STRUCTURAL INSPECTION AND ASSESSMENTguamwaterworks.org/documents/AddendumNo1_000.pdf · The API 653...

STRUCTURAL INSPECTION AND ASSESSMENT OF THE

MANGILAO 2 TANK RESERVOIR Mangilao Guam

April 6, 2011

ENGINEERING PLANNING SURVEYING CONSTRUCTION MANAGEMENT ENVIRONMENTAL SERVICES 238 East Marine Corps Drive, Diamond Plaza, Suite 201, Hagatna, Guam 96910 Tel: (671)646-7991 Fax: (671)646-6315 Website: [email protected]

Website: www.dcaguam.com Email: [email protected]

ENGINEERING * PLANNING * SURVEYING * ENVIRONMENTAL SERVICES * GEOGRAPHIC INFORMATION SYSTEM * CONSTRUCTION MANAGEMENT GUAM P.O. Box 8900, Tamuning, Guam 96931 / 238 E. Marine Corps Drive, Suite 201 Diamond Plaza, Hagatña, GU 96910 / Tel: (671) 477-7991 / Fax: (671) 479-6315 SAIPAN Caller Box PPP, Suite 164, Saipan, MP 96950 / Chalan Pale Arnold, Ada’s Building South Garapan, Saipan 96950 / Tel: (670) 234-9017 / Fax: (670) 234-3842

April 6, 2011 Guam Waterworks Authority PO Box 3010 Hagåtña, Guam 96932 Attention: Mr. Martin Roush, Chief Engineer Subject: Mangilao 2 Water Reservoir Dear Mr. Roush: We have completed our API 653 inspections and preliminary structural analysis of the existing Mangilao 2 Steel Water Tank Reservoir as per the initial scope of the Phase II work of our contract to assess GWA’s complete inventory of the island wide water reservoirs. API 653 REPORT FINDINGS: The API 653 inspections were performed by Engineering & Inspections, Hawaii Inc. and a report prepared on December 10, 2010 outlining the inspection findings and recommendations. (See Appendix A) The report cited severe metal loss due to corrosion and pitting by the tank base corner weld and the area 2” immediately above the corner weld along the 1st course tank shell wall. Thickness readings varied from 0.500” to 0.074” with at least 5 areas falling below the required 0.369”minimum 1st course shell plate thickness. Due to the excessive metal loss at the corner weld and the area immediately above the corner weld, the tank does not meet the 1st course minimum shell plate thickness requirements as set forth by API 653 Fourth Edition. Further thickness readings on the tanks shell were consistent with the as-built drawings and did not reveal any large areas of internal corrosion or pitting. The tank interior coating has deteriorated. The wind girder attached to the exterior tank shell was found to be in good condition. Numerous areas on the tank floor have “lake” type corrosion and the coating is failing. There are at least seven (7) areas where corrosion through holes were discovered on the tank floor. Two (2) of these holes occur along tank annular ring and corner weld which are considered part of the tank “critical zone”. Corrosion was also affecting the floor plate lap welds as well as the annular ring welds. Magnetic Flux leakage examination of the floor revealed numerous areas with at least 0.11” or greater of volumetric metal loss likely due to topside or underside corrosion. Interior drain piping in the tank is severely

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corroded with deposits present. The tank internal roof access ladder were severely corroded and in need of replacement. The tank roof shell thickness readings were consistent with the minimum construction standard roof thickness of 3/16”. The roof manway, hatches, and center vent have active and moderate to severe corrosion. All roof penetrations have active corrosion at the welds and roof plate interface. Approximately 110 linear feet of roof plate lap welds are corroded and need to be repaired. There is a 1” ball valve attached to the tank shell that does not meet the requirements of API shell mounted valves. There are areas with minor deterioration and cracking in the foundation were noted. There are not tank anchors that attach to the foundation. Grout that seals the exterior tank floor chime is cracked and loose in several places. Active corrosion and severe de-laminar corrosion was noted on the exterior tank chime to grout interface. The E&I Hawaii, Inc. report recommends that the tank remains out of service until Mandatory Major Repairs are completed. These major repairs include the following:

a) Replace the entire bottom floor of the tank with new floor plates. This can be achieve by either the complete removal and replacement of the existing floor with new or the installation of a new steel floor over the existing floor with 4” of concrete or sand fill between the floor plates. Recommendations also include installing a drip rings to the new tank chime which would extend the life of the floor plate edge and chime. (The latter option of raising the floor over the existing floor is the preferred option since it would also address the severe metal loss that occurs at the corner welds and base on the tank shell wall along the 1st course.)

Minor Repairs are also listed in the recommendations which include the following:

a) Repair by replacement the tank roof center vent.

b) Repair by welding the approximately 110 linear feet of corroded roof plate lap welds.

c) Repair by use of a lap welded patch, the through holes noted in the tank roof at

the knuckle to roof sketch plate.

d) Repair by use of a lap welded patch, all through holes where the roof mounted hanging anode system was installed; if not replaced with a new hanging anode system.

e) Repair by replacement the tank interior ladder and fall arrest system.

f) Repair by replacement the tank level float system and all appurtenances.

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g) Removal all vegetative growth around the tank exterior.

h) Re-coat the entire interior of the tank to meet the current sanitation requirements of AWWA.

i) Install or upgrade the cathodic protection system with a new hanging sacrificial

anode system, and perform yearly maintenance surveys as required by AWWA and API.

