Kiln Shell Inspection Checklist: 9 Checks at Every Reline

Kiln Shell Inspection Checklist: Key Points

• The kiln shell steel is visible only during a reline, so every reline needs the same nine checks, recorded the same way.
• Before the kiln stops: review shell scanner hot spots, cool zones and ovality, and pull campaign records (fuel changes, previous thickness grid, refractory failures, coating history).
• As the lining comes out: record refractory and anchor condition, then sample deposits and record visible corrosion and pit depth at the shell face.
• Measure ultrasonic thickness on a fixed grid and compare each zone's minimum with the structural minimum; in a Mexico study the 20 to 26 m zone was measured at 1 m intervals.
• On previously coated zones, check coating condition; KilnGard®-600SCW is typically renewed when the refractory is replaced.
• Before relining, confirm SSPC-SP10 preparation and coating inspection; final heat cured activation is completed during start-up using process heat.

A kiln shell inspection at every reline covers nine checks: scanner history, campaign records, refractory condition, anchor roots, shell-face deposits and corrosion, an ultrasonic thickness grid, thickness against the structural minimum, existing coating condition, and surface preparation and coating inspection before new refractory goes in. Record each the same way every reline so zones can be compared.

A kiln shell inspection at reline is the structured check of a rotary kiln's steel shell while the refractory is removed. It covers reviewing scanner and campaign data, recording refractory, anchor and deposit condition, measuring wall thickness against the structural minimum, and checking any existing coating and the preparation for new protection before relining.

What a Kiln Shell Reline Inspection Checklist Covers

A kiln shell reline checklist covers the steel shell of a cement or lime rotary kiln, not the refractory design itself. It runs alongside the refractory contractor's own work during the reline.

Scope: The Steel Shell While the Lining is Out

Refractory design, brick selection and kiln mechanical alignment sit outside this checklist except where they affect the shell steel. Polylloy's May 2026 International Cement Review (ICR) article notes that corrosion beneath the lining often remains undetected until significant metal loss is identified, and that it weakens the refractory-steel interface.

The steel can be seen, measured and protected only while the lining is out. Sulfur, chloride and alkali compounds pass through the lining and condense or deposit on the cooler shell; the mechanism is explained in corrosion behind refractory linings.

Checklist at a Glance

The nine checks, their timing, tool and record are summarized below; UT means ultrasonic thickness and DFT means dry film thickness.

Shell Scanner Data and Campaign Records Before the Kiln Stops

The first two checks happen before shutdown, because they tell the crew where to look when the lining comes out.

Check 1: Shell Scanner History

Pull the kiln shell scanner record for the campaign. Hot spots, cool zones and changes in ovality flag the zones that deserve a closer thickness grid, and the ICR article links both hot spots and shell thinning to corrosion under deposits beneath the lining.

Mark each flagged zone on a shell development drawing, so the crew goes straight to it when the lining is removed.

Check 2: Campaign Records

Collect previous UT readings with their exact locations, the refractory campaign history and failures, and any fuel or raw material changes. Polylloy's technical paper notes that fuel changes and alternative fuels alter chloride, sulfur and alkali inputs, as described in how alternative fuels changed kiln corrosion.

If zones were coated at the last reline, collect the coating records too: product and grade, surface preparation, film thickness and inspection results.

Refractory and Anchor Condition as the Lining Comes Out

Lining removal is the moment to record how the refractory and its anchors behaved against the shell, before the evidence is cleared away.

Check 3: Refractory Condition at the Shell

Record, by zone, lining that has lifted from the shell, open joints, cracks and areas where the lining came away easily. Corrosion products occupy more volume than the steel they replace, so they push the lining away from the shell, and shell and lining failures feed each other.

Compare these zones with the scanner map from check 1. Zones that ran hot often show where the lining had already thinned or failed.

Check 4: Anchor Roots and Welds in Castable Zones

Where castable and anchors are used, inspect the anchor roots and the shell around them, log corroded or loose anchors and replace them. Confirm anchor material with the refractory designer, because anchors create crevices and heat paths at the weld to the shell. Agree the anchor welding and coating sequence with Polylloy's technical team before the outage.

