What type of corrosion am I dealing with? 1

[MaterialsDude]

Here's some photos taken of a sample cut from a pipe which supplies cold process water to an ore preparation plant. The failure was detected when they observed a leak in the pipeline. Upon observing the photos you can see that there is obvious corrosion which probably led to the hole.

I am thinking that this is microbially influenced corrosion based on photos I've seen thus far but am not 100% sure. I don't know yet the conditions of the pipe (flow rate, temperature, pH) while it was in operation, so I can't provide you with that.

What type of corossion does this look like to you and what type of tests can I include in the scop of work to be done?

I appreciate your replies. I am still an inexperienced engineer and so I don't have too much experience analyzing failures.

 

[metengr]

Looks like either tubercle (under deposit corrosion) or MIC because of the black color within the pit region. I have seen both provide what you show in your photograph.

Need more information on operating conditions and water quality/type to decide. How many of these regions did you observe?

 

[unclesyd]

It looks like you might have MIC (Microbiological Induced Corrosion). Your picture has indications of a biological cell indicated by the light brown bacterial slime at the edge of the pit. The area of hole was a tubercle, small mound of material prior to being dislodged. probably by the leak. These tubercles along with the bugs will form differential aeration cells that can cause rapid corrosion plus the fact the bugs are dissolving the metal.

Can you get picture from a little further back to show some more of the pipe internal surface?

How long has the pipe been in service?

 

[unclesyd]

One thing you might do if there are tubercles present would be to take knife blade and flip the tubercle off the pipe and immediately take whiff. I believe you will get a hint of rotten eggs.

 

[MaterialsDude]

Thanks for the replies so far guys.I don't know how long the pipe has been in service for. I'll have to ask them next week when I go to the plant. This is the only portion of the pipe that failed and removed.

I tried to post more pics but I guess you can onlu post one at a time. Here's another shot.

 

[metengr]

The wider shot looks to me to be more under deposit corrosion by tubercle formation. One other question, are these locations on the pipe along the bottom side or top? If they occur randomly along the pipe run, I would go with MIC as the root cause.

If the pipe is horizontal and these corrosion pit locations are mostly along the bottom half of the run, this could be under deposit corrosion with no MIC.

 

[MaterialsDude]

metengr,

It's kinda almost exactly in the middle side of of the horizontal pipe. Here's a pic of the pipe where the sample came from.

I'm assuing that the combination of the MIC and under deposit (probably from a biofilm) caused pitting corrosion which caused the hole in the pipe. Does this make sense?

 

[unclesyd]

Your last picture is a prime example example of a MIC construction site. MIC can be happening a long time before any film will form. The initial stage all you will see is little rust spots sitting on the surface. Even in in this mode they can drill holes in metal. This changes if a source of food for flora or fauna comes along and starts a deposits. This deposit will quickly change the dynamics of the corrosion mechanism.

Here is an outfit that sells tests kits for three primary culprits in MIC corrosion.
They also have some very good information in their library.

http://www.mic-test.com/slime

 

[SJones]

Some more information on water source, composition, treatment, flow rates etc would help to firm up the hypotheses.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

I am usually in the camp of 'it is only MIC when you have disqualified all other options.'
There are plenty of other mechanisms that will result is similar corrosion damage, scaling is the most likely. Since this was at the mid-line of the pipe then the pipe have been half full for some time. You can get MIC, as well as scale formation and concentration of impurities along this interface.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[strider6]

could be oxygen corrosion.. without clear information on fluid chemistry and operating condition it could be a lot of things..

V.

Corrosion & Rust Prevention Control

 

[brimmer]

Still too early to tell, can you send a photo of a sandblasted section (close up of pits) when you complete your failure analysis?

 

[unclesyd]

The hole shown adjacent to the tape in the second picture is a very good indication of MIC.

I've never seen MIC be very selective when it come to water I've seen and tested for and found MIC in all types of water, pure, aerated, deaerated, treated, etc, and under all conditions of PH and many temperatures. The only water that I haven't found MIC is water treated with hexavalent Chromium.

The only way to tell is by a specific test for one or all of the three bacteria.

Just remember that the red color that sometimes comes from the tap is iron bacteria supposedly good for you.

 

[MaterialsDude]

Thanks guys! Right now we have sent the samples to a testing company after we put together a scope of work to be done. Also, the process engineer was in a meeting when I tried to go to his office and ask questions regarding the operating conditions in the pipe.

You guys provided some really good insight though and it is really appreciated. As more info is available, I will let you know of our findings.

 

[unclesyd]

Appreciate the offer to follow up as consequences of any corrosion is expensive, especially from MIC.

If we can only retain 10% of the knowledge and information we are exposed to we will be way ahead of the game.

 

[rconner]

While it may be hard to determine much from just pictures, this looks like internal corrosion, perhaps due to aggressive water exposure, in unlined steel pipe (that appears not too thick). A water analysis might be of interest. Might also ask if/interview anyone thought to put a light/look up inside the pipeline each direction from which they cut this out (if so, what did they see?)

Steel pipe for water service is often specified cement etc. lined, to minimize internal tuberculation (and/or such "failure").

 

[MaterialsDude]

Ok guys, I got some updates. The pipe is API 5L Gr.B carbon steel pipe. Pipe specification is CAJ. Typical operating pressure is 910 kPag and typical operating temperature is 2C. The typical flow velocity is 7000 cubic meters/second. The failure actually occured at the 12:00 position and the failutre location occured at a section of the pipe at a road crossing in culvert. Diameter was 24 in and wall thickness was 0.375 in. No water analysis will be done this time but it has been done before and bacteria was found in the pond water that this pipe carries.

The samples are still being analyzed at a company and hopefully we will have their findings next week. I am sure we can't come to a 100% conclusion of the cause of failure yet but this info is a start.

 

[rconner]

While I'm not sure it's pertinent, are you really sure about that level of flow??

 

[MaterialsDude]

rconner, It def doesn't make sense to me but the process engineer never got back to me when I questioned it so I just put down whatever info he gave me. I'm not even sure a biofilm could stay on a surface with that speed lol!

 

[metengr]

Keep in mind there could be no flow due to scheduled outages or off-line periods and with poor drainage you can develop corrosion.