Non-destructive testing of FOTR equipment

[John Ashworth]

For several years now FOTR member Brian Dadford has been carrying out non-destructive testing (NDT) of materials on our locomotives and rolling stock. What this means to the uninitiated (ie most of us!) is that he regularly pitches up at the site, paints buffer beams, axles and coupling rods with a white magnetic fluid, and then spends hours studying them with bits of arcane kit.

It is just one part of FOTR's safety regime, and it is a very innovative one - as Brian points out, there are no standards for steam locos, which were built before NDT came into vogue, so he is really breaking new ground.

Below is a technical paper Brian wrote recently for the South African Institute for Non-Destructive Testing, reproduced with his permission from their website at http://www.saint.org.za/ndt_news.htm#2_1

REVIVAL OF THE STEAM ENGINE

B E E Dadford
SNT Level III

PHASE I covers the Buffer Couplings on 14 Main Line Coaches, 4 Steam Engines and 4 Water Tankers

Revival of the steam engine and refurbishment of passenger coaches has taken on a new dimension, by the appointment of a Safety Regulatory Committee, Spoornet and Public Safety (legislated) to oversee compliance. In addition “Friends of the Rail” have extended outings to Warmbaths/Nylstroom, plus ever expanding overseas tourists who wish to experience a steam train ride.

The writer shall endeavour to embrace the concept of “Back to Basics” as the majority of NDT Practitioners are Level II’s and should be able to affiliate with Phase I of this article, namely buffer couplings. (We understand failures have occurred on coal trucks).

Main line coach buffers/couplings are composed of :

1. main body (cast steel) - magnetic particle test.
2. knuckle (drop forged) – magnetic particle test.
3. king and cotter pins (drop forged) – MPI/Dye penetrant.
4. tee coupling (drop forged machined) square threads - ultrasonic, MPI/dye penetrant.

Procedures were drawn up and proved to ASTM E 709, E165-02 and ultrasonic ASTM E 388 standards.

The Tee Coupling Rod specs are 1000m x 90mmØ square thread with a 75mm machined hole for the king pin (see sketch - attached). As no manufacturing blue prints were/are available on steel spec’s the UT scan revealed oil or water quenching during heat treatment, resulted in excellent grain structure.

A damaged rod was used to cut slots at various intervals in the root of the square thread in order to establish sensitivity using a 4MHz angle 60/70° angle probe. The sounds simpler than what it seems but the slot cutting had to be carried out in stages until satisfactory response was achieved. In most cases grain structure was excellent with no grass. So one could boost dB’s to verify any faint echoes. Anything closer to the root surface would have to be picked up by the MPI/dye penetrant results.

Compression probes of 5MHz x 10mmØ were used on diametrical scans and for a longitudinal scan along along the axis, a 2MHz x 15mmØ probe working around the 10mm split pin hole using the best part of the circumference of the king pin hole. A bit of a challenge to pick up a back wall echo but the use of a 60mmØx1000m shaft axle steel EN9 which is not very clear grain structure. A dB factor had to be used to bestpossible, relying on beam spread.

As the tee rod has to cope with torque plus tensile and compressive load due to coach movement and poor condition of the rails wihich puts tremendous reactive stresses on these components.

PHASE II WILL COVER AXLES/WHEELS.
Keywords : FSH = Full Scale Height, MHz = Megahertz, BWE = Backwall echo, ASTM = American Society of Testing Materials