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Engineer’s Guide to Marine Boiler Water Treatment & Testing

Dimitris Tsapis
January 8, 2022
Marine water boiler treatment is a very important maintenance process for yachts. Learn why it’s done and how to perform it by reading this post.

Marine engineers are responsible for many small maintenance tasks onboard, all of which ensure the proper function and operation of the vessel. 

One of these tasks takes a closer look at the ship’s boiler water, by performing a number of important tests to determine its chemical structure.

Marine boiler water treatment is a procedure usually done by junior engineers. The job is mainly focused on testing water samples for their chemical contents, the results of which determine what sort of chemical “treatment” is needed. This article aims to act as a guide for the new and experienced engineer, in order to help with all the steps of the process.


Marine boiler water treatment

Before delving into the tests, it is important to define boiler water. In short, boiler feed water is distilled water that is chemically adjusted. It floats through a closed system as depicted in the illustration bellow.

marine boiler water treatment

The water itself is constantly converted to superheated steam which is used for various operational purposes of the vessel’s engine. 

As you can see in the next picture, the steam moves the turbine, then condenses back to its liquid for in a hotwell or cascade tank, and returns back to the boiler to repeat the process.

marine boiler water treatment

So what makes testing of boiler water so important? Well, boiler water abides by certain parameters in order to protect the boiler (and other engine compartments) from corrosion, as well as protect from a scaling deposit formation. To check these parameters and adjust the water, engineers test water samples regularly, using a testing kit which we discuss in the next chapter.

Boiler water test preparation

Before getting started it is important to keep in mind that testing equipment differs slightly depending on the manufacturer, and so do the chemicals that you may need to use for your marine boiler water treatment. Since most of the testing tools are unique to the vessel’s chemical supplier, an experienced engineer will need to review the available options and choose the most reliable.

In this article, we will be using UNITOR boiler water test kit as an example.

water testing kit

The testing kit includes materials to test the water for Phosphate, P/M- Alkalinity, Chloride and pH. More specifically, the kit includes the following:

  • Sample water beakers (50ml, 100ml, 200ml)
  • Comparator vials (2 x 10ml)
  • Comparator
  • PH reagent
  • PH indicator strip
  • Hydrazine reagent
  • Phosphate tabs
  • Chloride tabs
  • P&M Alkalinity tabs
  • Color indicator discs (Phospate/Hydrazine)
  • Filters and pill crusher

In the next few chapters, we will take you through the steps you need to follow when testing different boiler parameters, what these parameters mean, and why they are important. Finally, when it comes to marine water boiler treatment, we will also discuss the UNITOR chemicals you need to use to keep the parameters of the water in operational range.

Boiler Water PH Test

A PH test indicates how alkaline or acidic your boiler water is. Ideally, the water should be maintained between 9.5-11.5 PH inside the boiler (alkaline environment). 

Engineers perform this test to prevent acidic corrosion from the water (low PH) as well as scale formation (high PH). Aside from that, some of the chemicals you need to use for water treatments require an alkaline environment to adjust the water’s levels properly.

To perform this test, perform the following steps.

  • Rinse and fill the plastic 50ml beaker with sample water
  • After that is done, add 600mg of PH reagent (one scoop) to the water sample
  • Mix the reagent in the sample water to completely dissolve it.
  • Next, take a PH indicator strip, dip it into the sample, and leave it submerged for one minute
  • Finally, compare with the colors shown on the box to determine the PH level visually.
boiler water ph testing process

Based on the results of the test, you can choose to alter the water’s PH levels in two points using these UNITOR chemicals:

  • Condensate control for feed water in the hotwell to ensure at least a PH level from 8.5 to 9.5 PH
  • Alkalinity control for inside the boiler to provide 9.5-11.5 PH, which is required for corrosion control

Boiler Water Phosphate Test and Hydrazine Test

For the next test, you are now going to check the phosphate levels in the boiler. Phosphate is important to maintain since it reacts with any calcium impurities within the water, and forms a precipitate that will accumulate at the bottom of the boiler. This can later be blown down or discharged (by releasing the bottom blow down valve).

To test the phosphate levels, we use the comparator, a small black device that holds both of your 10ml testing vials. And here are the steps you need to follow: 

  • First off, rinse and fill the two 10ml sample vials with boiler water. 
  • One vial contains the control sample and the placed on the left side of the comparator (not adjusted). 
  • The other sample requires a phosphate indicator tablet, which you will need to dissolve in the water and wait for 10 minutes before proceeding. 
  • After the 10 minutes are over, take the indicator disc and compare the vials. Once you identify the color match, you will get an indication of the phosphate concentration in the water. 

When it comes to water treatment for phosphate concentration, we use the UNITOR chemical Hardness Control, which has the following characteristics:

  • Maintains free phosphate levels in the boiler
  • Does not allow calcium to create scale and makes it easy to remove by blowdown
  • You can add 23gr per ton of feed water for 20ppm Phosphate boost

Note that Phospate levels in the boiler water should be maintained at 20-50ppm.

After finding the Phosphate levels, you will now need to test the hydrazine levels of the boiler. These are typically maintained between 0,1ppm and 0,2ppm.

