Glasslined Vessel Inspection: A Complete Guide
Glasslined vessels are critical in many industrial applications due to their corrosion resistance and durability. However, maintaining their integrity requires a disciplined inspection program. This guide outlines inspection procedures, frequencies, and best practices to ensure safe and efficient vessel operation.
Inspection Frequency
Before installation or startup, a baseline inspection must be completed for all equipment. This establishes a reference point for future evaluations.
Once in service, vessels should undergo routine inspections to monitor glass wear and overall condition. Operators must also be trained to recognize and report the following warning signs during daily operations:
Rust stains on the glass surface
Rust or liquid stains around tantalum repair plugs
Leaking gaskets
Corrosive liquids on the exterior surface
Glass fragments downstream
Nozzle loading issues
Seized J-bolts
Wet insulation
Qualified vessel inspections should initially be performed every 12 months. Based on historical data and wear rates, intervals may be adjusted. The goal is to record enough glass thickness readings to allow for accurate statistical analysis and predictive maintenance.
Inspection
A good preventative maintenance program includes routine scheduled inspections that provide numerous benefits. By consistently recording glass thickness, operators can make accurate estimates of a vessel's service life. Early detection of wear patterns also simplifies failure analysis and allows for smaller, less costly repairs.
For new vessels, inspections should be performed before removal from the carrier vehicle to ensure no damage occurred during transit. Additionally, a spark test should follow any major move, after installation, and once all piping is complete. Installed vessels should be inspected every 6 to 24 months while in operation to establish a baseline service record. This helps determine the wear rate of the glass lining and builds a comprehensive database that supports predictive maintenance of the vessel and its accessories.
Critical areas that require close monitoring include:
Manways
Bottom outlet
Nozzles
Agitator assembly
Leading and lagging edges of baffles
The 5-Step Inspection Process
A robust inspection consists of the following steps:
Vessel Mapping
Visual Inspection
Glass Thickness Measurement
Electric Testing
Data Analysis
1. Vessel Mapping
The first step in the inspection process is to create a detailed grid map of the vessel, which mirrors the inspection document. This grid allows for accurate location identification of each glass thickness measurement. Since glass thickness can vary by up to 15 mils within a square foot, properly locating and documenting each measurement point is essential. Vessel-specific data can typically be found on the nameplate or within the equipment file, and digital photographs—if permitted—can serve as valuable visual references for future inspections.
The top and bottom heads of the vessel should be mapped in degrees, using the manway as the 0° reference point, the baffle at 90°, and so on. Always reference both heads in relation to the manway. Sketch all critical components including the manway, its cover and attached nozzles, all process and baffle nozzles, dip pipes, side-entry nozzles, and bottom outlet nozzles. Be sure to include any vessel repairs, the agitation system, baffle configuration, drive system specifications, and relevant jacket piping.
CAUTION: Prior to vessel entry, all confined space protocols, lockout/tagout procedures, and nozzle blinding must be completed.
CAUTION: A qualified safety attendant must be stationed at the manway during any confined space entry.
Once inside, use a marker to replicate the vessel layout on the interior surface as outlined in the inspection sheet. Align the bottom and top head weld lines with the shell diagram on the inspection form. Mark at least three or more horizontal reference lines evenly spaced along the inside circumference, depending on vessel size:
200–1000 gallons: 3 lines
1500–4000 gallons: 4 lines
5000–8000 gallons: 6 lines
8000–12000 gallons: 8 lines
Apply vertical lines using the following references:
0° at the manway
90° to the left when standing outside the vessel
180° directly behind the agitator when standing at the manway
270° opposite 90°
For vessels over 4000 gallons, include 45° lines between the above points
This grid creates a series of squares that guide glass thickness readings. Begin measurements at any point, taking 2–3 readings per square and recording the average. This approach ensures a statistically accurate representation of overall glass thickness.
For the top and bottom heads, divide the area using vertical sidewall lines. Pay special attention to the bottom outlet and knuckle radius, both of which are high-wear areas due to frequent liquid drainage and exposure to sparging gases. The knuckle radius and adjacent sidewall may also be impacted by dip pipe discharge, abrasive materials, or chemical attack driven by impeller velocity. Thickness measurements should be taken from the outer diameter (OD) to the inner diameter (ID), with 2–3 readings per wedge section formed by the vertical lines.
Inspect the bottom outlet thoroughly, capturing thickness readings in the swage radius and nozzle neck. Similarly, examine all nozzles on the top head for wear caused by solids, liquids, static electricity, mechanical impact, or chemical exposure. Glass thickness should be measured in any suspect nozzles, particularly along the swage radius and neck.
