Tubing Failure Analysis: A Practical Troubleshooting Guide
Tubing Failure Analysis: A Practical Troubleshooting Guide
Tubing failure analysis should begin with the observed failure and service history, not with an immediate material change. Cracking, splitting, dielectric failure, loose fit, blockage, discoloration or leakage can originate from material selection, dimensions, manufacturing, storage, assembly or an operating condition that was missing from the original specification.
In this guide
First: Contain the Issue and Preserve Evidence
Separate affected and unaffected lots, record labels and quantities, and stop destructive handling of representative samples. Keep failed parts, unused tubing from the same lot, packaging and assembly records. Photograph the failure in place before removing the tube, because cut marks, routing, nearby edges and heat sources may explain the damage.
Record when the failure appeared: incoming inspection, cutting, insertion, winding, potting, thermal test, electrical test or field operation. A failure that occurs during insertion has a different evidence path from one that appears after months of thermal cycling.
Common Tubing Failure Symptoms and Likely Cause Families
| Observed symptom | Possible cause families | Evidence to check |
|---|---|---|
| Longitudinal split or crack | Interference fit, low bend radius, embrittlement, cut damage, wrong material or ageing | ID distribution, insertion force, edge radius, temperature history, microscopy |
| Loose or slipping tube | Oversize ID, thermal relaxation, shrinkage assumption, lubricant or wrong tolerance | Before/after dimensions, mating-part range, temperature cycle, surface condition |
| Dielectric breakdown | Insufficient wall, pinhole, contamination, sharp edge, moisture or test mismatch | Failure location, wall map, surface, conditioning, voltage setup and applicable standard |
| Flattening or collapse | Vacuum, tight bend, compression, heat softening, packaging deformation | Ovality, bend radius, load, pressure/vacuum and storage stack |
| Leakage or permeation | Crack, poor fitting, chemical attack, pressure, permeation or wall variation | Joint, medium, concentration, temperature, wall, pressure history and leak test |
| Discoloration or residue | Overheating, contamination, reaction, adhesive migration or cleaning process | Temperature map, chemistry, lot comparison, surface analysis and process records |
| Blocked bore or high flow loss | Undersize ID, ovality, debris, kink, thermal deformation or coating buildup | ID profile, cleanliness, routing, cut end and flow/pressure data |
These are hypotheses, not conclusions. Multiple mechanisms can create the same appearance, and one system can contain more than one contributing cause.
An Eight-Step Root-Cause Workflow
- Define the failure precisely. Replace “tube is bad” with a measurable symptom, location, quantity and acceptance criterion.
- Build the timeline. Record material receipt, storage, conversion, assembly, testing and service events.
- Compare populations. Examine failed, non-failed same-lot, prior-lot and reference parts where available.
- Verify identity and traceability. Confirm material grade, construction, supplier lot and any approved changes.
- Measure against the drawing. Use an agreed method for ID, OD, wall, length, ovality, seam and surface.
- Reconstruct the application. Include temperature, voltage or pressure, chemicals, bend, vibration, compression and duty cycle.
- Test the leading hypotheses. Change one controlled factor at a time and use a method linked to the suspected mechanism.
- Verify corrective action. Repeat the critical process and qualification cycle before closing the issue.
Measurement and Test Discipline
Agree on sample conditioning, instrument, location, contact force and calculation method before comparing results. Thin or flexible tubing can deform under measurement, creating apparent disagreements between customer and supplier. Read the technical data and test methods guide for a practical distinction between raw-material data, design qualification and lot inspection.
If the issue involves dimensions, link the analysis to the supplier’s dimensional inspection process. If material identity is uncertain, review material traceability and change records before running more tests.
How to Prevent Recurrence
- Convert critical application conditions into drawing notes and supplier acceptance criteria.
- Specify tolerances according to fit and function, not only nominal dimensions.
- Approve a production-representative sample through the real assembly and duty cycle.
- Define packaging, storage life, cleanliness and handling where deformation or contamination matters.
- Require notification and requalification rules for material, tooling or process changes.
- Retain samples and inspection records proportionate to failure risk.
Frequently Asked Questions
What should I send to a tubing supplier for failure analysis?
Send failed and unused same-lot samples, labels, drawing and revision, inspection data, assembly steps, service conditions, photographs and the exact failure rate. Do not clean, cut or mark every failed sample before the supplier reviews the evidence plan.
Does a dimensional result outside tolerance prove root cause?
It proves a specification nonconformance only if the measurement method is valid and agreed. It does not automatically prove that the dimension caused the field failure. Link the measured difference to a credible failure mechanism and controlled reproduction.
Should we change material after a crack?
Not until interference, sharp edges, bend radius, cutting, chemical exposure, ageing and actual temperature are checked. A stronger or more expensive material can fail again if the assembly mechanism remains unchanged.
What is the difference between containment and corrective action?
Containment protects current production by sorting or holding affected material. Corrective action removes a verified cause and prevents recurrence. A 100% sort can be valid containment but does not explain or eliminate the cause.
Request a Structured Failure Review
WELLELE can review available samples, drawings, lot information and application conditions to help define the next investigation step. The scope and test capability must be confirmed before analysis.