INDEPENDENT ASSESSMENT OF THE PREMATURE FAILURE OF THE X- 670A COOLING TOWER COILS

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3 INDEPENDENT ASSESSMENT OF THE PREMATURE FAILURE OF THE X- 67A COOLING TOWER COILS CONTRACT NO. PO SOLICITATION NO. FBP13SC364 DOCUMENT NO. PREPARED BY:

4 TABLE OF CONTENTS PURPOSE... 1 EVENT SUMMARY... 2 SUMMARY TIMELINE OF SIGNIFICANT EVENTS... 3 ORIGINAL DESIGN SPECIFICATION FOR COOLING TOWER COILS... 6 X-67 RCW SYSTEM WATER SPECIFICATIONS... 6 HISTORICAL WATER CHEMISTRY DATA... 8 WATER TREATMENT EFFORTS CAUSES OF PREMATURE FAILURE PROPOSED RECOMMENDATIONS Page i

5 PURPOSE A new Dry Air Plant, Bldg X-67, was constructed at the DOE Portsmouth Facility and placed in operation by September 21. Five cooling tower cells constructed as part of this project provided cooling water for Bldg X-67, X-3, and Bldg X-71. By September 213, all five of the cooling tower coils on the closed loop cooling system had failed due to leaks in the coils. An independent investigation was performed to determine the probable cause of the cooling coil failures and to evaluate proposed corrective actions. The investigation included: review of EVAL-TS-214-1; review of the Bldg X-67 and the X-67A Cooling Tower System P&IDs, design specifications, vendor data, as-built drawings, water quality data; and interviews with personnel associated with the project. Personnel interviewed or consulted included: NAME COMPANY POSITION Wayne Hacker FBP* Lead Engineer Bob Penn FBP* System Engineer Bernie Carrick FBP* Design Authority Al Hoffman FBP* Utilities Lead Dick Armstrong FBP* Utilities Manager Wendell Jenkins FBP* Technical Support Chris Kelly GE Water & Process Technologies FBP water quality vendor Brian Bridgeford Stoermer-Anderson, Inc. Manufacturer s Rep. for Marley Cooling Technologies/SPX, cooling tower supplier Scott Massie Geiger Brothers President, mechanical contractor Larry Smith Camp Dresser & McKee (CDM) Design Manager, design/build prime contractor Jeff Bowley Air Relief Technical Support, air compressor vendor Leisa Corbett Houghton Chemical Corp Water Treatment Business Manager, propylene glycol supplier Richard De Martino Industrial Water Technologies Corrosion consultant for Houghton Chemical Corp * USEC employee during the Dry Air Plant construction The purpose of this report is to address the following: a) Event Summary including a timeline of significant events for X-67A Cooling Tower and X-67 RCW Systems. b) Analysis of the original project design specification for the X-67A Cooling Tower coils and the required water quality. c) Analysis of the water specifications provided by the X-67 RCW systems and limitations d) Analysis of the historical X-67 RCW System water chemistry from day 1 (start-up) of the X-67A Cooling Tower to the present time. e) Analysis of the efforts to maintain and control the water chemistry over time. f) Conclusion summary of the cause(s) of the premature failure of the X-67A Cooling Tower coils and the cause(s) of other heat exchanger problems in the X-67 RCW system. g) Analysis of proposed recommendations of how to correct the problem for the long term. Page 1/16

