# Kiln Shell Metal Loss: Coated vs Uncoated Sections, and When to Replace Kiln shell metal loss decides the route: coat a section when ultrasonic thickness readings show it will stay above its structural minimum through the next campaign, and replace it when it is below minimum, cracked or deformed. In a Mexico field study, a section that lost more than 1.3 mm in 11 months uncoated showed no measurable loss 12 months after KilnGard-600SCW was applied. **Category:** Use cases **Written by:** Surjit Gill **Last updated:** Oct 12, 2026 **Source:** https://signals.polylloycoatings.com/use-cases/kiln-shell-thickness-loss-coated --- ## Kiln Shell Metal Loss: Key Points - In a Mexico field study, the 20–26 m kiln zone lost more than 1.3 mm of shell thickness in 11 months without coating. - The same section, protected with KilnGard®-600SCW before refractory installation, showed no corrosion and no measurable thickness loss when remeasured after a further 12 months. - Coat or replace is a thickness decision: compare measured thickness and loss rate with the shell's structural minimum over the next campaign. - A coating does not restore lost steel; sections below structural minimum, cracked or deformed need replacement, and the new plate can be coated before relining. - Cost comparisons are project-specific; the inputs are outage length, plate and fabrication, crane and welding access, surface preparation, coated area and inspection. - Certified partners apply KilnGard-600SCW under Polylloy specification and supervision; Mexico is covered by Polylloy's partner map. Kiln shell metal loss decides the route: coat a section when ultrasonic thickness readings show it will stay above its structural minimum through the next campaign, and replace it when it is below minimum, cracked or deformed. In a Mexico field study, a section that lost more than 1.3 mm in 11 months uncoated showed no measurable loss 12 months after KilnGard-600SCW was applied. Kiln shell metal loss is the reduction in steel thickness of a rotary kiln shell, measured by ultrasonic thickness surveys, caused by corrosion beneath the refractory lining, with abrasion from refractory contact adding to the chemical and thermal attack. The loss rate per campaign, compared with the shell's structural minimum thickness, decides whether a section is protected or replaced. ## Kiln Shell Metal Loss Challenges vs What the Mexico Thickness Study Answers Reliability managers on rotary cement kilns and lime kilns face the same handful of questions before a reline outage. The loss itself comes from sulfur, chloride and alkali compounds that pass through the lining and attack the cooler shell, a mechanism explained in the guide to [corrosion behind refractory linings](https://signals.polylloycoatings.com/articles/corrosion-behind-refractory-lining). ### Challenge vs Solution Table for Reliability Managers Each challenge below is matched with what the Mexico thickness data shows and the decision it supports. | Challenge | What the data shows | Decision it supports | | --- | --- | --- | | Loss hidden behind refractory until a reline | Mexico zone lost more than 1.3 mm in 11 months uncoated | Survey every exposed zone at reline | | No proof a coating holds thickness | Same section showed no measurable loss after a further 12 months coated | Coat sections with margin | | Section near structural minimum | A coating does not add steel | Engineering assessment before relining | | Section below minimum, cracked or deformed | Replacement restores thickness only | Replace, then coat the new plate | | Protection must fit the reline outage | Applied before refractory, renewed with refractory replacement | Schedule with the reline | | Cost question from management | Project-specific factors | Lifecycle evaluation, not a unit price | The table separates two questions that often get merged. Whether a coating holds thickness is answered by measured data; whether the existing steel is still fit to carry the kiln is answered by an engineer against the structural minimum. ## What the KilnGard-600SCW Mexico Field Study Measured The Mexico field study is the documented evidence behind this page. It compares the same kiln section before and after protection, measured on the same grid. ### Measurement Zone and Method Shell thickness was measured at 1 m intervals along the 20–26 m kiln section. The case study describes this as a high-disturbance zone, where thermal gradients and gas flow promote corrosion under refractory. The case study does not name the plant or state the application dates, so neither is given here. ### Uncoated vs Coated Result on the Same Section Without coating, the section lost more than 1.3 mm of steel thickness after 11 months of initial service. KilnGard-600SCW was then applied to the internal shell before refractory installation, and the section