When warm collides with cool, moisture condenses on and inside valves and piping. Chemicals and electrochemical reactions lead to corrosion. Either way, you’ve got corrosion that can pit seating surfaces, stick guides, slow closing and create a nuisance or worse, danger.
Where Problems Commonly Occur
- Outdoor/roof-mounted valves
- Long discharge runs
- Cold starts/idle equipment
- Stored spares
Early Warning Signs
- Beading water on bonnets or rust streaks around fasteners
- Green/white deposits at joints
- Moisture under caps or around test levers; sluggish lever action
- Weeping at the seat after a cycle or temperature change
Prevention
1. Control temperature and humidity
- Insulate exposed bodies and discharge piping
- Heat-trace problem stretches
- Keep enclosures ventilated to avoid trapped humid air; reduce indoor dew point
- For idle/standby service or stored spares, add desiccant breathers
2. Give condensate a way out
- Pitch discharge piping away from the valve
- Install a drip pan elbow with a free-flowing drain to remove condensate from the discharge
- Add drip legs/low-point drains
- Verify permissible back pressure and keep rain caps clear of restrictions
3. Choose materials that resist attack
- Where service and codes allow, upgrade wetted parts/fasteners to corrosion-resistant alloys.
- Use protective coatings on externals
- Avoid dissimilar metal couples
4. Tighten up maintenance timing
- Do a pre-season inspection
- Replace compromised gaskets/packing
- Confirm outlet supports are intact
- Function test as required to verify proper lift and reseat
5. Adjust operations to reduce moisture load
- After steam-out or washdowns, open drains until lines are dry
- Avoid thermal shock
- Bring systems up gradually to minimize internal condensation