DCA INSPECTION FINDINGS: DCA conducted independent inspections of the tank interior but focused primarily on the tank roof support structure. The roof of the Mangilao 2 tank is supported by 20 independent steel roof purlins that extend from the tank center support column to the intermediate support frames supported by five (5) columns. An additional 45 independent steel roof purlins extend from these intermediate frames to the perimeter shell plate wall. The column is comprised of circular 10” diameter steel pipes supported at the bases with channel shapes welded together that connect directly to a bottom tank floor plates and an upper roof support plate. The column supports are in relatively good shape with only minor surface corrosion. The roof purlins were found to have slight to moderate surface corrosion. The undersides of the tank roof plates, which are supported by the roof purlins, appear to have slight to moderate surface corrosion. The outer perimeter support channel that attaches to the tank wall shell has moderate corrosion. There appear to be metal spacer plates along the entire roof surface that have completely deteriorated from corrosion and are falling to the tank floor. The frame connection points along the intermediate frames are moderately to severely corroded. (The inspection finding were documented with Photos in APPENDIX B) Based on our visual findings and understanding of the rates of corrosion for this tank, we recommend cleaning and re-coating of the column supports and the steel roof purlin support system. The interior roof purlins do not appear to show significant metal loss and therefore could be re-used if cleaned properly. If severe metal loss is discovered on the purlins members after complete cleaning, the areas with significant metal loss should be repaired or replaced as necessary. All frame connection points should also be cleaned and re-coated. Similarly, if severe metal loss is discovered at the frame connection points after complete cleaning, the areas with significant metal loss should be repaired or replaced as necessary The DCA inspections also confirmed the severely corroded connections between the floor and wall shell plate corner welds and along the annular ring as reported by E&I Hawaii, Inc. This critical area of severe metal loss in the tank shell base and corner angle and along the annular ring is further discussed in the following Analysis Results section of this report.

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ANALYSIS RESULTS:

We used the AWWA Standards for Welded Steel Tanks for Water Storage as a basis for determining the safe level of operation for the tank being re-commissioned into service. This analysis was also compared to the analysis results using API 653 standards. An analysis was performed on the tank wall capacities based on allowable stress limits as specified by AWWA and API 653. (A fill height of 38’-6” was used in the analysis to be consistent with the fill height used in the API 653 report.) One reason for the utilizing both criteria was to compare the differences in the allowable stress on the walls between the two standards. We utilized an allowable stress of 15,000 psi for the Dead and Live Loading analysis as specified by AWWA. The required tank thickness at the first level of plates was calculated to be 0.7074 inches for the full tank depth of 38’-6” based on the AWWA formulas. However, thickness readings, as low as 0.074”, were measured at the base of the 1st course shell plate due to the severe metal loss from corrosion. Calculations using the reduced thickness of 0.08” would only support a 4’-0” head of fill height in the tank. We preformed the same calculation using the allow tension stress of 23,500 psi as specified by API 653. The required tank thickness at the first level of plates was calculated to be 0.4515 inches for the full tank depth of 38’-6” based on API 653 formulas. Similarly, calculations using the reduced thickness of 0.074” would only support approximately a 7’-0” head of fill height. The results of the AWWA standards proved to be more stringent than those calculated utilizing the API 653 standards bases on empirical formulas provided for both. The difference in the calculated minimum required shell thickness values for a tank fill height of 38’-6” between the AWWA and API 653 standards is approximately 36.17%. We also performed an analysis of the tank utilizing ETABS, a three dimensional dynamic analysis program based on the current International Building Code (IBC 2009) and AISC (American Steel Institute) criteria. (See APPENDIX C) For purposes of this model we utilized a fill height of 38-6” to obtain maximum possible stresses in the analysis. The results of the analysis for the tank with the minimum shell plate thickness of 0.074” show critical overstressing at the 1st course under normal loading conditions. The 1st course is also critically stressed with earthquake and wind loads applied to the tank filled to 38’-6”. If we perform the analysis with a restored wall plate thicknesses of 7/16” (0.449”), the stresses on the tank walls will be within allowable stress limits as specified by AWWA for a partial fill height of 23’-9”. Similarly, with restored thickness in the tank shell at the 1st course, stresses will fall within acceptable stress limits for earthquake and wind loads based on the AWWA standards for a full fill height of 38’-6” which allows for an increase in tensile stress limit to 20,000 psi for wind and seismic load cases.

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Performing the same analyses with allowable stress limits set by API 653 result in tank walls stresses within allowable limits for a full fill height of 38’-6” under normal service and wind and seismic loading conditions. DISCUSSION and RECOMMENDATIONS: The December 10, 2010 API 653 Inspection Report identified numerous issues with the tank bottom and the bottom 2 inches of 1st course of the tank shell. The DCA inspection of the roof support system identified surface corrosion on the roof purlins and moderate to heavy corrosion on the intermediate frame connection points and channel support at the perimeter shell wall. Recommendations from this inspection call for the cleaning and reuse of the roof purlin support system and the intermediate frames and connection points with the possibility of repair and/or replacement of severely corroded isolated areas of the frame members. The analysis based on the empirical formulas provided by AWWA and the ETABS analysis result in over stressing of the bottom plate course (t = 0.074”) based at a fill height of 38’-6”. Based on controlling thickness (t = 0.074”) of the shell elements at the 1st course, maximum fill height should not exceed 4’-0” for the Empirical Analysis and 7’-0” for the ETABS analysis. This fill height assumes the 1st course of the tank shell remains as is with no restoration and/or repair of the band of metal loss at the base of the wall shell welds. The calculated required minimum thickness of the tank shell at the 1st course was estimated to be 0.7074” based on AWWA and 0.4515” based on API 653 standards for a full fill height of 38’-6”. The measured controlling thickness (t = 0.074”) is only 10.46% and 16.39%, respectively of these values. The report states that there is a remaining life of 30 years for the tank 1st course based on the actual t = 0.449” thickness readings taken at the time of inspection. However, there were measured thickness readings of 0.074” which would essentially render the 1st course of that tank with no remaining life. Since the areas of severe corrosion are limited to the tank floor and bottom few inches of the 1st course shell plate, repair and/or replacement of these elements would mean continued extended use of the tank. Recommended fill heights after repair are 23’-0” and 38’-0" based on AWWA and API 653 Standards, respectively. . There are at least two scenarios to consider for the repair and re-commissioning of the tank into service condition: OPTION 1: Perform major repairs on the tank and re-commission with a full head of fill height for the water reservoir.

1. Furnish all material, labor, equipment, & appurtenances necessary to safely access each reservoir.

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2. Furnish all material, labor, equipment, & appurtenances for repair and/or replacement of Reservoir’s floor, shell, roof plates, all sizes, all thickness, including removal and disposal of old plates including painting and welding complete in place.

a. Install a new steel floor over the existing floor with 4” of concrete or sand fill between the floor plates. Recommendations also include installing a drip rings to the new tank chime which would extend the life of the floor plate edge and chime.

