Barksdale AFB Water Tanks Cathodic PWS 2021 (1).pdf

Performance Work Statement

CATHODIC PROTECTION SURVEYS AND

REPAIRS NINE (9) WATER STORAGE TANKS

BARKSDALE AIR FORCE BASE

28 June 2021

INTRODUCTION

These services relate to the assessment of cathodic protection systems afforded nine (9) water storage tanks within Barksdale Air Force Base. There are five (5) Ground Storage Fire Protection

Water Tanks and four (4) Elevated Potable Water Storage Tanks.

Ground Storage Fire Protection Water Tanks

Tank No. 7562 – This is a ground storage tank, with a diameter of 32 feet, a height of 45 feet and a capacity of 250,000 gallons. The tank is used to store fire protection water and was built in 1997. The tank is afforded an impressed current cathodic protection system consisting of an automatically controlled 30 volt – 18 amp rectifier in conjunction with five (5) TA-FW cast iron anodes. See Drawing A-1035-1 of Appendix L. The exterior bottom of the tank sets on compacted sand and is not afforded cathodic protection.

Tank No. 5857 – This is a ground storage tank, with a diameter of 64 feet, a height of 21 feet and a capacity of 500,000 gallons. The tank is used to store fire protection water and was built in 1955. The tank is afforded an impressed current cathodic protection system consisting of an automatically controlled 15 volt – 60 ampere rectifier in conjunction with twenty-four (24) type

FW cast iron anodes. See Drawing A-1035-2 of Appendix L. The bottom of the tank sets on compacted sand and is afforded a separate impressed current cathodic protection. This external system consists of a manually controlled 40-volt – 60-ampere rectifier in conjunction with four (4)

1½-inch diameter by 60-inch long cast iron anodes in 8-inch diameter by 84-inch long canisters.

Tank No. 6800 – This is a ground storage tank, with a diameter of 70 feet, a height of 20 feet and a capacity of 500,000 gallons. The tank is used to store fire protection water and was built in 1986. The tank is afforded an impressed current cathodic protection system consisting of an automatically controlled 24 volt – 12 ampere rectifier in conjunction with nine (9) type FW cast iron anodes. See Drawing A-1035-3 of Appendix L. This tank sets on compacted sand pad and is not afforded external cathodic protection.

Tank No. 7722 – This is a ground storage tank, with a diameter of 35 feet, a height of 22 feet and a capacity of 500,000 gallons. The tank is used to store fire protection water and was built in 1986. The tank is afforded an impressed current cathodic protection system consisting of manual controlled 40 volt – 10 ampere rectifier in conjunction with twenty-one (21) type TA-FW cast anodes. See Drawing A-1035-4 of Appendix L. The bottom of the tank sets on compacted soil and is afforded a separate impressed current cathodic protection. This system consists of a manually controlled 40-volt – 10-ampere rectifier in conjunction with eight (8) 1½-inch diameter by 60-inch long cast iron anodes in 8-inch diameter by 84-inch long canisters. Both rectifiers were replaced in

2012.

Tank No. 6209 - This is a ground storage tank, with a diameter of 26 feet, a height of 11 feet, a capacity of 40,000 gallons and was constructed in 2007. The tank is used to store fire protection water. The tank is afforded an impressed current cathodic protection system consisting of an automatically controlled 24-volt – 12-ampere rectifier in conjunction with three (3) type FW cast iron anodes. See Drawing A-1035-5 of Appendix L. This tank sets on compacted sand pad and is not afforded external cathodic protection.

Elevated Potable Water Storage Tanks

Tank No. 7298 – This is an elevated spheroid potable water storage tank, with a bowl diameter of 28 feet, a bowl height of 28 feet. The 200,000-gallon tank was built in 2015. The cathodic protection system is of the impressed current type, with a 30 volt – 8 ampere automatic potential control rectifier and five (5) mixed metal ribbon anodes in the bowl. See Drawing A-

1035-6 of Appendix L.

Tank No. 7417 – This is an elevated potable water storage tank, with a bowl diameter of

34 feet, a bowl height of 18 feet, and a riser pipe height of 104 feet. The 100,000-gallon tank was built in 1955. The tank is afforded an automatically controlled impressed current cathodic protection system to protect the bowl and riser pipe. There are thirty (30) type FW cast iron anodes in the bowl and fourteen (14) type FW cast iron anodes in the riser pipe. See Drawing A-1035-7 of Appendix L.

Tank No. 1358 – This tank is an elevated potable water storage reservoir with a capacity of

500,000 gallons. The tank was built in 1942. The tank is afforded an automatically controlled impressed current cathodic protection system to protect the bowl and riser pipe. The anodes were replaced in 2016. There are five MMO anode assemblies in the bowl and one MMO anode within the wet riser. See Drawing A-1035-8 of Appendix L.

