In this episode of Chemical Processing's Distilled podcast, host Traci Purdum talks with Brad Buecker, senior technical consultant at Samco Technologies, about sodium softening — the workhorse treatment for industrial boiler makeup water. Buecker explains how hardness ions cause scale, why residual bicarbonate drives corrosive condensate return lines, and how to spot early warning signs of a poorly monitored softener. He shares real-world cases where bypassing softeners or delaying maintenance led to rapid boiler tube failures and six-figure losses, walks through the regeneration cycle and its common pitfalls, and compares sodium softening with reverse osmosis for higher-pressure systems.

Edited Transcript

Welcome to the Chemical Processing Distilled podcast. This podcast and its transcript can be found at chemicalprocessing.com, and you can download the podcast on your favorite player. I'm Traci Purdum, editor-in-chief of CP, and joining me today is Brad Buecker, who has written several articles for us, many about water and wastewater. Brad joined me a few months ago as a podcast guest, and I enjoyed our conversation so much that I asked him to be a regular guest and talk water with us. Brad currently serves as senior technical consultant with Samco Technologies. He has many years of experience in or supporting the power industry, much of it in steam generation chemistry, water treatment and air quality control. Brad has a degree in chemistry from Iowa State University, with additional coursework in fluid mechanics, energy and materials balances, and advanced inorganic chemistry. Welcome, Brad. Thanks for joining me again.

Brad: Thank you, Traci, and thanks for inviting me. I look forward to this podcast and the ones down the road.

What Does A Sodium Softener Do?

Traci: Well, good. In this episode, we're going to dig a little deeper into another installment of your water series: "Sodium Softening, the Workhorse of Industrial Boiler Makeup Water Treatment." Let's set some foundation first. For listeners who aren't water treatment specialists, can you give us a quick overview of what a sodium softener actually does, and why boiler water chemistry is so affected by hardness?

Brad: Yes. Water that comes into boilers needs to be purified, and the requirements get more stringent at higher pressures, where the environment inside the boiler becomes more strenuous. Once water gets into that harsh environment, reactions can occur — both scale-forming reactions and corrosion reactions. Even simple, pristine surface water, say from a recreational lake, or treated municipal water, still contains a lot of dissolved ions, including hardness ions, chloride, sulfates, bicarbonate and alkalinity.

Once those ions get into the steam generator, a number of reactions can occur, and one of the most important is calcium carbonate scale formation. If you injected a typical water supply into a boiler, the first reaction you'd expect to see is calcium carbonate deposition. Sodium softening is designed to remove the hardness ions and eliminate most of these scale-forming reactions. It can also react with other ions, like sulfates and silicates.

So sodium softening is a very important primary treatment step for removing hardness ions from the water. One thing I'd point out: a lot of homeowners are familiar with the calcium carbonate reaction even if they don't know the chemistry behind it. If you've ever noticed scale building up on showerheads and faucets, particularly on the hot water side, that's calcium carbonate — which, in my opinion, is incorrectly termed "lime." You can go to the store and buy lime or limescale remover, but it's not lime, it's calcium carbonate. That's a side point.

Many systems are also equipped with downstream decarbonators to remove most of the bicarbonate and alkalinity. So the real purpose of sodium softening is to take out the primary scale-formers before the water reaches the boiler.

Bicarbonate In Makeup Water Woes

Traci: Now that you bring it up, I can visualize it — I have that calcium buildup on my showerhead, and even in my Keurig. You mentioned alkalinity and carbonic acid. Even with hardness removal, can you explain why bicarbonate in the makeup water can still cause corrosion problems downstream, after the softener has done its job?

Brad: Yes. Let's say we have a softener system but no decarbonator. It removes the hardness and greatly reduces the potential for scale formation in the boiler, but if bicarbonate alkalinity still proceeds to the boiler, heat will convert it through a stepwise process — bicarbonate to carbonate, and then most of that to carbon dioxide gas. Up to 90% of that bicarbonate and alkalinity can convert to carbon dioxide and carry over with the steam.

