Scrubber Inspection Checklist
A wet scrubber internal inspection is the only way to verify the condition of the packing, the FRP shell, the mist eliminator, and the liquid distribution system. External monitoring — pH, differential pressure, flow rate — can indicate a problem exists, but it cannot tell you whether the packing has 2 mm of scale or 8 mm, whether the corrosion barrier has 3 years of life remaining or 3 months, or whether a nozzle is 20 percent blocked or completely plugged. When instrument readings indicate a problem between scheduled inspections, use the scrubber troubleshooting diagnostic guide to identify the root cause before planning the next shutdown. This scrubber inspection checklist covers the nine critical inspection areas: pre-inspection safety, external inspection, packed bed, FRP/PP shell, mist eliminator, liquid distribution, sump and recirculation system, fan and ductwork, and post-inspection documentation. Each area includes specific inspection procedures, quantitative pass-fail criteria, and measurement protocols so the inspection produces actionable data rather than subjective opinions.
Key Takeaways
- Inspections must produce quantified data, not subjective opinions. Measuring fouling thickness at the same five marked locations every year creates a trend that tells you whether your water chemistry is working. “Looks clean” and “some scale” have no comparison value between inspections. Record the number, always.
- The FRP corrosion barrier inspection determines remaining service life. A Barcol hardness reading below 35 or visible fiber exposure over more than 4 in² means the corrosion barrier is compromised. Without annual ultrasonic thickness measurements at 12 standard locations, you cannot predict when the shell will fail — and a shell failure costs $20,000 to $80,000 plus lost production.
- Packing settlement of more than 8 percent requires immediate intervention. A 10-foot packed bed that has settled 6 inches loses 10 to 15 percent of its mass transfer capability because gas preferentially flows through the wall gap. The problem is invisible from outside the scrubber — only visual inspection through the access hatch catches it.
- A single plugged nozzle creates a dry zone that reduces efficiency by 8 to 12 percent. Nozzle spray pattern testing during every shutdown catches blockages early. Testing all 10 to 20 nozzles takes 1 hour and costs nothing. Replacing a full set of nozzles costs $150 to $1,600 — less than one week of operating with reduced efficiency.
- Documentation is the difference between a inspection and a maintenance event. An inspection with 20+ labeled photographs, quantified measurements for every parameter, and a severity rating for each finding creates a baseline that makes future inspections faster and more accurate. Without documentation, you cannot trend, you cannot predict, and you cannot justify capital expenditure for replacement.
Pre-Inspection Safety and Preparation
A scrubber internal inspection requires confined space entry. The scrubber vessel is a permit-required confined space under OSHA 29 CFR 1910.146 because it has limited means of entry and exit, is not designed for continuous human occupancy, and may contain hazardous atmospheres. Before any inspector enters the scrubber, four conditions must be met. Condition 1 — the scrubber is isolated from the process gas source by a blind flange or a locked valve, not by a closed valve alone. Condition 2 — the recirculation pump is locked and tagged out, and the electrical disconnect is verified in the off position. Condition 3 — the scrubber sump is drained, and the interior is ventilated with a blower rated for the vessel volume at a minimum of 4 air changes per hour for at least 30 minutes before entry. Condition 4 — the atmosphere inside the scrubber is tested for oxygen content (19.5 to 23.5 percent), lower explosive limit (below 10 percent), and toxic contaminants specific to the process (H₂S, CO, Cl₂, HCl, NH₃, or others depending on the application). The atmospheric testing results must be documented on the confined space entry permit and reviewed by the entry supervisor.
Tools and equipment for a standard scrubber inspection include: a flashlight with at least 500 lumens (two flashlights recommended in case one fails), a stainless steel ruler or caliper for fouling thickness measurement, an ultrasonic thickness gauge for FRP or steel shell thickness measurement, a Barcol hardness tester for FRP cure assessment, a spray pattern test kit or a bucket and stopwatch for nozzle flow verification, a camera with date/time stamping for photographic documentation, a marking crayon for identifying defects, inspection mirrors for viewing behind packing support grids, and the scrubber inspection checklist template printed on waterproof paper. All tools must be non-sparking if the scrubber has handled flammable gases. Personal protective equipment for scrubber entry includes a hard hat, safety glasses with side shields, a full-body harness with a retrieval line attached to a tripod or davit arm, chemical-resistant boots and gloves appropriate for the scrubbing chemistry, and a Tyvek suit if the interior surfaces are contaminated with hazardous residues. The average scrubber inspection takes 4 to 8 hours depending on the vessel diameter and the number of packed beds. Plan for a single inspector to spend 30 to 45 minutes inside the vessel, with a standby attendant outside at all times. Have the scrubber inspection checklist ready before entry so every item is checked systematically without relying on memory.
