How do Stainless-Steel Fittings Differ from Polymer-Based Fittings?

Both stainless-steel and polymer-based fittings are quite common in HPLC, and there are pros and cons for each. Deciding which to use for your lab depends on the application and requirements of your method. Let’s review some of the main differences between the fitting materials.

How to Tighten the Fittings

One of the key differences between stainless-steel and PEEK (or other polymeric) fittings is how they are tightened. Stainless-steel fittings are “swaged” onto the tubing and tightened with a wrench. Once the nut is firmly tightened, the ferrule is permanently attached to the tubing. This creates a very tight seal, but means that the ferrule (and that portion of tubing) cannot be reused. This is why many people opt for polymeric fittings. PEEK fittings and PEEK tubing are very easy to work with in comparison to stainless-steel alternatives. Polymeric fittings can be assembled in the system by simply finger-tightening. This reduces the chance for overtightening, and is much simpler than utilizing a tool to tighten.

High Pressure Applications

As mentioned above, stainless-steel fittings are tightened with a wrench, causing a very tight seal. Because of this, the stainless steel can withstand higher pressures than PEEK or other polymeric fittings. Especially in Ultra High Pressure Liquid Chromatography (UHPLC) applications, the polymeric fittings can’t withstand the pressures that the system is producing, therefore stainless-steel fittings are necessary. On the other hand, it is hard to find low pressure fittings (1/4-28 threading, vs. 10-32) in stainless steel or other metals. Almost all low pressure fittings are polymeric.

Biocompatibility/Inertness

Another reason people will opt for polymeric (often times PEEK) fittings is due to the biocompatibility that it offers. PEEK is chemically inert and is capable of safely existing in a biological setting. It also can withstand most sterilization protocols used in the laboratory setting. It also shows high resistance to most chemicals.

Conclusion

Depending on your applications, your pressure requirements, and a number of other considerations, you may have the option to choose between stainless-steel or polymeric tubing and fittings. If you’re not sure which is best for your lab, reach out to one of our chromatography product specialists for more information to help you make the best decision.