Chasing Faults in a Corrosive Plant

For maintenance techs and plant engineers at composting, organics and anaerobic digestion (AD) sites who keep getting intermittent control faults that nobody can pin down. This guide helps you tell an environment-driven instrument fault apart from a real process problem, before you spend another shift on it.

How to use this Work it symptom-first. Find the row that matches what you're actually seeing, run the checks in order, and write down what you find. The single most useful thing you can do on an intermittent fault is log it: time, weather, what the process was doing, and the exact reading. Half the corrosive-plant faults I get called on resolve themselves the moment somebody has three logged occurrences to look at instead of one story. Keep this near the panel, not in a binder in the office. A note on why this plant is different. In a clean packaging line, a signal problem is usually a signal problem. In a plant that makes hydrogen sulfide (H2S), ammonia (NH3) and warm wet air all day, the environment is a slow, active participant. H2S plus moisture attacks copper and silver: it turns bright terminations dull, then black, then powdery. Ammonia goes after copper too, and loves to creep into any enclosure that breathes. Warm humid process air hits a cooler panel overnight and condenses inside it. Dust from screening and grinding coats boards and bridges terminals once it gets damp. None of that shows up as a clean, repeatable fault. It shows up as drift, as intermittents that track the weather, and as things that work fine until you touch them.

Before you open a box or break a live loop Read this first — several rows below have you opening junction boxes and metering an energized loop in an atmosphere that can be both toxic and explosive. Confirm the hazardous-area (explosive-atmosphere) classification for the exact spot you're standing in, and whether a hot-work or energized-work permit is required, before you open an enclosure or break a live loop. In a plant making methane and H2S, opening a box or making and breaking a live connection can be an ignition source. That's a permit question, not a call you make alone at the panel.