showed no corrosion and no measurable thickness loss after an additional 12 months. | Condition | Period | Observed result | | --- | --- | --- | | Uncoated shell | 11 months of initial service | More than 1.3 mm thickness loss | | Coated with KilnGard-600SCW | Additional 12 months | No corrosion, no measurable thickness loss | Read this as a before/after field observation, not a controlled trial. The same zone was measured at the same 1 m interval in both periods, but the periods differ (11 against 12 months) and the data comes from one kiln. Results are project-specific. Another kiln's outcome depends on its fuel, gas chemistry, refractory condition and [surface preparation](https://signals.polylloycoatings.com/articles/coating-outage-planning-steps), and fuel changes are one reason shell attack shifts over time, as described in [how alternative fuels changed kiln corrosion](https://signals.polylloycoatings.com/articles/alternative-fuels-kiln-corrosion). ## How to Read Kiln Shell Thickness Data Between Relines Kiln shell thickness data is only useful for a coat-or-replace decision when it is turned into a rate and a margin. Single readings tell you where the shell is today, not where it will be at the next reline. ### Turning UT Readings Into a Loss Rate Ultrasonic thickness (UT) readings taken on a fixed grid at each reline give a loss per campaign for each zone. The Mexico study's 1 m interval is a practical model for the worst zones of the shell. Track the minimum reading in each zone, not the zone average. Corrosion under deposits is localized, so one thin patch governs the decision for the whole section. Remaining thickness margin is the measured minimum thickness minus the structural minimum. Compare that margin with the loss expected before the next planned reline: if the expected loss is smaller than the margin, the section can run another campaign; if it is equal or larger, it cannot. ### Who Sets the Structural Minimum The structural minimum comes from the kiln original equipment manufacturer (OEM) or a structural engineer, calculated for that shell course and its tyre and roller loading. There is no generic figure to apply across kilns, so this page does not give one. Kiln shell scanner data helps decide where to survey first, because hot spots and ovality flag zones that deserve a closer grid. The monitoring basics are covered in the list of [kiln shell corrosion protection options](https://signals.polylloycoatings.com/listicles/kiln-shell-corrosion-protection). ## Coat or Replace a Kiln Shell Section: Thickness-Based Decision Rules Coat or replace is decided zone by zone, using the measured minimum and loss rate against the structural minimum. Three thickness bands cover most situations at a reline. ### Three Thickness Bands - **Above structural minimum with margin for the next campaign:** protect the shell with KilnGard-600SCW at the reline so that the loss rate measured so far does not continue. - **Close to structural minimum:** the engineer decides whether the section can run another campaign; coating is only an option if the remaining steel is structurally acceptable. - **Below structural minimum, cracked or deformed:** replace the section, then coat the new plate before the refractory goes in, because new steel faces the same chemistry that thinned the old plate. The middle band needs the most care. A coating decision there should follow the engineering assessment, not substitute for it. ### What Each Route Does and Does Not Fix A coating is a barrier. It does not restore lost thickness, repair cracks or correct ovality, and it does not replace refractory. Shell section replacement restores thickness but not resistance. Uncoated new plate is exposed to the same attack from its first campaign, so the loss rate that justified the replacement starts again. Tie the decision to the measured loss rate. The Mexico section shows how quickly an unprotected high-disturbance zone can move toward its structural minimum, which is why the survey interval and the protection decision belong in the same reline plan. ## What Drives the Cost of Coating vs Replacing a Kiln Shell Section Polylloy does not publish prices, ranges or savings for either route. Pricing depends on the operating environment, selected coating system, equipment condition, project size, and application requirements. ### Cost Factors for Each Route Replacement cost is driven by plate supply and fabrication lead time, crane and welding access, alignment work and any outage extension beyond the planned reline. Coating cost is driven by coated area and surface preparation to Society for Protective Coatings (SSPC) SP10 near-white with a profile above 3 mils (75 µm). Partner labour and mobilisation, inspection, freight and delivery, and fit within the reline window complete the list. Separate material, installed