3. Furnish all material, labor, equipment, & appurtenances for spot repair and/or replacement of damaged interior tank coating, complete in place.

4. Furnish all material, labor, equipment, & appurtenances necessary to properly clean and washout the interior of each reservoir’s floor, repaired, and disturbed areas in accordance with American Water Works Association (AWWA) Standards.

5. Furnish all material, labor, equipment, & appurtenances necessary to disinfect each reservoir in accordance with AWWA C625 Standards.

6. Provide the services of an AWWA Certified Water Distribution Operator to monitor the disinfection process.

7. Demobilization

The costs for Option 1 major repairs are estimated to be in the range of $1,000,000 - $1,250,000. (Costs include Construction Management and QC Inspections)

OPTION 2: Perform minor repairs on the tank and temporarily re-commission with a limited head or fill height of 23’ for the water reservoir. (This a temporary fix until major repairs can be implemented.)

1. Furnish all material, labor, equipment, & appurtenances necessary to safely access each

reservoir.

2. Furnish all material, labor, equipment, & appurtenances necessary to thoroughly remove and dispose (off-site) all accumulated bottom sediment and debris from each reservoir.

a. Remove and dispose of all accumulated scale and corrosion on the tank interior columns.

3. Furnish all material, labor, equipment, & appurtenances for repair and/or replacement of Reservoir’s floor, shell, roof plates, all sizes, all thickness, including removal and disposal of old plates including painting and welding complete in place.

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a. Repair by welding the approximately 110 linear feet of corroded roof plate lap welds.

b. Repair by the use of lap welded patch, the through holed noted in the tank roof at the knuckle to roof sketch plate.

c. Repair by the use of lap weld patches, all through holes where the roof mounted hanging anode system was installed; if not replaced with new hanging anode system.

d. Repair by the use of lap weld patches the holes in the floor; 5 holes in the tank bottom plate and 2 holes in the annular ring and corner weld.

a. Repair lower 2” of the 1st course of the tank shell with a continuous lap weld plate 4” high x ½” thick around the perimeter of the entire tank exterior. . Welding should be made using low-hydrogen electrodes utilizing staggered fillet weld technique to minimize any shell bucking or warping.

4. Furnish all material, labor, equipment, & appurtenances for repair and/or replacement of severely corroded, damaged, and/or missing roof access hatch assemblies including removal and disposal of old plates assemblies in addition to painting and welding, complete in place.

a. Repair by replacement the tank roof access hatch.

5. Furnish all material, labor, equipment, & appurtenances for repair and/or replacement of roof vent assemblies including removal and disposal of old assemblies in addition to painting and welding, complete in place.

a. Repair by replacement the tank roof center vent.

6. Furnish all material, labor, equipment, & appurtenances for the removal of Reservoir’s internal access ladder including disposal of old assemblies in addition to painting and welding, complete in place.

a. Repair by replacement the tank interior ladder and fall arrest system.

7. Furnish all material, labor, equipment, & appurtenances for spot repair and/or replacement of damaged interior tank coating, complete in place.

8. Furnish all material, labor, equipment, & appurtenances necessary to properly clean and washout the interior of each reservoir’s floor, repaired, and disturbed areas in accordance with American Water Works Association (AWWA) Standards.

9. Furnish all material, labor, equipment, & appurtenances necessary to disinfect each reservoir in accordance with AWWA C625 Standards.

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10. Provide the services of an AWWA Certified Water Distribution Operator to monitor the disinfection process.

11. Demobilization

12. Miscellaneous and cleanup a. Remove all vegetative growth around the tank exterior.

The costs for Option 1 major repairs are estimated to be in the range of $130,000 - $160,000. (Costs include Construction Management and QC Inspections) A final option to consider would be complete removal and replacement of the existing steel tank reservoir. OPTION 3: Complete removal of the existing steel tank reservoir and replacement with either a new steel tank or reinforced concrete tank reservoir. The cost for Option 3A - complete replacement with a steel tank reservoir is estimated to be in the range of $2,750,000 - $3,000,000. (Costs include Construction Management and QC Inspections) The cost for Option 3B - complete replacement with a reinforced concrete tank reservoir is estimated to be in the range of $3,250,000 - $3,500,000. (Costs include Construction Management and QC Inspections) CONCLUSION: The Mangilao 2 Water Tank Reservoir has deteriorated over the years and is in need of major repairs prior to re-commissioning of the tank. Two options for repair work were presented with some limitation on the operating head or fill heights of the tanks that are temporarily repaired. Based on the findings from the E&I Hawaii, Inc. API 653 Inspection Report and DCA’s inspection and analysis findings, we recommend Repair Option 2 as an immediate approach to addressing the temporary re-commissioning of the tank to partial capacity. Option 1 would effectively complete the process of full restoration and repairs to the tank reservoir for full operation at maximum efficiency while extending the life of the tank. Please note that this assumes API 653 standards and stress limitations apply in lieu of the more stringent AWWA allowable stress requirements. The option for complete replacement of the tank was not considered feasible because of the amount of remaining life (30 years) on the tank shell as reported by E & I Hawaii, Inc. in the API 653 Inspection Report. The repair costs would still be substantially less than full replacement of the steel tank with the same sized steel tank or a new concrete tank estimated to be approximately $3,000,000 to $3,500,000 respectively.

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GENERAL LIMITATIONS:

The findings and conclusions contained in this report are based on various quantitative factors as they existed on or near the date of field investigations. Changes or modifications to facilities and/or conditions at the subject site made after the site visit are not reflected in this report. The assessments and evaluations are limited to visual observations and limited general analyses and are not the result of detailed analyses or independent calculations. Statements regarding code compliance and life safety issues are based purely on our knowledge of current building code and life safety requirements and are not necessarily an interpretation of the earlier codes. Dueñas Camacho & Associates, Inc. is responsible for the accuracy of the report, subject to what is stated elsewhere in these limitations. However, we recommend that the report be used only for the purposes for which it was intended. The report may be unsuitable for other uses. No changes to the form or content of the report may be made by any party without the express written approval of Dueñas Camacho & Associates, Inc. I will be available to discuss my findings, opinions, and recommendations with you at your convenience. Please call me if you have any questions or concern regarding the report. Sincerely,

Thomas P. Camacho, SE Chief Structural Engineer/Vice President

APPENDIX A API 653 INSPECTION REPORT

MANGILAO 2 TANK RESERVOIR Mangilao, Guam


P. O. Box 700217 • Kapolei, HI 96709-0217 • Tel: (808) 682-1667 • Fax: (808) 682-1834 • E-Mail: E I [email protected]

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API-653 OUT-OF-SERVICE GUAM WATER AUTHORITY

MANGILAO 2

To: Duenas, Camacho & Associates Inc.

