to perform MT on between 10% and 100% of the weld seams. CSCC caught early can be 'buffed out' and not require any repair welding.

CSCC ignored for decades will cause thru-wall leaks. Don't ask how I know that,

 

[Bluecat46]

Thanks Fegenbush.

Been looking on the Dupont website with no luck, Can you post a link please

 

[fegenbush]

Unfortunately, no, I cannot provide a link. However, if you are able to get in touch with the engineering group of the plant geographically closest to you, it might be possible to sweet talk them into getting you a scan of the appropriate one. That is, if you plan to use the standards in order to conduct business with them.

 

[MJCronin]

On a closely related subject,

As we all know, there seems to be no single nationally-recognized standard for the recommended design of Caustic Storage tanks.

My related question is this:

What specific features should be incorporated into the design of NEW caustic storage tanks to minimize CSCC and perhaps make inspection easier ?

Additionaly, we are all aware of the good information provided by Dow. Are there any Interational guidelines available relating to caustic soda storage and transfer systems ?

Thanks.......and best regards

 

[Duwe6]

Only ways to eliminate CSCC is to
PWHT all welds [too expensive]
Keep concentration below 30%, and keep the temperature only 10-20° above the freezing point of the concentration you are using.

Ease of Inspx: Slope floot to a sump-type floor drain.
Have clean-out nozzles around the roof about 10-ft in, and 20-ft apart. This allows a spray-ball inserted thru them to easily and quickly clean the walls of caustic "crusties".
Route the floor-drain line to somewhere that the effluent will be easy to acidize and get close enough to neutral pH to send to the sewer.
Have 120V power near the tank, so that the Mag Particle yoke is easy to plug in.