and lifecycle cost when comparing the two. Lifecycle evaluation considers preparation, application, maintenance, downtime, and replacement alongside the initial material cost. Equipment life also has a material dimension. Keeping existing shell in service reduces the need for replacement steel and the emissions from producing it. ## How KilnGard-600SCW Fits a Reline in Mexico and Other Kiln Markets KilnGard-600SCW is a two-component nano-ceramic composite rated to 600 °C (1,112 °F) for cement and lime kiln shells beneath refractory. Product details are on the [KilnGard kiln shell coating](https://www.polylloycoatings.com/kilngard) page. ### Application Sequence at the Reline 1. Prepare the internal steel shell and apply the coating before refractory installation. 2. Install the refractory over the coated shell. 3. Final heat cured activation is completed during the kiln start-up using process heat. 4. Renew the barrier when the refractory is next replaced, which the case study describes as typical. The qualification gate is practical: the site must be able to blast to SSPC-SP10 near-white with a profile above 3 mils and bring the kiln through start-up heat. Steel stacks raise a similar sequencing question, covered in [coating a refractory-lined stack](https://signals.polylloycoatings.com/articles/refractory-lined-stack-coating). ### Who Does the Work in Mexico Certified application partners apply the coating; Polylloy formulates, supplies, specifies, trains applicators and supervises. Polylloy works with 15 partners in 22 countries, and Mexico is listed on its partner map. ## Deciding Between Coating and Replacing a Kiln Shell Section at the Next Reline Before the next reline, assemble the inputs that decide each zone: - Latest UT grid by zone - Minimum readings against the structural minimum - Loss per campaign - Kiln shell scanner hot spots and ovality - Months to the next reline - Outage window - Ability to meet surface preparation and start-up heat requirements Then route each zone: margin left means coat at the reline, marginal means the engineer's call, and below minimum means replace and coat the new plate. To review your shell data with Polylloy, [Book a Coating Performance Review](https://www.polylloycoatings.com/contact) and share kiln type, affected shell area, operating conditions (temperature, fuel and gas chemistry, abrasion), location and reline timing. ### FAQs **Is There Evidence That a Kiln Shell Coating Stops Metal Loss?** Yes, for one documented case: in a Mexico field study, a 20–26 m kiln zone lost more than 1.3 mm of shell thickness in 11 months without coating. After KilnGard-600SCW was applied beneath the refractory, the same section showed no corrosion and no measurable thickness loss when remeasured 12 months later. Results are project-specific. **Should I Coat or Replace a Thinned Kiln Shell Section?** Decide on remaining thickness. If ultrasonic readings show the section will stay above its structural minimum through the next campaign, protecting it at the reline is the lighter intervention. If it is below minimum, cracked or deformed, replace it, then coat the new plate before the refractory goes in so it does not face the same attack. **Is It Cheaper to Coat or Replace a Corroded Kiln Shell?** The answer depends on the project, so Polylloy does not publish a general answer or figure; replacement cost is driven by plate, fabrication, crane and welding access and any outage extension. Coating cost is driven by area, surface preparation, partner labour, inspection and freight. Compare both on the same section, outage and evaluation period as a lifecycle cost. **Can a Coating Restore Kiln Shell Thickness?** No. A kiln shell coating is a barrier against further corrosion beneath the refractory; it adds no structural steel and does not repair cracks or ovality, which is why the coat-or-replace decision starts from ultrasonic thickness data. Sections already below their structural minimum need replacement, and the new plate can then be protected before relining. **Who Applies Kiln Shell Coatings in Mexico?** Certified Polylloy partners apply KilnGard-600SCW, and Mexico is one of the countries on Polylloy's partner map. Polylloy formulates and supplies the coating, writes the specification, trains applicators and supervises the work. The coating goes onto the internal shell before refractory installation, so the work is planned into the reline outage rather than as a separate shutdown. **How Often Should a Coated Kiln Shell Be Renewed?** The Mexico case study states that the barrier is typically renewed when the refractory is replaced, because the shell is only exposed for preparation at a reline. Use ultrasonic thickness readings at each reline to confirm the coated zones are holding thickness, and extend protection to any new zones where the survey shows loss.