Tank No. 4490 – This is an elevated potable water storage tank, with a bowl diameter of

50 feet, a bowl height of 50 feet, and a riser pipe height of 100 feet. The 500,000-gallon tank was built in 1994. The tank is afforded an automatically controlled impressed current cathodic protection system to protect the bowl and riser pipe. The anodes were replaced in 2016. There are five MMO anode assemblies in the bowl and one MMO anode within the wet riser. See Drawing

A-1035-8 of Appendix L.

Since all of the metal tanks contain water, the submerged surfaces will be subject to corrosion. The rate of corrosion is dependent on the water conductivity and chemical make-up.

The potable water within Barksdale Air Force Base is considered moderately aggressive to carbon steel. The water tanks would be expected to experience an undesirable degree of long-term metal loss due to corrosion. As a primary means of corrosion control, the tanks were coated inside and out when constructed. The coating acts as a barrier between the steel and water or condensation.

As long as the coating remains in place, no corrosion will occur. However, no coating is perfect when applied. Additional long-term coating loss is also expected due to leaching and abrasion.

Corrosion will occur to areas of coating loss. Typically, the rate of corrosion above the water line and on the outside of the tank is relatively low. These areas can also be accessed to repair the coatings. The rate of corrosion under the water can be aggressive, and it is often not practical to repair the coatings.

To control corrosion on the submerged steel, cathodic protection has been installed.

Cathodic protection is an electro-chemical method by which a DC current is applied to the metal surface. Through a series of electro-chemical reactions, the metal surface is passivated. However, it is important to ensure that sufficient cathodic protection is being applied to achieve corrosion control. This is a function of design and maintenance. Each of the subject water storage tanks utilizes impressed current type cathodic protection systems. A rectifier is mounted at each tank and converts AC power to DC output. The DC current is fed via cables to anodes suspended in the water within each tank. All of the elevated water tanks have anodes suspended down the wet riser pipes. The current returns to the rectifier via a cable connected to each tank. To monitor protection levels, permanent reference cells are suspended in the water within each tank. These cells monitor the electro-chemical potential of the metal, which determines its passivity.

The underside of the floor plates of the on-grade water storage tanks are in contact with the soil. Therefore, the exterior floors are subject to corrosion losses. Tanks No. 5857 and 7722 are afforded external cathodic protection systems to control this corrosion. The systems consist of 1½-inch diameter by 60-inch long cast iron anodes furnished in 8-inch diameter by 84-inch long coke breeze filled canisters drilled vertically into the soil around the tanks. The anodes are energized by manually controlled rectifier units.

In accordance with Air Force Policy and Industry Standards, cathodic protection systems within water storage tanks are to be monitored annually by a corrosion professional. The assessments are to include inspections of the rectifiers and components and obtaining electro-chemical potential profiles. This project was initiated to conduct the recommended assessment of the water tank cathodic protection systems, and the general condition of the coatings.

Tanks No. 8119, 8077, and 7291 have been permanently taken out of service and demolished. Tank No. 6209 was added in 2007. Tank No. 7298 was constructed in 2015.

SCOPE FOR SURVEY, CALIBRATION AND REPORT

1. Scope: Work shall consist of furnishing all labor, tools, equipment, materials, and transportation necessary to perform a water tank calibration survey of the cathodic protection (CP) systems in four elevated water tanks and five ground level water tanks located on Barksdale AFB, LA. All tanks are in service and have sufficient water for the operation of the CP systems. Surveys shall be performed

IAW MIL-HDBK-1136. Please see link for digital copy of MIL-HDBK-1136.

https://static.e-publishing.af.mil/production/1/af_a4/publication/afh32-1290(i)/afh32-1290(i).pdf

2. Background: Within Barksdale AFB, water is stored within nine (9) tanks for potable and fire protection service. The tanks are constructed of welded or riveted carbon steel. Since the tanks are exposed to the water, they are subject to corrosion. As a primary means of corrosion control, the tanks are internally coated. To supplement the coatings, each tank has been provided with an impressed current cathodic protection system. The cathodic protection systems consist of rectifier units mounted at ground level, suspended anodes and two (2) or more permanent reference cells. A listing of the tanks is as follows:

Elevated No. 1358 130' High 50' Wet Riser Potable

Elevated No. 4490 137' High 50' Wet Riser Potable

Elevated No. 7298 100' High 40' Wet Riser Potable

Elevated No. 7417 125' High 34' Wet Riser Potable

Ground No. 5857 20' High 64'

Ground No. 6800

Ground No. 7562

20' High

40' High

40'

32'

Ground No. 7722 25' High 34'

Ground No. 6208 15' High 20'

**Ground storage tanks No. 5857 and 7722 also have impressed current cathodic protection systems on the underside of the floors. These systems protect the external floor plates from soil side corrosion, so an internal and external test will be required.

a. As part of base operations, the impressed current cathodic protection system rectifiers are monitored monthly by base personnel. Annually, the cathodic protection systems are to be inspected and tested IAW MIL-HDBK 1136 to ensure they comply with NACE standards. The survey and associated reports are to be completed before the end of October 2021.

