316L Stainless Steel Compression Fittings — Pressure & Temperature Ratings
Understanding the pressure and temperature limits of 316L stainless steel double ferrule compression fittings is critical for safe system design. This reference guide provides the ratings and derating factors you need for proper specification.
Working Pressure Ratings by Size
Ratings are for 316L stainless steel fittings with 316L stainless steel tubing at ambient temperature (70°F). Ratings assume tubing wall thickness of 0.035" for 1/4" and 3/8", and 0.049" for 1/2" and 3/4".
| Tube OD | Working Pressure (PSI) | Burst Pressure (PSI) | Proof Pressure (PSI) |
|---|---|---|---|
| 1/4" | 6,000 | 24,000 | 9,000 |
| 3/8" | 6,000 | 24,000 | 9,000 |
| 1/2" | 6,000 | 24,000 | 9,000 |
| 3/4" | 5,000 | 20,000 | 7,500 |
Working pressure is the maximum recommended operating pressure. Proof pressure is 1.5x working pressure — the fitting should not leak or deform at this pressure. Burst pressure is 4x working pressure — the pressure at which fitting failure is expected.
Temperature Derating
Pressure ratings decrease at elevated temperatures. Apply the following derating factors to the ambient working pressure:
| Temperature (°F) | Derating Factor | Effective WP (1/2") |
|---|---|---|
| -65 to 100 | 1.00 | 6,000 PSI |
| 200 | 0.97 | 5,820 PSI |
| 400 | 0.88 | 5,280 PSI |
| 600 | 0.79 | 4,740 PSI |
| 800 | 0.65 | 3,900 PSI |
| 1000 | 0.48 | 2,880 PSI |
| 1200 | 0.30 | 1,800 PSI |
Vacuum Service
Double ferrule compression fittings are suitable for vacuum service down to 10^-6 Torr when properly installed. The metal-to-metal seal provides inherent vacuum integrity without O-rings or elastomers that could outgas. For ultra-high vacuum (below 10^-9 Torr), specify fittings with electropolished internal surfaces and metal-to-metal seals only.
Gas Leak Integrity
Properly installed 316L double ferrule fittings provide helium leak rates of 1 x 10^-8 std cc/sec or better. This makes them suitable for:
- Toxic and hazardous gas service
- High-purity process gas distribution
- Sampling and analyzer systems
- Vacuum systems
Safety Factors
Industry standard safety factors for instrumentation fittings:
- Working pressure = 1/4 of burst pressure (4:1 safety factor)
- Proof pressure = 1.5x working pressure (no permanent deformation)
- Cyclic service = derate working pressure by 20% for high-cycle applications