Boiler water testing

In the past, companies supplying boiler maintenance chemicals like “BOILER COMPOUND” had representatives visit your plant, take water samples and analyze them in order to prescribe the proper blow-down procedures and how much boiler compound to add and when. However, the business model which provided that type of high-level service is no longer workable in most areas. Therefore, these test procedures must now be carried out by either sending samples to a lab for analysis or by onsite water testing by plant personnel. The purpose of this series of articles is to teach how to use modern testing devices to analyze the water samples and determine the proper balance of boiler chemistry and blow-down procedure. The purpose of this series of articles to teach the methods used to obtain, measure, and evaluate boiler water samples.
 
Water is often referred to as the universal solvent and therein lies the problem. Water can dissolve almost anything that comes in contact with it. Salts, sugars, acids, bases, many gasses, water just doesn’t care; just dissolves them and keeps on rolling, rolling along. Take a moment and think about it. What barbarian amongst us would confuse a glass of sparkling San Pellegrino or Perrier with a glass of common tap water, after all, it’s just H2O, isn’t it? Well, the difference in taste is what is dissolved in the water (a solute is the term for something that is dissolved in a solvent, in this example water is the solvent) and water being added to the boiler must be treated in order to remove or control the concentration of most of these solutes.

There are three sources of water referred to in this and future articles on this subject:
A. TAP, MAKEUP, OR CITY WATER– this is the water raw water used to make up for water that has been lost in process of using the steam generated by the boiler.

B. FEED WATER– this is the combination of fresh makeup and condensate returning to the return (condensate) tank.

C. BOILER WATER– this is the water contained inside the boiler itself which will be converted to steam.

We will only be concerned with feed and boiler water from this point forward. There are maximum allowable quantities of dissolved impurities for both feed and boiler water, and these will vary slightly with each boiler manufacturer. Although there is a long list of impurities to be found in water entering a boiler, in the dry cleaning and laundry industries by far the major ones affecting the operation of boilers are:

1. Dissolved solids are known as TDS or total dissolved solids. This family of impurities provides the chemicals which form scale. As scale accumulates on the heat transfer surfaces inside the boiler it acts as an insulation blanket reducing the efficiency of the boiler which greatly increases fuel costs.  Additionally, over time scale clogs the tubes and/or internal flow-path of water inside the boiler resulting in local hot spots on the heat transfer surfaces leading to early boiler failure.
2.  Oxygen is dissolved in the new, city water entering the return tank. This oxygen combines with carbon dioxide to form carbonic acid, a destroyer of the metal in the boiler and piping throughout the steam/return systems. The concentration of acids in boiler water is indicated by the Ph (Ph-is a scale used to specify how acidic or basic [alkaline] a water-based solution is).

Fortunately, test equipment in the form of electronic meters is readily available, inexpensive, and easy to use provides the data to control the concentration of these bad actors. Measuring TDS and Ph levels can indicate the condition of the treated water entering as well as inside the boiler, allowing us to adjust the blow-down frequency and the volume and timing of boiler compound addition to the return tank to prevent boiler damage.

OBTAINING A WATER SAMPLE FOR TESTING

Where’s the best place to get a water sample? I’ve found the easiest and safest place to obtain a water sample is from the blow-off drain at the bottom of the sight glass on the water column.  After turning the boiler on wait until there is just a few pounds of steam pressure and while wearing a leather or rubber glove as well as eye protection drain about a cup of water for testing (If there is not a ball valve at the bottom of the sight glass fixture, install one).

CAUTION-STEAM WILL SCALD YOU ON CONTACT, OBSERVE EXTREME CAUTION WHEN OBTAINING SAMPLE!

That’s it for this issue, next month I’ll be continuing on how to use the two boiler water measuring devices, the TDS and PH meters.