© February 20, 2010
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Live Steam Boiler Treatment
Written by Kevin O'Neill
For most of us, water treatment has been one thing that is neglected or totally over simplified. To help protect a very expensive investment certain guide lines need to be followed. If you are using a mystery product and applying a cap full to the tender and cap full to the boiler fill water, you are already in trouble.
First, proper pH and alkalinity are needed for boiler metal protection. A metal passifier is also needed to help protect this very expensive investment from corrosion. When you first fire up the engine, a proper sulfite level for metal passivation would be from about 30 to 50 ppm and should be close to 200 ppm at the end of a day's run. Not only will this help to passify the metal, it will also prevent oxygen pitting. Proper boiler water pH should be close to 10.0 at the beginning of the run and no higher than 12.0 at the end. For the best magnetite layer formation, a pH of 11.0 to 12.0 is usually recommended.
Always add some treatment to the tender each time you take on water. Adjust your tender to 10 to 30 ppm sulfite and a pH of about 8.0. This will allow scavenging and buffering of your make-up (fresh) water. Using softened water is also a good idea. Make sure you have suction strainers on all injectors and feed pumps.
Test strips for both pH and sulfite are readily available and affordable. Sulfite drop test kits are also available along with conductivity meters. We carry all of these items if anyone is interested. Always record your test results on a log sheet with date and time. Free log sheets are included with our water treatment or they can be printed from our free catalog. Sulfite and pH level testing is a minimum requirement for most jurisdictions, along with proper water treatment.
Regarding scale forming products and total dissolved solids in the water, you need to hold them in suspension. Our soft water product, CWBT1, contains chelating and sequestering agents, a specific buffering agent, organic passivating agent, oxygen scavenger, alkalinity booster, and non- polymeric dispersing agents (polymers get too jumpy in applications like this where feed control, etc., can be all over the map). This product is designed for soft water use and will raise the TDS (total dissolved solids), as all chemicals will. As for our hard water product, RWTB1, it contains the addition of a hardness complexing agent. This will hold scaling components, such as hardness and dissolved matter, in suspension. These products are in powder form and are batch fed. You may also use TSP if you need added pH buffering with our products.
If you feel boiler carry over is a problem, you should do a heavy blow down just before the end of your run if you are using hard water. Scale-forming calcium and magnesium are less worrisome if you are using soft water. With soft water, blowing down more lightly at the end of a day's run should be fine. All softeners leak some hardness, but if you blow down heavily during the day's run you can have a negative effect on your boiler's pH. Remember that you are taking on alkalinity to buffer your boiler's pH in order to protect your boiler. If you blow down heavily, you will reduce your boiler's pH and will be taking on fresh make-up water (tender water). Blow down is truly dependent on your make-up water quality.
As for cycles (the concentration of the water due to boiling), go no more than 3,000 to 3,500 umhos (a measurement conductivity) for boilers operating up to 300 psi. This will allow you quite a few cycles for a day's run, as you want to maintain proper water chemistry. If you leave the safe range of boiler pH, metal wasting will start very quickly. Remember that any treatment will raise the conductivity and TDS in your boiler. If your water make-up water has a conductivity of 200 umhos, then ten full tender fills would result in conductivity in the boiler of about 2,000 umhos. Most tenders are roughly the volume of the boiler so this is a good rough measurement. Of course, this value is different for each locomotive.
When beginning any new water treatment regimen, do a complete water side and fire side cleaning and a thorough inspection of both. Look for wasting, pitting, cracks, and scaling on the water side and acid corrosion on the fire side. Pull all doors, steam dome covers, and entryways into the boiler. Soot and ash contain sulfur which forms sulfuric acid as the boiler cools, causing rust and pitting on the fire side.
While firing up and shutting down, temperature should not increase or decrease by more than 100o F. per hour. This is known as a “ramp rate”. Accepted practice for most clubs is to completely empty the boiler at the end of a run when the pressure gauge is just below three pounds. This will insure a warm and dry boiler. Once the boiler cools, you can clean the fire side, oil your valve gear, and wipe the locomotive down.
Copper and Steel
Rolled steel fire tubes are made of fairly thin material. They are roughly 0.100” to 0.120” in thickness or, more likely, less. We know of several very expensive locomotives that have dropped tubes with just three years of light service. This is a very serious indication that you may have a problem. You can be assured that corrosion has already set in on the boiler steel and the water side of the fire box.
Please note that treatment levels are different for steel boilers with copper tubes. Also, realize that proper water treatment will only slow corrosion and not halt it altogether. With proper water treatment, water testing, regular inspections, proper record keeping, and chemical adjustments you will allow many years of service life for your boiler.
Written by Kevin O'Neill
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