CWR stands for continuous welded rail: rail welded together into lengths exceeding 400 feet, as defined in 49 CFR 213.119. US rail is usually flash-butt welded in a plant into strings of about 1,440 feet, then joined in track with field welds such as thermite welds. Every track owner with CWR must follow a written CWR plan filed with FRA.
With no expansion gaps, CWR carries thermal movement as force. Managing that force through the rail neutral temperature is what keeps CWR from buckling in heat or pulling apart in cold.
In this guide
- What CWR means and how it differs from jointed rail
- How continuous welded rail is made and joined
- Rail neutral temperature, sun kinks and pull-aparts, with worked numbers
- What a 49 CFR 213.119 CWR plan must contain
- Ultrasonic testing and weld inspection on CWR
What does CWR stand for, and how is it defined?
CWR is short for continuous welded rail, and FRA gives it a legal definition. The definitions in 49 CFR 213.119(l) on eCFR say continuous welded rail "means rail that has been welded together into lengths exceeding 400 feet." The same paragraph adds that rail installed as CWR stays CWR, "regardless of whether a joint or plug is installed into the rail at a later time."
So a bolted repair joint or plug rail cut into a string doesn't take the track out of the CWR plan.
Under 49 CFR 213.121(f), joints designed so the rail can't slip, with a locked-up length over 400 feet, are also treated as CWR.
Key takeaway: Over 400 feet of welded or locked rail puts track under a CWR plan.
How is continuous welded rail different from jointed rail?
Jointed rail is bolted together in short lengths with gaps that let the steel expand; continuous welded rail removes those gaps. Norfolk Southern, for example, described its older track as "39- or 78-foot sections of track that are bolted together," and its CWR as "1,440-foot sections of rail that are welded together" (Progressive Railroading, November 2012).
| Feature | Jointed rail | Continuous welded rail (CWR) |
|---|---|---|
| Typical lengths | 39 ft or 78 ft rails, bolted | Plant-welded strings, commonly 1,440 ft, field-welded into continuous track |
| Thermal movement | Taken up by gaps at joints | Restrained; becomes longitudinal force in the rail |
| Main thermal risks | Joint gaps close or open; bolt-hole cracks at joints | Track buckling (sun kinks) in heat; pull-aparts and broken welds in cold |
| Key federal rule | 213.121 (joints) | 213.118 and 213.119 (CWR plan), plus 213.121 for any CWR joints |
The FRA's 2013 buckling report lists the reasons railroads moved to CWR: "Improved ride quality, increased rail and rolling stock fatigue life, and reduced track maintenance costs" (FRA, DOT/FRA/ORD-13/16). The trade-off is that restrained thermal forces create the risk of summer buckles and winter pull-aparts.
For background on joint bars and bolted joints, see our guide to rail joints.
How is continuous welded rail made and joined?
Continuous welded rail is built in two stages: electric flash-butt welding in a fixed plant to make long strings, then field welding, usually thermite, to join the strings in track.
Stage 1: plant welding into strings
At a rail welding plant, mill-length rails are joined by flash-butt welding: electric current heats the rail ends, which are then forged together with no filler metal. The string is delivered by rail train.
String lengths are set by the plant and the customer, not by federal rule. Published examples:
| Source | Mill rail length | String length |
|---|---|---|
| Norfolk Southern (Progressive Railroading, 2012) | not stated | 1,440 ft |
| Steel Dynamics plant design (Progressive Railroading, 2005) | 240 or 320 ft | 1,600 ft, "with as few as four welds" |
Treat 1,440 feet as common, not universal; check the owner's specification.
Stage 2: field welds that join strings
Once laid, strings are joined to each other and to existing track in the field:
| Method | Where it's done | How it works | Inspection points |
|---|---|---|---|
| Flash-butt (plant) | Fixed welding plant | Electric resistance heating and forging, no filler metal | Plant QA; head and web covered by later rail-flaw testing |
| Flash-butt (mobile) | In track, from a mobile welding unit | Same process, done on site | Alignment, upset removal, finish grinding |
| Thermite (aluminothermic) | In track | Molten steel from a thermite reaction fills a gap between the rail ends inside a mold | Porosity, slag and sand inclusions, lack of fusion, weld-collar fatigue at the web/base fillet |
Mobile flash-butt welding is established practice; European standard EN 14587-2 covers flash-butt welding of new rails "by mobile welding machines at sites other than a fixed plant" (BSI listing).
