Cooling coil corrosion in 316L reactor 4

[scchemeng]

We have several reactors made of 316L SS. One of our new reactors is exhibiting significant corrosion on the cooling coils inside the reactor, which is not evident on the rest of the reactor or any of the other reactors. There aren't any products that are unique to this reactor. The manufacturer of the vessel has been less than candid with us about other design flaws with this vessel and we are inclined to believe that the cooling coil wasn't made with 316L as was specified. Is there any way to determine the type of SS the coil is made of in situ, or will we have to remove part of it to be analyzed elsewhere? Is there any reason we might see corrosion on the cooling coil and not the rest of the reactor? Has anyone encountered a similar problem? Any help would be appreciated.

Thanks

 

[ENC]

Taking the cooling coil out and preforming a chemical analysis does not give conclusive results to metallurgy. We tried this once when we had questions of the matal supplied and the lab gave us results but could not provide concrete evidence that the metal was 304 or 316 or 316L.

It seems as if the cooling coil should be replaced anyway, so make sure the cooling coil has the proper ASTM marking on it and that the fabricator provides material certifications. You may want to inspect the fabricated coil prior to shippment to confirm that everything meets specifications.

Insure that the cooling coil is not failing from some other mechanism, such as Stress Corrosion Cracking (SCC) that may be caused by the stress cycles contributed by chemicals in the reactor. Stainless Steel is susceptible to SCC under certain conditions, even if the supplier provided 316L on the coils. Under these conditons the vessels can be fine and you can see failure of the coils. A metallurgical lab can look at the microstructure and determine if SCC is a mechanism of failure. If it is then the new coil can still be supplied in 316L but must have lower stress values for a longer service life.

Good Luck

 

[quark]

SS!

There are test kits available to know whether a steel is of 316 grade or not. (Which shows you Mo content) But not for 316L which indicates low carbon content. You have to go for chemical analysis test.

If the welding rods used or not proper there may be problems of corrosion. (check where the corrosion is starting from)

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[jhartis]

A test coupon of 316SS may be useful to see if the problem is material or process related

 

[rolledalloy]

Many labs have portable spectrometers that are made by Niton or TN Technologies, others. These machines, if the coil is accessible, can analyze a clean surface and differentiate between 304 or 316 and other materials in a non destructive manner. They provide a percentage composition read out for heavier alloying elements. These would not be able to determine percentages of lighter elements such as carbon, nitrogen. Many independent labs offer access to these units. It would be interesting to note what type of corrosion is occuring general corrosion, pitting, stress cracking. This may assist in determining the problem.

 

[slowlearner]

You can get the material composition of the coil by sparking (spectrometer) in any metallurgical labs (especially in steel industry) or any independent labs that involve in standradization. There is possible that the coil is made of any other material instead of SUS 316. The different can be easily trace with spectrometer. You also need to check if the corrosion started at the welding area. It is possible that the welding electrode used is not stainless steel. You can put magnet to this area. If the there is a trace of magnetism, it mean the welding is not stainless steel. You also check you process if there is any Chlorine/Cloride because stainless steel can corrode due to present of this element.

 

[mcguire]

Rolledalloy gave the best advice of the above. You can ascertain whether you have 316 or not, but you will need coupons to determine the actual cause of failure and wrong alloy is only one possibility. Why don't you hire a consultant and then go after the manufacturer?