In industrial plants, steam is typically used for heating processes, and to save money and energy, plants usually return a lot of that condensed steam — the condensate — back to the boiler rather than wasting it. When the steam converts back to water, the carbon dioxide dissolves in it and forms carbonic acid. Carbonic acid isn't a strong acid, but it's still an acid, and it will attack carbon steel. There are excellent photos showing condensate return lines with a channel, or groove, at the bottom, where carbonic acid has gradually dissolved the carbon steel as the condensate is returned to the steam generator. That can be a very serious corrosion issue.

Carbonic acid, by lowering the pH, can also affect corrosion of other metals, including copper alloys to some extent, since those alloys typically show minimal corrosion in a low-8 pH range. Once you're down to the upper 4s or lower 5s, and if there's dissolved oxygen present, you can get significant corrosion from those two factors combined. That's a critical reason why removing bicarbonate and alkalinity matters, even with a sodium softener on the makeup system.

Early Warning Signs

Traci: You bring up some good points about what neglect looks like when you're not paying attention to water and steam chemistry. Are there early warning signs that a softener isn't being properly monitored?

Brad: Yes. If nobody pays attention at all, the warning signs may not show up until you get boiler tube failures from accumulated scale deposits. But if the system is being monitored — say an operator checks it once per shift — the logbook is usually the first thing my colleagues and I look at. I've worked more with demineralizer systems for power plants, but in any case, that's the first thing we ask to see: the softener logbook.

If whoever's operating the softener has been at least somewhat conscientious, there will be data indicating whether there have been overruns — even a grab sample showing hardness in the effluent tells you there's been an overrun. Even minor overruns can accumulate over time and eventually cause major problems. That's the first thing I look at: the operator logbook. If there's no data in there, you have to look elsewhere — interview the operating staff and find out what problems or issues they've noticed.

There's an excellent photo I've used in a few presentations and articles that shows layered calcium carbonate deposits in a boiler tube. You can distinctly see the layers: an overrun, then a correction, then another overrun, then another layer of calcium carbonate — you end up with a cake-like deposit in the boiler tubes. Those are a couple of things to look for early, because if you don't catch it, by the time tubes start failing, that's often when a plant contacts a water treatment chemical company. By then, it's usually not just one or two tubes — it's throughout the boiler. You don't want to wait that long.

That puts me on my soapbox a bit, because I've been on both sides of this. I always encourage plant owners, managers, operators and technical personnel to invest in people and instrumentation for these systems, because being proactive is a lot less costly than being reactive.

First Steps To Better Softener Performance

Traci: In a perfect world, everyone's monitoring this. But what about plants that have never audited their softener performance? What should their first steps be to right the ship?

Brad: This goes back to a couple of projects I worked on at power plants, where we installed equipment to help monitor steam generation chemistry. We didn't ask the managers, operation superintendents or operators to become chemistry experts. What we recommended was, first, get the instrumentation to detect problems and examine what's going on in the system. Second, invest in personnel and training so you have people on staff who understand the chemistry. We're not trying to force people who aren't chemistry-minded to become experts — if they want to learn more, great, but you shouldn't force it. If you're not going to do it yourself, make sure you have people on staff who do understand it.

Water Maintenance Mistakes

Traci: You gave an example in the article about learning the hard way — a case where management ordered the water treatment staff to bypass the softener and feed raw water directly to the boilers. What were the consequences, and how quickly did the damage show up?

Brad: As I was reviewing that question, I actually remembered two separate cases, both at refineries several hundred miles apart. I wasn't there personally — both were relayed to me by trusted friends in the industry. In both cases, the makeup water system had malfunctioned and couldn't be used, so a manager told the operators to bypass it and send raw water straight to the steam generators. I don't recall the exact pressures, but they probably weren't as high as power plant boilers, though still a reasonable pressure.

In both cases, they started experiencing boiler tube failures within days. Essentially, you're sending the impurities we've already discussed straight to the boiler at full concentration. You get scaling, and ions like chloride concentrate under deposits once they form in the steam generator — iron oxide deposits in particular are porous and troublesome. Chlorides, sulfates and other impurities concentrate under the deposits and start attacking the boiler tube metal.