Shell Face Deposits and Visible Corrosion

Deposits at the shell face record what reached the steel during the campaign, so they are sampled before anything is cleaned.

Check 5: Sample Deposits, Then Record Corrosion

Sample deposits at the shell face before cleaning, because deposit chemistry helps show what reached the steel during the campaign. Polylloy's technical paper recommends assessing actual deposits and condensates rather than relying on bulk gas data.

After cleaning, photograph each zone and record scaling, pitting and localized attack with pit depth. The same paper notes that a low average loss can conceal a penetration risk.

Note refractory rub marks as well. The ICR article explains that bricks can rub against the shell during operation, adding abrasion to the chemical attack.

Ultrasonic Thickness Grid and the Structural Minimum

Thickness data turns the visual record into numbers that can be compared from reline to reline and checked against a structural limit.

Check 6: Ultrasonic Thickness Grid at Fixed Points

Take UT readings on a fixed grid and repeat them at the same points every reline, so loss per campaign comes from comparison rather than single readings. Track the minimum reading in each zone, not the average.

A Polylloy field study in Mexico shows the method. Shell thickness was measured at 1 m intervals along the 20 to 26 m kiln section, which the case study describes as a high-disturbance zone.

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.

The plant is not named, and results are project-specific. The full study is set out in kiln shell metal loss: coated vs uncoated sections.

Check 7: Each Zone Against the Structural Minimum

Compare each zone's minimum reading and loss per campaign with the structural minimum set by the kiln original equipment manufacturer (OEM) or a structural engineer for that shell course and its tyre and roller loading. No generic figure applies.

Zones with margin left are protected at this reline, marginal zones go to the engineer, and zones below minimum, cracked or deformed are replaced and the new plate protected. A coating does not restore lost steel.

Coating Condition on Previously Protected Shell Zones

Zones coated at an earlier reline get their own check, because they show whether the protection held through the campaign.

Check 8: Existing Coating Condition

On zones coated at a previous reline, record continuity, any disbonded or lifted areas, abrasion from refractory contact, and corrosion at edges and anchor bases. Take DFT readings where the film is intact and compare them with the original specification.

Compare the coated zones' UT readings with their own baseline and with uncoated zones; a before-and-after comparison of the same section on a fixed grid is what produced the Mexico result. Polylloy's inspection and maintenance services include condition assessment and thickness and continuity verification.

Renewal at the Reline

KilnGard-600SCW is typically renewed when the refractory is replaced, because the shell is only exposed for preparation at a reline. Treat each reline as the point to renew coated zones and to extend protection to new zones where the survey shows loss.

Surface Preparation and Coating Inspection Before Refractory Goes Back In

The last check is a release step: once the refractory installer starts, the steel will not be seen again until the next reline.

Check 9: Preparation and Coating Release

Before any coating, confirm that thinned plate and anchors are repaired and soluble salt deposits removed, because chlorides left under a coating keep working on the steel. Then confirm the shell is blasted to SSPC-SP10 / NACE No. 2 near-white with a profile above 3 mils (75 µm).

The bulletin application conditions are steel at 10 to 50 °C, relative humidity below 90%, and steel at least 5 °C above the dew point. Kiln shells may still be hot after shutdown, so plan cooling.

A certified Polylloy partner applies KilnGard-600SCW, with Polylloy specifying and supervising. Verify DFT against the bulletin's single-coat range of 15 to 25 mils, check coverage at edges and anchor bases, and repair defects.

Before final activation, the film can be inspected for thickness and integrity and any defect recoated. Sign the release before the refractory installer starts. The protection steps themselves are covered in coating outage planning steps.

How a Kiln Shell Coating is Cured on Site

Final heat cured activation is completed during start-up using process heat. The start-up after the reline, run to the refractory supplier's heat-up procedure, is therefore part of the coating job.

