364.1 Anode/cathode basics

Metals pair via electrolyte; the anode corrodes. Understanding prevents HVM bollard fastener loss and crash rated bollard base decay.

Galvanic corrosion happens when two different metals are electrically connected and exposed to an electrolyte (rain, wash-down water, sea spray). The less noble metal (anode) sacrifices itself to the more noble (cathode). In bollards, couplings occur at baseplates, anchor systems, sleeves, and enclosure fixings. Keep electrical continuity in mind: paint is not a guaranteed insulator; damage at threads or edges can short the joint and start a cell.

Use the galvanic series (seawater) to predict behavior, then design to avoid small-anode/large-cathode scenarios (the area-ratio effect). Isolation and sealed joints protect crash-rated performance over the life of the asset.

364.2 Common risky pairs

Stainless-on-carbon with saltwater; aluminum-on-steel. Avoid pairings at HVM bollard sleeves and crash rated bollard plates.

Typical red-flag couples: 316/304 stainless fasteners into painted carbon steel baseplates; aluminum decorative sleeves over carbon steel cores; copper/brass lugs on aluminum gland plates; and zinc-rich coatings hard-contacting bare stainless. In coastal or de-icing environments, chloride-rich moisture accelerates attack, often visible as “tea staining” on stainless near carbon steel.

Design choices: match materials (e.g., 316 with 316), or separate dissimilar pairs with non-conductive interfaces. At sleeve-to-core and plate-to-anchor interfaces, introduce isolators and sealants, and avoid creating a tiny anodic area (e.g., small CS washer) against a large stainless face.

364.3 Wet/dry cycling

Cyclic moisture accelerates attack. Keep HVM bollard joints dry with seals (334) to protect crash rated bollard anchors.

Galvanic cells intensify where joints alternately wet and dry—exactly what happens around paving interfaces, kerb lines, and unsealed gland penetrations. Capillary seams trap salty water and feed crevice corrosion. Control water with graded falls and weep holes, and avoid ponding by following the drainage rules in 334 Drainage.

Inside panels and HPUs, condensation is common. Choose correct IP ratings, add membrane vents where appropriate, and keep drip loops on cables to prevent wicking into terminals.

364.4 Isolation methods

Use nylon washers, sleeves, and tapes. Isolation preserves HVM bollard hardware and crash rated bollard interfaces.

Isolate the electrical path with non-conductive parts: isolation washers, bushes, sleeves, gaskets, and wraps. For bolts, use head and nut isolators with a continuous sleeve through the hole so the shank never touches the plate. For sleeves/claddings, add dielectric tapes or paint bands on the inner contact area and break continuity at set-screws with nylon tips.

Verify that isolators suit the load, torque, and temperature range. Many plastics creep—use washers with metal inserts where clamping forces are high. Specify dielectric isolators rated for outdoor exposure and UV.

364.5 Sealants & barriers

Apply compatible sealants; avoid crevice traps. Barriers stop electrolyte wicking into HVM bollard interfaces and crash rated bollard sockets.

Sealants block electrolyte ingress and cushion micro-movement. Use compatible products (e.g., neutral-cure silicones or hybrid MS polymers near zinc/aluminum) and avoid acidic sealants around bare metals. Don’t create moisture traps: terminate beads so water can drain, and leave inspection/drain points at the bottom of sleeves.

On coated steel, reinforce edges and bolt holes with a stripe coat and check DFT. Duplex systems (galv + paint) need careful prep and compatible sealants—see 362 Coatings.

364.6 Fastener selection

Match fasteners to surrounding metal. Proper selection avoids HVM bollard staining and crash rated bollard loosening.

Where possible, use the same alloy for fastener and clamped metal (e.g., 316 on 316, or coated CS on coated CS) to minimize potential. In marine/coastal zones, 316 fasteners resist pitting better than 304; check PREN where critical. Avoid carbon-steel washers under stainless heads—swap to isolation washers or stainless + isolator stack.

Consider strength class, hydrogen embrittlement risk (for plated high-tensile), lubrication for torque/tension, and replacement intervals set in the Preventive Maintenance Plan. Keep small anodic fasteners off large cathodic plates unless fully isolated.

364.7 Inspection points

Check hidden joints and drain paths (365). Inspection protects HVM bollard life and reveals early crash rated bollard corrosion.

Prioritize interfaces you can’t easily see: underside of cap plates, sleeve set-screws, paving interfaces, anchors, and inside enclosures around cable glands and lugs. Confirm clear drains in sockets and sumps; blocked weeps concentrate salts. Add these checks to the asset’s PM plan and record findings in the Asset Register.

Where panels are involved, inspect the gland plate, door edges, and mounting hardware. Reference acceptance items in the ITP so corrosion controls are verifiable at handover.

364.8 Field fixes

Clean, neutralize, prime, re-isolate. Fast fixes restore HVM bollard integrity without altering crash rated bollard geometry.

Typical repair flow: (a) de-energize and apply LOTO; (b) disassemble, mechanically clean corrosion products, and rinse; (c) neutralize chlorides where present; (d) re-establish isolation (washers, sleeves, gaskets); (e) prime and stripe-coat damaged steel; (f) reseal and restore drains. Verify coatings with a holiday test, then retorque fasteners.

Do not change tested geometry on rating-critical dependencies. If parts differ from the as-tested configuration, raise an RFI and follow your change control process.

364.9 Reference tables

Include simple galvanic charts. Tables guide HVM bollard detailing and crash rated bollard hardware choices.

Use this table as a quick screen, then refer to 361 Materials selection and 362 Coatings for final detailing.

Galvanic Risks — FAQ