In our high pressure boilers, which are over 50 years old, we have dirty control air. We have new dryers for low dewpoints but the damage to the piping has already been done and our DVCs fail from fine debris in the air. We have tried placing air filters next to each device but this is driving up our outage workload. Replacing all the piping is very costly. Any other suggestions?

Dirty control air can pose a huge problem to your devices...shorting its life. Seems like you have two choices, the cheap route is to place fine mesh filters on the inlet of the device but each time the DP is high it would require an outage to clean and replace before its forced offline. Second choice is to replace all of the piping with some long lasing stainless steel tubing. This is very costly but in the long run, youll save on reducing forced outages, rework, and manpower required to maintain DVCs and pre-filters. I would go with the option to replace all tubing with good quality stainless.

I believe all facilities have some issues with the quality of their control air supply. Our station experiences rust and scale from our carbon steel piping. Carbon steel piping is less expensive (both in material and installation costs) than stainless steel. However, when carbon steel comes in contact with moisture from a failed dryer or a dryer in bypass for maintenance, it begins to rust. Since re-piping our entire plant is not cost effective, we have chosen to add large air filters in various locations. These filters are installed where they will encompass numerous pieces of equipment to reduce the installation time and cost (such as one filter set per burner elevation). The filter sets we installed also include a dual set of filters with a manual bypass. This allows the operators to take the dirty set offline for replacement without waiting for a system shutdown. We then re-pipe all the air lines downstream of the filter with stainless steel to prevent further containment from the piping after the filters.
If money was no object, we would replace all our control air piping with stainless steel or aluminum.

Make sure the compressor after-coolers are not leaking (if applicable).

Verify that the air driers are functioning proper. Often, on old plants, driers become neglected, dessicants need replaced, heaters for tower regeneration are not working or cycling properly.

Replacement of deteriorated air lines is sometimes not practicle, but often necessary. This will not help much IF the air supplies are not performing properly.

Have the operators start blowing pots on regulators and controllers ie fisher, leslie etc etc. Often, you can remove a lot of build up. You can isolate controllers or go on manual bypasses if load and plant conditions allow, cut out controllers, break fittings and blow out as much as possible to "purge" the lines. This is labor intensive at first but over time, it will improve. The key is doing this often.

Try to come up with a reliable set of control air dew point indicators at different points. These can be purchased but they can be "homemade" or at least "in house" made for a reasonable cost.

Do what you have to to keep the air dew point -20 F or less.

The rust and scale will eventually diminish.