238 E Marine Corps Dr;. Suite 201 Hagatna, Guam 96910

From:

P.O. Box 700217

Kapolei, HI. 96709-0217

“Providing Excellence in NDE and Quality Inspection Services to Industries Worldwide”

P. O. Box 700217 • Kapolei, HI 96709-0217 • Tel: (808) 682-1667 • Fax: (808) 682-1834 • E-Mail: E I [email protected]

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ENGINEERING INSPECTIONS HAWAII, INC.

& December 10 2010

Mr. Thomas Camacho S.E. Duenas, Camacho & Associates Inc. 238 E Marine Corps Dr;. Suite 201 Hagatna, Guam 96910

Tank No. “Mangilao 2” Built: 1991 Constructed By: CBI Services; APSCO 92’ 6” Dia. X 41’ 0” High Capacity: 2.0 Mil gal Design S.P.G. 1.0 Material: A588 Grade A Subject: API-653 Inspection of the above referenced tank.

Mr. Camacho, On November 20, 2010, Engineering & Inspections Hawaii, Inc. performed an Out-of-Service inspection on tank Mangilao 2. This inspection was performed in accordance with the latest edition of API Standard 653, Tank Inspection, Repair, Alteration, and Reconstruction by a certified API 653 inspector and additional “scope of work” as provided by Duenas Camacho and Associates. All personnel performing nondestructive examinations are certified to at least SNT-TC-1A level II. This is the first known inspection of this tank since original construction in 1991. Surrounding Area: The tank is located along route 15 in Eastern Guam. The site is shared with one other water storage tank, which was constructed in 2008. The tank has no secondary containment system in place. The asphalt roadway around the tank has thick vegetation and weed growth.

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PO Box 700217 • Kapolei, Hawaii 96709-0217 • Tel: (808) 682-1667 • Fax: (808) 682-1834 • E-Mail: E I [email protected]

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Foundation: The tank foundation is a concrete ring wall with earthen fill. The foundation was visually inspected with areas of minor deterioration and cracking noted. The area between the foundation and the tank floor chime has been sealed by grouting. The grout was cracked and loose in several places. The grout was removed during this inspection to facilitate inspection of the tank chime and ringwall. Areas of vegetation growth and moss between the grout and ringwall were noted. Anchorage: Tank “Mangilao 2” does not have tank anchorage. Based on the design drawings provided by GWA, the tank was supposed to be constructed with 24 equally spaced shell mounted anchors. Calculations based on the current requirements of API-650 for tank “Mangilao 2” does not require the tank to have anchorage. Bottom Extension / Shell-to-Floor weld area (Exterior) The tank corner weld and floor protrusion from the shell, defined as the tank “chime” area was visually inspected and hammer tested. Numerous areas with severe de-laminar corrosion was noted at the tank chime to grout interface. Active corrosion was also noted on the topside of the tank chime. Cathodic Protection; Grounding The tank cathodic protection system was of an internal hanging sacrificial anode design. The anodes hung from the tank roof on the tank interior and extended from approximately from the five foot elevation to the thirty foot elevation in alternating five foot increments. The hanging anodes were found lying on the tank floor by the tank cleaning contractor upon initial tank entry. The exterior cables and roof covers have been removed or vandalized at some point in the past leaving most of the anodes and interior wiring fallen to the tank floor. Shell The tank shell exterior appears to be in good condition. The coating system has deteriorated and the tank is in need of a complete re-coat. Ultrasonic thickness readings on the tank shell revealed areas of corrosion and pitting down by the tank corner weld. The readings varied from full shell plate thickness of 0.500” to


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readings at or lower than 0.100” when measured at the bottom portion near the corner weld. Per API-653 the first course shell plate is required to be a minimum of 0.369” An intermediate wind girder is attached to the tank shell at the 26 foot elevation. Visual inspection of the wind girder topside revealed that all of the drain holes appear to be working properly as there was no sign of standing water against the tank shell or areas of shell plate corrosion at the wind girder. Nozzles The tank has four shell mounted nozzles. The nozzles were checked for size and spacing requirements as defined by API-653 and were found acceptable. All four nozzles were noted to have the proper reinforcement pad installed for size and thickness. A 1” thread-o-let fitting was noted welded to the tank shell next to the tank manway. The thread-o-let has a 1” ball valve attached and diverts downward directly into the ground. This valve does not meet the current requirements of API for a shell mounted valve. Auto Gauge The tank has an internal float with an exterior mounted level indicator board. None of the components associated with the auto gage were in working order during this inspection. All components of the auto gage are in need of repair or replacement. Fire Suppression The “Mangilao 2” tank is an above ground water storage tank. Fire suppression is not required. Access Structure The tank roof is accessed by a shell mounted ladder. The ladder supports are welded directly to the tank shell instead of doubler or bearing plates. The ladder has a safety containment cage around it which has signs of moderate corrosion. The roof access platform was in fair condition with the handrails and vertical supports having signs of active corrosion at all of the welds attaching it to the roof and shell.