Normal Hours of Operation: Monday through Friday from 0730- 1630

Base POC: Allen L. Spillers, phone: 318-456-2094, email: allen.spillers.1@us.af.mil

3. Inspection of Water Tanks:

a. Rectifiers - Record model, make, serial number, tap settings, mode of operation, set potential, current output, voltage output and On/Off potential of each permanent reference cell. If a rectifier unit is inoperable or malfunctioning, conduct troubleshooting to determine the cause. Make minor repairs and adjustments to ensure proper operation where possible. Record any changes in settings, output and operation mode.

b. Condition - Visually observe the condition of the cathodic protection components including the rectifier, conduits, cables, hand hole covers, hangers, reference cells and anodes. Remove at least one (I) anode assembly of each type of array and inspect for cable condition and consumption.

Note general condition of exterior and interior coatings on tank. Obtain photographs documenting coating and cathodic protection system conditions.

c. Potential Measurements - Insert a current interrupter in the rectifier negative circuit. Set the interrupter on a cycle of 30 seconds "On" and 2 seconds "Off". Open manholes, hand holes and/or vents to provide at least three (3) points of access to obtain potentials in tank/bowl, and another opening for access to the riser pipe on elevated tanks. The access points on the tank/bowl should be out toward the shell. Using a sealed test cable connection, lower a portable copper/copper-sulfate reference cell to the floor of the tank or bottom of the riser pipe. Use care to judge the bottom of the riser. The portable reference cell must be freshly charged, immediately before starting the survey.

Obtain potential measurements utilizing an M. C. Miller Model LC-4 voltmeter or equal. Record

"On" and "Instant Off" potentials on 5-foot centers up the shell/riser at each access point. From the manhole, also obtain a profile on 5-foot centers across the floor starting at the center and ending at the shell. The "On" potential to be recorded is the highest negative value observed during the current applied cycle. The "Instant Off" potential to be recorded is the lowest or least negative value displayed during the "Instant Off" cycle. Once the potentials have been obtained secure all covers, remove the interrupters, and return the rectifier to operation. Adjust the control settings as required based on the test results.

d. Safety - The Specialist must use an OSHA approved climbing harness. The base will provide mechanisms to connect to the ladder climbing slide devices. The Specialist must be securely tied off at all times when climbing and testing on the roof. The tie off must include a shock reduction devise. An assistant must provide ground support and safety watch. On the elevated tanks, an approved radio must be used to provide communications between the Specialist and ground support.

Elevated tanks shall not be climbed in heavy rain, high winds, or when lightning is near by. When materials are transported to/from the roof, they must be secured so they do not fall.

4. Criteria: The internal & external criteria is an "Instant Off" potential of -850 millivolts or more negative.

5. Reports: A report shall be prepared for the Water Tank System inspections. The report shall be of executive summary format, with sections addressing objectives, conclusions, recommendations, descriptions of structures and cathodic protection systems, test procedures and results narrative.

Appendices shall include tabulated field data, photographs, material lists, and drawings. Any recommendations for repairs and additions must be supported in the report through a described analysis of the field data. If repairs/additions are recommended, the report must include a scope of work, cost estimates for implementation and material lists.

6. Qualifications: All field tests and reports are to be conducted by a NACE certified Cathodic

Protection Specialist. The Specialist must be familiar with performing evaluation of water storage tanks on DoD facilities. This experience must include design, troubleshooting and repair of cathodic protection systems, and coating assessments. The Specialist must be supported by at least one (1) person capable of assisting with the field evaluation.

TEST PROCEDURES

The test procedures used in evaluating the water storage tank cathodic protection systems shall be conducted in accordance with the National Association of Corrosion Engineers (NACE)

Recommended Practice RP0388-95. All of the equipment shall be inspected and calibrated immediately before the survey. Personnel must be certified to perform tests in accordance with

NACE standards.

SCOPE FOR REPAIRS

1. General – The following descriptions shall be used to furnish materials and labor to repair the identified cathodic protection systems. The work shall be overseen by an NACE certified

Cathodic Protection Specialist. The Specialist must ensure the proper materials are provided, that the materials are installed correctly, and that the repaired cathodic protection systems are re-energized and tested. A report must be issued with as-built drawings, photographs, test data and analysis of the data. Provide a project-specific health and safety plan. Follow USACE and

OSHA standards.

