Chemical tests to identify seawater induced steel corrosion 1

[cesaref]

I would like to know if you can describe a method to prove that steel suffered corrosion when transported by sea (due to contact with seawater) instead of a normal air corrosion. The steel bars are 12 m long, and all of them are corroded (pitch corrosion)on the first 2 m,suggesting seawater contacted this section of the steel rods. The transporter claims that this did not happen. Cheers.

 

[Goahead]

It is improbable you could find such a test because seawater is not a well specified element but its action on steel (undefined) is the product of many factors, a list of which can be found in page

http://www.corrosionsource.com/technicallibrary/corrdoctors/Modules/Seawater/Frames.htm

A Marine Corrosion Forum operates at

http://www.marinecorrosionforum.org/main_frame.html

and could probably be consulted on this issue.


Regards,

http://www.welding-advisers.com/

 

[EdStainless]

You can have samples tested for residual chlorides in order to prove that they were not well protected, but this isn't definitive. Even fog at sea will contain salt.

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Plymouth Tube

 

[strider6]

cesaref

seawater contains salts that are not carryed by air or salt spray and also bacteria. I think that if you make a chemical analisys of the corrosion products and deposits you can prove that the steel was in contact with seawater.

S.

http://www.corrosionist.com

 

[cesaref]

Thanki you for the tips.

I tried the residual chlorides approach (silver nitrate test), and chlorides were detected, but the test is too sensitive (positive even for small amounts of chlorides). I would like to quantify these chlorides (don't know exactly how).

Regarding strider6 approach, how can we test the corrosion products? X-ray diffraction? or other technique? What are we looking for?

Cheers

 

[knowlittle]

cesaref:

Most scanning electron microscopes have EDS attachment and can easily quantify chloride content for you. It will be much less expensive than x-ray diffraction.

I am unfamiliar with "pitch corrosion." Please explain to us what you mean by it.

Are you trying to differentiate between corrosion from salt water spray and salt water immersion? It will be difficult. But if you are trying to put blame on the shipper for inadequate protection from the sea, salt analysis will help your case.

 

[cesaref]

Thanks, knowlittle

What i mean by pitch corrosion is that the rust on the steel is not uniform, some points are much more corroded than others.

YES, I want to blame the shipper for inadequate protection from the sea (i'm almost surre he didn't seal the doors of the cargo area).

 

[knowlittle]

I would try this. Rinse the steel bar with deionized water just to remove any salt sitting on the surface and dry. Take rust sample and analyze it for chloride. You don't need much. Say 1/5 of q-tip should be enough for EDS. Repeat the same with the rust sample taken from the non-pitch area. This will work if rust has some thickness.