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

Stainless-steel and polymer-based fittings are both commonly used in HPLC, each with its own set of advantages and disadvantages. The choice between them depends on the specific application and method requirements of your lab. Let’s take a look at some of the key differences between these fitting materials.

How to Tighten the Fittings

A key difference between stainless-steel and PEEK (or other polymer) fittings is the method of tightening. Stainless-steel fittings are "swaged" onto the tubing and secured with a wrench. Once the nut is tightly fastened, the ferrule becomes permanently attached to the tubing, creating a strong seal. However, this also means that the ferrule and that section of tubing cannot be reused. In contrast, many people prefer polymer fittings because they are easier to work with. PEEK fittings and tubing can be assembled by simply finger-tightening, which reduces the risk of overtightening and eliminates the need for a tool, making the process much simpler.

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.