It was mentioned in the thread on Amtrak disposals that SST (Stainless Steel) passenger cars still had carbon steel underframes. Was this true of all Budd-built SST cars, even the early stuff?

I ask because when Pennsylvania Trolley Museum (PTM) preserved one of the 1960 Budd SST cars from the Market-Frankford subway/elevated line in Philly we discovered that the entire carbody, including the frame, was made of SST. If this approach worked for subway cars, was the compression strength requirement for mainline rail so much greater that it demanded the use of carbon steel frames?

Were there any other transit car groups that were entirely SST?

That would seem to be the way to build a "forever" car--if the specs would permit.

I think only the bi-level Budds (commuter cars and ATSF cars) have carbon steel underframes, the rest are all-stainless.

CD

Remember that the issue is that at least some carbuilders out there built "stainless steel" cars with these carbon underframes. As I am to understand it, and those who make more money than I do understanding this stuff can chime in, Budd cars were well-built, while cars by Pullman-Standard, AC&F, etc., weren't, and thus "fall apart" or are more vulnerable to body rot issues in spite of supposed "stainless steel construction."

Okay, you guys that really know better, make me look stupid or whatever.

Only nitpick I have is post-war Budds are well built. The pre-war cars aren't as good as the post-war cars.

Treading more in to territory I don't know, was the reason that Pullman built stainless sheathed cars with carbon steel frames because Budd held the sole rights to the shotwelding process that made stainless usable as a frame?

Correct.

Because of the patents that Budd held, P-S (and AC&F) could not manufacture all-stainless steel cars using the same techniques (shotwelding, etc.), until said patents expired in c. 1953, at which time P-S began constructing all-stainless steel cars, if the railroad which placed the order specifically requested this (during the lightweight era, the railroads had a lot of say regarding what materials were used in the construction of cars which they ordered). The first car that Pullman built of all-stainless was MKT 72 seat coach #1202R J. Pinckney Henderson, which was ordered in March 1953 and delivered in March 1954. The original #1202 J. Pinckney Henderson, built in 1947, was wrecked in 1953, so the Pullman all-stainless demonstrator was a replacement, hence the "R" in the car number.

What's interesting is that there was at least 1 order of cars built by Pullman before 1953 which had stainless fluting over stainless underframes: the SOU sleeper order of 1949 (Lot #6814), which included 10RM-6DB and 14RM-4DB sleepers, 1MR-2DR sleeper-21 seat buffet lounges, and 5DB sleeper-22 seat buffet lounge observations. In discussing these cars in the "Surviving SOU Lightweight" thread, it was mentioned that these cars were not entirely stainless: the crash posts and some other structural components were of carbon steel (or "corten") construction, with the framing under the fluting being of stainless construction (SOU had had a bad experience with a prewar order of P-S fluted cars, which would explain their insistence of the stainless-over-stainless construction). What's also interesting is that not every car built in this Lot was stainless-over-stainless: the PRR 10-6 sleepers built in this Lot were of the more typical stainless fluting over corten framing.

Now, regarding what railroads did to address the stainless-over-corten issue, the AT&SF probably had the most progressive retrofit program: as P-S (and AC&F) cars were brought in for shopping and corrosion was identified, AT&SF would remove the stainless fluting and replace the corten framing underneath with new stainless framing. This would explain why there are so many surviving examples of AT&SF P-S and AC&F fluted cars.

Amtrak also did some repair work on the stainless-over-corten cars which they received, but I don't think this involved replacing the corten framing with new stainless framing. One thing that was done was to resecure the stainless fluting, which as corrosion advances, becomes more and more loose, in some extreme cases, falling off completely (there are several photos of retired CRI&P cars in the 1970's where the fluting has done just that). But in resecuring the fluting, the components which Amtrak used to do this were not stainless, so after several years, the fluting became loose all over again!

Budd built cars were constructed ALMOST entirely of stainless steel, but there were always LAHT (Low-Alloy High Tensile) steel components in the underframe. The center sills were always stainless steel, but the end underframes (bolsters, center plates, coupler pockets, collision post "stub posts", etc) were always either all steel (cast or fabricated) or mostly steel with some stainless components.

A big problem that we are seeing with these now 60 +/- year old Amtrak Heritage cars is the bolsters can be badly rusted away underneath the stainless steel floors. This is what has done in some of the Heritage diners that were completely gutted for installation of new interiors. Severe rust deterioration was discovered in the bolsters under the kitchen. And no, it had nothing to do with so-called "dissimilar metals". We have also seen some issues where the end underframe is riveted or plug/ring welded to the stainless center sill. Water can get trapped in the various pockets in this area and after 50 - 60 years rust away sections of the steel portion. This can in turn press against the adjacent stainless, causing it to crack. Kind of hard to describe, but at any rate very difficult and expensive to repair.

All the Carbuilders built very good cars. Each material and method of construction has it's plusses and minuses. There is not really one "best" builder or construction material. Potential buyers of these old cars should always consider each car on a case by case basis.