Baffle & Agitator Inspection
Due to the high-speed operation of the drive system, the agitator is exposed to significant wear in multiple areas. To ensure thorough evaluation, both the agitator and baffle should be marked with at least four evenly spaced horizontal reference lines along their height.
For the agitator shaft, take two thickness readings at each level—positioned 180 degrees apart—to monitor wear symmetry. The baffle should be inspected at each level with readings taken on the leading edge, lagging edge, as well as on the side facing the vessel wall and the side facing the agitator.
Each agitator blade requires three readings: one on the leading edge, one on the lagging edge, and one at the blade tip. This comprehensive inspection helps identify early signs of wear and supports proactive maintenance planning.
2. Visual & Microscopic Inspection
A visual inspection is always the first step upon presentation of the vessel. Begin with a thorough examination of the exterior, focusing on key components and any signs of damage or wear, including:
This includes assessing the condition of the drive system and motor, mechanical seals, and the lubrication system.
Inspect all nozzle connections, flanges, and bolting for integrity, along with the clamps and gaskets.
Look closely for any rust stains, product buildup, or oil leaks around the nozzles, drive system, motor, or seals.
Also, check the condition of jacket connections, steam traps, pressure relief valves, and lower sealer ring drain valves.
Be sure to inspect the lower and upper sealer rings for leaks and note any evidence of product leakage into the vessel insulation.
CAUTION: Before entering the vessel, ensure all required entry and work permits are in place.
DANGER: A hot work permit is mandatory for any electric testing performed during this inspection phase.
For the internal visual inspection, the following tools are required:
A bright light
A 3x–5x magnifier
A low-power microscope
A clean damp cloth
Before entry, perform a preliminary scan of the vessel's interior for obvious signs of damage to the glass or steel surfaces, including:
Use a bright light to inspect flat surfaces and glass-lined areas within all nozzles.
Use a 3x-5x magnifier and 20x-30x microscope to closely evaluate questionable areas for signs of damage propagation such as delamination or stress lines.
Inspect the drive nozzle and baffle nozzles for wear, chemical attack, or impact damage
Gently move the agitator shaft laterally to check for excessive play; this may indicate gearbox failure.
Ensure the baffle is secure and does not move.
Check the valve stem beneath the agitator for signs of impact or wear.
3. Thickness Measurements
Several types of thickness gauges are available for measuring glass thickness, but it’s essential to select one that is properly calibrated and suitable for the application. Accurate readings depend on both the condition of the gauge and the surface being tested.
Key guidelines for glass thickness measurement:
Use a calibrated device capable of measuring between 10 to 125 mils.
Ensure the sensor head is clean and free from debris before use.
Clean all vessel surfaces to remove any residue prior to taking readings.
Record readings directly on the inspection form or relay them to the safety watch at the manway.
At GTI, the Fischer Scientific FMP-30 is the standard device used.
This unit includes a statistical analysis function for advanced tracking and evaluation.
4. Electric Testing
While new or reglassed equipment is typically tested at 15,000–25,000 volts in the plant, field testing is performed at a lower voltage—5,000–6,000 volts—to avoid exceeding the dielectric strength of the glass and causing potential damage.
Best practices for electric (spark) testing in the field:
Use a nonabrasive test probe to prevent scratching or marring the glass surface.
Ensure the glass surface is completely dry to avoid false readings caused by corona discharge.
Test each grid block both vertically and horizontally to achieve full surface coverage.
Use a paint marker to highlight any pinholes or damaged areas for follow-up.
Conduct a thorough inspection after the electric test to evaluate all highlighted areas.
Document all defects clearly on the inspection form for proper tracking and repair planning.
5. Data Analysis & Record Keeping
Maintaining detailed records is essential for monitoring the condition of a vessel and streamlining communication with offsite vendors regarding repairs or maintenance.
Best practices for inspection documentation:
Keep copies of all inspection reports—they are valuable references when discussing service or repairs with third parties.
Transfer handwritten forms to a digital format to ensure data is organized, legible, and easily shareable.
Photograph damaged areas and the overall vessel during each inspection to visually track wear and changes over time.
Store documentation in a centralized system—Glasslined Technologies, Inc. keeps all inspection records on a secure intranet for consistent access and historical tracking.
Final Thoughts
A successful glasslined vessel inspection program is proactive, not reactive. By implementing regular inspections and keeping detailed records, facilities can:
Extend the life of their vessels
Prevent costly failures
Schedule repairs more efficiently
Protect your investment—inspect regularly and record thoroughly.
