Highway & Rail Transit Tunnel Maintenance & Rehabilitation Manual
Chapter 3: Preventive Maintenance
A. Preventive Maintenance Of The Tunnel Structure
The primary objectives of incorporating regular preventive maintenance procedures into the tunnel structure and its systems are to provide a safe and functional environment for those who work in or travel through the tunnel and to extend its useful life. Since it is usually not possible to have advance knowledge of where structural defects will occur, it is important that regular in-depth inspections be performed in which structural defects are identified and subsequently scheduled for repair based upon their severity. Chapter 4 deals with methods for repairing such structural defects. Aside from predicting structural defects, there are other preventive maintenance tasks that can be performed regularly to ensure safe operation of the tunnel. These tasks include:
- Tunnel Washing
- Drain Flushing
- Ice/Snow Removal
- Tile Removal.
A description of each maintenance task is provided below.
1. Tunnel Washing
It is recommended that highway tunnels that utilize an interior finish, such as ceramic tile, porcelain enameled panels, etc., be washed according to the following procedure: first, spray tunnel with water or a water/detergent mixture if permitted and scrub with mechanically rotating brushes; second, rinse tunnel with water using high-pressure jets. The primary reason for performing tunnel washing is to maintain proper tunnel luminance, which is dependent on the reflectivity of the tunnel finish. Highway tunnels with unfinished surfaces (bare concrete or exposed rock) and rail transit tunnels do not typically require washings, because reflectivity of the surface is not critical.
The frequency of this procedure may vary for each tunnel owner and depends on environmental conditions. It is recommended that washings be suspended during winter months for tunnels that are located in a region where wintertime temperatures are below freezing. Another factor in determining frequency would be the average daily traffic (ADT) that uses the tunnel. Since most of the dirt is from vehicle exhaust and tire spray, tunnels with a lower ADT would not accumulate dirt as quickly and can be washed less frequently.
2. Drain Flushing
Roadway drain inlets or drainage troughs in the case of direct fixation track should be kept free of debris and should be flushed with water to verify that drains are operating correctly. This should be done on a semi-annual basis. For highway tunnels, it can be performed concurrently with tunnel washing since the flushing equipment will be available.
3. Ice/Snow Removal
In regions where the temperature within the tunnel drops below freezing, ice forms at locations of active leakage. When such ice could build up on the roadway or safety walk, it is critical that deicing agents be used to prevent accumulation of ice that could present a danger to automobile traffic or tunnel personnel using the safety walk. During these potential icing conditions, it is suggested that the tunnel be inspected daily to observe and to take action to mitigate such leakage.
Also, in similar regions where snow and ice may accumulate for a certain distance within the tunnel from the portals, it is essential that proper plowing be performed and deicing agents be applied to maintain safe traveling conditions. As can be expected, the frequency of such a task is dependent on the natural conditions that produce the snow and ice.
4. Tile Removal
During an in-depth inspection, areas of loose tiles should be identified and those that are in danger of falling should be removed. It is recommended that those loose tiles which remain be inspected on a quarterly basis to determine if more tiles need to be removed to ensure safety to the motorist. Another time of identifying and removing possible loose tiles is during the monthly tunnel washing procedure. Often, tiles will become dislodged during the scrubbing or pressure washing of the tunnel. Any new areas should be noted and added to the list of areas to be inspected on a quarterly basis. Any tiles that are removed should be scheduled for replacement.
B. Preventive Maintenance Of Mechanical Systems
The tunnel mechanical systems are comprised of multiple individual components, many of which must work together for the overall systems to function properly. Since these overall systems are critical for providing a safe environment for the tunnel users and staff, it is paramount that they be well maintained to prevent unforeseen breakdowns. To achieve this goal, it is recommended that a routine preventive maintenance program be developed that includes every major piece of equipment and that work orders be generated on a set schedule for the tasks that are to be performed. To assist in this process, multiple computerized database systems have been developed that can be adapted to a particular tunnel owner's needs. If a computerized database system is used, it would have the capability of storing historical repair, replacement, and cost data for use in properly predicting the life-cycle costs for a particular piece of equipment.
