Can I mix 304 and 316L clamps on the same line?

Only on non-chloride dry service. In any aqueous environment with chloride above 50 ppm, the 304 clamp pits while the 316L stays intact.

Is 316Ti the same as 316L?

No — 316Ti has titanium stabilisation for high-temperature service (550-800 °C) but slightly lower corrosion resistance at ambient. Use 316L for ambient hygienic, 316Ti for high-temperature.

Why is PRE the right metric?

PRE (pitting resistance equivalent number) captures the combined effect of Cr + Mo + N on chloride pitting resistance, which is the dominant corrosion mode in process piping. Other metrics like crevice corrosion temperature (CCT) supplement but don't replace it.

Where do you stock duplex clamps?

Standard duplex 1.4462 sizes (DN 25 to DN 100) are stocked in Oisterwijk. Larger sizes and super duplex are made to order, 4-6 weeks lead time.

NIBRO by ARAMFIX — Stainless Steel Pipe Clamps

The same family, very different behaviour

AISI 304, 316, 316L and Duplex 1.4462 are all "stainless" in casual conversation. In application they are four very different materials with chloride resistance, mechanical strength and cost varying by factors of 2-4 between them.

Choosing the right grade is not a question of buying the best material — it is a question of matching corrosion resistance to the actual service environment, then accepting the price that comes with it.

This blog is the decision matrix we use internally when quoting custom clamp projects, and the same logic applies to off-the-shelf catalogue ordering.

The three killer questions

Before specifying a grade, answer three questions:

What is the chloride concentration at the clamping face?
What is the maximum surface temperature in service?
What is the cleaning chemistry, and how often?

The combination of those three determines whether 304 will last 20 years or 18 months. Everything else (price, availability, fastener compatibility) is a secondary optimisation.

AISI 304 (V2A, EN 1.4301)

The default European stainless for dry utility and ambient-water service.

Chromium: 18%. Nickel: 8%. Molybdenum: 0%.
PRE: 18. Insufficient for any chloride exposure above 50 ppm.
Service envelope: dry indoor, freshwater, low-temperature steam, food contact (no salt, no acid).
Lifetime expectation: 25+ years in clean indoor environment.
Cost: baseline (1.0×).

Specify 304 for: HVAC supports, freshwater distribution, dry compressed-air lines, bottle-fill packaging halls.

Do not specify 304 for: dairy with caustic CIP, brewery, any chloride-containing process, marine applications, swimming pool plant rooms.

AISI 316 / 316L (V4A, EN 1.4401/1.4404)

The default for chloride-exposed and acid-cleaning service.

Chromium: 17%. Nickel: 10-12%. Molybdenum: 2-3%.
PRE: 24-26. Adequate for moderate chloride exposure (up to 500 ppm at ambient).
Service envelope: hygienic food/dairy, brewery CIP, freshwater offshore (splash zone with care), most chemical service.
Lifetime expectation: 20+ years in dairy and brewery with daily caustic CIP.
Cost: 1.4× over 304.

316 vs 316L: 316L has lower carbon (0.03% vs 0.08%), avoiding carbide precipitation at weld zones. Always specify 316L for any installation with welding or 60+ °C service. Standard NIBRO clamp range is 316L.

Specify 316L for: dairy, brewery, food, light pharmaceutical, water treatment, ambient marine.

Do not specify 316L for: continuous seawater service, hot brine, swimming pool chemistry, sub-sea offshore.

Duplex 1.4462 (UNS S31803, EN 1.4462)

The high-chloride answer at moderate cost.

Chromium: 22%. Nickel: 5%. Molybdenum: 3%. Nitrogen: 0.15%.
PRE: 35. Suitable for continuous seawater up to 50 °C.
Service envelope: seawater desalination, brine handling, swimming pools, salt-spray manufacturing.
Lifetime expectation: 12-15 years in seawater splash zone where 316L pits in 18 months.
Mechanical: yield strength 450 MPa (vs 240 MPa for 316L) — thinner sections possible.
Cost: 1.6-1.8× over 316L.

Specify Duplex 1.4462 for: salt-spray industries, swimming pool plant, marine ambient, battery brine, gold-leaching circuits, paper-mill bleach plant.

Do not specify Duplex for: > 90 °C service in chloride (sigma phase precipitation), sub-zero applications below -40 °C without verification.

Super Duplex 1.4410 (UNS S32750)

For everything Duplex cannot handle.

Chromium: 25%. Nickel: 7%. Molybdenum: 4%.
PRE: 41-44. Suitable for hot seawater up to 90 °C.
Service envelope: offshore topside seawater, subsea umbilicals, sour service per NACE MR0175.
Mechanical: yield 550 MPa, allows even thinner sections.
Cost: 2.5-3× over 316L.

Specify Super Duplex for: offshore platform topside, subsea, hot brine evaporators, geothermal high-chloride condensate, sour gas processing.

Selection matrix

| Service | Recommended grade | PRE required | Cost ratio | |---|---|---|---| | HVAC, freshwater | 304 | ≥ 18 | 1.0× | | Dairy, brewery CIP | 316L | ≥ 24 | 1.4× | | Light pharma | 316L EP | ≥ 24 | 1.6× | | Swimming pool plant | Duplex 1.4462 | ≥ 35 | 2.2× | | Continuous seawater | Duplex 1.4462 | ≥ 35 | 2.2× | | Offshore topside | Super Duplex 1.4410 | ≥ 41 | 3.5× | | Sour service | Super Duplex 1.4410 | ≥ 41 | 3.5× |

The galvanic question

When clamp grade differs from pipe grade, a galvanic potential develops at the contact interface. The general rule: clamp grade should be the same or higher in PRE than the pipe grade. A 304 clamp on a 316L pipe in chloride service galvanically attacks the 304 clamp; the reverse is acceptable.

Conclusion

The choice between 304, 316L, Duplex and Super Duplex is engineered, not negotiated. Run the three killer questions through the matrix above, pick the grade that satisfies the lifetime budget, and let the price difference reflect the corrosion difference. Over-specifying once is cheaper than under-specifying once.

304 vs 316 vs Duplex — Stainless Selection Matrix