2. Tank No. 7562 – Provide five mixed-metal oxide anode assemblies. The anodes shall have

0.118-inch diameter mixed-metal oxide anodes, with 30 feet of active anode material. Each anode must be rated to produce 1 ampere of current for 20 years. Provide #8 Halar cables, with factory splices at the top and bottom of each anode, and 20 feet of pig tail. Each anode must be provided with a factory assembled sealed weight. Provide five stainless-steel eye bolt anode supports with washers and nuts. Provide new #10 AWG/RHW-USE positive cable from the rectifier, up the existing conduit, and around the loop of hangers. Provide five new non-metallic 6-inch hand hole covers with stainless-steel hardware.

The five existing anode assemblies are to be removed, cutting the existing cables at the positive loop. Remove the existing hangers and hand hole covers. Remove the positive cable to the rectifier. Clean and coat the hanger and hand holes, with epoxy mastic. Allow coating to cure overnight. Install new ½-inch stainless-steel eye bolt hangers with washers and nuts. Run a new #10 AWG/RHW-USE positive cable from the rectifier to the top of the tank, and around the tank through the hangers. Lower each anode assembly into the tank, setting the weights 36 inches above the floor. Secure the anode cables to the new hangers. Splice the new anode cables to the new positive loop, using copper compression crimps and three layers of rubber splicing tape. Energize the rectifier and adjust the output. Allow system to polarize at least

48 hours. Record the On/Off potential profile and rectifier output, verify potential readings meet NACE criteria. Issue a report with as-built drawings, photos, test data and analysis of the data.

3. Tank No. 7722 – Visit the base and mark the location of the proposed anode holes and cable trenches. Process a One Call Ticket and submit a dig request using approved forms.

The four anodes shall be 1-inch diameter by 60-inch long mixed-metal oxide with 15 feet of

#8 Halar cable. The anodes shall be rated to produce at least 3 amperes of current in coke breeze for 20 years. The coke breeze shall be DW-1. Provide 400 pounds of coke breeze per anode. The positive cable loop shall be #4 AWG/HMWPE. Connect the anode cables to the loop using copper compression crimps and epoxy splice kits. Provide 6-inch wide detectable

“Cathodic Protection” warning tape.

Once the dig permit is approved, auger four 10-inch diameter holes to a depth of 20 feet. Place

100 pounds of coke breeze in the bottom of each hole. Lower the anodes into each hole, with

1-inch diameter by 10-inch diameter steel centralizers. Pour 300 pounds of coke breeze in each hole. Allow coke breeze to settle overnight. The top 10 feet of the hole should remain open.

Place native soil in each hole, compacting in 12-inch lifts. Cut a trench 24 inches deep, interconnecting the four anodes in a loop around the tank. Lay the #4 AWG/HMWPE cable in the trench. Splice the anode cables to the positive cable with copper crimps and epoxy cast kits. Run both ends of the cable loop into the rectifier, with a new 1.5-inch GRS conduit riser.

Connect the cables to the rectifier positive lug. Backfill the trench with compacted native soil, placing the warning tape 6 inches deep. Provide seed and mulch over trench.

Record native potentials at 8 points around tank, with cell set 6 inches out from chime. Energize rectifier unit and adjust based on potential shift. Allow system to polarize for 48 hours. Record

On/Off potentials and rectifier output. Verify that NACE criteria has been achieved. Issue a report with as-built drawings, photographs, test data and analysis of the data.

4. Tank No. 5857 – Provide two new air-cooled rectifier units to provide protection for the internal and external surfaces of the tank. Both of the rectifier units shall operate on the 115

VAC input, provide surge arrestor on AC and DC circuit, manual voltage control, 6 course and

6 fine transformer settings, DC rating of 50 volts and 6 amperes, individual voltmeter and ammeter, wiring diagram on inside door, efficiency filter, hot-dipped galvanized enclosure.

Universal Rectifier model ASAI 50-6 AACFP.

Turn off and lock out the AC power to both rectifier units. Remove the existing rectifier cabinets, saving the existing cables and conduit. Mount the new rectifier units in place of the removed units. Reconnect the existing conduits and cables. Allow for new fittings entering the cabinets. Remove the lock-outs and re-energize the new rectifiers at the output levels of the original units. Dispose of the rectifier at base recycle center.

Provide a report with photographs and rectifier test data.

Contractor will be required to mark any areas where digging will be required and physically run an Air Force Form 103 (Digging Permit) to have the area marked. The area will have to be marked and the contractor will be responsible for keeping markings in place as required. Having utilities marked could take a couple of weeks, so time should be considered/allotted for performing this action.