6 EVENT SUMMARY The X-67A cooling towers were installed as part of a design-build project to provide recirculating cooling water (RCW) to the Portsmouth DOE site. The recirculating cooling water system was designed to provide cooling to the Bldg X-67 Dry Air Plant, the X-3 Plant Control Facility chiller, and the two X-71 Laboratory chillers. The RCW system was started up on September 3, 21. Flushing was performed using Ferroquest FQ713 to clean and passivate the steel piping. The initial flushing was noted to have been incomplete, in that the water in the system was still visibly rusty after three flushes. A corrosion inhibitor, Corrshield OR447, and glycol were added to the glycol closed-loop system and startup activities continued. The Dry Air Plant system was put into operation on Although efforts were made to filter out the iron, the system was plagued with excess iron in the glycol system. This apparently caused fouling of the equipment which necessitated increased flow and lower cooling water temperatures. The ph declined steadily from the point of startup. Within a year of startup, the copper corrosion coupon indicated increased corrosion rate, from mpy to.3 mpy. A copper corrosion inhibitor was added in December 211, which reduced the rate of corrosion and increased the ph briefly, but the system continued to decline in ph and the corrosion issue persisted. Almost two years after the system was put in operation, the plant began experiencing issues with leaks in the compressor and dryer cooling systems. During repairs by the air compressor vendor, it was discovered that the cooling water side of the system was filled with iron sludge. The X-67 Dry Air Plant compressed air system was shut down but the cooling towers continued to operate to provide cooling for the X-3 and X-71 chillers. Copper corrosion rates appear to have increased to.8 mpy by December 212. A maintenance shutdown from March 213 to May 213 prevented treatment of the system during this time period. Copper corrosion inhibitor was added to the glycol system in April 213 with no noticeable impact. Leaks began developing in the cooling tower closed-loop coils in May 213. Between May 213 and September 213, GE Water added copper corrosion inhibitor and borate to the glycol system, in an effort to raise the system ph. During this time, each of the cooling tower closed loop coils developed leaks. Eventually, the cooling tower glycol system coils failed, resulting in total shutdown of the X-67A RCW system. The X-3 and X-71 chillers were switched over to the X-726 RCW system. A summary timeline of events is shown below. Page 2/16

7 SUMMARY TIMELINE OF SIGNIFICANT EVENTS DATE EVENT X-67 RCW initial construction completed, flushing performed using Ferroquest FQ713 Three flushes completed but the water was still visibly rusty X-67 RCW system filled with corrosion inhibitor, CorrShield OR447, and propylene glycol solution X-67 air compressors placed in service GE Water performs particle size analysis to determine filtration requirements Corrosion coupons installed Iron sludge sample provided to GE Water for analysis Jan 211 GE Water recommends filtration to remove excess iron from glycol system Meeting to discuss iron removal Aug 211 Side-stream filter skid installed Aug Dec 211 Coupons indicate increase in corrosion rate in glycol system (up to.2 mpy for mild steel and.4 mpy for copper) GDP M&O responsibilities transferred to FBP Azole copper corrosion inhibitor (AZ814), dispersant (DIANODIC DN23), and phosphate added to glycol system Corrosion rates drop, ph increases Page 3/16

8 DATE EVENT #1 Compressor shut down on high vibration after cooler leak discovered, due to tube pitting cooler cavities full of iron sludge #2 compressor shut down on surging Oct #3 Compressor shut down on surging Intercooler leak discovered Replaced intercooler #2 Compressor aftercooler leaks found Iron sludge in water side of cooler #3 oil cooler failed Found leaks in oil cooler Iron sludge in water side of cooler GE Water performs test to determine feasibility of using polymers for coagulation of iron to improve filtration from glycol system Tests indicate polymer use to be impractical #3 Compressor surging All three compressors shut down until water quality resolved X-67 RCW continues to operate for cooling X-3 & X Brass corrosion coupon exhibits signs of tarnish Mar May 213 Work activities suspended until JHAs and work packages prepared Corrosion inhibitor (azole) added to glycol system Cooling Tower Cell #2 glycol system coil failure, leaks gallons of azole (AZ814) added to glycol system Page 4/16

9 DATE EVENT Replaced side stream filter skid with larger capacity filter system (2% f system flow) Marginal decrease in glycol system iron content Meeting held to discuss changes in chemical treatment in order to remove iron Ordered mixed metal corrosion inhibitor (Corrshield MD41), dispersant (GENGARD GN74), and a biodispersant (SPECTRUs BD157) Cooling Tower Cell #1 glycol system coil failure, leaks gallons of borate (Corrshield BT431) added to glycol system copper coupon corrosion rate drops to.2 mpy gallons of azole (AZ814) added to glycol system Borate (Corrshield BT431) added to system ph increases from 6 to Cooling Tower Cell #3 glycol system coil failure, leaks gallons of borate (Corrshield BT431) added to glycol system ph increases to gallons of borate (Corrshield BT431) added to glycol system Cooling Tower Cell #4 glycol system coil failure, leaks GE performed analysis to determine borate concentration required to neutralize the glycol system Cooling Tower Cell #5 glycol system coil failure, leaks All cooling towers out of service X-71 and X-3 chillers switched over to X-626 RCW system Page 5/16