It is impossible for the scope of this manual to incorporate preventive maintenance procedures for every conceivable piece of equipment; however, the major components of the mechanical systems are included. Many tunnels may not utilize all of the components listed due to their size, location, or age; whereas, newer tunnels and tunnels yet to be built may incorporate new technologies that to date have not been addressed. For this reason, it is always necessary to follow the manufacturers' suggested preventive maintenance procedures for a given piece of equipment, particularly if it differs from that given below.
Also, it should be noted that the preventive maintenance functions given are sometimes general and therefore should be made specific to the actual equipment that exists in a particular tunnel. Table 3.1 lists the preventive maintenance functions for each of the major pieces of equipment or mechanical systems along with the suggested frequency for performing the preventive maintenance.
Table 3.01 - Preventive Maintenance of Mechanical Systems Procedure Description Frequency Weekly Monthly Bi-
Air Compressor Clean or replace air filters if necessary X Clean external cooling fans X Manually operate safety valves and drain tank X Inspect oil for contamination and change if necessary X Check belt tension, clean motor, and operate safety valves on receiver X Inspect for air leaks X Tighten or check all bolts and lubricate motor bearings X Inspect and clean compressor valves X Verify operation of low-level oil switch X Check all pressure and safety controls X Air Conditioning Unit Clean or replace air filters X Check coils and clean if necessary X Inspect controls and verify proper operation of unit X Boilers (Furnaces) Check chimney and flue for obstructions and make sure all joints are well supported and properly sealed X Lubricate pumps and motors as required X Clean entire boiler, inside and out X Replace fuel filter and oil atomizing nozzle X Check hot water levels and fill as necessary X Restart boiler and test burner performance, flue gas CO2, smoke, and temperature X Verify operation of all limit switches and primary controls X Test relief valve or safety valve (use extreme caution) X Chiller Check and lubricate compressors X Check safety controls X Clean and inspect barrel X Check and add chemicals (as indicated or as required) X CO Monitoring Equipment Local Sensors (Calibration and/or sensor replacement) X Vacuum Tubing (Leak Test) X Vacuum Pump (lubrication) X Central Sensor Calibration (as required by individual system) X Comparison Gas Refill (as required) X Cooling Towers Check and lubricate pumps and fans X Check safety controls X Clean sump X Check and add chemicals (as indicated or as required) X Domestic Water Pump and Tank Visually inspect pump (when accessible) X Lubricate pump and motor X Check pump operation in conjunction with well tanks X Lubricate ejector pumps X Measure water drawdown to verify proper operation X Check air pressure in tank and correct as necessary X Verify start and stop settings of pressure switch (differential should not exceed 172 kPa (25 psi)) X Drainage System Grate inspection X Flushing of inlet and piping system X Dewatering Pumps (Fixed and Portable) Clean and visually inspect X Lubricate pumps (prior to use for portable) X Emergency Eyewash If bacteria control solution is not used, flush and clean unit with pure water X Drain unit and flush and clean the storage tank and refill with water and water treatment X Exhaust Fans and Dampers (Not Tunnel Fans) Operate fans and motor operated dampers and listen for unusual noises and vibrations X Check bearings and inspect V-belts for tightness X Clean centrifugal wheel, inlet, and other moving parts X Lubricate shaft bearing pillow blocks and motor bearings X Fire Extinguishers Inspect each fire extinguisher in the tunnel X Fire Hydrants Grease top nut X Fire Lines Freeze Protection Pumps Clean and visually inspect X Lubricate and grease pumps X Heat Tracing Equipment Verify system operation (prior to system operation) X Fire Pumps Visually inspect pump X Operate pump X Lubricate pump, motor, and coupling X Operate pump and measure current X Check shaft endplay X Check and correct pressure gauges as required X Fire Pump Controller Exercise isolating switch and circuit breaker X Operate pumps from both alternate and primary power supplies X Conduct annual test of system including flow and no flow conditions in accordance with NFPA 72 X Fire Tank Fill Pump Visually inspect pump X Lubricate pump and motor X Fuel Oil Day Tank Inspect tank for damage, corrosion, or leakage on both inside and outside of tank. Perform during same week as boiler inspection X Hot Water Pump Visually inspect plumbing connections for signs of corrosion X Visually inspect exterior of water heater for signs of leakage X Lubricate pump and motor