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Finding the Root Cause - Which technique is better?

Bev D

Heretical Statistician
Staff member
Super Moderator
actually he's confuding a single solution set as a cure for an actual casue that hasn't been identified.

while it is correct that oxygen and iron - and some catalyst for the reaction - is the immediate cause of rust it may not be sufficient to solving this problem. for example, the parts may in fact be coated and properly packaged, but some parts may have been scratched during handling and then there may have been packaging damage and the storage environment may have been very humid - or the package even left on a loading dock in the rain...we don't know and the OP hasn't responded to the diagnostic questions yet.


Stop X-bar/R Madness!!
The "root cause" of the existence of rust on a product may not be the chemical reaction itself. The definition of the problem may not be "can rust occur", but better framed as "was the protection against rust adequate." If there is a failure of the protection provided against the initiation of the reaction, such as acid in fingerprints defeating plating, or not providing adequate protection - such as using a bag, but not a VCI bag - may be the root cause of the the failure of the protection is what needs addressed.
Guys, there is no reason to complicate it. The root cause for rust is, in fact very simple
As before, I agree that the root cause for rust is not only very simple, but also well known. There is, however, no reason to oversimplify things either. The answer depends on what Terry wants to know, and right or wrong, I interpret his question a bit differently:
There are 22 pieces of part rust defects in PDI report last month, I want to establish a projct and organize a team to analysis the root cause
What I would want to know in his situation is why rust formed on those particular pieces? I.e: What went wrong with the measures taken to prevent rust from forming on them? The answer to that question would enable Terry to correct the problem.


Ajit Basrur

Staff member
Hello everyone,

I have a question and needs you to help me.

There are 22 pieces of part rust defects in PDI report last month, I want to establish a projct and organize a team to analysis the root cause with cross function dept. guys, but now I think up two kinds of ways to analysis it, I don't know which ways is better?

The first ways is that I directly input " part rust" into the result column of fish bone diagram, then we use brainstorming to get some possible causes or root causes.

The second ways is that we ask "5 why" to each rust defect to find root cause.

I am a new man for the use of quality tools.

I hope you can give me some good advice.

Thanks & regards!

To the OP, Terry's question, yes use a Fishbone Diagram and list all causes. For the example you mentioned use a 5M method - Machine, Method, Man, Materials, Measurement and Environment for your causes.

Once identified all causes, go on to use the 5 Whys to come to root causes.

Pl let us know your progress of investigation.


This problem is being made far too complicated! Rust occurs through inadequate protection or inadequate storage. Determine where in the process the rust was detected then work upstream looking at where the process went wrong. Is the protection adequate at each stage? Is the storage area and packaging suitable? Is there good stock rotation?
The causes and countermeasures should be apparent!


Captain Nice
Staff member
Yes - And each case is different, so here we're theorizing because, as you pointed out, the OP hasn't come back to give us additional information.

But it is often this type of discussion thread that makes one think and brings out a lot of opinions to consider. A good way of 'calibrating' ourselves and our perceptions. One person says "It's easy, oxidation is the root cause", while another (in this case me) says "No, oxidation is the effect of a cause".

We may go around the tree a bit but it makes one ponder how to determine Root Cause. I used to teach a class in it and even to today there are times it is difficult to assign a specific, individual Root Cause.

I do remember my first experience in Root Cause analysis almost 30 years ago. It had to do with component failure on a 3 layer hybrid printed circuit card. We didn't realize what was happening until we did thermal analysis of the card and found an upstream component was heating up and spiking the voltage on one leg which killed a downstream IC. We had to get a design change to get the up stream IC replaced with a more robust one.

Each Root Cause Analysis is like a detective story, but the Root Cause is never (at least so far in my experience) the Butler.... ;)
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