I actually observed this myself on a 1,250-psi power boiler, similar to some industrial boilers, where in-leakage of contamination let impurities concentrate under deposits and cause a very serious corrosion problem known as hydrogen damage — and that was from just a small leak. In the cases where a manager said "bypass the makeup system, we've got to keep running," that's taking it to an extreme. In one case, my source told me the lost production time and maintenance repairs to the steam generator ran into eight figures. That's a lot of money.

Traci: Absolutely. What are some other common maintenance mistakes you've witnessed, or colleagues have witnessed?

Brad: This overlaps maintenance and operational mistakes, so I'll combine both into one answer. We've already talked about softener overruns — that's more of an operational issue than a maintenance one, most of the time, though malfunctions can also cause overruns and poor chemistry. I'll talk about regenerant concentration issues in a bit; that's really about following proper procedures, both operating a softener and maintaining it over time.

One issue I've seen, which affects many makeup water treatment systems, is a component or valve that starts to malfunction. Operators bring it to management's attention, and management says there's no money in the budget to repair it right now — we'll put it off to the next cycle. The next budget cycle comes and goes, and there's still no money.

A case in point: this was at a power plant where I worked, not an industrial plant. It was during a time when the power industry had changed a lot over the years, but large units that stayed online — particularly in spring and fall — could earn a company a huge amount of money, because less efficient systems could be shut down instead. This was a very large unit with a valve arrangement on the front of an ion exchange unit — more advanced than a sodium softener, but the same principle. We'd argued for years that it needed repairs; it had been in service for about 20 years, and each budget cycle, the money wasn't there.

I happened to be away from the plant at the time, at a conference. A piece of equipment failed and sprayed water across a roughly 10-foot walkway, soaking a controller on another piece of equipment and shutting down the entire unit. They got it started back up within a day, but it probably cost the utility $500,000 in lost production — maybe a bit more. That would have paid for most of the repairs if they'd just left them in the budget. It sounds like a drastic example, but that's what can happen when issues are neglected or overlooked.

Traci: The bottom line: you want things to look good in the moment, but you're robbing Peter to pay Paul when that happens.

Brad: Yes. Especially at the companies I worked for — two power plants and a chemical plant — when it came to budget time, we'd talk amongst ourselves and think: we wish the accountants had to come out here for a day or two and see how the process actually works. It's easy to cut things from a budget when you don't understand the process.

Traci: Or have the accountants come in and help fix everything themselves.

Brad: Right, that's a very good point.

Regeneration Cycle Steps

Traci: You alluded to the regeneration cycle earlier. Can you walk us through it — the purpose of each step, and where operators might cut corners they shouldn't?

Brad: Yes. The steps are backwash, brine injection, slow rinse and fast rinse. Any ion exchange system — and sodium softeners specifically — takes out hardness and exchanges it for sodium, which then goes into the water. Sodium doesn't cause the scale problems hardness does. But in the process, the resin is gradually "exhausting," and systems are often set up to go into regeneration before complete exhaustion, so you don't start sending unwanted ions downstream.

The first step in regeneration is a backwash. Resin accumulates crud over time and breaks down somewhat from the mechanical flow of water through it, so you want to wash the resin fines and crud out of the bed. Next comes brine injection. Resin has what's known as an affinity for ions — it holds calcium and magnesium much more strongly than sodium, which is why it works so well to remove them. To regenerate it, you have to force the reaction backward with a strong brine solution. Where the incoming water might have 100 to 200 parts per million of calcium and 20 to 30 ppm of magnesium, regenerating the resin takes an 8% to 12% brine concentration — 8,000 to 12,000 ppm — because you need that concentration to strip out the ions the resin captured.

After brine injection, you rinse the resin to remove impurities before returning the unit to service. A slow rinse — at least one bed volume, at the unit's normal flow rate — lets residual brine keep regenerating while it rinses. Then a fast rinse, at an increased flow rate, gets the unit back online more quickly. Typically, a conductivity measurement or other test on the effluent confirms the resin is rinsed down to an acceptable level before the unit returns to service.

Where corners get cut: One recurring issue is in the backwash step. Water temperature changes seasonally — colder in winter, warmer in summer — and colder water is denser. If you don't correct for that, some of the resin can actually backwash out of the system, reducing the resin volume, which shortens run times and causes more frequent regenerations. It's an easy corner to cut: set the backwash flow rate once and forget about it, without accounting for seasonal variation.