Hydrazine is very important as it reacts with dissolved oxygen inside the boiler tank to form hydrogen and water. Here are the steps you need to follow in order to test it:

  • Start by repeating the steps from above, filling two vials with 10ml sample water, which we will then use in our comparator.
  • This time, the right cell will include 1 gram of hydrazine reagent, which will need to be fully dissolved as we did previously.
  • Two minutes after the agent is fully dissolved, you can once again use the color indicator disc to determine the levels of hydrazine within the water.

To control and alter hydrazine levels we use a UNITOR chemical known as “Oxygen Scavenger/Control”. These chemicals remove the dissolved oxygen that causes corrosion like we previously mentioned. Once again, your choice will depend on the chemical partners of the vessel.

Boiler Water Chloride Test

For this test, you will need the 100ml beaker and Chloride testing tabs.

Testing for Chloride is very important as it indicates whether sea water is contaminating the boiler. This causes increased conductivity between the boiler metal and its water, which accelerates oxidation.
To start this test, fill the 100ml beaker with sample water. Next, dissolve chloride tabs one by one until the color of the water changes from yellow to brown. Depending on the number of pills we use, we can then determine the chloride concentration of the water (use the color indicator to determine the levels).To start this test, fill the 100ml beaker with sample water. Next, dissolve chloride tabs one by one until the color of the water changes from yellow to brown. Depending on the number of pills we use, we can then determine the chloride concentration of the water (use the color indicator to determine the levels).
To start this test, fill the 100ml beaker with sample water. Next, dissolve chloride tabs one by one until the color of the water changes from yellow to brown. Depending on the number of pills we use, we can then determine the chloride concentration of the water (use the color indicator to determine the levels).

water chloride test

To start this test, fill the 100ml beaker with sample water. Next, dissolve chloride tabs one by one until the color of the water changes from yellow to brown. Depending on the number of pills we use, we can then determine the chloride concentration of the water (use the color indicator to determine the levels).

When it comes to chloride concentration, there isn’t a “chemical treatment” to reduce its levels in the vessel’s boiler water. If the concentration is too high, you will simply need to blowdown and make sure that the replacing water has a lower chloride concentration. This is heavily depended on feed water, which comes from distilled water created in the fresh water generator.

P & M Alkalinity Test

For this test, you will need to use the 200ml flask as well as the P&M Alkalinity tabs (indicator pills). P & M Alkalinity calculates the total amount of inorganic carbons inside the sample, which in turn indicates the total alkalinity in the sample. Remember that boiler water should be in an alkaline environment but not in excess, in order to promote the formation of precipitates and protect from corrosion. 

We test P&M Alkalinity by rinding and filling the 200ml flask with sample water and adding tabs in a consecutive manner.

P Alkalinity test in boiler water - Start by placing P indicator pills in the sample water (one by one) until the color changes from blue to yellow. Depending on the number of tabs added to the water you will be able to identify the P Alkalinity.
(Formula: PAlk = P Alk Pills x 20 - 10 = ppmCaCo3)

M Alkalinity test in boiler water - This test starts with the same water sample you previously used to determine the P Alkalinity (yellow). Add M indicator pills consecutively until the color of the sample turns from yellow to purple. Then, based on the number of pills that were used, you will be able to calculate the M Alkalinity of the sample 

(Formula: MAlk = (P Alk Pills + M Alk Pills) x 20 - 10 = ppmCaCo3)

Once you know the P&M Alkalinity levels, you can easily control them by using the UNITOR chemical “Alkalinity Control”. By doing so, you will be able to create an alkaline boiler water environment, which in turn prevents corrosion and protects the water from oxidation.

Is there any other marine boiler water test I can perform?

Boiler water testing is primarily focused on the maintenance tasks mentioned above. That said, there are a few more procedures you can perform to further examine the condition of your boiler's water. Below, we discuss an additional boiler water test procedure that you can perform whenever the next round of maintenance occurs.

UNITOR cooling water test procedure

This test is performed to test the temperature of your boiler water and make sure it is within the prescribed limits. To perform this test, you will need to acquire a separate boiler water test kit from UNITOR known as SPECTRAPACK 309. While we won't delve into boiler water analysis procedure, we will offer a short indication of the levels you need to be looking at:

  • Nitrite - For Nitrite, the prescribed limits range between 700 and 2400 ppm as NO2. For more precise control limits, refer to the Product Data Sheet of the inhibitor. By keeping nitrite levels within the recommended range, you ensure that corrosion and scaling action will not become a problem. Too high concentrations will be too costly when it comes to your vessel's maintenance while low concentrations can accelerate corrosion.
  • pH - As previously indicated, water PH should be maintained between 9.5-11.5 PH inside the boiler (boiler alkalinity).
  • Chlorides - The indicated limit here is a max. 50 ppm. More specifically chloride levels of the cooling water should be on the low end, as sudden or gradual increases in temperature could indicate sea water contamination. For more specified limits check with the manufacturer.

Wrapping up

You should now have a better idea of at least a small part of the processes you need to follow them it comes marine water boiler treatment and testing. Note that there are more minor tests you can perform for further examination of your vessel’s boiler water. Therefore, if the above tests do not include specific information you might be looking for, make sure you continue your research.