A good preventative maintenance program will include scheduled inspections
- An accurate estimate of the vessel service life can be made as glass thickness is recorded.
- Failure analysis is more easily performed as wear patterns are discovered early.
- Repairs are generally smaller and less expensive when detected early on
Installed vessels should be inspected every 6-12 months while in operation to establish a baseline service record to determine the wear rate for the glass lining. These inspections will build a database of data that can determine corrosion rates leading to predictive maintenance of the vessel and accessories.
Each vessel should undergo a 5 step process for accuracy.
A. Vessel Mapping
The first step is to map the vessel in a grid similar to the inspection document. This will provide a more accurate location identification for each measurement.
Glass thickness within a vessel can vary 10 mils within a square foot. Locating each point on the inspection form is very important.
Vessel data can be located on the nameplate or documents within the equipment file. Digital pictures are valuable as a visual record for future reference if authorized.
The Top and Bottom Head are laid out in degrees with the manway 0 degrees, baffle 90, etc… The top head and bottom head are referenced to the manway.
Draw in nozzles along with sizes starting with the Manway, indicate main cover openings along with attached nozzles, sketch all process nozzles baffle nozzles and dip pipes. All side entry nozzles should be included as well as bottom outlet nozzles.
Include any vessels repairs, agitation system, baffle configuration, drive system specifications and relative jacket piping.
Prior to vessel entry all confined space, lock out tag out, and nozzle blinding must be performed prior to entry.
Any confined space entry must have a qualified safety attendant stationed at the manway.
Inside the vessel use a marker to layout the vessel as shown on the inspection sheet.
The bottom and top head weld lines will correspond with shell diagram on the inspection form. Mark 3 or more horizontal lines equidistant along the inside circumference of the vessel for reference during the inspection..
Note: Vessels 200-1000 3 lines
Vessels 1500-4000 4 lines
Vessels 5000-8000 6 lines
Vessels 8000-12000 8 lines
Apply vertical lines as follows:
manway at 0 degrees
90 degrees left of manway standing outside
180 degrees directly behind agitator standing at manway
Vessels larger than 4000 gallons should have 45 degree lines.
The resulting squares will provide a guide for replicating glass thickness measurements.
Start glass thickness readings at any point. 2-3 readings per square with the average recorded will provide a more statistical accurate representation of overall glass thickness within the vessel.
The top head can be divided by the vertical lines on the sidewall.
The bottom head is divided by vertical lines on the sidewall. The bottom head can be subject to wear at the bottom outlet and the knuckle radius. Thickness readings are important in both areas.
The bottom outlet is a critical wear point as all liquids are drained and some gases are sparged through the valve into the vessel during operation.
The knuckle radius and adjacent sidewall are subject to effects of dip pipes, abrasion, and chemical attack related to the process velocity of the impeller tips.
Thickness readings on the top and bottom heads should be taken for OD to ID. 2-3 readings per wedge created by the vertical lines should be recorded.
The bottom outlet should be inspected closely for wear. Thickness readings should be taken on the swage radius and nozzle neck.
Nozzles on the top head should be inspected for wear points related to solids, liquids, static electricity, impact or chemical attack. Glass thickness should be recorded in susupect nozzles along the swage radius and neck.
Baffle & Agitator Inspection
The agitator is subject to wear in several areas as a result of the speed of the drive system.
The baffle and agitator should have at least 4 equally spaced horizontal lines. The agitator should have 2 readings at 180 degrees apart at each level.
The baffle should have readings taken on the leading edge, lagging edge, and on the sidewall and agitator sides at each level.
The agitator blades require 3 readings on the leading and lagging edges with an additional reading on the blade tip for each blade.
A visual inspection is always performed upon presentation. The exterior of the vessel will include:
The drive system and motor
Mechanical seals and lubrication system
Overall condition of all nozzle connections, flanges, and bolting.
Overall condition of clamps
Overall condition of gaskets
Note any rust stains or product buildup on the exterior of all nozzles
Note any oil leaks from the drive, motor, or seals.
Note condition of jacket connections, steam traps, pressure relief valves, lower sealer ring drain valves.
Check lower and upper sealer rings for leaks.
Note any product leaks into vessel insulation.
Prior to vessel entry ensure all entry permits, work permits are in force.
This phase of vessel inspection will require a hot work permit. This permit is required for electric testing of the vessel.
Prior to vessel entry observe the vessel interior for signs of obvious glass or steel damage.
During the visual stage of the inspection the following items are necessary:
A bright light
A 3x-5x magnifier
A low power microscope 20-30x
A clean damp cloth
A bright light is necessary to observe the glass in all nozzles and along flat surfaces inside the vessel.
The magnifier is essential in studying small damaged areas in much closer detail. This may be necessary to determine possible delamination or stress lines that may lead to propagation of damage . The strength of magnifier is related to the extent or size of the damaged area.
The drive nozzle and baffle nozzles should be inspected for wear or impact. The agitator shaft should be moved laterally to determine gearbox condition. Excessive movement indicates gearbox failure.
The baffle should be checked for movement.
Close inspection of the valve stem below the agitator for impacts or wear to the Teflon seat are necessary.
Several thickness gauges are available on the market to measure glass thickness. The device used must be calibrated and meet the ability to record thickness from 10 mils-125 mils in thickness. Ensure the sensor head is clean and free from debris for accurate readings.
All vessel surfaces must be clean and residue free.
Record vessel readings on the inspection form or relay readings to the safety watch at the manway.
While new or reglassed equipment is tested at 15k-25k in the plant field testing of vessels is performed at 5k-6k volts. The lower testing levels in the field is prevent damage to the vessel with higher voltage rates that may exceed the dielectric strength of the glass.
A nonabrasive test probe is recommended to prevent marring the glass surface.
The glass surface must be dry to prevent misleading corona discharges.
Test each block vertically and horizontally to ensure full coverage of the vessel. Use the paint marker to highlight a pinhole or damaged area. Further inspection will occur following thorough electric test. All damaged areas must be noted on the inspection form.
Handwritten inspection forms should be transferred to a computer generated model. Photos of damaged areas and the vessel are invaluable in determining progress over the life of a vessel.
Glasslined Technology, Inc., maintains a copy of all inspections on our intranet system indefinitely. Copies of inspection reports can be very useful when discussing repairs or maintenance with an offsite vendor.