In the maintenance of railways and urban rail transit, continuous welded rail (CWR) is widely adopted because it eliminates rail joints and reduces wheel-rail impact. However, precisely because the rail is 'locked,' temperature changes generate enormous thermal forces within the rail. Many field personnel ask: at what temperature can continuous welded rail not be worked on? This question has no off-the-cuff answer; it requires a comprehensive judgment based on rail temperature, stress-free temperature (SFT), and the type of work being performed.
1. At What Temperature Can Continuous Welded Rail Not Be Worked On: First Clarify What 'Degrees' Refers To
The 'degrees' here usually refer to rail temperature, not air temperature. Rail temperature is the actual temperature of the rail body itself, affected by sunlight, wind speed, and ballast condition. At noon in summer, rail temperature can exceed air temperature by more than 20°C.
The core of determining whether work can proceed is comparing the 'actual rail temperature' with the 'stress-free temperature.' The stress-free temperature is the rail temperature at which the long rail is finally locked, and it is the baseline value for continuous welded rail.
The general principle is: when the rail temperature exceeds the stress-free temperature by a certain range, work that disturbs the ballast or loosens fastenings is prohibited. The common control range is stress-free temperature ±(15–20)°C; beyond this range, work that affects track stability is generally not permitted.
Therefore, 'at what temperature can continuous welded rail not be worked on' is more accurately expressed as: when the rail temperature exceeds the upper limit of the stress-free temperature (e.g., +15°C or +20°C), the relevant work should be stopped.
2. How to Apply It: On-Site Judgment and Execution
Step one: check the stress-free temperature. Each continuous welded rail unit has a designed stress-free temperature range, usually recorded in technical ledgers. Field personnel should not estimate it based on experience.
Step two: measure the rail temperature. Use a rail thermometer to measure at the rail web or the side of the rail head, avoiding direct sunlight. Record the reading after it stabilizes.
Step three: refer to the type of work. Work that loosens fastenings, lifts track, shifts track, or replaces sleepers—operations that reduce ballast resistance—has the strictest restrictions; inspection and observation work that does not disturb the track has looser restrictions.
Step four: set up protection and monitoring. Once the rail temperature approaches the upper limit, increase observation frequency, prepare anti-buckling materials, and apply to stop work if necessary.
It should be noted that different track classes, ballast types, and stress-free temperature designs have different thresholds. The specific limits should be based on the track technical documents and the regulations of the managing authority.
3. What to Watch Out For: Several Common Pitfalls
First, using air temperature instead of rail temperature. This is the most common mistake. When the air temperature is 35°C in summer, the rail temperature may already exceed 55°C. Judging by air temperature can easily lead to misjudgment.
Second, ignoring 'low-temperature' risks. Not only does high temperature cause track buckling, but loosening fastenings at low temperatures can also cause rail breakage due to tensile thermal stress. Therefore, the restrictions are bidirectional.
Third, failing to restore the track promptly after work. If fastenings and ballast are not repositioned in time, track resistance decreases, and hidden hazards may remain even if the rail temperature has not exceeded the limit.
Fourth, ignoring sudden weather changes. Rail temperature changes rapidly before and after thunderstorms or when cold fronts pass. Work windows should be adjusted dynamically on site.
4. Application Scenarios: Track Assurance in Major Event Security
During sports events, exhibitions, and summits, rail transit often undertakes high passenger flow transport tasks, and the track must maintain high reliability. At such times, the work windows for continuous welded rail are even narrower: it is necessary to avoid high-temperature periods while also coordinating with operational shutdown windows.
Track assurance under a security system usually emphasizes three points: first, assess the rail temperature trend during the event in advance and schedule track-disturbing work during periods with suitable rail temperatures; second, strengthen inspections and monitoring, focusing on ballast, fastenings, and track alignment changes; third, coordinate with security screening and dispatch to ensure controlled access for workers and equipment.
Regarding security screening configuration, workers and tools entering key areas must undergo identity verification and item inspection to prevent foreign objects from being left behind. These measures do not conflict with rail temperature control; rather, they together form the track safety defense line.
Back to the frequently asked question: at what temperature can continuous welded rail not be worked on? Remember, the key is not a single number, but a combined judgment of 'stress-free temperature + work type + measured rail temperature.' On site, it is better to be conservative than to take risks. Measuring rail temperature accurately, checking ledgers thoroughly, and implementing proper protection are the fundamentals of safe work on continuous welded rail.