General External Inspection
The external inspection is performed before the scrubber is opened for internal entry. It takes approximately 1 hour and covers the vessel exterior, connected piping, instrumentation, and structural supports. Many defects are visible from the outside and can be addressed during the same shutdown without requiring a second outage.
Vessel exterior condition. Inspect the entire FRP or PP vessel exterior for cracks, crazing, UV degradation, or impact damage. FRP exposed to sunlight develops a chalky surface layer over time — this is cosmetic and does not affect structural integrity as long as the depth of degradation is less than 0.5 mm. Check the exterior at all support saddles and attachment points, where stress concentration can cause cracking. Tap the exterior shell with a plastic mallet at 1-foot intervals around the vessel circumference at three elevations: bottom third, middle third, and top third. A dull or hollow sound indicates delamination between the FRP layers. Mark any delaminated areas with a marking crayon for ultrasonic thickness measurement during the internal inspection.
Piping and valve inspection. Inspect all connected piping for leaks at flanges, threaded connections, and valve packing glands. Check the recirculation supply pipe for external corrosion or pitting, particularly at the pump discharge where velocity is highest. Verify all isolation valves operate through their full range of motion — open to closed — without binding. A valve that does not operate smoothly should be scheduled for overhaul or replacement during the shutdown. Check flexible connections (expansion joints, vibration isolators) for cracking, swelling, or signs of chemical attack. A flexible connection that shows any cracking should be replaced before the scrubber returns to service.
Instrumentation check. Verify each instrument is within its calibration date. Remove the pH probe from its holder and inspect the glass bulb for cracks, coatings, or physical damage. Check the differential pressure transmitter impulse lines for blockage or liquid accumulation by opening the bleed ports at the transmitter. A steady stream of liquid from the bleed port indicates the impulse line is clear. A slow drip or no flow indicates a blocked line that needs to be rodded out or blown clear before the scrubber returns to service. Verify the flow meter sensor face or electrodes are clean and free of coating. A handheld communicator, if available, can be used to check the flow meter’s internal diagnostics for electrode fouling or empty pipe alarms.
Support structure and foundations. Inspect the scrubber support steel for corrosion, particularly at the base plates where moisture and chemical spillage accumulate. Check anchor bolts for tightness — a hammer strike to the bolt head should produce a clean ring, not a dull thud. Inspect the foundation concrete for cracking, spalling, or erosion around the base of the vessel. A foundation that has settled more than 1/4 inch out of level should be evaluated by a structural engineer before the scrubber is returned to service. Check all access platforms, ladders, and handrails for structural integrity and compliance with OSHA walking-working surfaces standards.
Packed Bed Inspection
The packed bed is the heart of the scrubber. If the packing is fouled, damaged, or channeling, the scrubber cannot achieve its design removal efficiency regardless of how well the other systems perform. The packed bed inspection is performed after the packing surface is exposed by removing the access hatch at the top of the packed section. The inspector should enter the scrubber through the side manway above the packed bed and work downward across the packing surface.
Packing surface condition and fouling assessment. Visually inspect the packing surface for three types of deposits: chemical scale (white, gray, or tan crystalline deposits), biological growth (brown, green, or black slimy film), and particulate solids (dust, corrosion products, or process debris). Measure the fouling thickness at five locations across the packing surface — center and four quadrants — using a stainless steel ruler inserted between the packing elements. Record the thickness at each location in millimeters. Acceptable: average fouling thickness less than 3 mm across all five locations. Marginal: average fouling thickness 3 to 8 mm — schedule a chemical wash within 30 days. Unacceptable: average fouling thickness greater than 8 mm or any location with fouling bridging between adjacent packing elements — perform a chemical wash or packing replacement before the scrubber returns to service.
