As chromium reacts with oxygen, it builds a protective oxide layer. This film grows back if someone scratches it during installation or if it wears away from vibration. Hydraulic adapters are manufactured from different stainless grades, with 304 being the most common. The 316 grade contains molybdenum along with chromium and nickel. That molybdenum makes a real difference when fittings get exposed to chlorides. The surface of carbon steel rusts without zinc plating. These coatings chip and peel when you tighten them with wrenches. Once the coating breaks, rust starts. The protection goes through stainless steel without a coating. It holds its strength well below freezing. Carbon steel also keeps working at high temperatures. Unlike softer materials, metal resists deformation better than threads.
Corrosion resistance properties
Salt water eats through regular steel fittings fast. Different industries use various fluids that create their own corrosion challenges:
- Phosphate ester fluids in aircraft hydraulics attack many common metals
- Water glycol mixtures for fire resistance need specific material compatibility
- Petroleum hydraulic oils carry additives that react with certain alloys
- Cleaning solvents during maintenance can strip away protective coatings
- Process chemicals in manufacturing include both acids and alkalis
Pressure handling capacity
Hydraulic systems run at pressures that would burst weak fittings. Stainless steel keeps its strength under constant pressure loads. This matters especially during pressure spikes when shock waves move through the lines. A cracked fitting shoots out dangerous fluid jets and ruins equipment. Threads need to stay in good shape for connections to seal properly. Stainless steel resists galling, which happens when metal threads seize together. Many maintenance workers assemble and disassemble these fittings without damaging them. It is strong and flexible, so it absorbs impacts without cracking. Carbon steel fittings often have thicker walls than stainless steel fittings. The alloy handles mechanical stress better.
Industry application areas
- Food and beverage plants choose stainless steel to meet health codes. The fittings survive daily washdowns with hot water and harsh cleaners. Bacteria can’t find places to grow on the smooth surface. Everything comes clean during the sanitizing process. Pharmaceutical manufacturing has even tighter rules about contamination. Every component that touches product streams has to be made from approved materials.
- Stainless steel is the preferred material for ships and offshore rigs. The pipes of chemical plants use stainless steel fittings. A leak from a corroded connection in these facilities means evacuations and environmental problems. Semiconductor factories need ultra-clean conditions. Particles from corroding fittings would destroy production yields and waste expensive materials.
Temperature range performance
Cold makes some metals brittle. Stainless steel fittings work in cryogenic equipment where temperatures go far below zero without any brittleness problems. The same fittings also handle high temperatures in thermal oil systems and steam lines. Carbon steel develops an oxide scale at high temperatures. That scaling creates rough surfaces that mess up seals. Stainless steel keeps its smooth finish through heating and cooling cycles.
All metals expand when heated. Stainless alloys expand at rates that engineers can predict and account for. The threads stay engaged properly even as temperatures change. Steam systems hit fittings with both heat and moisture together, which speeds up corrosion dramatically in vulnerable materials. Refrigeration equipment cycles between hot and cold repeatedly. Those swings would loosen connections or cause damage in materials that change their properties across temperature ranges.