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Fixed External Roof The tank roof is in fair condition. The roof manway has active corrosion and the hatch cover was noted to have moderate to severe active corrosion. Ultrasonic thickness readings averaged .185” which is consistent for standard roof plate meeting 3/16” construction standards. The tank had one centered mounted roof vent which is severely corroded and in need of replacement. All other roof penetrations have active corrosion at the welds and roof plate interface. Roof plate lap welds were noted to be corroded at the welds with approximately 110 linear feet of weld being affected and in need of repair. One through hole was noted at the knuckle to roof plate lap weld. Other through holes were noted in the roof plate, but are where the past cathodic protection system was installed. Tank Interior: The tank interior was noted to be in poor condition. The interior of the tank was previously coated including the floor, shell, and roof underside. Large areas of coating failures were noted on the tank floor. Areas with coating failure were noted to have large areas of “lake” type corrosion present. The tank floor is made of a standard lap weld design with an outer butt welded annular ring. Visual inspection of the tank floor in the areas of corrosion revealed seven through holes. Two of the holes were noted in the tank annular ring and corner weld, which are considered part of the tank “critical zone”. Other areas of corrosion were noted to affect the floor plate lap welds as well as the radial annular ring welds. A Magnetic Flux leakage (MFE) examination was performed on areas without the severe topside corrosion and pitting. Floor plates in these areas alarmed and confirmed the presence of underside corrosion. The equipment utilized was a MFE Enterprises model Mark IV tank floor scanner, which was calibrated to alarm at a volumetric loss of .110” or greater. The tank has a floor mounted drain which is welded directly to the tank floor underside. The welds were slightly corroded with the interior drain piping having severe corrosion and deposits present.


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The tank roof is supported by one central support column and five outer periphery columns. The columns are manufactured from ten inch pipe with channel bracing at the base to prevent movement. None of the pipe portion of the support rest directly on the tank floor thus allowing drainage with the load to be spread over the channel beam support system. API requires any support structure to have a “doubler” or load bearing plate under them, separate from the tank floor. The 1st course tank shell has severe shell pitting in the lower two inches extending down into the tank corner weld. Ultrasonic thickness readings taken from the tank exterior revealed areas where the first course tank shell was as thin as 0.080” well below the API required 0.369”. Visual inspection of these areas revealed a corner weld that is severely corroded with significant metal loss. The tank has an interior roof access ladder which is severely corroded and in need of replacement. The level float gage was noted with broken guide wires with the floor mounting hardware completely corroded to the tank floor. Additional Comments The drawings provided by GWA for this tank were thought to be representative of the actual tank, as the drawings are labeled for Mangilao, 2.0 mg, “as built” and of the correct time frame 1990. It was noted however that the drawings reflect a tank with five 8’ high shell courses, actual tank is four 10’ high shell courses. The drawings indicate the roof plate to be 0.250” thick, actual roof plate thickness is 0.187”. Tank anchors and design details are called out on the drawings, actual tank does not have any anchorage. All roof support columns should have a 0.500” thick bearing plate under them. As stated above none of the roof support columns have bearing plates. The tank nozzle reinforcement pads are of a circular design. Drawings detail a six sided plate with rounded edges. The drawings provided by GWA specify the tank shell plate thickness which should be utilized when performing tank shell remaining life calculations. The calculations provided at the end of this report are based on shell plate thickness’s nearest to the actual ultrasonic thickness reading obtained.


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Based on the internal inspection of the “Mangilao 2” tank, the tank is not approved for continued service until major repairs are completed. Recommendations

Mandatory Major Repairs: (Internal) Repairs that affect the overall operability and integrity of the tank; and must be performed in the immediate near future.

1. Replace or repair (by use of the “double bottom” method) the entire tank floor. Based on the random locations of known and suspected near through holes in the tank floor and the severe lake corrosion of the existing floor plate and annular plate butt welds, repair by the use of lap welded patches and repair welding would not be sufficient.

a) The floor can be replaced by completely removing the old floor and installing a new floor in its place. Evaluation and testing of the sub soil should be included if this method is utilized. This new floor will require welding by certified welders and approved welding procedures. Nondestructive examinations as required by AWWA D100 will also need to be performed.

b) Repair by the use of the “double bottom” method. This method

constructs a new tank floor over the old existing floor with a concrete or clean river sand media between the two floors. Industry standard is to utilize four inches of concrete or sand on the old tank floor, installing a leak detection system within this area and then setting new floor plates on top of the concrete or sand. The new floor will require welding by certified welders and approved welding procedures. Nondestructive examinations as required by AWWA D100 will also need to be performed.

Either of the above repair methods should be designed and constructed by a company familiar with tank repair and construction to AWWA D100 and/or API-650 / API-653. API-653 further recommends installing a drip ring to the new tank chime; extending the life of the floor plate edge and chime.


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Note: Due to the presence of severe metal loss in the corner weld and the area immediately above the corner weld; utilizing repair method “b” above would both repair the tank floor and raise the elevation above the area of severe metal loss.

Minor Repairs: Repairs that do not adversely affect the overall operability or integrity of the tank and can be performed in the near future.

1. Repair by replacement the tank roof center vent. 2. Repair by welding the approximately 110 linear feet of corroded roof plate

lap welds. 3. Repair by the use of a lap welded patch, the through hole noted in the tank

roof at the knuckle to roof sketch plate. Additionally; repair by the use lap welded patches, all through holes where the roof mounted hanging anode system was installed; if not replaced with a new hanging anode system.

4. Repair by replacement the tank interior ladder and fall arrest system. 5. Repair by replacement the tank level float system and all appurtenances. 6. Remove all vegetation growth around the tank exterior. 7. Re-coat the entire interior of the tank to meet the current sanitation

requirements of AWWA. 8. Install or upgrade the cathodic protection system with a new hanging

sacrificial anode system, and perform yearly maintenance surveys as required by AWWA and API.


