blog explained the purpose of using membrane filters and how they can be helpful in identifying iron in your condensate system.
The equipment that is frequently used in this sampling includes the following:
- 0.45 micron filters
- Filter Support
- Filtering Flask
- Rubber Tubing
- 2-Way Valve
- Vacuum pump. Any type of hand vacuum pump (commonly found at automotive parts stores for bleeding brake lines) or electric vacuum pump (commonly found in laboratory supply catalogs).
There are other equipment arrangements that also provide satisfactory results - simpler arrangements with smaller filter discs also provide meaningful results. The small filters have an advantage in that more of them can be mounted on a page for comparisons and historical records.
The 0.45 micron filter will pick up virtually all of the suspended iron in the condensate sample and will appear as a colored circle against the white background of the outer rim of the filter.
When a number of filters are run from differing condensate streams, it will be noticed that there are large variations in color from one disc to another. A darker color indicates the presence of magnetite, which is the more desirable corrosion product. A more orange tint indicates hematite, organic matter, or possible copper. Systems with minimal corrosion show little or no color or deposition on the filter. This is the most desirable. Since much, if not most, of the iron in steam condensate lines is suspended iron, a good indication as to the amount of corrosion taking place becomes evident immediately.
The procedure for running these samples is as follows:
- Assemble the apparatus with the filter in place. If a standard 47mm filter size is used, filter a 1 liter sample. For the smaller filters, a 250 ml sample will do.
- Allow the sample stream to run for 10 to 15 minutes if possible prior to collecting the sample.
- Using a clean container, collect a 1 liter sample.
- Filter through the Millipore apparatus, using a vacuum pump to pull the sample through the filter.
- After allowing the filter to dry for several minutes, mount it on a sheet in a page protector. Black paper and a very small amount of rubber cement works well. You can write on the edge of the filter with a ballpoint pen to label where the sample was taken.
As you gain experience in using the membrane filter test, more ways to use them becomes evident. Check out next week's blog for examples.