Packing depth and settlement measurement. Measure the distance from the top of the packed bed to a fixed reference point such as the top of the packing support grid or the vessel shell flange. Compare this measurement to the as-installed packing depth recorded in the scrubber documentation. Acceptable: settlement less than 3 percent of the installed packing depth. Marginal: settlement 3 to 8 percent — top up with additional packing elements at the next shutdown. Unacceptable: settlement greater than 8 percent or visible gaps between the packing bed and the vessel wall — remove and reinstall the packing to eliminate channeling paths. A typical 10-foot packed bed that has settled 6 inches has lost approximately 5 percent of its effective height and 10 to 15 percent of its mass transfer capability because the gas preferentially flows through the settled gap at the vessel wall.
Channeling detection. Channeling paths are visible as areas where the packing surface is lower than the surrounding bed, creating a funnel-shaped depression. These depressions allow gas to bypass the packed bed through a low-resistance path. Probe each depression with a ruler to measure its depth. A channeling path more than 2 inches deep and wider than 4 inches must be corrected by redistributing the packing. Channeling is most common at the vessel wall where the packing settles away from the shell, creating a gap of 1/2 to 2 inches. This wall gap can be eliminated by installing a packing retaining ring during the next packing replacement.
Packing support grid integrity. The packing support grid carries the weight of the packed bed plus the liquid holdup. Inspect each grid member for deflection, corrosion, cracking, or FRP delamination. The grid should show no visible sagging between support points. Measure the deflection of each grid member with a straightedge. Acceptable: deflection less than 1/4 inch. Marginal: deflection 1/4 to 1/2 inch — monitor and re-inspect at the next shutdown. Unacceptable: deflection greater than 1/2 inch or any cracked or delaminated grid member — replace the affected grid section before the scrubber returns to service. A support grid failure during operation can dump the entire packed bed into the sump, causing pump blockage, impeller damage, and a minimum of $15,000 in repair costs plus lost production.
Fouling thickness measurement protocol. For consistent year-to-year comparison, always measure fouling thickness at the same five marked locations. Use a stainless steel ruler — not a tape measure or a gauge — inserted perpendicular to the packing surface. Record the thickness in millimeters and take a photograph with a reference object for scale. The five-location average is the key trending metric on the scrubber inspection checklist. An increase of 0.5 mm per month or faster indicates that the blowdown rate, water chemistry, or inlet particulate loading needs adjustment. An increase of less than 0.2 mm per month is normal for most scrubber applications and can be managed with scheduled chemical washes at 12 to 24 month intervals.
FRP and PP Shell Inspection
The scrubber shell provides the structural containment for the gas and liquid phases. FRP (fiberglass-reinforced plastic) and PP (polypropylene) shells degrade through chemical attack, thermal degradation, and mechanical stress. The shell inspection is the most critical part of the scrubber inspection checklist because a shell failure — unlike a packing or nozzle failure — cannot be repaired during operation and typically requires an emergency shutdown. The internal shell inspection is performed after the packing and internals are removed or moved aside for access.
Corrosion barrier assessment. The corrosion barrier is the inner 2.5 to 5.0 mm of the FRP laminate, consisting of a resin-rich layer and a veil mat. Inspect the entire interior surface of the scrubber shell from the sump floor to the mist eliminator support. Look for areas of softening, discoloration, fiber exposure, or resin loss. Press the surface firmly with a dull screwdriver or a wooden dowel — if the screwdriver penetrates the surface or leaves a visible indentation, the corrosion barrier has been compromised. Acceptable: surface is hard, no fiber exposure, no discoloration beyond a slight yellowing. Marginal: surface is slightly soft (screwdriver leaves a mark but does not penetrate), or isolated fiber exposure in an area smaller than 4 in² — schedule repair within 90 days. Unacceptable: screwdriver penetrates the surface, fiber exposure in an area larger than 4 in², or any area where the corrosion barrier has blistered and delaminated — repair or recoat before the scrubber returns to service.