as required X Septic System Pump out tank (as indicated or as required) X Ejector Pumps Check local indications (verification of proper functioning from control panel) X Visually inspect pumps X Tunnel Fans Check motor bearings X Listen for any unusual noise or vibration X General cleaning of motor, interior and exterior X Disconnect motor from power supply and regrease, making sure chamber is 75 percent full of grease X Operate fan through entire range of speeds and note any noises or vibrations (Balance fan if required) X Inspect inside and outside of housing and impellor for wear, deterioration, or build-up of material X Inspect mounting bolts, anchors, and connections for failures or damage X Change oil in pillow blocks and drive guards (mineral oil is recommended) X Remove inspection cover from drive guard and inspect chain to verify proper lubrication and wear and adjust if necessary X Check all oils and greases for contaminants X Verify that any dampers operate properly through all positions, and lubricate if necessary X Unit Heaters Clean unit casing, fan, diffuser, coil, and/or motor thoroughly, and clean and repaint any corrosion spots on casing X Tighten the fan guard, motor frame, and fan bolts, and check fan clearances X Inspect any control panel wiring to ensure that the insulation is intact and that all connections are tight X Examine all heater and relay contacts for pitting or burning and replace if necessary X Lubricate motor if necessary X Check operation of hydronic controls Underground Fuel Oil Tank Remove liquid level sensor from reservoir to check low-level alarm X Immerse sensor into bucket of water to activate high-level alarm X Water Storage Tank Visually inspect tank exterior X Drain sediment X Observe water system operation and note any abnormal happenings X Measure water draw down to verify proper operation X Check air pressure in tank and correct as necessary X Verify start and stop settings of pressure switch (differential should not exceed 172 kPa (25 psi)) X Visually inspect tank interior X
C. Preventive Maintenance Of Electrical Elements
Similar to tunnel mechanical systems, many individual components make up the tunnel electrical systems. However, one difference is that many of the electrical components are interconnected and rely on each other for proper functioning of the entire system. Also, the electrical systems could be viewed with higher importance because the mechanical systems and other tunnel systems need electricity for them to function properly. Given the importance of an electrical system that is constantly being used and is vital for the overall safety of the tunnel, it is suggested that the preventive maintenance system that was recommended for the mechanical systems be adapted to include preventive maintenance functions for the electrical systems.
As with the mechanical systems, only the major components of the electrical systems are included herein. Many tunnels may not utilize all of the components listed due to their size, location, or age; whereas, newer tunnels and tunnels yet to be built may incorporate new technologies that to date have not been addressed. For this reason, it is always necessary to refer to the manufacturers' suggested preventive maintenance procedures for a given piece of equipment. Additionally, the InterNational Electrical Testing Association (NETA), in their Maintenance Testing Specifications (MTS-2001), provides detailed information and guidelines regarding maintenance of electrical equipment. More specifically, Appendix B of MTS-2001 provides recommended frequencies for maintenance procedures that are comparable to what is given in this section. Another reference is the National Fire Protection Association's NFPA 70B: Recommended Practice for Electrical Equipment Maintenance.
For the procedures given below to be performed efficiently and safely, it is recommended that in-house maintenance staff be trained in the current Occupational Safety and Health Administration (OSHA) and NFPA standards, including but not limited to NFPA 70E: Standard for Electrical Safety Requirements for Employee Workplaces. If the tunnel owner does not have qualified in-house personnel, it is recommended that an outside electrical testing agency be contracted that meets the requirements of NETA full membership. Also, a switching procedure and one-line safety diagrams of the electrical system should be prepared and posted in all electrical rooms.
As with the mechanical preventive maintenance functions, the electrical preventive maintenance functions given are sometimes general and should be made specific to the actual equipment that exists in a particular tunnel. Table 3.2 lists the preventive maintenance functions for each of the major pieces of equipment or electrical systems along with the suggested frequency for performing the preventive maintenance.
