Most skid-mounted extraction equipment adopts a composite structural design: a carbon steel base frame with stainless steel extraction vessels fixed on top. Carbon steel features low cost, high strength and easy weldability, while stainless steel provides excellent corrosion resistance and clean production conditions. This combination seems perfectly complementary.

However, equipment deployed in coastal areas will develop obvious corrosion problems within six months of operation due to this structural design.

We once served a client in Zhangzhou, Fujian Province. During a six-month follow-up inspection, we found severe pitting corrosion on the stainless steel flange surfaces connected to the carbon steel frame. The client was confused: "Stainless steel is supposed to be corrosion-resistant – why is it rusting?"

The root cause is galvanic corrosion.

Carbon steel and stainless steel have different electrochemical potentials. Coastal areas feature high humidity and high salt content in the air, and condensed saltwater forms a conductive electrolyte film on metal surfaces, creating a complete galvanic cell loop. Carbon steel acts as the anode and undergoes accelerated sacrificial corrosion, while stainless steel acts as the cathode and is temporarily protected.

As carbon steel corrodes, rust and corrosion products adhere to the stainless steel surface and destroy its original passive film. Once the protective film fails, the stainless steel surface begins to develop pitting corrosion, eventually leading to damage of the entire equipment structure.

The solution to this problem is extremely simple: install insulating gaskets at all contact positions between carbon steel and stainless steel structures.

We recommend 2–3 mm thick PTFE insulating gaskets. These gaskets cut off the conductive loop between dissimilar metals, prevent the formation of galvanic cells, and completely eliminate galvanic corrosion risks.

It is critical to install matching insulating sleeves for all connecting bolts during installation. Metal bolts will form a conductive bridge between structures and render the insulating gaskets completely ineffective without these sleeves.

This simple few-millimetre-thick insulating accessory can extend the service life of coastal skid-mounted equipment from 3 years to more than 10 years. It is a low-cost, high-return optimization solution.