YOUR BOILER ~ What you can’t see ~

The inside story
By Earl Winter

There are many opinions about the effects of scale on the internal surfaces of your boiler, but one thing that is not in dispute is the high cost of the excess fuel usage that results. A client recently showed me a boiler fuel invoice after a contractor had made an error in connecting the boiler chemical feed lines. The fuel bill had increased $10,000 in one month due to the scale buildup that resulted. The client was a typical laundry and the boiler was a common 500 HP package boiler.

One of the primary reasons that we must treat the water in our boilers is to keep natural elements found in water such as calcium and magnesium, from forming scale on the boiler tubes. Most companies that must use boilers in their businesses pay a high price to have a third party provide boiler chemicals. Yet it is not uncommon for the representative (salesman) from that company to tout the beneficial effects of scale to protect the metal from damage from oxygen. The most common recommendation is an “eggshell thickness” of scale.

The simple chart below, taken from a B & W boiler manual shows the increased fuel usage caused by the insulating effects of scale buildup on the boiler tubes.

Effect of Scale on Heat Transfer
- Increased Fuel Usage %
1/32” 8.3
1/25” 9.9
1/20” 11.2
1/16” 12.6
1/11” 14.3

Scale buildup on tubes is an excellent insulator. In fact, an inch of scale is equivalent to several inches of asbestos in insulating quality.

An “eggshell” thickness is approximately 1/32 of an inch, and as you can see, compared to a clean tube your fuel costs will increase 8.3% as a result of this scale. Even with smaller boilers, this can be thousands of dollars annually in unnecessary costs.

It is unclear why so many in the boiler industry either tout the presence of some scale in your boiler or are at least complacent about its existence. I am sure some are quite sincere and are only passing on what they have heard and believe. Perhaps others find it convenient to preach this doctrine because it is clear that their program is not providing a clean efficient boiler. In any case, it is a gross disservice to the boiler owner / operator.

In addition to insulating and thereby reducing maximum heat transfer from the flame to the water, driving up fuel costs, scale is the number one source of damaging heat stress in your boiler. Heat stress, in this instance, is defined as the uneven expansion of the boiler components as heat is applied. Expansion is a normal result of applying heat, and as long as that expansion is applied evenly and slowly, there is no cause for concern. The boiler is built to handle this phenomenon for many, many years. But if the boiler is brought up to pressure too fast, expansion occurs in some places more rapidly than others, and damage will occur.

The same applies if scale has formed in your boiler. It is impossible to form scale throughout the entire boiler evenly as it tends to form on the hottest surfaces first. Therefore, the scale insulates some parts of the boiler more than others. It doesn’t take a metallurgist to comprehend that expanding the boiler unevenly, or expanding some parts and not others will be very stressful to the boiler. Over time, usually a short time, the mechanical bond will break down between the tubes and the tube sheet, and eventually cracks will develop in the tubes themselves. The least case scenario then is a very expensive repair that is disruptive to the production process. The worst case is catastrophic failure that endangers the plant and the people in it.

There is no need for a scale coating on your tubes for protection from oxygen. In fact, scale does not protect from oxygen attack. It only hides the damage for a time. There are other, much more effective methods of preventing oxygen corrosion. But even if you disagree with this point, consider this. Controlling a chemical program designed to keep the boiler’s internal surfaces clean is relatively easy to do. Allowing scale build up is even easier. Trying to control a chemical program that is attempting to maintain 1/32 inch of scale on your boiler tubes is impossible.

A clean boiler is a healthy boiler, and by far and away the most cost effective option. The keys to a clean boiler are soft water and the proper chemical program. The payback on the cost of soft water and the proper chemical program is weeks, not years. Yet, this advice will often go unheeded because the cause is on the inside where it is difficult to see (out of sight, out of mind) and the effect is hidden in the utility bill.

So what can the business owner / manager do to protect the business from this hidden problem? First, find a chemical provider that can show that their program works as advertised. Then it is important to inspect the boiler every six months. Regardless of what you may be told, there are no indicators as reliable as that look inside to see how the program is working. One last word of caution. Many “experts” will tell you that the appearance of scale breaking loose from the tubes in large chunks means the program is working. What this probably means is that your boiler is experience serious heat stress. Remember that uneven expansion issue?

Make sure you have a chemical program that is designed to keep boiler internals clean. Then follow that with verification that the program is working. Your bottom line will thank you and your boiler will last almost indefinitely.

	This is a photograph of the internal boiler tubes looking through the opening at the top of the boiler. Although you may not have an experienced eye, you can see that the edges of the tubes do not appear even. That uneven appearance is evidence that a coating of scale is present. It is further evidence that scale does not form evenly. This boiler has experience the need for repairs recently to stop tube leaks, and unless some serious corrective action to their chemical program is enacted soon, some very expensive repairs will follow.
	This is a photograph of the internal boiler tubes looking straight down through the opening at the top of the boiler. Of special interest is the writing stamped on the tubes by the manufacturer that is clearly visible after more than two years of usage. It is obvious that there is not a protective scale coating of any kind on these tubes, and also obvious that there is no resultant damage. The tubes are protected using chemicals, not scale, and the boiler operates at peak efficiency as a result. If this program is maintained and the boiler is fired properly, boiler life expectancy is at least 50 years without major problems.

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