FRA's buckling report links the weld gap to stress control: rail is cut so that "an adequate amount of gap for welding (usually 1 in.)" exists when the rail reaches the target neutral temperature.
For the full range of weld processes, see types of rail welding. Inspection of each weld type is covered in flash-butt weld inspection and aluminothermic weld inspection.
What is rail neutral temperature, and why does it matter?
Rail neutral temperature (RNT) is the rail temperature at which the rail carries no longitudinal force. 49 CFR 213.119(l) defines it this way:
"Rail neutral temperature is the temperature at which the rail is neither in compression nor tension."
Above the RNT, continuous welded rail is in compression and the track can buckle. Below it, the rail is in tension and can break at a defect or weak weld. FRA's 2013 report states that railroads "strive to maintain a high neutral temperature, typically between 90 °F and 115 °F, depending on regional temperature variations." FRA's 2023 training module gives a preferred laying range of typically 90 to 110 °F (FRA, Track Buckling Prevention Module 2, July 2023).
The federal rule doesn't set a number. Under 213.119(a)(1), each track owner designates its own "desired rail installation temperature range for the geographic area." A desert line and a northern plains line would normally choose different ranges.
How much force is in the rail?
FRA's training material gives the thermal force as:
P = EAα × (T_rail − RNT)
where E is the modulus of elasticity of rail steel, A is the rail's cross-section area and α is the coefficient of thermal expansion. FRA gives α for rail as 0.0000065 in/in/°F, and gives EAα as about 2,600 lb per °F for 136 lb rail and about 2,185 lb per °F for 115 lb rail (FRA Module 2, 2023). FRA's 2013 report lists the 136 lb rail area as 13.35 in².
Worked example 1: summer compression on 136 lb rail
Assume CWR laid with an RNT of 100 °F. On a 105 °F day, the rail itself runs hotter than the air. FRA's 2013 report says the difference "can be 25–35 °F based on the field data," so take a rail temperature of 140 °F.
| Case | T_rail − RNT | Force per rail (2,600 lb/°F) |
|---|---|---|
| RNT held at 100 °F | 40 °F | 104,000 lb compression (52 tons) |
| RNT has drifted down to 70 °F | 70 °F | 182,000 lb compression (91 tons) |
FRA found that the neutral temperature "can fall to 60 °F or lower because of rail and track movement and maintenance actions," such as curve realignment or rail repair. The track looks the same, but each rail carries 75% more force on the same hot day.
Worked example 2: winter tension
The same rail with an RNT of 100 °F, at a rail temperature of 0 °F on a cold night:
- T_rail − RNT = −100 °F
- Force = 100 × 2,600 = 260,000 lb tension per rail (130 tons)
A high RNT lowers summer compression but raises winter tension. FRA explains that "High tensile force is instrumental in causing rail fractures at locations of internal defect and or weak welds." Cold-weather breaks tend to start at existing flaws.
Worked example 3: how much to stretch a string
A 1,440-foot string (17,280 inches) is laid on a cool morning at a rail temperature of 70 °F, but the target RNT is 100 °F. To set the right RNT, the string must be made as long as it would be at 100 °F before it is anchored and welded:
ΔL = α × L × ΔT = 0.0000065 × 17,280 in × 30 °F ≈ 3.4 inches
The crew stretches the string about 3.4 inches with hydraulic rail tensors, or heats it, before the closure weld. If they weld it without that adjustment, the string's RNT is about 70 °F, 30 °F below target. That is also why 213.119(d)(2) says rail should not be added when it's colder than the designated range "without provisions for later adjustment."