Blister and delamination detection. Blisters appear as raised bumps on the interior surface, ranging from 1 mm to 20 mm in diameter. Count the number of blisters per square foot and measure the diameter of the five largest blisters. Acceptable: fewer than 10 blisters per ft² with none larger than 5 mm diameter — cosmetic, no action required. Marginal: 10 to 20 blisters per ft² or any blister 5 to 10 mm in diameter — monitor at the next shutdown and investigate the cause (osmotic pressure, temperature excursion, or chemical attack). Unacceptable: more than 20 blisters per ft² or any blister larger than 10 mm — the corrosion barrier integrity is compromised and requires recoat or relining. Blisters that have ruptured and are weeping liquid indicate active chemical attack on the structural laminate and require immediate repair regardless of the blister count.
Ultrasonic thickness measurement protocol. Ultrasonic thickness measurement (UTM) is the primary method for quantifying the remaining shell thickness. This is the most data-intensive item on the scrubber inspection checklist. Mark 12 permanent measurement locations on the exterior shell: four quadrants at three elevations — lower shell at sump level, mid-shell at the packed bed midpoint, and upper shell above the mist eliminator. Measure and record the thickness at each location in millimeters using an ultrasonic thickness gauge calibrated for the shell material. Compare each reading to the original design thickness. Acceptable: remaining thickness greater than 85 percent of original at all locations. Marginal: remaining thickness 70 to 85 percent of original at any location — increase inspection frequency to every 6 months. Unacceptable: remaining thickness less than 70 percent of original at any location — schedule a structural evaluation and plan for repair or replacement. A 5-year UTM database showing a consistent thickness loss of 0.3 to 0.5 mm per year allows accurate prediction of remaining service life and eliminates emergency shell failures.
Weld and joint inspection. Inspect all PP welds (butt welds, fillet welds, extrusion welds) for cracks, pinholes, or discoloration. A sound PP weld has a consistent bead width with no visible voids or burn marks. Tap the weld along its length with a plastic mallet — a cracked weld produces a different sound than a sound weld. For FRP vessels, inspect all secondary bond joints (where the shell is joined to the bottom head or top head) for separation or delamination. The joint between the shell and the bottom head is the most critical — a failure at this location releases the entire scrubber contents. Mark any weld defect with a crayon and photograph it with a reference scale.
Waterline and sump area inspection. The sump area experiences the most severe chemical and thermal exposure because the scrubbing liquid collects at the highest concentration of reaction products. Inspect the sump floor and walls for pitting, erosion, and chemical attack. Pay particular attention to the area at the normal liquid level line, where wet-dry cycling accelerates degradation. Measure the depth of any pits with a depth gauge. Acceptable: pitting depth less than 1 mm. Marginal: pitting depth 1 to 3 mm — monitor and measure at each shutdown. Unacceptable: pitting depth greater than 3 mm or any pit that penetrates through the shell wall — repair before returning to service. The sump drain nozzle and the pump suction nozzle should be inspected internally for erosion at the trailing edge of the nozzle bore, where the velocity is highest.
Mist Eliminator Inspection
The mist eliminator removes entrained liquid droplets from the exhaust gas before it leaves the scrubber. A failed mist eliminator causes liquid carryover, which is a visible emission that violates the facility’s air permit. The mist eliminator is inspected from both the top and bottom sides. Access is typically through a manway above the mist eliminator support grid.
Vane-type eliminator inspection. Vane-type (chevron) mist eliminators consist of a series of corrugated plates that force the gas to change direction, causing droplets to impinge on the vane surface. Inspect each vane section for solids buildup between the vanes. Solids accumulation reduces the open area, increases the gas velocity through the remaining openings, and causes re-entrainment of captured liquid. Measure the open area blocked by solids at three locations across each vane bank. Acceptable: less than 20 percent of the vane cross-section blocked. Marginal: 20 to 40 percent blocked — schedule cleaning during the current shutdown using a 3,000 to 5,000 psi water spray. Unacceptable: more than 40 percent blocked or any vane section with complete bridging between adjacent vanes — clean immediately or replace the affected vane section. After cleaning, inspect the vanes for pitting, erosion, or perforation from chemical attack. Vane material in corrosive service should be the same alloy or FRP grade as the scrubber shell. Check the vane-to-housing seal at each end of the vane bank. A gap of more than 1/4 inch between the vane pack and the vessel wall allows gas to bypass the eliminator entirely, carrying mist directly to the stack. Seal any bypass gaps with a high-temperature silicone or a compressible gasket material rated for the service temperature and chemistry.