Table 3.02 - Preventive Maintenance of Electrical Systems Procedure Description Frequency Weekly Monthly Bi-
Closed Circuit TV Clean, align, and focus all cameras after tunnel washing X Emergency Lighting Operate test buttons on emergency light fixtures X Operate battery pack for emergency lighting for 90 minutes X Electrical Switchboard and Switchgear Inspect switchgear bus and connections by infrared scanning X Perform ultrasonic inspection of medium voltage switchgear bus supports, insulators, and barriers X Visually inspect all equipment for unusual conditions X Check tightness of all connections X Remove and replace defective lighting contacts X Review results of last visual, infrared, and ultrasonic inspection X After power shutdown, clean entire switchgear interior X Clean all bus insulators and check for cracks and chips X Clean, lubricate (if applicable), and verify operation of all control switches, auxiliary relays, and devices X Clean, lubricate, adjust, and add anti-oxidant grease to contacts of all disconnect switches X Clean and perform insulation resistance testing on all lightning arrestors X Perform insulation resistance testing on any bus bars X Perform calibration test and verify proper operation of all meters X Low Voltage Air Circuit Breakers Remove covers and thoroughly clean each breaker and contact surfaces X Apply anti-oxidant grease to breaker's main contacts X Lubricate and verify operation of all mechanisms X Apply current equal to 90 to 110 percent of the breaker trip coil setting to verify proper pick-up of tripping mechanism X Record trip times for long-time, short-time instantaneous, and ground fault breakers when passing loads equal to multiples of their listed ratings through each phase of the breaker X Measure contact resistance and adjust where possible X Perform and record results of insulation resistance test from each pole to other two poles and to ground X Clean and lubricate breaker carriage and racking mechanism on any draw out breakers X Molded Case Circuit Breakers Inspect breaker for proper installation X Remove cover (if possible) and fully clean interior and exterior X Inspect for burning, overheating, wear, and proper alignment X Perform contact resistance and insulation resistance measurements and test X Apply current equal to 300 percent of breaker rating to test the long-time element X Test and compare any breakers with instantaneous trip units to manufacturer's characteristic curve X Automatic Transfer Switch (600 Volt Class) After total outage is obtained, clean all contact surfaces, apply anti-oxidant contact grease, measure and record contact resistance, and make any adjustments if necessary X Lubricate bearings, links, pins, and cams X Perform insulation resistance test X Test all settings of voltage, frequency sensing, and timing relays X Low Voltage Insulated Cable (Less Than 600 Volts) Check all cable terminations for tightness X Perform and record results of insulation resistance test from each phase to the other two and to ground for one minute using a test voltage of 1,000 volts Direct Current (DC). Compare results with previous tests. X Electrical Transformer Inspect transformer connections by infrared scanning X Perform ultrasonic inspection of medium voltage bus supports, insulators, and barriers X Visually inspect all equipment for unusual conditions X Test transformer and circuit breaker insulating oil X Dry-Type Remove cover and visually inspect all cable/bus connections for evidence of overheating or burning, check for tightness and clean windings X Liquid-Filled Inspect transformers for leaks, deteriorated seals/gaskets, proper oil level, and test oil sample X Inspect transformer tank and cooling fins for corrosion, chipped paint, dents, and proper connection to ground X Inspect all bushings for cracks/chips, proper tightness, and evidence of overheating X Inspect all gauges and alarm devices X Clean core, coils, and enclosures and inspect any filters X Perform primary and secondary insulation resistance test where possible. X Perform polarization index test on transformers 500 KVA and larger X Perform turns ratio tests X Perform calibration test and verify proper operation of all meters X Fire Alarm System Perform all tests and inspections in accordance with NFPA 72 Make and file a permanent record of all inspections and tests conducted
Open primary power supply to fire alarm panel and note sounding of trouble alarm and light X Perform fire drill by use of drill switch on fire alarm panels, and check that all visual and audible signals emit a sound and tunnel SCADA system (if any) receives alarm X Visually inspect all supervisory and water flow alarms on any standpipe systems X Test all heat detectors with a calibrated heat source and replace all failed units X Test all smoke detectors by measuring and recording sensitivity; replace all failed units X Clean all smoke and heat detector housings and check battery voltage under load X Verify that proper alarm devices operate for the appropriate initiating device circuit X Verify that all remote annunciators operate X Check all lamps, alarm devices, and printers for proper operation X Make a discharge test of batteries to determine capacity for operating system for 24 hours X Generator Operate unit under load for 4 hours and check lubrication levels X Change oil, coolant, and filter X Compare nameplate information and connection with drawings and specifications X Inspect for proper anchorage and grounding X Perform insulation