Key takeaway: The rail neutral temperature is invisible and drifts in service. Every cut, repair and realignment can lower it, and a 30 °F loss of RNT can add roughly 78,000 lb of compression per 136 lb rail on a hot day.
What causes sun kinks and pull-aparts in continuous welded rail?
Sun kinks are lateral buckles caused by compression when rail temperature rises far above the RNT; pull-aparts are breaks caused by tension when rail temperature falls far below it.
| Failure | When | Driving force | What it looks like | Conditions that raise risk |
|---|---|---|---|---|
| Track buckle (sun kink) | Hot rail, above RNT | Compression | Lateral misalignment; FRA reports amplitudes up to 30 in and buckle lengths of about 40 to 60 ft | Low RNT, disturbed ballast, weak lateral resistance, curves, tight or kinky rail |
| Pull-apart or broken weld | Cold rail, below RNT | Tension | A gap at a broken weld, defect or joint; usually under 4 in if the rail is well anchored | Internal defects, weak welds, stripped joints, poor anchoring |
FRA's 2013 report found an average of 34 buckled-track derailments a year over the 10 years it reviewed (FRA reportable accidents through 2003). It judged pull-aparts "less severe than buckles" because the gap is small and a broken rail may be detected by the signal system.
Under 213.119(l), a buckling incident is a lateral misalignment that deviates from the Class 1 limits in 213.55. Our article on sun kinks on the railroad covers heat-related speed restrictions and field signs in more detail.
What must a 49 CFR 213.119 CWR plan contain?
Every track owner with CWR must have, file and follow a written CWR plan. 49 CFR 213.118 requires each owner with CWR track to "have in effect and comply with a plan". The plan is filed with FRA's Associate Administrator for Railroad Safety, and FRA reviews it within 30 days.
Section 213.119 then lists what the plan must contain:
| Paragraph | The plan must cover | Notable specifics |
|---|---|---|
| (a) | Installation and adjustment | A desired rail installation temperature range for the area, and destressing methods to reach it |
| (b) | Anchoring and fastening | Patterns that limit longitudinal rail and tie movement, with special attention to bridges and bridge approaches |
| (c) | CWR joints | At least two bolts per rail at each CWR joint; rules for new and failed bolted joints (below) |
| (d) | Cutting and repairs | Account for actual rail temperature when rail is removed or added; no adding rail below the designated range without later adjustment |
| (e) | Curves | Monitor curves for inward shifts of alignment after track is disturbed |
| (f) | Speed restrictions | Slow orders when ballast is disturbed and rail temperature versus RNT creates buckling-prone conditions; consider tie type and ballast reconsolidation |
| (g) | Track inspections | When to look for buckling-prone and pull-apart-prone conditions, and the remedial actions |
| (h) | Joint inspections | On-foot inspections, crack detection, a minimum frequency table, records |
| (i) | Training | A training program with annual retraining for qualified CWR supervisors and inspectors |
| (j) | Records | Rail temperature, location and date of each CWR installation, kept at least one year; non-conforming work; joint inspections |
| (k) | Availability | A copy of the CWR procedures at every job site, in one CWR standards and procedures manual |
Source: 49 CFR 213.119 on eCFR.
The 60-day rule for bolted joints
The joint rules in 213.119(c) are the most specific numbers in the section. For a bolted joint installed during CWR installation after October 21, 2009, the owner must, within 60 days, do one of three things:
- Weld the joint.
- Install a joint with six bolts.
- Anchor every tie 195 feet in both directions from the joint.
A failed bolted CWR joint with a rail gap must be welded, or rebuilt with new bars and bolts plus one of: a weld within 30 days, an extra bolt per rail end, 195 feet of anchoring each way, or added rail with later adjustment.
How often must CWR joints be inspected?
At least as often as the table in 213.119(h)(6) requires, based on track class, train type and annual tonnage. The inspections are on foot and look for cracked bars, loose or missing bolts, rail-end batter and signs of rail running, such as a wide gap or displaced anchors.