10 ORIGINAL DESIGN SPECIFICATION FOR COOLING TOWER COILS REQUIREMENTS USEC ESO E3373, Specification , MAJOR EQUIPMENT PROCUREMENT SPECIFICATION, X-67A Dry Air Plant Cooling Tower Procurement, Par. 2.1 J. identified the cooling tower Heat-Exchanger Coils requirements as: 1. Tube and Tube Sheet Materials: Prime-coated steel tube and sheet with outer surface of tube and sheet hot-dip galvanized after fabrication. 2. Heat-Exchanger Arrangement: Serpentine tubes 3. Field Piping Connections: Vent, supply, and return suitable for mating to ASME B16.5, Class 15 flange Par. 2.1.T.3. identified the following heat exchanger coil requirements: a. Fluid Type: 4% Propylene Glycol and Water b. Fluid Flow/Cell: 125 gpm per cell c. Fluid Pressure Drop: psig d. Entering-Fluid Temperature: 1 deg. F e. Leaving-Fluid Temperature: 85 deg. F f. Entering-Air Wet-Bulb Temperature: 78 deg F EVALUATION The SPX vendor data for the cooling tower coils, submitted by Stoermer-Anderson, was consistent with the performance requirements identified in the specification. The specification did not directly address water quality requirements for the closed loop (glycol loop). REQUIREMENTS X-67 RCW SYSTEM WATER SPECIFICATIONS USEC ESO E3373, Specification , MAJOR EQUIPMENT PROCUREMENT SPECIFICATION, Air Compressor Procurement, Par. 4, identified the following design criteria: Cooling Water Design Temperature: 85 F +1/-5 F Cooling Water Design Pressure: 7 psig +5/-35 psig USEC ESO E3373, Specification , Par required the cooling water for the dryer aftercooler to be treated for corrosion control and have a supply design temperature of 65 F at 5-65 psig. USEC SOW-ENG-1-21, Specification Section 1574, Cleaning of Utility Piping, addressed cleaning of the internal surfaces of piping designated as utility piping for tower cooling water service (TWC) and Process Water (PW). Par. 1.3 required the Contractor submit a TWC Pipe Cleaning and Flushing Plan. Par. 3.2 required that all pipelines shall be flushed at no less than their design flow rate unless a lesser rate is approved by the STR. USEC SOW-ENG-1-21, Specification Section 1551-F138, Process Cooling, Raw and Cooling Tower Water, indicated that, unless otherwise specified, all material includes a minimum corrosion allowance of.65 inch. Page 6/16

11 The proposed New Coolant Piping Cleaning Sequence reviewed for this assessment required charging the new X-67 system piping with cleaning chemicals then recirculating the water for hours while controlling ph in the 6.5 to 7. range. Par. 2.1 required replacing one-half the system volume with fresh water and new cleaning chemicals if the iron level exceeded 12 ppm. Par required flushing the entire new X-67 piping system when the iron levels reached a plateau. Section 3. proposed addition of the propylene glycol to the X-67 piping then adding inhibitors through the equalization tank. EVALUATION The cooling water heat transfer requirements appear to be adequate. More information is required to perform a detailed analysis of the cooling capacity of the system. The design documents did not provide details of the design basis. Specific water quality requirements for the glycol loop were not located during this assessment. The proposed New Coolant Pipe Cleaning Sequence recirculation duration of hours is not consistent with the product data sheet for Ferroquest FQ713, which indicates a minimum recirculation period of 72 hours, followed by a 24 hour rinse. The propylene glycol product sheets provided by the project were for Safe-T-Therm, which is inhibited. Conversations with Houghton Chemical, the propylene glycol supplier, indicated that the product that was ordered and delivered was uninhibited glycol. Uninhibited glycol is corrosive to steel and copper, which could have a detrimental impact on the system until corrosion inhibitors are added. The impact of the contact with the uninhibited glycol would be proportionate to the amount of time between introduction of the propylene glycol and addition of the corrosion inhibitor. Page 7/16

12 HISTORICAL WATER CHEMISTRY DATA The water chemistry data indicate the following trends: The general trend over time was an increase in iron and copper (See FIGURE 1 below). This would be consistent with an increase in corrosion over time. FIGURE 1 METAL CONCENTRATION vs TIME Iron (ppm) Copper (ppm) Linear (Iron) Linear (Copper) Iron (ppm) Copper (ppm) Date Page 8/16