resistance test on generator winding with respect to ground and determine polarization index X Perform phase rotation test to determine compatibility with load requirements X Functionally test engine shutdown and alarm controls for low oil pressure, overtemperature, overspeed, and other features X Perform vibration base-line test and plot amplitude versus frequency for each main bearing cap X Perform load bank test and record voltage, frequency, load current, oil pressure, and coolant temperature at periodic intervals during test X Monitor and verify correct operation and timing of normal voltage-sensing relays, engine start sequence, time delay upon transfer, alternate voltage-sensing relays, automatic transfer operation, interlocks, limit switch functions, time delay and retransfer upon normal power restoration, and engine cool down and shutdown feature X High Voltage Disconnect Inspect disconnect switch bus and connections by infrared scanning X Perform ultrasonic inspection of medium voltage bus supports, insulators, and barriers X Visually inspect all equipment for unusual conditions X Busing Inspection Review results of last visual, infrared, and ultrasonic inspection X Check for proper tightness of all exposed bus connections X Thoroughly clean and check for cracks/chips of all bus insulators X Clean, lubricate (if applicable), and verify operation of all control switches, auxiliary relays, and devices X Clean, lubricate, adjust, and add anti-oxidant grease to contacts of all disconnect switches X Clean and perform insulation resistance test on all lightning arrestors X Perform insulation resistance test on any bus bars X Service Enclosed Air Break Switches After shutdown, clean and inspect entire switch mechanism X Check switch contacts for proper alignment and apply anti-oxidant grease to main contacts X Check switch's arcing contacts for proper opening sequence relative to main contacts X Inspect fuses and record size and type used X Clean all phase isolation barriers and check for contamination and corona damage X Thoroughly clean and check for cracks/chips of all insulators X Clean and perform insulation resistance test on all lightning arrestors X Inspect all ground connections X Perform contact resistance and insulation resistance tests and record results X Motor Control Center Inspect controller bus and connections by infrared scanning X Perform ultrasonic inspection of medium voltage bus supports, insulators, and barriers X Visually inspect all equipment for unusual conditions X Review results of last visual, infrared, and ultrasonic inspections X After power shutdown, clean entire controller interior X Check for proper tightness of all exposed bus connections X Clean all bus insulators and check for cracks and chips X Clean, lubricate (if applicable), and verify operation of all control switches, auxiliary relays, and devices X Clean, lubricate, adjust, and add anti-oxidant grease to contacts of all disconnect switches X Perform an insulating resistance and polarization test of the bus and the motor feeder with the motor connected X Test overloads at 125 percent and 600 percent of rating against the tripping curve X Perform calibration test and verify proper operation of all meters X Lighting Relays and Contactors Clean all contacts and replace all worn and pitted contacts X Check tightness of contactors X Measure load current and verify proper operation X Traffic Signals Inspect and verify operation of Lane Control Devices X Inspect and verify operation of Variable Message Signs X Clean, replace filter, tighten connections, replace lamps, etc. X Tunnel Control System Check all controls on consoles for proper operation of tunnel lighting and fans X Test all alarm and lights for proper feedback from devices X Check all connections for tightness X Clean cabinets X Tunnel Lights Verify proper operation of the lighting fixtures in the tunnel areas X Count and record number of lights out on night lighting and day lighting X Replace any inoperable bulbs or ballasts with similar or increased efficiency X Clean exterior of lenses on all lighting fixtures in the tunnel X If required clean interior of lenses X Perform group relamping for specific lamp types X Underground Tank and Piping Monitor Perform built-in test (if any) and verify that each circuit is operational. If not, identify circuit using troubleshooting guide and replace parts as necessary X
D. Preventive Maintenance Of Track Systems
1. Track and Supporting Structure
The track and its supporting structure should be inspected more frequently than other systems within a tunnel. In fact, the tasks of inspection and preventive maintenance may often overlap in order to make efficient use of the inspection and maintenance staff and equipment. This does not detract from the importance of proper documentation of the inspection process; it just allows for certain simple procedures to be performed immediately after the condition is discovered. This serves as a means of preventing any further degradation that could occur before a scheduled maintenance is performed. If items are going to be repaired or replaced, it is important that some internal guidelines be followed to ensure accuracy and consistency of repairs or new installations. In lieu of such guidelines it is recommended that the USDOT's Federal Railroad Administration - Office of Safety's Code of Federal Regulations for Title 49, Track Safety Standards Part 213 Subpart A to F, Class of Track 1-5 (TSS Part 213) be used.