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If you have any questions, please feel free to contact me at our Kapolei office (808) 682-1667 or by cellular phone at (808) 630-8636. Regards,

Ken McNamara Engineering & Inspections Hawaii, Inc. Tank Specialist API-653 Cert. No. 0873 STI SP-001 Cert. AC24310 [email protected] Attachments: Appendix A: Photographs Appendix B: Ultrasonic Thickness Data Appendix C: Drawings Appendix D: T-min Remaining Life calculations

mailto:[email protected]�


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Appendix A

Photographs


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Tank name plate data

Typical design of Manway Nozzles N1 and N3


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Vegetation growth around tank circumference

Vegetation growth between concrete foundation and asphalt


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Topside of tank wind girder

Light debris in topside of wind girder


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Overview of tank roof

Condition of roof center vent


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Location of through hole in roof plate

Tank roof manway; location of old cathodic protection hanging anode


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Roof access ladder and platform

Roof manway with interior ladder


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Overview of topside corrosion on floor annular plate

Through hole at tank corner weld in annular plate


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Through hole in floor plate

Through hole in floor annular plate


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Severe shell plate pitting affecting the tank corner weld

Lake type floor plate corrosion


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Large areas of topside corrosion around the floor drain

Topside corrosion


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Roof support column without a bearing plate

Hanging anode system piled on the tank floor


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Heavy corrosion on interior ladder

Level float gage with broken guide wire


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Overview of roof underside with a hanging anode and holes where anodes used to be


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Appendix B

Ultrasonic Thickness Data


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Nozzle Thickness readings

UT Locations: 0 deg = Top (See shell layout drawing for Nozzle Locations)

Shell

Nozzles Size Location Reinforcement

Pad 0 deg 90 deg 180 deg 270 deg

N1 South Manway 24” .497 .478 .500 .482 .500

N2 North Manway 24” .502 .507 .502 .509 .513

N3 Outlet 12” .707 .705 .688 .679 .501


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Appendix B (Continued)

UT Measurements Tank Shell 1st Course

Location 1 2 3 4 5 6 7 8 9

C1 P1 0.465 0.467 0.074 0.460 0.463 0.458 0.463 0.463 0.461

C1 P2 0.462 0.463 0.117 0.463 0.464 0.464 0.463 0.466 0.463

C1 P3 0.466 0.467 0.469 0.465 0.467 0.423 0.471 0.471 0.395

C1 P4 0.463 0.463 0.461 0.464 0.463 0.461 0.463 0.464 0.458

C1 P5 0.471 0.474 0.468 0.470 0.471 0.467 0.462 0.468 0.445

C1 P6 0.465 0.466 0.459 0.462 0.465 0.089 0.468 0.458 0.461

C1 P7 0.474 0.475 0.474 0465 0.460 0.461 0.465 0.465 0.461

C1 P8 0.468 0.460 0.483 0.464 0.465 0.464 0.467 0.468 0.462

C1 P9 0.466 0.466 0.468 0.462 0.467 0.473 0.467 0.466 0.088

Note: Plate 1 starts at the South Manway and proceeds in a CCW direction around Tank.

Typical UT Measurement Location for every plate on the 1st course

1

2

3

4

5

6

7

8

9


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Tank Shell Readings Every 12” In Elevation South Manway Is 12 o’clock Proceeding CCW In 18 Equal Points

Location 12 o’clock

1 2 3 4 5 6 C1- 1 0.466 0.461 0.452 0.460 0.470 0.467

2 0.456 0.452 0.452 0.449 0.454 0.464 3 0.468 0.452 0.465 0.444 0.446 0.472 4 0.451 0.453 0.459 0.452 0.451 0.478 5 0.451 0.453 0.462 0.451 0.460 0.481

6 0.477 0.461 0.464 0.455 0.460 0.499 7 0.462 0.458 0.456 0.459 0.452 0.466 8 0.453 0.462 0.457 0.449 0.461 0.466 9 0.450 0.469 0.452 0.449 0.449 0.461

10 0.457 0.466 0.450 0.450 0.460 0.464 C2- 1 0.354 0.359 0.350 0.350 0.361 0.386

2 0.346 0.351 0.347 0.348 0.361 0.371 3 0.357 0.351 0.350 0.348 0.361 0.376 4 0.350 0.361 0.352 0.350 0.361 0.380 5 0.349 0.362 0.359 0.349 0.361 0.385

6 0.349 0.366 0.352 0.345 0.373 0.385 7 0.347 0.355 0.348 0.344 0.372 0.380 8 0.347 0.353 0.346 0.345 0.351 0.376 9 0.348 0.354 0.347 0.357 0.349 0.372

10 0.352 0.360 0.352 0.355 0.358 0.383 C3- 1 0.320 0.326 0.309 0.304 0.312 0.320

2 0.306 0.309 0.296 0.300 0.310 0.329 3 0.308 0.301 0.296 0.296 0.310 0.311 4 0.309 0.303 0.296 0.297 0.305 0.315 5 0.303 0.302 0.300 0.296 0.312 0.316

6 0.295 0.303 0.302 0.300 0.316 0.315 7 0.298 0.309 0.304 0.299 0.308 0.318 8 0.301 0.302 0.305 0.296 0.307 0.310 9 ------- Wind Girder ------ ------ ------

10 0.301 0.289 0.298 0.305 0.310 0.311


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Tank Shell Readings Every 12” In Elevation Manway Is 12 o’clock Proceeding CCW

Location 12 o’clock

1 2 3 4 5 6 C4- 1 0.300 .0298 0.299 0.305 0.310 0.301

2 0.299 0.305 0.302 0.303 0.310 0.308 3 0.296 0.301 0.296 0.304 0.308 0.305 4 0.298 0.301 0.299 0.306 0.305 0.301 5 0.296 0.302 0.302 0.305 0.308 0.304

6 0.299 0.298 0.296 0.301 0.305 0.302 7 0.300 0.301 0.298 0.305 0.303 0.310 8 0.300 0.298 0.295 0.300 0.299 0.306 9 0.297 0.301 0.305 0.307 0.305 0.310

10 0.299 0.299 0.301 0.308 0.310 0.312 Roof Slope 1 0.305 0.308 0.312 0.315 0.308 0.316

Note: Course heights are as follows: Roof Slope 2’ 0” Course 4 10’ 0”

Course 3 10’ 0” Course 2 10’ 0” Course 1 10’ 0”


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Location 7 8 9 10 11 12 C1- 1 0.477 0.469 0.452 0.449 0.460 0.434

2 0.485 0.452 0.452 0.448 0.461 0.439 3 0.484 0.454 0.451 0.452 0.458 0.441

4 0.490 0.455 0.453 0.457 0.462 0.447 5 0.485 0.460 0.464 0.461 0.468 0.448

6 0.471 0.467 0.457 0.479 0.488 0.466 7 0.467 0.460 0.447 0.466 0.477 0.452 8 0.467 0.457 0.444 0.455 0.462 0.439 9 0.476 0.459 0.445 0.457 0.462 0.438

