Greetings:
I received an inquiry today asking for advise on doing an x-ray inspection of steam locomotive frames.
I replied:

"My experience has been with x-ray inspections of welds (a front tube sheet repair at the Huckleberry and, of course, boiler seams at Tangshan Locomotive Works). The x-ray films I have seen have been rather small (say 3"X8"), and although larger film is available, it would take a lot of "shots" to do a frame and that said you must have access to both sides (one side for film, one side for isotope) so areas adjacent to cylinders, waist bearers and the like could be done only if the locomotive were dismantled.But the real problem isn't taking the "shot", it is the INTERPRETATION of what you see on the developed film, ie: is the "indication" you see something of concern or not. Considering that most frames are cast steel, I would guess that an x-ray would find lots of little pockets of air or sand or whatever which are totally benign. I think that if you want to condemn a locomotive, all you have to do is inspect it enough, raise as many unanswerable questions as possible and then ask a mechanical engineer, (totally unfamiliar with steam locomotives) for their professional opinion.
If the customer is concerned about possible frame cracking, I think that the HARDNESS of the material is more of an issue, ie: work hardening in high stress areas. The x-ray won't find that.
I would note that passenger car truck frames for AMTRAK service are "magnetic particle" tested. This might be a more practical testing method (a lot cheaper too), but again, proper interpreting is essential."

Has anyone "out there" had personal experience with the x-ray testing of steam locomotive frames?
J.David

Radiographic testing inspection, (RT), or x-ray inspection is a very useful tool when applied correctly. You have described the situation rather well in your post. Just to amplify a bit.... it should be mentioned that RT is best used to find foreign material or voids. It really does a poor job finding cracks. As a genral rule it ought to be used only if you are looking for a specific defect or condition for which it works. Your mention that the typical small voids and inclusions in cast steel frames are great confusers unless you have the films shot and interpreted by a radiographer with steel foundry experience. There are good ASTM defect standards for radiographers to compare the films against to "grade" them. It also requires a judgement as to what steel casting specification the old parts might represent. Alsmost certainly they would predate the current specs for modern steel foundry products.

The other non-destructive testing methods have similar issues. Magnetic particle inspecton, (MT), or Magnaflux is also confusing when applied to steel castings. It works best on forged or rolled steel products when the "grain" has a preferred orientation due to the rolling or forging process. The MT technique is sensitive to interruptions in the grain due to cracks. Obviously, this works for materials that can be magnetized. A good all around alternative is penetrant inspection using fluorescent dye or visible red dye. A properly cleaned part will reveal cracks that can't be found any other way.

Bottom line is that except for inspecting welds for porosity and slag inclusions, x-ray inspection has little value for the restoration efforts on locomotives. J. David's explanation as to why this is so is good counsel.

Fred F.
Foundry Metallugist

I am a retired Metallurgical Engineer who spent part of his career working for a major NDT laboratory. The test that would have been magnetic particle at both the foundry and maintenance shops. In later years, suspect areas from MPI inspections might be confirmed by isotopic radiography, but it still would be hard to separate casting defects from crack propagation. The only radiographic standards that I knew about were for the cast steel drivers for steam locomotives. In service tests of drivers and trucks used a penetrant inspection involving "whiting" in a kerosene solvent. Today, we use a red dye (Dye Check) to do the same test.

ASTM has issued radiographic standards for both steel and aluminum castings. But, the only acceptance standard that I know of was for aircraft, aluminum castings. In steel castings, it was also an engineering decision.

The modern way of radiographic inspection is to do digital radiography. The exposed plate is transferred to a computer where the interpretation is done. Magnification of suspect areas is easily done via the computer image.

Henry E. Fairman,
Life Member, ASM International