13 The ph trend for the X-67 glycol cooling system was a fairly consistent drop from the time the system monitoring began until the system was shut down (see FIGURE 2 below). Chemical addition accounts for the local points of rise in ph. FIGURE 2 ph vs TIME 9. ph Linear (ph) ph DATE Page 9/16

14 The trend for the level of iron and copper in the water was consistent with the ph level (see FIGURE 3 below), which would be expected. Data for events such as water addition, glycol addition, and removal of metals by filtration was not available but did not appear to have a significant impact on the overall trend. FIGURE 3 METAL CONCENTRATION vs ph Iron (ppm) Copper (ppm) Linear (Iron) Linear (Copper) 6, 4 5, , 25 Iron (ppm) 3, 2, 2 15 Copper (ppm) 1 1, ph Page 1/16

15 The trend for propylene glycol concentration over time (FIGURE 4) is similar to the trend for ph over time (FIGURE 2), which is consistent with the fact that glycol breaks down into organic acids at an accelerated rate when the ph drops below about 7. The general trend for propylene glycol concentration was to drop as the ph decreased (FIGURE 5), which would be expected. The individual points would be affected by glycol or make-up water addition, if they occurred. These events were not identified in the timeline but seem likely to have been necessary. 45 FIGURE 4 GLYCOL CONCENTRATION vs TIME Propylene Glycol % Linear (Propylene Glycol %) Propylene Glycol (%) DATE FIGURE 5 GLYCOL CONCENTRATION vs ph Propylene Glycol % Linear (Propylene Glycol %) Propylene Glycol (%) ph Page 11/16

16 The level of potassium in the cooling water is an indicator of the amount of corrosion inhibitor present. The levels of potassium were generally too low to determine the impact on the amount of iron in the water, which would be an indication of the rate of corrosion. FIGURE 6 shows the relationship between the amount of iron in the water and the amount of corrosion inhibitor. FIGURE 7 shows the change in the level of corrosion inhibitor over time. The increase in potassium in January 212 correlates with the addition of corrosion inhibitor in December 211. Data points for potassium were not provided for the period after July 213. FIGURE 6 METAL CONCENTRATION vs POTASSIUM CONCENTRATION Iron (ppm) Copper (ppm) Linear (iron) Linear (Copper) Potassium (ppm) Iron (ppm) , 5, 4, 3, 2, 1, Potassium (ppm) FIGURE 7 POTASSIUM CONCENTRATION vs TIME Potassium (ppm) Linear (Potassium) Copper (ppm) DATE Page 12/16

17 6 The level of azole in the water was typically too low to contribute to a trend. Azole is a copper corrosion inhibitor. The comparison of the level of copper to azole in the glycol water is shown in FIGURE 8. The level of azole in the water over time is shown in FIGURE 9. FIGURE 8 METAL CONCENTRATION vs AZOLE CONCENTRATION Iron (ppm) Copper (ppm) Linear (Iron) Linear (Copper) Iron (ppm) Copper (ppm) Azole (ppm) FIGURE 9 AZOLE CONCENTRATION vs TIME Azole (ppm) Linear (Azole) 1 Azole (ppm) DATE Page 13/16

18 The corrosion rates for the mild steel and copper were generally low. The mild steel corrosion rate varied from to 1.3 mpy with half of the readings at mpy. The copper corrosion rate varied from to 1 mpy, with 3% of the readings at mpy. The coupon corrosion rates would be expected to correspond with the levels of iron and copper in the solution but the general trend indicated no significant change in metal level with change in corrosion rate. The design allowance for corrosion was identified as.65 inches. Assuming a useful life of 3 years for the equipment results in an allowable corrosion rate of mils per year (mpy). The corrosion rates measured for mild steel never exceeded 1.3 mpy, with the majority of the rates at mpy. FIGURE 1 shows the relationship between the amount of iron in the cooling water and the mild steel corrosion rate. FIGURE 1 IRON CONCENTRATION vs CORROSION RATE Iron (ppm) Linear (ppm) 6, 5, 4, Iron (ppm) 3, 2, 1, Mild Steel Corrosion (mpy) Page 14/16

