6 Ways to Prevent Corrosion Failure Analysis Frustration
A successful failure analysis starts with obtaining information that leads you to the root cause of the failure.
Have you ever run into the following situation? A component within your product broke or your manufacturing line was producing bad components, and you wanted to determine the root cause of the failure. This required determining the failure mode and failure mechanism, and also determining whether there were any metallurgical deficiencies in the metal. So, you sent a sample to a metallurgical lab and got a report, but the report didn’t have the information you needed or you didn’t know what to do with the information in the report.
There are things you can do to prevent these problems from occurring and improve your chances of determining the root cause of the failure. This article discusses how to work with a metallurgical lab to increase the likelihood of getting the information needed to determine the root cause of a failure and to ensure that working with the lab is a positive experience. (For another example of finding a root cause, see An Introduction to the Root Causes of CUI with Monica Chauviere.)
Step 1: Provide Samples and Background Information before Asking for a Quote
It’s difficult for a metallurgist to accurately quote the costs and time required to perform a failure analysis without getting a chance to visually examine the samples and without getting some information about the failure circumstances. The type of failure and the information needed by the client are factors in determining which analyses will be required. Also, the size and shape of the samples and the materials that comprise the samples will influence the preparation required for the analysis and whether all the required analyses can be performed.
Step 2: Select the Analyses to Perform
To many people, metallurgical failure analysis techniques are a mystery. Is scanning electron microscopy or a metallographic exam necessary? Many people don’t know what to ask for when submitting a sample for failure analysis.
The best thing to do is to provide the metallurgist with detailed background information about the failure and ask them to determine the failure mode and failure mechanism. Also, ask them to determine whether there were any metallurgical deficiencies that might have contributed to the failure. Metallurgical deficiencies include alloy composition, microstructure, tensile properties and hardness that did not meet specifications or were not appropriate for the application. (Discover the role that corrosion plays in the article Effect of Corrosion on a Material's Tensile Strength and Ductility.)
Let the person performing the failure analysis select the analyses needed to obtain the desired information. It’s best not to try to steer the metallurgist in any direction without first getting their input. I’ve seen reports from metallurgical labs that provided the information that the client requested, but did not lead to a complete understanding of the failure or its cause. Many labs will do what a client requests. It’s best not to constrain the metallurgist by giving too much direction.
Also, ask the metallurgist to determine the root cause of the failure, if it is possible. However, the ability to do this often depends on the background information you can provide.
Step 3: Send Samples for Analysis for Manufacturing or Assembly Problems
For manufacturing or assembly problems, send samples of components or sub-assemblies that meet specifications, along with the samples that do not meet specifications. If needed, analysis results of the “good” samples can be used for comparison. Also, if a metallurgical exam has never been performed on “good” samples, the results will be helpful to verify whether the “good” samples are in fact metallurgical stable.
Step 4: Get Help if You Don’t Understand the Report
What’s transformed austenite? What’s dimple rupture or a cleavage fracture? What’s a grain boundary precipitate? Let’s face it – metallurgists have their own language. It makes plenty of sense to them. Unfortunately, many reports require a translator. After reading the report, call the metallurgist and ask them to go through the report with you. Have them explain the results and what they mean. By the way, do this soon after receiving the report, when the analysis and results are still fresh in the metallurgist’s mind.
Step 5: Don’t Expect the Metallurgist to be able to Determine the Root Cause of the Failure
Assuming that it was possible to determine the failure mode and mechanism, you still need to figure out the root cause of the failure.
It may be possible for the metallurgist to determine the root cause if you provided enough background information about the failure. However, in many cases, especially for manufacturing and assembly failures, you will probably need to get more information about the circumstances leading up to the failure. Sometimes the information from the failure analysis will point you in the direction of where to look for the additional information. (For an example of a failure that took significant research to find the root cause, read The Role of Corrosion in the Flint Water Crisis.)
Step 6: Treat the Metallurgist like a Member of your Engineering Team
Find a metallurgist you’re comfortable working with and treat them like a member of your team. Invite them to meetings about the failure. The information they gain from participating can be huge in helping them figure out the analyses required, the samples to analyze and, possibly, the root cause of the failure. Too often, people keep the metallurgist in the dark, which can slow down the failure analysis and root cause analysis process. Remember, this person is supposed to be an expert.
What a Successful Failure Analysis Looks Like
A successful failure analysis obtains information that leads you to the root cause of the failure. Following the advice in this article will increase the likelihood of getting the information you need, and make the process less frustrating (or maybe even enjoyable—if a failure analysis can be enjoyable).
The article and images previously appeared at https://www.imetllc.com/