Mesh pad eliminator inspection. Mesh pad mist eliminators consist of a knitted wire or plastic mesh held between two support grids. They are more prone to fouling than vane-type eliminators because the tortuous path traps both droplets and solids. Inspect the mesh pad from both sides. Look for solids accumulation that bridges the mesh openings, physical damage to the mesh structure, and corrosion of wire mesh materials. Measure the pressure drop across the mesh pad with a manometer if the scrubber is equipped with pressure taps above and below the eliminator. A clean mesh pad shows 0.5 to 1.5 in. W.G. pressure drop at design flow. A pressure drop above 2.0 in. W.G. indicates fouling that requires cleaning or replacement. Mesh pads cannot be effectively cleaned in place — the standard practice is to remove the pad, lay it flat, and wash it with a 3,000 psi water spray, then dry and reinstall. If the mesh is corroded or damaged, replacement is the only option. The replacement cost for a typical 8-foot-diameter mesh pad mist eliminator is $1,500 to $4,000 depending on the material.
Solids buildup measurement. Measure the thickness of solids buildup on the mist eliminator at three locations: the leading edge (facing the gas flow), the midpoint, and the trailing edge. The leading edge accumulation is typically 2 to 5 times thicker than the trailing edge because impingement captures solids at the entry. Record the maximum buildup thickness and the percentage of eliminator cross-section blocked. A buildup of more than 5 mm on the leading edge of a vane-type eliminator reduces efficiency and should be removed during the shutdown.
Structural support check. The mist eliminator support grid must carry the weight of the eliminator plus any accumulated solids, which can add 50 to 100 percent to the design load. Inspect the support grid for deflection, corrosion, or weld failure at the grid-to-shell connection points. A support grid that has sagged more than 1/2 inch between support points should be reinforced or replaced during the shutdown. A mist eliminator support failure during operation can drop the entire eliminator assembly into the packed bed below, blocking gas flow and requiring an emergency shutdown that costs $20,000 to $50,000 in lost production and repair.
Liquid Distribution System Inspection
The liquid distribution system delivers scrubbing liquid evenly across the packed bed cross-section. Uneven liquid distribution is the leading cause of reduced removal efficiency in scrubbers with normal pH and normal ΔP readings. The liquid distribution inspection covers the distribution nozzles, the distribution piping, and the distribution troughs or deck if present.
Nozzle spray pattern test. Each nozzle in the liquid distribution system must produce a uniform spray pattern within its design cone angle. Before the scrubber is opened for the internal inspection, perform a spray pattern test by running the recirculation pump at normal flow with the scrubber access hatch open and the packing below the nozzles removed. Observe the spray pattern from each nozzle. A healthy full-cone nozzle produces a solid cone of droplets with no gaps or streaks. A healthy hollow-cone nozzle produces a uniform annular pattern with no dripping from the center. Acceptable: all nozzles produce a uniform pattern within ±15 degrees of the design cone angle. Marginal: one or two nozzles show a partially blocked pattern — remove and clean those nozzles. Unacceptable: three or more nozzles show blocked or distorted patterns, or any nozzle is completely plugged — remove all nozzles, clean in a 5 percent acid bath, and test each one before reinstallation. A single completely plugged nozzle in a 10-nozzle array reduces liquid distribution uniformity in that sector by 100 percent and creates a dry zone in the packing below that reduces overall removal efficiency by an estimated 8 to 12 percent.