Listed below are several preventive maintenance procedures that are recommended to prolong the working life of the track and the supporting structure.
a) Rail Lubrication
It is commonly known that periodic lubrication of curves can extend rail life. The lubricant should be placed on the gage face of the rail, with care taken to minimize the amount of lubricant to prevent migration to the top of the rail head. The application can be performed by hand, by the use of wayside lubricators (a train actuated device that first applies the lubricant to the wheel flanges and then subsequently to the rail), or by railcar-mounted lubricant sticks that apply a thin coat of grease to the gage face during train operation. The frequency of this procedure is based on durability or life expectancy of the lubricant used and the amount of train traffic to which the rail is subjected. The procedure can also be performed if excessive wear is identified during a routine inspection or if noise abatement is desired. Additionally, asphalt based dipping oil should be applied to tie plates and spikes when they are subjected to corrosive conditions. This oil can be applied using a spray machine.
b) Rail Grinding
In addition to removing defects that are identified using specialized rail defect detection equipment, performing scheduled "out-of-face" grinding and profile grinding of the rail head can help prevent the development of surface defects by optimizing the rail-wheel interaction. The frequency of this procedure is dependent upon the amount of gross tonnage traveling over the track and can range from one year for track with very high tonnages to five years for track with low tonnages.
c) Ballast Cleaning/Replacement
Within a tunnel, the ballast is not subjected to the sedimentation of fine particles within the voids due to excessive vegetation growth; however, if severe water infiltration exists, the ballast can be negatively impacted in a localized area. If known areas exist where the ballast is either being eroded or undermined by water flow, or being fouled with silt carried by the water infiltration, certain tasks can be periodically performed in lieu of addressing the water infiltration problem using methods given in Chapter 4. The ballast can be removed and cleaned using a ballast cleaner and subsequently replaced, or a new layer of ballast (track surfacing) can be applied to the affected area and tamped to match the specified cross section. The entire ballast section along the tunnel should be maintained at all times.
d) Tie Renewals
A routine program of replacing crossties that do not meet inspection standards should be implemented to ensure that the proper number of quality crossties are located within each length of rail.
e) Joint Maintenance
All joints should be fully bolted and the bolts should be retightened as required within a range of 9,070 to 13,610 kg (20,000 to 30,000 lb) per bolt for the initial tightening of a new bolt and between 6,800 to 11,400 kg (15,000 and 25,000 lb) per bolt for all subsequent retightening. It is recommended that the initial retightening be performed one to three months after installation and all subsequent retightening be done on an annual basis. Also, if initial petrolatum or petrolatum-based compound for preserving the joint is deficient, then a new coating should be applied. The spray method can be used so that the integrity of the joint is not disturbed.
