Measurement of Stress Free Temperature

The Vortock® VERSE SFT measuring equipment is a cost effective, non-intrusive method of determining stress free temperature without having to break into the track, and is particularly suited for:

• Sites where no stressing records are available
• Following lifting or slewing of the track
• Sites where no rail movement was recorded during rail replacement
• Auditing prior to hand-back
• Straight or curved track

This method, which is approved for use by Network Rail, uses a simple hydraulic lifting device coupled with accurate transducers to lift an unclipped length of rail and record the applied force and displacement achieved.

The recorded data is used to calculate the vertical stiffness of the rail, from which the neutral temperature is calculated.

Measurement time: (2 x measurements): 90 mins - Accuracy: +/- 1°C

The measured SFT data is processed in several ways:

• Information logged on data logger – verbal report of nonconforming sites direct to engineer
  
• On return to base, data is download into PC and analysed
• Data analysed off site – certificate prepared (within 48 Hrs)
• All data stored for statistical analysis – if required
• Source files transferred electronically to client to input into STRESSROUTE NR – national database

We currently have three complete VERSE sets, and with additional units on loan are able to provide up to 5 mobile measurement teams, normally comprising of an engineer and an assistant, with all necessary ancillary equipment for site measurement. In addition we can provide support P.Way resources to assist with unclipping and re-clipping the rails. Site safety protection is normally provided by the client. We have now recorded in excess of 1000 measurements in track, in addition to which we are an approved training agent for the equipment supplier and can provide both out of track operator training and workplace competency assessment.

Measurement of SFT using Railscan

Our RAILSCAN Neutral Temperature measuring unit uses non contacting magnetic probes to generate an alternating magnetic field in the rail. Interaction between this field and the internal magnetic properties of the rail microstructure produces Magnetic (Barkhausen) noise. The amplitude of this noise is related to the longitudinal stress in the rail.

The equipment automatically measures and records the amplitude of the Barkhausen noise, and also records the rail temperature using its integral infrared pyrometer. The data is input into an algorithm containing standardized magnetic data produced in the laboratory, the modulus of elasticity and coefficient of linear Thermal expansion, is used to provide an on-line record of variation in SFT.

• Measurement is virtually instantaneous, and non disruptive
  
• No rail preparation is required
• Rail does not have to be unclipped
• Works on all types of track, including tight curves
• Equipment is lightweight, water proof and self powered

The technology has been tested on a number of railways worldwide and is currently undergoing approval in the UK, where it is of interest for measuring SFT in Bull Head rail, tight curves, and where the rail may be in compression.