Keeping track of regenerant concentration is important too — I worked with this directly on demineralizer systems. If you don't feed enough regenerant, regeneration takes longer. In brine systems, overfeeding can cause the resin to shrink — high salt concentration does that — and too high a concentration can actually fracture the resin through chemical stress, causing breakdown. And you need to make sure the slow and fast rinses run their proper duration — don't just set it and forget it. The resin needs to be rinsed down to proper purity before it goes back into service, or you're sending impurities to the boiler.

Traci: It sounds like a cascading effect — like creeping change. You don't notice it happening, but it keeps building until all these issues surface. You mentioned countercurrent regeneration as a meaningful design improvement. Why isn't it universally adopted, and what does it buy you operationally?

Brad: When ion exchange units were first developed in the 1930s, they were designed as co-current systems: service water flows through the bed top to bottom, and when it needs regeneration, you backwash it — which moves the resin around some — then regenerate through the same flow path.

The problem is that the captured ions come out in layers. Calcium has the strongest affinity for the resin, so it forms the top layer, followed by magnesium — both divalent ions — then a bit of potassium, and finally sodium, which has the least affinity. When you start the regeneration step, you're forcing all those unwanted ions all the way through the bed to get them out, which requires more regenerant and more time. You can also get what's known as a "heel" — picture a circular ion exchange vessel — a ring formation around the bottom that, once the unit is back in service, leaks some of those ions into the effluent. So rinsing takes longer, and you still get some ion leakage. It's the simplest process, though, and it's been used for almost a century, so it's not bad technology — just basic.

What was developed later, and what's used in the power industry for ion exchange demineralizers, is countercurrent regeneration. Process flow might still go top to bottom, but the regenerant is introduced in the opposite direction. That way, you're not forcing calcium and magnesium — the strongly held ions — all the way through the bed; you're pushing them back out the way they came in, so they don't have to travel through the whole resin bed. You might still have some hardness ions left at the top after regeneration, but they don't show up in the effluent, because they're at the top, not the bottom. That means faster regeneration, quicker rinse-downs and lower regenerant chemical usage.

The drawback is that countercurrent regeneration needs additional piping and controls compared to co-current. For a plant that doesn't want that complexity, co-current may make more sense. But for plants that want maximum efficiency and are willing to spend the extra money and provide the extra training, countercurrent is the way to go.

When Does Sodium Softening Stop Working?

Traci: Is there a pressure or steam quality threshold where sodium softening stops being adequate, and reverse osmosis or ion exchange demineralization becomes mandatory?

Brad: That can be a bit of a gray area, but the number that's always stuck with me is around 600 psi. It's interesting you ask — just last week I was talking with a company that provides industrial boiler water treatment chemicals and methods. The engineer I spoke with mentioned they work with a lot of units operating at or under 600 psi, which basically confirmed the number I've used for years. I've heard the same figure from others too.

That said, every unit needs to be evaluated individually — I wouldn't walk into a plant running at 600 psi and simply say "use sodium softening." There are extenuating circumstances. I worked with a couple of power boilers running at 900 psi, which some people would call low for a power plant, but that's what those units needed when they were built. Others consider 900 psi still within range for sodium softening.

A deciding factor is whether the steam feeds a turbine rather than just a process. That's a different ballgame — you need to consider steam purity closely, whether the turbine is for power production or, say, producing air for blast furnaces at a steel mill. Impurities on turbine blades can cause issues quickly, and turbines are such high-precision machines that if one goes down from deposits, scale buildup or corrosion, you can't just call the hardware store for a replacement. That's a long lead time and a lot of money. But long story short, 600 psi is the general guideline I've kept in mind for years.

Reverse Osmosis Advantages

Traci: What advantages does RO bring that sodium softening can't, and what are the drawbacks?

Brad: That ties in with the 600-psi question. Modern RO membranes can remove more than 99% of dissolved ions in water. Some smaller, monovalent ions — a little sodium, a little chloride — will work through the membrane, but in the big picture, you get 99% removal. For makeup water to high-pressure units, you need high-purity water, but even for industrial units, RO can feed very pure water without the chlorides, sulfates and hardness that sodium softening and decarbonation leave behind. That reduces blowdown frequency, reduces corrosion issues and improves steam purity. From a purely technical standpoint, there are a lot of advantages to RO over sodium softening plus decarbonation — you're removing nearly everything and sending very good water to the boiler.

