I’ve spent a lot of time on plant floors and inside OEM cabinets diagnosing nylon tubing issues that look “random” but aren’t. Nylon is a workhorse for pneumatics because it’s light, stiff, and has clean flow, yet it’s unforgiving when environmental, chemical, and installation realities aren’t matched to the grade and duty cycle. When tubing cracks next to a ferrule, flattens under cable trays, or turns chalky near skylights, I don’t blame manufacturing defects—I look for moisture, stress, UV, heat, fitting practices, and chemical exposures that quietly erode the polymer’s integrity.
Nylon pneumatic tubing commonly fails by stress cracking, hydrolysis, UV photo‑oxidation, creep deformation under sustained load, and chemical attack—particularly acids, phenols, and certain salts—often amplified by thermal cycling and poor installation (over‑tightened compression fittings, sharp bend radii, abrasion). Selecting the right nylon grade (e.g., Nylon 12 over Nylon 6/6), controlling moisture/temperature/UV, and following proper routing and fitting torque significantly reduces burst and leak events. Routine inspections tied to service environment and pressure/temperature deratings catch wear early and prevent downtime.
In the sections that follow, I break down why nylon cracks, flattens, or creeps under long‑term load; how heat, UV, and chemicals drive swelling or softening; the installation mistakes that precipitate burst events; and how I set practical inspection intervals for production reliability. I’ll anchor the guidance in real material behavior—hygroscopic swelling, stress corrosion cracking, notch sensitivity—so maintenance teams, system integrators, and OEM designers can prevent failure instead of chasing it.
Why does my nylon tubing crack, flatten, or creep under long-term load?
Stress cracking and notch sensitivity
Under sustained tensile stress—especially at fittings—nylon develops microcracks that propagate into brittle failure. I most often see cracks initiate at:
- Over‑tightened compression ferrules (stress concentrations and “notch” effects).
- Sharp edges on push‑to‑connect collets or improperly deburred tube cuts.
- Areas experiencing vibration plus pre‑load from cable ties or clamps.
Hydrolysis and UV exacerbate this by reducing molecular weight, making cracks propagate faster under the same stress. Thermal cycling (expansion/contraction) can turn microcracks into pinhole leaks or longitudinal splits.
Creep and flattening under constant load
Nylon exhibits viscoelastic creep. If tubing is constrained in a bundle, pinched under a tray, or tied too tight around a radius, long‑term load relaxes the polymer chains:
- The round cross‑section slowly becomes oval (“flattening”), increasing pressure drop and local stress.
- Fittings loosen as dimensional changes reduce interference, causing intermittent leaks.
- Kinking occurs when bend radius is below ~3–4× OD; the kinked zone shows whitening/crazing and becomes a future leak site.
Moisture uptake aggravates creep and dimensional drift. Nylon 6/6 can absorb ~9–10% water by weight, swelling up to ~3% dimensionally and losing stiffness—fittings that were tight at installation may be loose six months later in humid service.
Cold brittleness and impact
Below nylon’s glass‑transition region, impact resistance drops sharply. I’ve seen thin‑wall lines shatter near freezer conveyors when a tool bumps them. If low‑temperature exposure is routine, use Nylon 11/12 with appropriate impact modifiers or switch to PTFE or PFA where flexibility isn’t required.
How do heat, UV, and chemicals contribute to swelling or softening in my lines?
Heat and hydrolysis
Elevated temperature accelerates both oxidation and hydrolysis. In humid, warm enclosures or near ovens:
- Polymer chains are cleaved, reducing tensile strength and elongation.
- Tubing may first soften (plasticizer mobility) then embrittle and crack.
- Pressure ratings must be de‑rated; nylon’s burst margin at 23°C does not hold at 40–60°C.
Hot water service (>50–60°C) is a common misapplication—nylon slowly degrades, leading to unpredictable bursts well below nameplate pressure.
UV exposure and photo‑oxidation
Unstabilized nylon is susceptible to UV. Outdoors or under skylights:
- Surface chalking, yellowing, and loss of impact resistance appear.
- After months, minor bending causes catastrophic cracking.
- Black, carbon‑black‑stabilized Nylon 12 (or UV‑stabilized grades) is mandatory for outdoor lines.
Chemical incompatibilities
Nylon’s Achilles’ heel is specific chemicals:
- Strong mineral acids (HCl, H2SO4, HNO3) and phenolic compounds attack amide bonds, causing swelling, softening, and rapid failure.
- Metal salts, notably zinc chloride (from galvanic corrosion near galvanized steel, battery vapors, or certain cleaners), drive stress corrosion cracking when tubing is under load.
- Some hydrocarbons cause swelling; check chemical resistance charts and flush/segregate accordingly.
Moisture itself is a “chemical” for nylon—hygroscopic uptake reduces modulus and changes size, complicating precision assemblies and lowering pressure capacity in wet environments.
Material grade matters: Nylon 6 vs. Nylon 11/12
Selecting the wrong nylon is a root cause I see frequently.
| Attribute | Nylon 6/6 (Commodity) | Nylon 11/12 (Engineering) |
|---|---|---|
| Water absorption | High (~9–10% by wt) | Low (~1–2% by wt) |
| Dimensional stability | Poor in humidity | Good; outdoor capable |
| UV resistance | Unstabilized: poor | Better with black/UV grades |
| Typical failure mode | Moisture swelling, stiffness loss | Long‑term plasticizer migration risk |
| Best use | Dry, indoor, low cost | Precision lines, variable humidity, DOT air brake |
If uncertainty exists, Nylon 12 is my default for critical pneumatic runs where ambient swings and light exposure are realities.
