It’s tough for me to hear about accidents in the news caused by faulty parts and materials.
Take, for example, the most recent SpaceX dilemma that caused Elon Musk’s rocket company to cut ties with PMI Industries. Because of falsified metal tests, faulty parts were shipped to SpaceX in order to build their Falcon 9 and other Falcon Heavy rockets.
"Failure to comply with quality control measures undermines the integrity of essential equipment and technology." - U.S. Attorney James P. Kennedy, Jr.
It’s possible that as many as 10 of SpaceX’s government missions have been impacted by the defective materials, including those with NASA, the Air Force, and NOAA.
That’s a preventable blunder with a huge impact. PMI Industries is now out of business.
Luckily, SpaceX had multiple points in the supply chain where PMI testing took place. They were able to identify at 76 individual parts that were rejected before making it to the final mission. Well done, SpaceX.
With the right positive material identification (PMI) testing in place, fatal disasters can be avoided.
That’s why I’ve dedicated this series of The Manufacturing Show to #MastersofPMI.
In this article, we’re going to cover:
- What is positive material identification (PMI) testing?
- Why is positive material identification important?
- When should positive material identification be performed?
- How do you perform a PMI test?
- What is the cost of PMI testing?
- How has PMI testing evolved?
Let’s jump in!
This post is based on a podcast with co-host Chris Carolan. To hear this episode (and more like it), subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.
What is positive material identification (PMI) testing?
Positive material identification (PMI) testing is the examination of a material, usually a metallic alloy, to confirm the material is consistent with the user’s request. In general, this is done using one or more of three testing methods: Handheld XRF, Handheld LIBS, or Portable OES. These test methods determine the chemical composition of the metal and match the chemistry to an alloy grade library to provide an alloy grade ID as the result.
As a nondestructive testing (NDT) method for analyzing the composition of metals and alloys, PMI testing is the most efficient way to test large batches of material at all points of the metal supply chain.
PMI testing for metals and alloys
Determining the precise composition and grade of an alloy enables everyone in the supply chain to match specifications. People that come into custody of the materials along the supply chain include suppliers, distributors, facility workers, manufacturers, and other responsible parties.
Other properties that an alloy can be tested for are
- heat resistance
- corrosion resistance
- surface contamination
- grain flow
- weld qualification
Depending on what the metal is going to be used for, other non-destructive and destructive tests can be conducted.
Alloy chemical compositions
It’s important to note that each alloy has its own recipe and there are literally hundreds documented in every alloy group.
The purpose of alloy groups is to categorize different compositions of metals. For instance, an alloy of nickel with one-third copper is known to resist corrosion from seawater, some acids, and many substances involved in chemical and petrochemical processing.
Here are some more examples of alloy groups:
- Heat-resistant alloys all contain nickel and chromium in order to withstand high operating temperatures.
- Corrosion-resistant alloys — like the one I mentioned above — are specifically intended for use in industrial chemicals, corrosive waters, pollution control, food and beverage processing, and more corrosive environments.
- Special alloys vary in composition and properties. They’re grouped together because their utility depends on mechanical properties (thermal, magnetic, electric) and not necessarily corrosion-resistance or strength.
The Unified Numbering System (UNS) for metals and alloys is the process for designating compositions to groups.
Why is positive material identification important?
Just like we saw with SpaceX’s supplier, there are major ramifications for failing to properly test alloys and metals.
In the end, it's about quality over profitability.
Not only did PMI Industries go out of business, but the quality assurance engineer who falsified 38 inspection reports pleaded guilty and faces up to 15 years in prison and a $500,000 fine. Fortunately for everyone involved, the distortion has not proven fatal yet.
But, you can see how easily a person can be harmed from materials failing to undergo accurate PMI testing.
Texas City Refinery explosion
You might remember the explosion that occurred at BP’s Texas City refinery in 2005.
Due to numerous organizational and technical failings at the refinery and within BP, 15 people were killed by a hydrocarbon vapor cloud being ignited and exploding. 180 others were injured in the accident.
Only a handful of months later, a hydrogen gas heat exchanger pipe overheated and ruptured in the same refinery causing $30 million in property damage. The release of hydrogen erupted into a massive fireball. Luckily, only one individual received minor injuries from the eruption.
After an investigation of the fireball incident, the Chemical Safety Board uncovered that a contractor had swapped a low-alloy steel elbow with a carbon steel pipe elbow during maintenance.
"Merely disassembling and reassembling piping components during maintenance resulted in an unacceptable hazardous system modification. BP should have required positive materials verification of these pipe elbows using an x-ray fluorescence test device. This would have identified the mistake in the reassembly of the identically appearing elbows before the unit was returned to service. The accident would not have occurred." - CSB Lead Investigator
Proper PMI testing prevents fatalities
If just one defective metal part can cause an enormous fireball, think of the damage faulty metals can do on a larger scale.
