Corrosion, rust and coastal sites

How playground metal actually fails

Corrosion is an electrochemical process that needs a metal, an electrolyte (water, made much more aggressive by dissolved salt) and oxygen. Everything that accelerates corrosion on a playground works by supplying one of those three more generously.

Four mechanisms account for nearly all of it.

General atmospheric corrosion is the slow, even rusting of exposed steel where a coating has failed. It is predictable, visible and manageable.

Galvanic corrosion happens where two different metals are in electrical contact with moisture present. The less noble metal corrodes faster than it would alone. On play equipment this shows up at a stainless fastener through an aluminum bracket, a plain steel bolt in a galvanized frame, or a stainless clamp on a galvanized post. The damage concentrates at the joint, which is also the place carrying load.

Crevice corrosion occurs in tight gaps where water sits and oxygen is depleted: inside hollow posts and rails, between lapped plates, under washers and clamps, in the gap between a bearing housing and a shaft. It is the most dangerous type on a playground because it is invisible from the outside and it attacks the inside of structural sections.

Pitting produces small deep holes rather than general loss. A pitted component can look almost sound and have lost much of its local strength, which is why a visual pass over hardware is not enough on a site where pitting is present.

The four environments that accelerate it

Coastal sites are the most demanding. Airborne chloride reaches well inland, and equipment within roughly a mile of surf sees it continuously. The practical program is specification plus rinsing: a fresh water rinse of hardware and structure on a regular cycle removes deposited salt before it does its work, and it is the highest value maintenance task on a beachfront site. Use low pressure and follow the method notes in cleaning and sanitizing.

Pool and splash environments are underestimated. Chlorinated and brominated atmospheres are aggressive toward some stainless grades, particularly in warm, poorly ventilated indoor settings, and coated steel suffers too. Anything specified for a pool deck or a splash pad should be confirmed by the supplier as suitable for that chemical environment in writing. Pools and play areas covers the adjacency issues, including the fencing and separation ones.

De-icing salt reaches play equipment mostly by runoff and on boots. Check where meltwater from a salted lot or path goes, because a footing at the low point of that flow path is being washed in chloride every thaw. Fold a spring rinse into seasonal maintenance and, for home equipment, into winterizing.

Inspection: where to look and what to look for

Corrosion inspection is a hands on job at specific points, not a general look over the structure.

1. Post bases at and below the surfacing line. Scrape surfacing back and look at the transition zone. Hollow posts corrode from the inside out here.
2. Every swing hanger, hook, chain and connector. Look for rust bloom, pitting, wear flats and elongated holes. Move each one and listen.
3. Bolted joints. Rust weeping from under a washer means water is inside the joint. Streaking down a post from a bolt head is a reliable indicator.
4. Dissimilar metal junctions. Any place a fastener, bracket or clamp is a different metal from the part it joins.
5. Welds and weld heat affected zones, which frequently corrode before the parent metal.
6. Hollow section drainage holes. Are they present, and are they clear?
7. Bearings, bushings and pivots on spinners, seesaws and gates.
8. Ground level cut edges where a coating was drilled or cut on site.

Sound hollow members with a light tap and compare notes along the length. A dull note low down on an otherwise ringing post suggests internal corrosion product or water. Where a load bearing hollow section is suspect and cannot be assessed, take the component out of service pending proper examination, using the disposition logic in inspection schedule.

Treatment and recoating

For structure with a sound section and a failed coating, the sequence is the same every time:

1. Remove the corrosion back to sound metal by hand or power wire brush, or by abrasive methods where scale is heavy. Vacuum or sheet the debris so it does not land in the surfacing.
2. Check the section. If metal is thin, pitted deeply or perforated, stop. This is a replacement, not a repaint.
3. Prime with a rust inhibitive primer suitable for the substrate. Zinc rich repair products are made specifically for damaged galvanized coatings and restore a comparable level of protection to the repaired area³.
4. Topcoat with a compatible system, two coats, respecting the recoat window on the technical data sheet.
5. Seal the detail. Where water was getting into a joint, address the path as well as the rust. A sealed lap or a new drainage hole outlasts any paint.

Full method, preparation detail, cure times and costs are in painting, staining and refinishing. Keep in mind that equipment old enough to carry lead based coatings needs testing before anyone takes an abrasive to it.

Specification choices that avoid the problem

Corrosion is far cheaper to design out than to maintain out. At specification stage, on any site with a corrosive environment, ask for these in the tender documents.

Two points make a disproportionate difference. Isolate dissimilar metals with a non conductive washer, sleeve or coating, which costs pennies per joint and removes the galvanic cell. And ask for the environment in the specification, not just the material: a tender that says "site is within 1,000 feet of open ocean, specify accordingly" gets a better answer than one that names a grade. The mechanism for getting this into a contract is in procurement and RFP, and the material trade offs are in steel, wood and plastic as playground materials.

Drainage holes: the cheapest prevention there is

Every hollow section on a playground should have a clear drainage hole at its low point. Water gets into hollow posts, rails and tubes through fastener holes, through the open tops of rails, through condensation and through capillary action, and once inside it does not leave.

• Check that holes exist. On older equipment they frequently do not.
• Check that they are clear. They block with sand, wood fiber, mud, leaves and insect nests. Clearing them takes a piece of wire and a few seconds.
• Add them where they are missing, but only with the manufacturer's agreement, because drilling a structural member without approval can void a warranty and can create a stress concentration in the wrong place.
• Dress the edge and coat it. A drilled hole exposes bare steel, which is where corrosion will start if the cut edge is left untreated.

Add drainage hole checks to the detailed inspection form. This one item prevents a failure mode that otherwise gives no warning at all, and it is the least expensive thing on any maintenance list.

What to do next

Walk your site and do two things: check every hollow post for a clear drainage hole at the bottom, and put a hand on every swing hanger, hook and chain. Those two checks cover the invisible structural failure and the most consequential hardware failure. Then set the inspection frequency to match your environment, monthly detailed checks on a coastal or pool adjacent site, and confirm at your next annual audit that corroded hardware has been replaced rather than cleaned up.