10 0.474 0.466 0.452 0.454 0.466 0.439 C2- 1 0.371 0.362 0.352 0.355 0.346 0.345

2 0.368 0.357 0.346 0.354 0.342 0.341 3 0.368 0.360 0.352 0.350 0.340 0.338 4 0.369 0.357 0.356 0.347 0.350 0.360 5 0.368 0.373 0.360 0.350 0.341 0.354

6 0.375 0.360 0.350 0.350 0.352 0.344 7 0.367 0.362 0.347 0.350 0.345 0.342 8 0.367 0.370 0.352 0.347 0.352 0.345 9 0.363 0.366 0.354 0.351 0.344 0.345

10 0.365 0.377 0.359 0.352 0.346 0.347 C3- 1 0.316 0.280 0.295 0.293 0.318 0.311

2 0.309 0.307 0.290 0.286 0.310 0.303 3 0.309 0.294 0.298 0.289 0.307 0.306 4 0.299 0.304 0.284 0.291 0.315 0.306 5 0.302 0.312 0.288 0.289 0.318 0.313

6 0.310 0.314 0.298 0.288 0.318 0.313 7 0.305 0.311 0.300 0.306 0.317 0.316 8 0.302 0.299 0.305 0.306 0.304 0.315 9 ----- Wind Girder ----- ----- -----

10 0.306 0.305 0.311 0.299 0.303 0.304


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Location 7 8 9 10 11 12 C4- 1 0.289 0.296 0.288 0.278 0.296 0.297

2 0.288 0.294 0.292 0.291 0.287 0.296 3 0.300 0.296 0.285 0.289 0.291 0.298

4 0.310 0.289 0.299 0.297 0.298 0.300 5 0.301 0.299 0.298 0.295 0.289 0.300

6 0.305 0.301 0.288 0.298 0.304 0.298 7 0.301 0.297 0.294 0.287 0.301 0.299 8 0.300 0.298 0.301 0.287 0.298 0.300 9 0.301 0.289 0.295 0.299 0.300 0.299

10 0.305 0.291 0.300 0.298 0.284 0.300 Roof Slope 1 0.311 0.301 0.299 0.302 0.305 0.307




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Location 13 14 15 16 17 18 C1- 1 0.443 0.457 0.456 0.481 0.482 0.431

2 0.442 0.452 0.457 0.459 0.446 0.438 3 0.444 0.456 0.462 0.459 0.448 0.446

4 0.450 0.453 0.459 0.461 0.448 0.441 5 0.448 0.461 0.460 0.467 0.448 0.485

6 0.446 0.459 0.474 0.500 0.453 0.472 7 0.444 0.461 0.455 0.469 0.441 0.454 8 0.441 0.457 0.446 0.462 0.448 0.454 9 0.438 0.457 0.450 0.459 0.444 0.448

10 0.436 0.459 0.455 0.464 0.445 0.444 C2- 1 0.351 0.354 0.350 0.355 0.340 0.343

2 0.344 0.340 0.347 0.345 0.334 0.339 3 0.344 0.344 0.339 0.355 0.337 0.335 4 0.350 0.352 0.342 0.346 0.332 0.337 5 0.351 0.363 0.345 0.348 0.339 0.339

6 0.358 0.344 0.360 0.350 0.350 0.344 7 0.354 0.344 0.344 0.349 0.332 0.340 8 0.354 0.342 0.341 0.342 0.339 0.341 9 0.359 0.346 0.344 0.341 0.339 0.340

10 0.368 0.352 0.347 0.344 0.334 0.340 C3- 1 0.307 0.296 0.304 0.288 0.288 0.316

2 0.291 0.291 0.288 0.286 0.295 0.295 3 0.286 0.286 0.281 0.294 0.282 0.282 4 0.296 0.299 0.289 0.279 0.285 0.281

5 0.297 0.299 0.289 0.279 0.284 0.294 6 0.295 0.296 0.289 0.283 0.276 0.282 7 0.300 0.291 0.294 0.280 0.289 0.291 8 0.301 0.299 0.287 0.294 0.289 0.294 9 ----- Wind Girder ----- ----- -----

10 0.304 0.297 0.299 0.296 0.296 0.283


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Location 13 14 15 16 17 18 C4- 1 0.309 0.295 0.288 0.301 0.294 0.301

2 0.304 0.305 0.285 0.295 0.286 0.290 3 0.307 0.301 0.280 0.296 0.290 0.296 4 0.307 0.307 0.279 0.306 0.291 0.284 5 0.301 0.296 0.288 0.300 0.296 0.294

6 0.314 0.315 0.294 0.301 0.302 0.294 7 0.310 0.312 0.306 0.302 0.300 0.294 8 0.309 0.302 0.289 0.306 0.291 0.296 9 0.307 0.305 0.286 0.300 0.290 0.295

10 0.311 0.304 0.298 0.295 0.283 0.290 Roof Slope 1 0.300 0.304 0.286 0.296 0.304 0.291




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Floor Sump Thickness Readings

Tank “Mangilao 2” does not have a floor sump


E I


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Appendix C

Drawings

Tank No. Mangilao 2

Tank Floor Plate Layout 11-21-2010

E I & ENGINEERING INSPECTIONS

HAWAII, INC.

Guam Water Authority578 N Marine Corps Dr

Tamuning, Guam

N (Ref.)1

= Location of through holes

.256 .260

.262.254

.247 .204.128

.251 .208.219

.238

.188.120

.142

.131

.233

.072

.149

.170.229

.188

.135

.204

.144

.194

.110

.198

.251

.256

.112

.203

.123

.227

.256

.226

.145

.211

.250.106

.228

.250

.075

.215

.125

.091

.152

.237.131

.188

.109

.235

.256

.107.188

.254

.206

.137

.197

.175

.156

.216

.116

.262

.206

.205

.088

.226

.117

.109

.225

.143

.182

.126

.264.178

.156

.231

.227

.109

.236

.108.234

.206

.215

.219

.188

.229

.165

.208

.157

.217 .241

.251.233

.264 .234 .225.206

.196 .207 .215

Side View Plate Layout 11-21-2010


HAWAII, INC.