Minimum inspections of CWR joints per calendar year:
| Track class | Freight, under 40 MGT | Freight, 40–60 MGT | Freight, over 60 MGT | Passenger, under 20 MGT | Passenger, 20 MGT or more |
|---|---|---|---|---|---|
| Class 5 and above | 2 | 3 | 4 | 3 | 3 |
| Class 4 | 2 | 3 | 4 | 2 | 3 |
| Class 3 | 1 | 2 | 2 | 2 | 2 |
| Class 2 | 0 | 0 | 0 | 1 | 1 |
| Class 1 | 0 | 0 | 0 | 0 | 0 |
| Excepted track | 0 | 0 | 0 | n/a | n/a |
Where freight and passenger trains share track, the more frequent interval applies. Inspections must fall in set periods and be at least 60 days apart (4 per year), 90 days (3), 120 days (2) or 180 days (1).
Extreme weather can extend an interval by up to 30 days for the 3- and 4-per-year schedules. CWR joints in switches, turnouts, track crossings and moveable-bridge lift assemblies must be inspected on foot at least monthly under 213.235.
Worked example. A Class 4 freight line carries 45 MGT a year. The table gives 3 inspections: one between January and April, one between May and August and one between September and December, each at least 90 days after the last. On Class 5 track at 65 MGT freight, it rises to 4.
Each joint inspection record must be made the same day and signed. For how cracks in joint bars are found, see rail joint inspection with ultrasonic testing and insulated rail joint inspection.
How do ultrasonic testing and weld inspection apply to continuous welded rail?
CWR is tested for internal flaws on the same schedule as any other rail, but its welds need closer attention, because a flaw in a weld under winter tension is a likely break point.
Rail-flaw testing under 213.237
49 CFR 213.237 sets internal rail inspection intervals for welded and jointed rail alike. On Class 4 and 5 track, inspections "shall not exceed a time interval of 370 days between inspections or a tonnage interval of 30 million gross tons (mgt) between inspections, whichever is shorter." Equipment must also be "capable of detecting defects between joint bars." Our guide to 49 CFR 213.237 explains valid searches and intervals.
On CWR, a rail-flaw search typically uses 70° shear-wave probes for transverse defects in the head and 0° probes for horizontal and vertical splits and web conditions. Exact probe sets vary by system.
What counts as a defective weld
FRA defines the weld defect it expects testing to find. Under 49 CFR 213.113, a defective weld is:
"a field or plant weld containing any discontinuities or pockets, exceeding 5 percent of the rail head area individually or 10 percent in the aggregate, oriented in or near the transverse plane"
The listed causes include incomplete penetration, lack of fusion, slag or sand entrainment, under-bead or shrinkage cracking, and fatigue cracking. If the defect runs lengthwise through the weld, 213.113 treats it as a split web for remedial action. Codes and remedial actions are summarized in FRA defect codes explained.
Where field welds fail
An AAR survey of revenue-service thermite weld failures (TTCI Technology Digest TD-00-013, July 2000) found:
| Finding | Share |
|---|---|
| Slag inclusions and/or gas porosity, the most common defect | 40% of reported failures |
| Of those, located mainly at the web/base fillet | 56% |
| Fatigue from weld-metal run-out at the web/base fillet or base | 32% |
The same digest warns that the data is "likely skewed as the ultrasonic rail flaw detection process only scans the head and web of the rail, and not the majority of the base." It also stresses that most thermite welds in service are sound.
What that means for CWR weld inspection
| Inspection | What it covers | What it misses |
|---|---|---|
| Rail-flaw test car or cart (213.237) | Rail head and web along the whole string, including welds | Most of the rail base, where many thermite defects start |
| Hand UT of a field weld | Head, web and base of a single weld, with angle beams placed by the technician | Large lengths of rail; it's slow and done weld by weld |
| Visual inspection and finish checks | Weld collar shape, run-out, cracks, mismatch, grinding quality | Internal porosity and lack of fusion |
| Magnetic particle testing | Surface and near-surface cracks at the collar and fillets | Defects deeper in the weld |
Part 213 doesn't set a separate test for each new field weld. Whether a new weld gets hand UT, MT or only a visual check, and when, is set by the owner's specification and welding procedures, so confirm what yours calls for.