As gage deficiencies are identified during inspection, regaging should be performed if changes in gage are severe or abrupt.
g) General Aligning
Independent of whether the track structure is direct fixation or ballasted construction, the general vertical and horizontal alignment should be periodically adjusted to conform to specified standards. This can be accomplished by using automatic track aligning equipment for ballasted track or by manually raising and lining direct fixation track and placing shims under the rail plates as necessary.
h) Spike Replacement
If it is suspected that stray current corrosion is occurring in a tunnel, the spike will most likely need to be replaced on a routine basis. The normal life expectancy of 25 years for spikes can be as little as 6 months if stray current corrosion is occurring in combination with the presence of moisture.
2. Power (Third Rail/Catenary)
a) Third Rail System
The proper operation and efficiency of third rail power systems is crucial to those tunnel track segments that contain them. Therefore, it is beneficial to perform routine inspections of the systems as outlined in the complementary Tunnel Inspection Manual and also to conduct routine preventive maintenance of certain elements that make up the third rail system. Possible procedures to accomplish this are listed below.
- Perform general aligning on third rail to ensure consistency with the running rails alignment.
- Periodically clean rail insulators to prevent stray current from entering the ground or supporting structures and increasing the amount of corrosion. This is especially true in wet environments near portals or areas of water infiltration within the tunnel since moisture also advances the onset of corrosion.
- Repair/replace deficient protection boards and brackets to ensure that they do not interfere with connections to the train or fail to provide safety to tunnel personnel.
- Repair/replace splices and joints that could be impeding the current flow for the contact rail or redirecting flow causing stray current corrosion.
b) Catenary System
Similar to the third rail power systems, catenary systems are crucial for the proper operation of the transit systems that utilize them. For that reason, it is necessary to perform regular preventive maintenance in addition to the periodic visual and in-depth inspections that are presented in the complementary Tunnel Inspection Manual. Apart from major repairs or complex preventive maintenance tasks, many of the suggested procedures below can be performed at the same time as the in-depth inspections in order to minimize disruption to the system's schedule.
- Replace broken, chipped, or otherwise deficient sheds on all insulators.
- Align hangers to vertical position and rectify condition that may have caused hangers to be out of alignment.
- Replace segments of contact wire with vertical thickness less than 10.7 mm (0.42 in).
- Remove, clean, and tighten "C" jumpers, feeder points, and full section overlap jumpers that have signs of corrosion or burning. Apply high melting point grease to all stranded conductors.
- Adjust contact wires at overlaps for proper matching alignment.
- Adjust turnbuckles on hangers of section insulators to keep units level.
3. Signal/Communication Systems
Signal/communication systems relate directly to the overall safety of the rail transit system. As ridership and train frequencies increase, so does the dependence on a reliable efficient method for maneuvering the cars through the system and for communicating with them during that process or during emergencies. Since a majority of the components that make up these systems are electric or electronic, their proper operation is or can be tested continuously. However, there are mechanical devices that are operated manually or by electric power that should be consistently maintained. Most problems with this equipment are identified during a routine inspection and thus can be fixed immediately or scheduled for immediate action. On the other hand, it is recommended that a routine program be implemented to lubricate moving components, clear debris from path of moving components, and replace light bulbs in crucial equipment.
E. Preventive Maintenance Of Miscellaneous Appurtenances
1. Corrosion Protection Systems
Corrosion protection systems may be used in either highway or rail transit tunnels. Two types of corrosion protection exist: cathodic protection and stray current protection. A description of each of these systems is provided below.
a) Cathodic Protection Systems
Cathodic protection systems are designed to protect any metal components of the tunnel structure or other systems (such as buried pipelines, surrounding buildings, or the rail system itself) from deteriorating prematurely due to corrosion resulting from the presence of any aqueous electrolyte. Corrosion from electrolysis is specifically prevalent in areas where moisture is present and where there are dissimilar metals attached together.
These systems may be as simple as providing connections between metal components and the ground so that electrolysis does not take place in the critical metal components. Also, passive cathodic protection systems with anodes buried in the ground, can be used to sacrificially attract the stray current away from the critical metal components. Another method is to counterbalance the effects of stray current by inducing an impressed current using rectifiers.