Orifice condition and blockage check. Remove each nozzle and inspect the orifice for scale, debris, or erosion. Calcium carbonate scale in caustic scrubbers deposits preferentially at the orifice exit where the pressure drop causes CO₂ release and localized pH increase. Measure the orifice diameter with a pin gauge and compare to the original specifications. Acceptable: orifice diameter within ±5 percent of design. Marginal: orifice diameter 5 to 15 percent reduced by scale or enlarged by erosion — clean or replace as appropriate. Unacceptable: orifice diameter more than 15 percent from design or any nozzle with a cracked or chipped orifice — replace the nozzle. Nozzle replacement cost is $15 to $80 per nozzle depending on material and type. Replacing a full set of 10 to 20 nozzles costs $150 to $1,600 in materials and 2 to 4 hours of labor.
Distribution troughs and piping. Inspect the distribution troughs or deck for levelness, solids accumulation, and corrosion. A distribution trough that is not level by more than 1/8 inch per foot of trough length creates an imbalance in liquid flow to one side of the packed bed. Check the trough weirs for nicks, corrosion, or buildup that would distort the weir overflow pattern. Inspect the liquid distribution piping for internal scale or debris accumulation. The distribution pipe is most vulnerable to blockage at the end cap, where solids carried in the recirculation flow settle and accumulate over time. Remove the end cap of the distribution header and flush the pipe with clean water to verify it is clear of debris.
Flow distribution uniformity. The overall flow distribution uniformity can be assessed by measuring the liquid flow rate at each distribution point or by performing a dye test. Add a food-grade dye to the recirculation sump and observe the color distribution across the packing surface through the access hatch. Uniform color across the entire packed bed cross-section within 30 seconds of dye injection confirms acceptable liquid distribution. Patchy or delayed coloration indicates uneven distribution that requires investigation. A quantitative alternative is to collect the liquid flow from each distribution nozzle individually using a graduated bucket and stopwatch during the spray pattern test. Individual nozzle flow rates should be within ±10 percent of the average flow rate for all nozzles. Any nozzle that deviates by more than 15 percent should be cleaned or replaced.
Sump and Recirculation System Inspection
The sump collects the scrubbing liquid after it passes through the packed bed. The recirculation system delivers it back to the distribution nozzles. The sump and recirculation system inspection covers the sump interior, the pump strainer, the suction piping, and the bleed and makeup valve assemblies. These components are inspected after the sump is drained and the interior is ventilated for confined space entry.
Sump interior condition. Inspect the sump floor and walls for sludge accumulation, pitting, and chemical attack. Measure the sludge depth at the sump low point using a measuring rod. Acceptable: sludge depth less than 2 inches. Marginal: sludge depth 2 to 6 inches — schedule sump cleaning during the current shutdown. Unacceptable: sludge depth greater than 6 inches — the sump must be cleaned before the scrubber returns to service. Sludge accumulation reduces the effective sump volume, shortens the liquid residence time, and increases the solids loading on the recirculation pump strainer. The sump sludge composition provides valuable diagnostic information — white or gray sludge indicates precipitated chemical salts, brown or black sludge indicates biological growth or corrosion products, and gritty sludge indicates process particulate carryover. Record the sludge color and consistency in the inspection report for trend comparison with previous shutdowns.
Pump strainer and suction piping inspection. Remove the pump strainer cover and inspect the strainer basket for debris type and quantity. A clean strainer basket should have no visible debris on the upstream side. Photograph the debris before cleaning. Record the debris type (packing fragments, scale flakes, biological solids, process debris) and approximate volume in cubic inches. An increasing trend in strainer debris volume between successive shutdowns indicates a developing problem — packing breakdown, excessive scaling, or upstream particulate carryover — that should be addressed before it causes a strainer blockage during operation. Inspect the pump suction piping interior for scale, debris, or biological growth. A bore scope inspection of the suction pipe is recommended if the pipe diameter is less than 4 inches and cannot be visually inspected from the sump end. Check the suction pipe inlet for a vortex-breaking screen or baffle. If the screen is missing or damaged, the pump may pull air into the suction during low sump level conditions, causing cavitation that damages the impeller.