Key takeaway: A rail-flaw car finds most head and web defects in CWR, but a thermite weld's base is the weak spot it largely can't see. Targeted weld UT closes that gap.
What are the limits of CWR rules and inspection?
No single rule or test tells you a CWR string is safe. Each tool covers part of the risk:
- UT doesn't measure neutral temperature. A flawless string can still buckle if its RNT has drifted down. FRA notes that "at present no convenient way of measuring the rail neutral temperature exists," though strain gages can track changes.
- 213.119 sets plan contents, not values. The rule requires each owner to choose its own installation temperature range, anchoring patterns and slow-order triggers. Two compliant plans can use quite different numbers.
- Destressing has a long reach. FRA says the force-change zone after a cut "can be as long as 1000 ft on either side of the cut." If less rail is unfastened than needed, the wrong RNT stays locked in near the weld.
- Records only go back so far. Installation temperature records under 213.119(j) need be kept for only one year.
- Transit systems have extra oversight. Rail transit lines not part of the general railroad system may fall under state safety oversight instead of, or as well as, FRA; in California that is the CPUC. Check which rules apply to your track.
How EMA Industries applies this
EMA Industries performs ultrasonic rail flaw testing and rail weld inspection for transit agencies, short lines and industrial track owners. We're based in Southern California and mobilize nationwide. On CWR, a useful report gives the weld type and location of each flaw, notes any stretch where a valid search wasn't possible, and flag field welds that need hand UT of the base. To scope CWR rail testing or a field-weld inspection program, see our ultrasonic rail testing services or contact us for a quote.
Frequently asked questions
What does CWR stand for on a railroad?
CWR stands for continuous welded rail. Under 49 CFR 213.119, it means rail welded together into lengths of more than 400 feet, and it stays CWR even if a joint or plug rail is later cut in.
How long is a string of continuous welded rail?
Plant-welded strings in the US are commonly about 1,440 feet, and some plants make 1,600-foot strings from 320-foot mill rails. The strings are then field-welded together, so the finished continuous rail can run for miles between joints.
What is a typical rail neutral temperature for CWR?
FRA research says railroads aim for a neutral temperature typically between 90 °F and 115 °F, depending on climate. The federal rule leaves the exact range to each track owner's CWR plan.
Why does continuous welded rail break in cold weather?
Below the neutral temperature the rail is in tension. On 136 lb rail that's about 2,600 lb of force per °F, so at 100 °F below RNT each rail carries about 260,000 lb. That tension opens existing internal defects and weak welds into breaks.
Does FRA require a CWR plan?
Yes. Under 49 CFR 213.118, every track owner with CWR track must have and follow a written plan, filed with FRA, that covers installation, destressing, anchoring, inspections, joints, training and records as listed in 213.119.
Sources
- 49 CFR 213.119, Continuous welded rail (CWR); plan contents, eCFR; text checked on Cornell LII, October 2026
- 49 CFR 213.118, Continuous welded rail (CWR); plan review and approval, eCFR; checked on Cornell LII
- 49 CFR 213.121, Rail joints, eCFR; checked on Cornell LII
- 49 CFR 213.113, Defective rails, eCFR; checked on Cornell LII
- 49 CFR 213.237, Inspection of rail, eCFR; checked on Cornell LII
- Kish, A. and Samavedam, G., Track Buckling Prevention: Theory, Safety Concepts, and Applications, FRA report DOT/FRA/ORD-13/16, March 2013
- FRA, Track Buckling Prevention and Improved Rail Stress Management (Module 2), training presentation, July 31, 2023
- Kristan, J., Thermite Weld Failure Survey, TTCI Technology Digest TD-00-013, July 2000
- NS names Atlanta rail fabrication plant after former MOW group leader, Progressive Railroading, November 19, 2012
- Railtech Schlatter helps Steel Dynamics design CWR plant, Progressive Railroading, October 25, 2005
- EN 14587-2, Flash butt welding of new rails by mobile welding machines, BSI catalog listing