Having worked with RO systems quite a bit and seen what they can do, if I were starting over and someone asked me to be the water chemistry supervisor at an industrial plant — not a power plant — I'd recommend RO. But there's a big caveat, and it comes back to what we discussed about needing good operator attention and instrumentation for sodium softening — that's equally, if not more, important for RO.

RO membranes are more advanced technology. The common configuration is spiral-wound: a flat sheet combined with support and spacer material, wrapped around a central core several times to form a cylindrical element, typically 8 inches in diameter by 40 inches long, housed in pressure vessels. Without good pretreatment to remove small particulates, those particulates will clog the spacer material and can shut down an RO quickly.

As water flows through a basic single-pass, two-stage RO system, it concentrates roughly four times from front to back — membrane manufacturers and water treatment firms have excellent software to calculate this; I'll cover it in the next installment of the makeup water series. That fourfold concentration raises scaling potential significantly. The cartridge filters ahead of the RO, which serve as final particulate removal, and the RO membranes themselves are also prime sites for microbiological fouling.

One issue I've directly observed and worked with several times: feed water to the RO is often treated with an oxidizing biocide — chlorine or sodium hypochlorite (liquid bleach) — but any residual has to be removed before the water reaches the membranes, because chlorine will attack RO membranes. That's typically done with an activated carbon filter or a reducing agent like sodium bisulfite. Some microbes go into hibernation when they sense the oxidizing biocide, chlorine being the most destructive to membranes. Once the biocide is removed, those microbes start flourishing again, and RO membranes are ideal sites for microbiological growth. That growth can be explosive — exponential — and if it's allowed to take hold, it can cause fouling in a very short time, sometimes irreversible fouling that can only be resolved by replacing the membranes.

So yes, RO can remove almost all the ions headed to the steam generator, which is a real benefit, but it requires great care in both pretreatment and ongoing process treatment to prevent particulate accumulation, fouling and scaling.

Advice

Traci: Well, Brad, you've given us a master class today. Last question: if you had to give one piece of advice to a plant operator running a sodium softener today, what would it be?

Brad: I'll try to keep this short. First, following up on what I said about caring for RO systems — this is something that's often overlooked, and I'll probably include a dramatic but realistic case history on it in an upcoming installment of the series: you can install a great makeup treatment system at an industrial plant, but impurities coming back through condensate return can completely mask its benefit. A great makeup system can be undone by impurities in the returning condensate, so plant owners and managers need to look at the entire system, not just the makeup side.

As for quick advice: be diligent about watching for softener overruns, and advocate for instruments and lab equipment to monitor performance. At a chemical plant where I worked, makeup water was split into two streams. One went through a strong acid cation ion exchanger — required, to strip out all the cations before the process. The other, the more critical stream, had a sodium softener and a decarbonator, and removing calcium was critical to that process. Even after I arrived and found a diligent staff monitoring the softener, one upset could shut down the chemical processing line. So we installed an online calcium monitor on the effluent that would trigger an alarm the instant something went wrong, rather than relying on a lab tech pulling a grab sample every couple of hours and discovering hardness that might have been present for hours already. That instantaneous warning made a real difference.

And again, be proactive rather than reactive — invest in personnel and equipment up front, and it pays off in the long run.

Traci: Absolutely — and if not, we'll bring in the accountants and have them start swapping out the decks with us.

Brad: Right — you clean out the equipment yourself.

Traci: Exactly. Well, Brad, thank you. As you mentioned, we'll be chatting again next month about how pure makeup water may be meaningless if impurities consistently enter the boiler through condensate return systems. Until then — if you want to stay on top of best practices in the chemical industry, subscribe to this free podcast on your favorite platform. You can also visit us at chemicalprocessing.com for more tools and resources aimed at helping you succeed. On behalf of Brad, I'm Traci Purdum, and this is Chemical Processing's Distilled podcast. Thanks for listening, and thanks again, Brad.

Brad: Thank you so much, Traci.