The Use of Rail Flaw Data in Replacement Planning

Rangecam’s Rail Replacement Planning capability works by projecting measured wear trends to condemning limits. The projection is based on average rail wear measurements for each track side and segment (full curve or tangent section). From that projection, a rail replacement date is calculated. Rail flaw data can be used to adjust the projected date. A Rail Defect Index (RDI), which is based on rail flaws recorded within a specified time period, is calculated for each track segment and side. If the RDI for a given segment and side exceeds a condemning threshold, the rail is scheduled for immediate changeout. If RDI is lower than a minimal threshold, it has no effect on the scheduled changeout date. If RDI falls between the minimal threshold and the condemning threshold, it accelerates the scheduled changeout date calculated on the basis of rail wear.

Rail Defect Index

RDI is calculated by the formula: RDI = (S) / (L x T), where,

S: defect severity

L: segment length in miles

T: time in years 

If the selected time window for rail defect analysis is 3 years, and that during the 3-year period, 4 rail defects were detected on the low rail of a 528-foot (0.1 mile) curve:

2 detail fractures (TDD) of severity 7.0

1 defective weld (DWF) of severity 5.0

1 horizontal split head (HSH) of severity 8.0

The total severity of the 4 defects is 27.0.

The RDI of this low rail, then is: 27.0 / (0.1 x 3) = 90.0

RDI Formula in Rail Replacement Planning

The rules for using RDI in rail replacement planning are as follows:

1. If RDI exceeds the condemning threshold, immediate replacement is forecast.

2. If RDI is less than the minimal threshold, the replacement date calculated from rail wear trend analysis is used.

3. If RDI falls between the minimal and the condemning threshold, the following formula is used: Dr = Dt + ((Dw - Dt) * (CDI-RDI)/CDI) where:

Dr: forecast rail replacement date

Dt: date of most recent test

Dw: rail replacement date forecast from rail wear trend data

CDI: rail defect index condemning threshold

Examples of RDI in Rail Replacement Planning

The railroad adopts the RDI thresholds: Condemning: 100 / Minimal: 20.

Rail wear has been measured over several years, with the latest measurement in February 2010. Based on wear trend analysis, the high rail of curve 123 is forecast to require replacement in July 2012.

Case 1: RDI = 10

Because the RDI of this high rail is below the minimal threshold, the forecast replacement date is unchanged.

Case 2: RDI = 120

Because the RDI of this high rail is above the condemning threshold, the forecast replacement date is revised to February 2010 (immediate replacement).

Case 3: RDI = 90

RDI is between the minimal threshold and the condemning threshold. By the above formula, the forecast replacement date is revised as follows:

Dr:  Feb 2009 + ((Jul 2011 – Feb 2009) * (100-90)/100).

Substituting decimal years for dates gives approximately:

Dr : 2009.1 + ((2011.5 – 2009.1) * (100-90)/100) = 2009.34 Reconverting the decimal year gives the revised forecast date of April 2009.ࠀ