19 DISCUSSION WATER TREATMENT EFFORTS The timeline indicates that water treatment for the X-67 project glycol loop consisted of cleaning and passivation of the glycol pipe, prior to introduction of propylene glycol. The cleaning and passivation plan included adding Ferroquest FQ713 to the cooling water loop and circulating the water for 48 to 72 hours while flushing as needed to ensure the iron levels remained below 1,2 ppm. The actual sequence of events from the construction logs is not clear. The timeline information provided indicates that three flushes were performed and the flush water was still visibly rusty. It is not clear as to whether water quality data was taken. The decision was made to discontinue the cleaning effort and add the necessary quantity of propylene glycol to bring the glycol concentration in the system to 4%. The plan for propylene glycol addition included adding propylene glycol then circulating the mixture through the glycol cooling loop. Corrosion inhibitors were then to be added to the glycol loop through the equalization tank. The timeline shows that corrosion inhibitor, CorrShield OR447, was added to the propylene glycol solution between and No water quality data was available until November 21, so the condition of the glycol loop water is unknown until that date. The data for November 21 shows the ph was 8.8, copper was <.5 ppm, iron was 91 ppm, and tolyltriazole was 1 ppm. No value was provided for potassium. Treatment efforts from that point on appear to have been primarily focused on removal of the iron particles in the water through filtration. Filtration appears to have had little impact on the total iron in the water. In December of 211, corrosion inhibitors were added in response to what was characterized as increased corrosion in the test coupons. A brass corrosion coupon was installed prior to January 213. Indication of corrosion in the coupon resulted in addition of a copper corrosion inhibitor in April 213 and May 213. In June 213, the side stream filtration rate was increased in an attempt to reduce the level of iron in the glycol loop water. In July, the decision to change chemical treatment resulted in a plan to treat the water with a corrosion inhibitor, dispersant, and biodispersant. These chemicals were ordered but not received before the system was shut down. A buffer (Corrshield BT431) was added several times in August 213 in an attempt to control the corrosion by increasing the glycol system ph. The ph did increase but the system failed before further treatment could be applied. EVALUATION It appears that the treatment of the glycol water system was primarily limited to removing excess iron through filtration and controlling perceived accelerated corrosion of copper until the system was close to failure. At that point efforts to control corrosion by adding corrosion inhibitor and dispersants were curtailed by failure of the cooling tower coils. Page 15/16

20 CAUSES OF PREMATURE FAILURE Excess iron in the X-67 glycol loop, left from incomplete cleaning and passivation of the system, appears to have caused restrictions through the heat exchangers and coils of the equipment. This required increased flow and lower cooling water temperatures in order to achieve the required cooling. The excess iron may have contributed to consumption of the initial batch of corrosion inhibitor and a drop in ph of the system. As the ph dropped, the degradation rate of the propylene glycol increased, resulting in the presence of organic acids which caused the corrosion of the steel to increase. The continued corrosion of the steel prevented the filtration from significantly impacting the iron levels in the water. The use of uninhibited propylene glycol compounded the difficulty in the initial treatment of the system and may have contributed to the increased rate of system degradation. Corrosion inhibitor for the steel was not added to the system until August 213, when the cooling tower coils were failing. By this time, the propylene glycol had been subjected to low ph levels for extended periods of time, resulting in accelerated degradation of the glycol and increased production of organic acids. The degradation of the glycol may have caused bacterial colonies to develop. The restrictions in the coils may have caused high velocities and erosion may have caused excess wear in the coils. It is also possible that the copper in the water may have caused pitting in the coils. Microbial corrosion could also have been a factor in the coil failure. PROPOSED RECOMMENDATIONS The X-67 loop should be emptied of the existing treated water and flushed clean. The failed coils should be removed and the failed sections examined to determine the cause of the leaks. Examination should reveal the type of failure and provide insight into possible issues impacting corrective actions. All components of the system should be physically cleaned and examined for damage. The extent and method of cleaning should be determined, based on the component characteristics, so that the majority of deposits are removed and so as to limit interference with examination. The method and frequency of examination should be based on the salient features of the component and the failure modes determined from the analysis of the failed components. The fill lines into the equalization tank should be extended beneath the operating level of the tank, to limit aeration of the water. The lines should be thoroughly flushed and passivated prior to adding glycol. Leak testing of the system should be performed prior to glycol addition. An inhibited glycol solution should be added to the system. Monitoring of the water quality should be performed regularly, including testing for biological activity. Page 16/16