on Systems Thinking

In this original post, A Mechanic’s Story: Basic Component Fatigue, we took a detailed journey through the physical side of a shaft failure RCA. We stopped at the physical side of that failure, parallel misalignment. However, stopping at the component level of failure does not constitute a credible and thorough RCA. Actually stopping at this level is more along the lines of a Shallow Cause Analysis (SCA). So let’s explore what makes the difference between a Shallow Cause Analysis and a Root Cause Analysis (RCA).

In the previous post we stopped at parallel misalignment. We will continue drilling from that point down. We ask ‘How could we have had parallel misalignment?’ Our team of subject matter experts (SME) hypothesizes 1) it was either misalignment at installation or 2) it became misaligned during operations. 

As many of you know, I have been encouraging my LI contacts for years to take me up on my offer to review any pictures they have of failed parts, and we would try and provide them some preliminary feedback. Well, someone finally took us op on the offer and we wanted to share what was learned (we obtained permission to do so providing the company name was not used).

Here was the original inquiry via LI instant messenger along with the pictures:

“Dear Sir, As per your advise, I’m sending you a photo of failed flange bolts. I belief they were failed due to fatigue. Could you please review them and identify/ label their failure mode. After your comments on this photo, I’ll put up a recommendation on my RCA. Looking forward to hear from you. Regards.”

“Assumption 1: Safety is increased by increasing system or component reliability. If components or systems do not fail, then accidents will not occur. (p. 7)

This assumption is one of the most pervasive in engineering and other fields. The problem is that it is not true.

Safety is a system property, not a component property, and must be controlled at the system level, not the component level. 

New Assumption 1: High reliability is neither necessary nor sufficient for safety. (p.13)”

These statements were excerpted from Nancy Leveson’s “Engineering a Safer World“. 

This contradicts the common belief there is a direct correlation between Safety and Reliability. I personally, being in the Reliability field for 30+ years, believe there is a correlation between Reliability and Safety. But I would assert that it is not a direct correlation. 

In past articles, we have explored the basics of Erosion, Corrosion, Fatigue and Overload. Our emphasis has been on creating an awareness and appreciation for the value of failed components, to any investigation.

In this article we are going to delve into Fatigue a little bit more (because it is the most common fracture pattern) and see how we can use an evidence-based, deductive logic process to determine what elements of Fatigue may have been at play. We are trying to create an intellectual curiosity within the front lines about ‘making the call’…is it Fatigue, or some other fracture pattern?

I recently received an interesting LI inquiry that I felt others could learn from the answers that I was able to get. This is not my expertise so I sought out answers from some colleagues who were more familiar with fasteners.

Here is the original inquiry (translated from Portuguese so I hope Google Translator did a good job):

“I would like to know if you can help me clarify my doubts about:

1. The purpose of conducting a study of the coefficients of friction in screws, threads and nuts?
2. Is there an accurate standard for such testing?
3. What methods can be perfected in projects that target this type of trial and application?
4. Can surface treatments influence changes in results?
5. Who is responsible for such testing (the manufacturers and suppliers of raw materials, the assembler and/or its various final assembly applications)?

Lets start with a fresher on general Component Fatigue.

• Fatigue occurs when a material is subjected to repeated loading and unloading.
• When the loads are above a certain threshold, microscopic cracks will begin to form at a material’s surface.
• Cracks always begin in high stressed areas of a material.
• Eventually a crack will reach a critical size, and the structure will suddenly fracture.

Let’s start off with some honesty…the term ‘RCA’ (Root Cause Analysis) is quite vague, misleading and easily misinterpreted by those who are not immersed in its use. It is a useless and counter-productive term because there is no universally accepted, standard definition. Therefore, any process/tool someone is using to solve a problem is likely to be labelled as ‘RCA’. It could be troubleshooting, brainstorming and/or some other more structured problem solving approaches such as 5-Whys, fishbone diagrams, causal factor trees and/or logic trees. 

Author’s Note: I want to reiterate that this Series about reading the basic fracture surfaces, is for novices who often come into contact with such failed components. This Series is about the basics (101), and is intended to give readers an appreciation for the value of such ‘broken’ parts to an effective investigation/RCA. While this information will be rudimentary to seasoned materials engineers/investigators, I know they will all appreciate heightening awareness to the need to retain such failed parts for formal analysis, versus throwing them away and just replacing the part. Throwing away failed parts is a recipe for a repeat failure. When one does not understand why the part failed in the first place, they can’t prevent it from failing again.

In this article we will focus on how to actually incorporate the evidence (failed parts) from a failure, into a disciplined Root Cause Analysis (RCA) process.

[Read more…]

To those following this Series, I will apologize for the front-end redundancy. I am doing so for those that are NOT following the Series and will read these articles independent of each other. If you are following the series (Thank You!) and proceed past the front-end stuff and to the shaft pics below:-)

Abstract. In our last series highlighting the 4 primary Failure Modes (FM) of component failures (erosion, corrosion, fatigue and overload), we discussed how to read fractured surfaces. In this follow up series, we will take a look at tips on how to collect, preserve and examine such failed components.

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I recently attended a conference where I listened to a presentation on Human Performance Improvement (HPI) by Dr. Todd Conklin and other speakers advocating Dr. Conklin’s ‘Learning Team’ approach. This was the first time I had heard Root Cause Analysis (RCA) referred to as ‘old school’ and obsolete. This got me to thinking, given I have been in the RCA business for decades, is what I do for a living…obsolete?

[Read more…]

In our last series highlighting the 4 primary Failure Modes (FM) of component failures (erosion, corrosion, fatigue and overload), we discussed how to read fractured surfaces. In this follow up series, we will take a look at tips on how to collect, preserve and examine such failed components.

[Read more…]

Author’s Note: I want to reiterate that this Series about reading the basic fracture surfaces, is for novices who often first come into contact with such failed components. This Series is about the basics (101), and is intended to give readers an appreciation for the value of such ‘broken’ parts to an effective investigation/RCA. While this information will be rudimentary to seasoned materials engineers, I know they will all appreciate heightening awareness to the need to retain such failed parts for analysis, versus throwing them away and just replacing the part. Throwing away failed parts is a recipe for a repeat failure, when one does not understand why the part failed in the first place.

[Read more…]

Author’s Note: I want to reiterate that this Series about reading the basic fracture surfaces, is for novices who often come into contact with such failed components. This Series is about the basics (101), and is intended to give readers an appreciation for the value of such ‘broken’ parts to an effective investigation/RCA. While this information will be rudimentary to seasoned materials engineers, I know they will all appreciate heightening awareness to the need to retain such failed parts for analysis, versus throwing them away and just replacing the part. Throwing away failed parts is a recipe for a repeat failure, when one does not understand why the part failed in the first place.

[Read more…]

This article is directed at those ‘first responders’ who arrive immediately at the failure scene. These are the people who have to ensure the area is safe, preserve the scene for investigators and contribute to a plan to expedite a quick, safe return to production norms.

Many do not understand how valuable failed parts are to the metallurgical/forensic investigators. Broken parts are to metallurgists’, like the murder weapon is to a forensic crime investigator.

[Read more…]

Can you identify and name this fracture pattern?

How can you tell it is that fracture pattern?

Where are the origin(s) of the failure on the fractured surface?

How can you tell where the origin(s) are?

[Read more…]