What installation mistakes lead to burst events at my working pressure?
Fitting practices that create stress risers
- Over‑torquing compression fittings: Ferrules bite too hard, creating notch‑sensitive regions where cracks start. Use manufacturer torque specs and avoid re‑tightening to chase leaks—fix cut quality and alignment instead.
- Poor tube preparation: Angled cuts, burrs, and ovality concentrate stress. I use a sharp tube cutter, square the end, deburr ID/OD lightly, and ensure full insertion depth in push‑to‑connects.
- Mismatched tolerances: Mixing metric tubing with inch fittings (or vice versa) creates marginal seals that fail under heat or vibration.
Routing and support errors
- Bend radius too tight: Any radius <3–4× OD risks crazing and kinked zones that later burst under pressure spikes.
- Rubbing/abrasion: Tubing fretting against sheet metal or cable tray edges thins the wall. In dust‑laden air (abrasive media), internal erosion can also increase risk. Use grommets, saddles, and protective sleeves.
- Thermal proximity: Lines near heaters or high‑temperature manifolds see localized softening, creep, and rating de‑rate. Add standoffs, reflective sleeving, or reroute.
Ignoring temperature/pressure derating
Nameplate burst or working pressure is typically given at 23°C. At 40–60°C:
- Working pressure often drops 40–50%.
- Pressure spikes from fast‑acting valves (high Cv) create transient loads well above steady‑state values. I size tubing and fittings to handle dynamic spikes and consider snubbers or soft‑start valves.
Chemical and environmental cross‑talk
Locating nylon near galvanized hardware, battery rooms, acid wash stations, or coolant mists invites stress corrosion cracking. I segregate materials, add drip shields, and specify compatible cleaners.
How can I set inspection intervals to catch wear before downtime in my plant?
Risk‑based interval setting
I set intervals by environment, pressure, temperature, and criticality:
- Low‑risk (indoor, dry, <7 bar, ambient 20–30°C): Inspect visually every 6 months; replace at 3–5 years or per OEM.
- Moderate (humidity swings, 7–10 bar, UV through skylights, 30–40°C): Quarterly inspection; annual replacement of highly flexed runs.
- High‑risk (chemicals present, hot zones 40–60°C, outdoor UV, dynamic pressure spikes): Monthly visual plus semiannual replacement of exposed lines; consider switching to Nylon 12 black or PTFE.
What I check during inspection
- Surface condition: Chalky, yellowed, or whitened bend marks indicate UV or stress; replace.
- Fitting zones: Look for hairline cracks at ferrule or collet; re‑cut and reinstall with proper torque.
- Geometry: Ovalization, flattening, or kinks signal creep or routing issues; re‑route with proper supports.
- Abrasion/thinning: Any rub marks or exposed braid (if reinforced) are red flags.
- Leak rate: Use ultrasonic leak detection; a rising baseline is often the earliest indicator.
- Environment changes: New cleaners, relocated lights, added heaters—adjust intervals accordingly.
Preventive measures tied to intervals
- Material upgrades: Migrate critical runs to Nylon 12 UV‑stabilized or fluoropolymer (PTFE/PFA) where heat/chemicals are unavoidable.
- Air preparation: Good FRL practice (filtration 5–40 µm, coalescing for oil mists, dryer for dew point control) reduces internal chemical stressors and moisture effects.
- Routing standards: Maintain bend radius, add strain relief, use abrasion sleeves, segregate from corrosive sources.
- Documentation: Tag tubing with install date/grade; log inspections and leak rates to spot trends.
Quick reference: temperature and UV risk vs. inspection cadence
| Condition | Example Environment | Suggested Cadence |
|---|---|---|
| Ambient indoor, clean | Assembly cells, cabinets | 6‑month visual; 3–5‑year replace |
| Humid/variable temp | Washdown areas | Quarterly visual; 2–3‑year replace |
| UV exposure | Near skylights/outdoors | Quarterly visual; 1–2‑year replace; use black Nylon 12 |
| Hot zones (40–60°C) | Oven adjacent | Monthly visual; semiannual replace; de‑rate pressure |
Visual aids for maintenance teams
Integrating material selection with system performance
I always balance cost, reliability, and flow. Nylon’s smooth bore supports low pressure drop, but creep/UV/chemical sensitivity must be mitigated. When valves with high Cv produce frequent transients, I upsize tubing one step to reduce stress and consider soft‑start valves to control inrush. For lines exposed to chemicals or heat, PTFE tubing paired with stainless push‑to‑connects eliminates most corrosion and hydrolysis risks, albeit at higher cost and lower flexibility. The savings show up in avoided downtime.
Conclusion
Nylon tubing doesn’t “randomly” fail—it responds predictably to stress, moisture, UV, heat, and chemicals, with installation choices acting as multipliers. The most common patterns I see are stress cracking at fittings, creep‑induced flattening and kinks, hydrolysis in warm humid service, UV embrittlement, and chemical‑driven swelling or SCC. Specifying the right grade (favor Nylon 12 for variable environments), respecting bend radius and torque, de‑rating for temperature, and insulating against abrasion and corrosives eliminates most burst and leak events. Finally, risk‑based inspection intervals—grounded in environment and duty cycle—catch wear early and keep lines reliable without over‑maintaining.