This section recommends maintenance procedures for effective and efficient operation of cathodic protection systems. As with other systems, specific cathodic protection components will vary from one tunnel to another depending on the how the original design provided protection. Therefore, for complex electrical components such as rectifiers, the manufacturer's recommended maintenance procedures will always take precedence over any recommendations given in this section. Any testing of the cathodic protection effectiveness shall be performed in accordance with the National Association of Corrosion Engineers (NACE) recommended practices and procedures. Also, ensure that any test equipment is in good operating condition and that the calibration effective period has not expired.
Perform electrical measurements (voltage and current) and inspection of a cathodic protection system annually. The electrical measurements and inspection will be performed to:
- Make certain that protection is being provided in accordance with established criteria in the design documents.
- Make required adjustment to accommodate changes.
- Locate areas of inadequate protection levels.
- Identify areas that may be affected by future or ongoing construction.
- Adjust frequency of test and inspections to reflect changes to field conditions, safety, and economic considerations.
- Select areas to be monitored more frequently.
- Provide additional equipment as needed to maintain an effective cathodic protection system.
- Assess the effectiveness of isolated joints and continuity jumpers to achieve proper isolation.
Perform semi-annual inspection and testing of the following cathodic protection equipment:
- All impressed current sources (rectifiers and power supplies).
- All impressed current protective devices (protective relays, circuit breakers, fuses, wiring, and lightning protection).
- Reverse current switches, diodes, fuses, and wiring.
Other remedial tasks that may be performed on the cathodic protection system could include the following:
- Replace anodes per manufacturers' criteria.
- Repair or replace any defective components of the cathodic protection system.
- Clean and coat as required to provide isolation.
- Repair or replace jumpers.
- Replace defective wiring.
- Remove any accidental metallic contact.
- Repair or replace any defective isolating device.
Sufficient testing should be performed following any adjustment to the cathodic protection system to assure proper protection to the tunnel structure and that no adverse effects will occur to other nearby structures.
b) Stray Current Protection Systems
Stray current occurs within DC electrified rail transit systems and in conjunction with moisture from water infiltration, can cause significant amounts of corrosion of tunnel and rail components. The risk of stray current corrosion can be reduced by increasing the resistance of the leakage path to the earth through increasing rail insulation, and reducing the amount of moisture present in the tunnel by addressing the water infiltration problem (as described in Chapter 4, Section A). Aside from the above measures, most new DC traction power systems in tunnels are designed to minimize leakage of DC stray currents. However, older tunnels may require that the DC systems be modified or retrofitted to eliminate corrosion resulting from DC stray currents.
2. Safety Walks, Railings, and Exit Stairs/Ladders
It is important to ensure that tunnel elements such as safety walks, railings and exit stairs/ladders that are accessed either by tunnel personnel or tunnel occupants in the event of an emergency, be properly maintained such that they will be able to support the pedestrian loadings during their use. This can be accomplished by providing the following preventive maintenance functions:
- Keep areas clean and free of debris. Do not use stairs or walkways as storage space.
- Do not allow water or ice to accumulate on these surfaces to prevent users from slipping and falling.
- Ensure that steel structures are adequately painted or pre-conditioned to prevent corrosion and subsequent reduction in load carrying capacity.
- Consider coating concrete or steel walking surfaces with an anti-slip finish.
- Maintain all doors or gates to guarantee proper operating condition. Also, do not lock doors or gates that are necessary for emergency exit.
- Ensure that all metal components are isolated from any electrification system.
3. Ventilation Structures and Emergency Egress Shafts
In rail transit systems, ventilation structures are often utilized in urban settings where tunnel intake or exhaust occurs through grates in the sidewalk or street above the tunnel. Subsequently, the air travels though a shaft structure that extends to the depth of the tunnel, which could be constructed from any of the same materials available for tunnel construction. If the routine inspection identifies structural deficiencies in this shaft or in emergency egress shafts, then they can be repaired using techniques given in Chapter 4. Otherwise, a preventive maintenance program should be instituted to ensure the following:
- Keep areas clean and free of debris. Do not use as storage spaces.
- Maintain grates at top of vent structures to prevent corrosion and dislodging, which could pose a safety hazard to pedestrians walking across the grating.
- Perform maintenance on any fans at top of vent structures as described in Section B of this chapter.