Bleed and makeup valve function check. The bleed valve controls the blowdown rate and directly affects the chemical balance of the recirculation liquid. Operate the bleed valve through its full stroke — from fully closed to fully open and back to closed. Verify the valve stem position indicator matches the actual valve position. Check for leakage past the seat when the valve is closed by observing the downstream sight glass or drain. A bleed valve that leaks when closed adds an uncontrolled blowdown of 1 to 5 GPM, which wastes caustic and increases water consumption by 500 to 2,500 gallons per day depending on the leak rate. The makeup water valve should be inspected using the same procedure. A makeup valve that leaks when closed adds excess water to the sump, diluting the scrubbing chemistry and increasing the blowdown requirement. Replace any valve that leaks past the seat or does not operate smoothly through its full stroke.
Heater and temperature control inspection. If the scrubber is equipped with a sump heater to maintain minimum operating temperature during cold weather, inspect the heater element for scale buildup, corrosion, and physical damage. Measure the heater element resistance and compare to the manufacturer’s specifications. Check the temperature sensor and controller calibration by comparing the sump temperature reading to a calibrated handheld thermometer immersed in the sump liquid (or residual liquid at the sump low point). A temperature sensor error of more than ±2°C should be corrected by recalibration or sensor replacement before the scrubber returns to service.
Post-Inspection Documentation and Reporting
The value of a scrubber inspection is determined by the quality of the documentation. An inspection that produces detailed, quantified, and photographed findings creates a baseline that makes every future inspection faster and more accurate. An inspection that produces a single paragraph saying “everything looks fine” has no value for trend comparison or maintenance planning. The scrubber inspection checklist documentation must include the following elements for each inspection area.
Inspection report template. Each inspection area requires five data fields: (1) the parameter measured, (2) the measured value, (3) the acceptance criteria, (4) the pass-marginal-unacceptable rating, and (5) the corrective action taken or recommended. Use a standardized template for all scrubber inspections so the data from successive inspections can be compared directly. The recommended format is a table with the five columns and one row per inspection item. A complete scrubber inspection report requires 25 to 35 rows covering all nine inspection areas. The report must include the scrubber identification number, the inspection date, the inspector’s name and certification, the date of the previous inspection, the operating hours since the previous inspection, and the current status of any open corrective actions from the previous inspection report.
Photographic documentation standards. Every finding with a marginal or unacceptable rating must be photographed with a reference object for scale. Recommended reference objects: a stainless steel ruler for fouling thickness and pit depth, a US quarter or a coin of known diameter for general area photos, and a color calibration card for photos that document discoloration or chemical attack. Each photograph must be labeled with the inspection area, the location within the scrubber (elevation and quadrant), the direction of the view, and the date. A minimum of 20 photographs per complete inspection is recommended, with at least 2 photographs of each inspection area showing the overall condition and any specific defects.
Severity rating system. Each inspection finding should be assigned a severity rating that determines the required follow-up action. Rating 1 — acceptable: no action required, re-inspect at the next scheduled shutdown. Rating 2 — marginal: corrective action recommended within 90 days or before the next scheduled shutdown, whichever comes first. Rating 3 — unacceptable: corrective action required before the scrubber returns to service. Rating 4 — critical: the condition poses an immediate safety or environmental risk and requires corrective action before the scrubber can be operated under any conditions. Any Rating 4 finding must be escalated to the facility manager and the scrubber OEM within 24 hours of identification.
Repair priority matrix. When the inspection identifies multiple defects, prioritize repairs using a simple matrix that combines the severity rating and the estimated repair cost. High-severity, low-cost items (for example, cleaning a partially plugged nozzle at $40 per nozzle) are done immediately during the shutdown. High-severity, high-cost items (such as replacing a corroded FRP shell section at $8,000 to $25,000) are scheduled for the next planned shutdown with a detailed scope of work prepared during the current shutdown. Low-severity, low-cost items are completed during the current shutdown if time permits. Low-severity, high-cost items are deferred to the next major shutdown with annual monitoring in the interim. The EPA wet scrubber monitoring reference provides additional guidance on performance indicators that should be tracked between inspections. The completed inspection report, including all photographs and repair recommendations, must be filed in the CMMS and retained for the life of the equipment. A scrubber inspection that is documented properly pays for itself by identifying problems while they are still repairable, before they become emergency shutdowns that cost 10 to 20 times more to address.
Scrubber Inspection Checklist FAQ
How often should a wet scrubber internal inspection be performed?