Polylloy's technical team agrees the start-up approach for each kiln, and the detail is project-specific. A site that cannot blast to SSPC-SP10 or bring the kiln through start-up heat is not a fit for this protection.

How Often to Inspect a Kiln Shell

How often to inspect is set by the reline cycle, with monitoring in between.

Every Reline, with Monitoring Between

The full nine-check inspection runs at every reline, because that is when the shell is exposed. Between relines, the shell scanner and thermography locate hot and cool zones; they detect damage but do not protect the steel.

No universal interval is published. Add closer attention after fuel changes, higher alternative fuel rates or a campaign with refractory failures, and inspect a coated shell at every reline too, because its steel can be checked only while the lining is out.

Deciding What Your Next Kiln Reline Needs

Deciding what the next reline needs comes down to what the nine checks found:

• Zones with margin and active loss: protect at this reline with KilnGard kiln shell coating, rated to 600 °C (1,112 °F) for cement and lime kiln shells beneath refractory.
• Marginal zones: the engineer's assessment comes first.
• Below minimum, cracked or deformed: replace, then protect the new plate.
• Previously coated zones holding thickness: renew with the reline.
• Zones above 600 °C at the steel: a refractory problem, not a coating question.

Options other than coating, such as refractory redesign, shell temperature management and replacement, are compared in kiln shell corrosion protection options. For refractory-lined stacks, use the steel stack inspection checklist.

Certified partners apply; Polylloy formulates, supplies, specifies, trains and supervises, through 15 partners in 22 countries. To book a Coating Performance Review, request a coating evaluation with kiln type, affected shell area, UT and scanner data, operating conditions (temperature, fuel and gas chemistry, abrasion), location and reline timing.

FAQs

What Should Be Checked on a Kiln Shell During a Reline?

Nine things: shell scanner history, campaign records, refractory condition at the shell, anchor roots, deposits and visible corrosion, an ultrasonic thickness grid, each zone against its structural minimum, the condition of any existing shell coating, and surface preparation and coating inspection before relining. Record them the same way every reline so zones can be compared.

How is a Kiln Shell Coating Cured on Site?

Final heat cured activation is completed during start-up using process heat. The coating goes on the prepared shell before the refractory, and the start-up after the reline, run to the refractory supplier's heat-up procedure, completes it, so no separate curing outage is needed. Polylloy's technical team agrees the start-up approach for each kiln.

How Much Thickness Does an Uncoated Kiln Shell Lose Compared with a Coated One?

Loss rates are kiln-specific, so measure your own. In one Mexico field study, the 20 to 26 m section lost more than 1.3 mm in 11 months uncoated; after KilnGard-600SCW was applied before refractory installation, the same section showed no corrosion and no measurable thickness loss after a further 12 months. Results are project-specific.

How Do You Measure Kiln Shell Thickness at a Reline?

Take ultrasonic thickness readings on a fixed grid in each exposed zone and repeat them at the same points every reline, so loss per campaign comes from comparison. Track the minimum reading in each zone, record pit depth, and compare the results with the structural minimum set by the kiln OEM or a structural engineer.

Does a Coated Kiln Shell Still Need Inspection at Every Reline?

Yes. At each reline, check the coating for continuity, disbonded areas and abrasion from refractory contact, take thickness readings on coated and uncoated zones, and compare them with the baseline. KilnGard-600SCW is typically renewed when the refractory is replaced, so the reline is also the point to renew coated zones.

What Does a Kiln Shell Scanner Show Before a Reline?

A kiln shell scanner maps shell temperature during operation, locating hot spots, cool zones and changes in ovality. Hot spots often mark where the lining has failed or corrosion under deposits has thinned the shell, so the scanner record tells the inspection crew where to put a closer thickness grid once the lining is out.

Can a Kiln Shell Coating Be Applied If the Shell is Badly Thinned?

Only if the remaining steel is structurally acceptable. A coating is a barrier against further corrosion; it does not restore lost thickness or repair cracks and ovality. Sections below the structural minimum, cracked or deformed need replacement first, and the new plate can then be protected before the refractory goes in.