Anything made of metal can be subject to failure when the wrong material is used:
- Medical devices
- Food processing plants
And, of course, rocket ships and refineries.
Positive material identification can be the difference between successful production and human fatalities.
When should PMI testing be conducted?
Ideally, positive material identification should be administered every time a metal switches hands throughout the supply chain.
The metal supply chain
Supply chains for all sorts of materials have become wildly complex. That’s why consumers have taken more interest in where their products or food originate from.
Metals are no different. Therefore, it’s crucial to perform PMI testing at every point on the supply chain.
Points of the metal supply chain can include
- scrap to foundry,
- foundry to parts fabricator,
- fabricator to refinery or airplane,
- and inspection of in-service parts during maintenance or safety audits.
Check out our API 578 Supply Chain Diagram
PMI testing at each of these checkpoints should be done with the utmost care and attention to detail.
Globalization has led to a very complex, diverse, and less confident supply chain.
So back to my quality over profitability comment. As the supply chain diversifies, there are basically two primary ways that a supplier could jeopardize the material by prioritizing profits over quality.
- Filler or residual elements can drastically change the properties of a material when not limited or removed properly.
- Elements like nickel in steel have a higher cost than the rest of the composition. So in the case of SS 304, the UNS specification calls for 8-12% Ni. A profit-hungry producer might cut it too short of 8% trying to ensure no excess Ni is used in production. A quick PMI test will ensure your incoming material is up to specifications and prevent major mix-ups or disasters down the road.
100% PMI is the standard
It used to be that only 10-20 percent of batches needed to be PMI tested. Now, understandably, 100 percent testing is often required of batches of metals by the next receiver in the supply chain.
The SpaceX incident demonstrates how crucial it is to test all metal materials before the next step in production. Because the quality assurance engineer falsified many of those tests, billion-dollar projects and inimitable work were compromised.
How do you perform a PMI test?
There are three primary technologies you can use to carry out positive material identification. You can find testing equipment available for purchase or rental in most cases. Test methods for PMI include:
- Handheld XRF (X-ray fluorescence)
- Portable Spark or Laser OES (optical emission spectroscopy)
- Handheld LIBS (laser-induced breakdown spectroscopy)
To determine which tool best fits your PMI needs, check out our LIBS vs OES vs XRF comparison.
How much does PMI testing cost?
With any quality assurance testing, costs depend on the industry, urgency, and the critical nature of the application.
Whether you choose to hire a consultant, rent PMI testing equipment, or buy the necessary equipment will also vary the prices.
Hiring a PMI testing contractor
If your company doesn’t employ the expertise to carry out a positive material identification, hiring an expert in the field is a good idea. Normally, teams of contractors are available for around $300/hour plus the cost of transporting them to the site.
Many refineries will bring in teams to work 12-hour shifts in order to get maintenance done as quickly as possible.
Rental PMI testing equipment
You can usually rent PMI equipment for $1995-$7000 per month depending on the type of tools you choose. Some suppliers, however, offer weekly or even daily rentals.
Check out our new MAG Premier Equipment Access subscription service. Use LIBS, OES, or XRF testing equipment for as low as $1995 per quarter! EVERYTHING INCLUDED!!
Purchasing PMI testing equipment
To purchase PMI equipment be prepared to offer up $20k-$40k for handheld tools and up to $60k for the portable OES. Those prices don’t include the costs of ownership and maintenance. (Which can be very expensive for Handheld XRF and Spark OES.)
While these prices may sound excessive, they’re nothing compared to the costs or soiled reputation your organization would incur from an accident (think BP and PMI Industries).
How has PMI testing evolved?
It’s clear that globalization has created a more complex and diverse supply chain than ever before. Positive material identification has had to adjust to the vastness of the metal supply chain.
Like I mentioned earlier, the percentage of material verification that suppliers are requiring has grown from 10-20 to now 100 percent in many cases.
Additional recent developments in PMI testing include:
- a better understanding of liability and risk in the metals industry
- quality being prioritized over profitability throughout the metal supply chain leading to improved material testing programs
- improved analyzer performance thanks to lighter-weight tools, lower detection limits, and easy-to-use software
Not all developments are positive, though. Because the software we have to help us analyze data is so simple to use, valuable training has been pushed to the side.
As an industry, we should keep in mind that without a deep understanding of the data we collect, accidents are more probable. Properly training new professionals is crucial to passing on the knowledge and skills we’ve obtained.
PMI verifies the structure of our world
As our world continues to develop with the help of metals, it’s up to quality assurance professionals to carry out accurate positive material identification.
PMI verifies the structure of the world around us.
Remember the lessons we’ve learned from companies like PMI Industries and BP. Preventing accidents and fatalities due to defective alloys starts with honest and consistent PMI testing.
It affects everything and everyone around us. So always remember to...
Never stop testing your metals.