On Testing Steel

There was a life before I started to write about politics at Moon of Alabama. So when a news story comes up that relates back to my previous life as an industrial engineer I will certainly read it and at times even write about it. Here is one of these.

Metallurgist admits faking steel-test results for Navy subs

A metallurgist in Washington state pleaded guilty to fraud Monday after she spent decades faking the results of strength tests on steel that was being used to make U.S. Navy submarines.

Elaine Marie Thomas, 67, of Auburn, Washington, was the director of metallurgy at a foundry in Tacoma that supplied steel castings used by Navy contractors Electric Boat and Newport News Shipbuilding to make submarine hulls.

From 1985 through 2017, Thomas falsified the results of strength and toughness tests for at least 240 productions of steel — about half the steel the foundry produced for the Navy, according to her plea agreement, filed Monday in U.S. District Court in Tacoma. The tests were intended to show that the steel would not fail in a collision or in certain “wartime scenarios,” the Justice Department said.

The strength of the special kind of steels that allows submarines to go deep without imploding must be assured under all circumstance. Especially when one wants to move undersea mountains by running into them, as the USS Connecticut recently tried. Special castings on submarines are often used where things like the periscope or cooling water lines penetrate the hull. To have any potentially brittle material at those places could be catastrophic. Due to the falsified test results the navy might have to reduce the maximum allowed diving depth for some of its submarines.

But the reason given by Thomas for falsifying the test results is what I find really concerning:

When confronted with the doctored results, Thomas told investigators, “Yeah, that looks bad,” the Justice Department said. She suggested that in some cases she changed the tests to passing grades because she thought it was “stupid” that the Navy required the tests to be conducted at negative-100 degrees Fahrenheit (negative-73.3 degrees Celsius).

This is an alarmingly ‘stupid’ quote from someone who is supposed to be a metallurgist. These tests are not ‘stupid’ but necessary.

There is one standard test for impact strength of steel that is regularly done at subzero temperature. It is the Charpy V-notch toughness impact test (video).

For a Charpy impact test a part of a casting is cut off and machined into a well defined piece with a notch. Its edges are then put against an anvil. A swinging hammer comes down and destroys the test piece. The difference in heights of the hammer at the starting position and at end of the swing is an expression of the energy that was needed to destroy the piece.

It is a simple, easy to do test and the results can tell a lot about the material characteristics of the test piece. The pictures below shows the test results for two kinds of steel. The upper piece fractured but did not break apart. The more brittle one below snapped.

Depending on its inner crystal structure the toughness of a metal can change with its temperature. More brittle material has a body centered cubic structure (BCC) with one atom sitting in the middle of a cube formed by six other atoms. Tougher steel alloys have a face centered cubic crystal structure (FCC) where an extra atom sits at each face of the cube.

BCC structure 

FCC structure 
To find out which type of structure a piece of metal has one can cool it down and do a Charpy impact test at very low temperatures.

Below a certain temperature steel with a body centered (bcc) cubic crystal structure will suddenly become weak while steel with a face centered cubic structure (fcc) keeps it toughness. A Charpy impact test at low and normal temperature allows to differentiate between those.

The crystal structure of steel can be influenced in the foundry during the casting. The alloying, the temperature of the melt, the speed of cooling and/or an additional tempering will all effect the structure.

If the foundry has made a mistake during a cast it might have produced a steel with the wrong structure and characteristics. Material testing is the way to find out about possible mistakes. A Charpy test at different temperatures is a simple way to determine if mistakes were indeed made.

To skip the test or to falsify its values, as the person in question has done in this case, is a big no no.

But what really concerns is me that Thomas either did not know or ignored the above. She thought it was “stupid” that the Navy required the sub zero tests even while there are sound and rather simple reasons for these. It is not only the U.S. Navy which requires such tests. The classification societies and insurers for civil ships and the oil and gas industry have similar procedures.

When the metallurgist who was being trained to replace her found out that Thomas was falsifying test results he immediately recognized the gravity of the problem and informed the company. It was the right thing to do. 

During a part for my engineering education I did an internship in the material testing lab of a large shipyard. We did the coooold Charpy tests only once a week because we needed liquid nitrogen to cool down the test pieces. Liquid nitrogen has a boiling point of −195.8 °C (-321 °F). It evaporates fast but is fun to play with (vid) which I, of course, did a lot.

Via https://www.moonofalabama.org/2021/11/on-testing-steel.html#more