Minimum once per year for scrubbers in continuous service. The scrubber inspection checklist is designed for annual shutdown inspections. Scrubbers handling corrosive chemicals at temperatures above 60°C, scrubbers with a history of corrosion or fouling problems, and scrubbers operating near their design limits should be inspected every 6 months. The inspection frequency should be increased after any process upset, chemical spill, or temperature excursion that exceeds the scrubber’s design limits.
What is the most important part of a scrubber inspection?
The FRP or PP shell corrosion barrier inspection is the most critical because a shell failure cannot be repaired during operation and requires an emergency shutdown. The corrosion barrier condition determines the remaining service life of the scrubber. A scrubber with a compromised corrosion barrier has 6 to 18 months of safe operating life remaining before the structural laminate is affected.
How is packing fouling thickness measured?
Insert a stainless steel ruler between the packing elements at the same five marked locations during each inspection. Measure the fouling thickness at the center and four quadrants of the packing surface. Average the five readings. Acceptable: less than 3 mm average. Marginal: 3 to 8 mm. Unacceptable: greater than 8 mm or any bridging between adjacent packing elements.
What is Barcol hardness testing and why is it done?
Barcol hardness testing measures the degree of cure of the FRP resin. The tester presses a sharp indenter into the FRP surface and reads the resistance on a scale of 0 to 100. A reading above 35 on the interior corrosion barrier surface indicates the resin is properly cured. A reading below 35 indicates resin degradation from chemical attack or thermal exposure. Barcol hardness readings below 35 on more than 10 percent of the inspected surface area require further investigation and probable repair.
How do I inspect the mist eliminator?
Inspect from both the top and bottom sides. For vane-type eliminators, measure the percentage of cross-section blocked by solids at three locations. For mesh pad eliminators, check for bridging, corrosion, and physical damage. Measure the pressure drop across the eliminator if pressure taps are available — a clean eliminator shows 0.5 to 1.5 in. W.G. at design flow. A pressure drop above 2.0 in. W.G. indicates fouling that requires cleaning.
What tools are needed for a scrubber internal inspection?
500+ lumen flashlight, stainless steel ruler, ultrasonic thickness gauge, Barcol hardness tester, camera with date stamp, non-sparking tools, marking crayon, inspection mirror, and the inspection checklist template on waterproof paper. For confined space entry: full-body harness, tripod or davit arm with retrieval winch, atmospheric monitor calibrated for the expected contaminants, and continuous ventilation equipment.
How is ultrasonic thickness measurement performed on an FRP scrubber?
An ultrasonic thickness gauge sends a high-frequency sound wave through the FRP laminate and measures the time it takes for the echo to return from the back wall. The gauge converts the transit time to a thickness reading. The standard measurement locations are 12 permanently marked points on the exterior shell — four quadrants at three elevations. The remaining thickness is compared to the original design thickness to determine the corrosion rate and remaining service life.
What should be included in the scrubber inspection report?
The report must include the parameter measured, the measured value, the acceptance criteria, the pass/marginal/unacceptable rating, and the corrective action for each inspection item. Photographs of every marginal and unacceptable finding with a reference object for scale. Severity rating (1-4) for each finding. Comparison to previous inspection data. Repair priority matrix. The report should be filed in the CMMS and retained for the life of the equipment.
Conclusion: Make Inspection Data Drive Your Maintenance Decisions
A scrubber inspection checklist is only as valuable as the data it produces and the actions that follow. A well-designed scrubber inspection checklist ensures no critical component is missed and every measurement is recorded against the same criteria year after year. Measuring fouling thickness at the same five locations every year creates a trend that tells you whether your water chemistry program is working. Photographing the same FRP surface area every shutdown creates a visual record that shows you whether the corrosion rate is accelerating. Recording nozzle spray patterns every inspection tells you whether your preventive nozzle cleaning schedule is adequate. The facilities that get the most value from their scrubber inspections are the ones that treat the inspection report as a living document — comparing each year’s data to the previous year, trending the key parameters, and adjusting the maintenance program based on what the data shows. For OEM-grade scrubber inspection services or replacement parts, contact our applications engineering team at sales@xichengep.com or visit the Air Emissions contact page.