Tank No. Mangilao 2Guam Water Authority

578 N Marine Corps DrTamuning, Guam

Nozzle 0 90 180 270 Re-Pad

N1N2

24" Manway

12" Outlet

.500.497 .478 .482 .500

.513.502 .507 .509 .502

10'

10'

10'

10'

2'

Wind Girder

24" Manway

N3

N3 N1 N2

.707 .705 .679 .688 .501

Individual Plate Layout Pg. 1 11-21-2010


HAWAII, INC.

1 - 1

1 - 5

N2

N1

Tank No. Mangilao 2Guam Water Authority

578 N Marine Corps DrTamuning, Guam

54"

38"

54"

38"16"

N3

26" x 30"

A1

Tank No. Mangilao 2

Tank RoofPlate Layout 11-21-10


HAWAII, INC.

Guam Water Authority578 N Marine Corps Dr

Tamuning, Guam

.181

.199

.187

.201

.202

.209

.192

.187

.202

.188

.179

.192

.201

.209

.188

.181

.202

.191

.185

.190

.188.187

.200.187

.178

.182

.196.189

.194

.185.196

.194

.185

.192

.197

.201

.171

.179

.191

.191

.178

.186

.188

.198

.191

.182

.178

.183

.191

.189

.204

.201

.200

.189

.196

.171

.178

.188

.168

.187

.188

.185

.202

.191

.185

.181

.184.201

.196

.196

.192

.189

.172

.191

.186

.181

.201

.184

.191

.179

.180

.188

.172

.189

.197

.192

.189

.188

.192

.203

.191

.191.188

.191


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Appendix D

T-Min Remaining Life Calculations

The calculations provided are based on the plate thickness nearest to the actual thickness measurement from this inspection interval, not the design drawings as provided by GWA. Continued service must be evaluated by an Engineer experienced in the disciplines associated with evaluating mechanical and material characteristics that affect the integrity and reliability of above ground storage tanks.

File No3

Report No10-278

InitialsGuam

ClientDCA / GWA

Tank NoMangilao 2

Date 12/6/2010

Temp. °F120

Tank Shell Minimum Thickness and Remaining Life Calculations

Material Crs H (ft)38.5H (ft)

28.518.58.5

tmin (in)

0.0.0.0.

0.A588A588A588A588

92.5 1.00 0.85D (ft) G E 38.5Fill Height (ft)

2.6D(H-1)GSE

tmin =

Where:

H = The height above the bottom of the course of study to the maximum liquid level height of the product, in feet. For corroded or pitted areas, H = the height from the bottom of the corroded or pitted area to the maximum liquid level height of the product, in feet.

tmin = The calculated minimum acceptable shell thickness, in inches (can not be less than 0.100 inch for any course). The minimum acceptable shell thickness allowed by API-653 and STI-SP001 for tank size, in inches .

D = Nominal diameter of tank, in feet.

G = Highest specific gravity of the contents (including test water if tank will, or may, be tested in the future).

S = Maximum allowable stress, in psi. For welded tanks; use the smaller of 0.80Y of 0.429T for bottom and second course or the smaller of 0.88Y or 0.472T for all other courses. For riveted tanks; S = 21,000 psi. For STI Tank Inspections S = 26000 (E = 1)

Y = Specified minimum yield strength of the plate, in psi; use 30,000 psi if not known (N/A for riveted tanks).

T = The smaller of the specified minimum tensile strength of the plate or 80,000 psi; use 55,000 psi if not known (N/A for riveted tanks).

E = Original joint efficiency for the tank. For welded tanks; use API-653, Table 2-1 ; use E = 1.0 when evaluating the retirement thickness in a corroded plate, when away from welds or joints by at least the greater of one inch or twice the plate thickness. For riveted tanks; use E = 1.0 for shell plates greater than 6 inches away from rivets; use the value of E from API-653 Table 2-1 when within 6 inches of rivets. For STI Tank Inspections E = 1 where S = 26000.

10101010

Course 1Course 2Course 3Course 4

SHELL MINIMUM THICKNESS CALCULATIONS

S (psi)28743287432973629736

0.2710.1670.100

0.369

Report No 10-278

File No3

Report No10-278

InitialsGuam

ClientDCA / GWA

Tank NoMangilao 2

Date 12/6/2010

Temp. °F120

Tank Shell Minimum Thickness and Remaining Life Calculations

tmin

0.2710.1670.100

0.3690.4490.3540.2840.282

tact0.5000.3750.3000.300

tprev Ca

0.0830.1170.182

0.080Cr

0.0027RL30

0.00110.00080.0009

75140192

Where:

Ca = Remaining corrosion allowance of the shell course under consideration, in inches.

Cr = Corrosion rate of the shell course under consideration, in inches per year.

FHc = Calculated fill Height = (SEtact/2.6DG+1) + (product height below course of interest)

tact = Minimum thickness measurement of the shell course under consideration, as recorded at the time of inspection, in inches.

tmin = minimum required thickness of shell course, at the maximum allowable fill height

tprev = previous thickness measurement of shell course under consideration, as recorded at last inspection or nominal thickness if no previous thickness measurements, in inches.

RL = Estimated remaining life of the shell course under consideration, in years.

Y = Time span between thickness readings or age of the tank if nominal thickness is used for tprev, in years.

SHELL REMAINING LIFE CALCULATIONS

Ca = tact-tmin = Remaining Corrosion Allowance (inches)Cr = tprev-tact / Y = Corrosion Rate (inches per year)RL = Ca / Cr = Remaining Life (years)

19Y = = Tank age (years)

Course 1Course 2Course 3Course 4

Course FHc46.6146.9650.8560.64

Report No 10-278

File No1

Report No10-278

InitialsGUAM

ClientDCA - GWA

Tank NoMangilao 2

Date 12/7/2010

Temp. °F120

API-650, 5.11 CALCULATIONS

STORAGE TANK WIND LOAD EVALUATION

Ca Shl0.000 lbs/in30.2833

Total Weight

337611 lbs

lbs

Other Rf Wt

0

V155

Wp 30 psf (shell)

Ex 3793 psf (shell) 6720 psf (roof)

50 psf (roof)

Material Catagory

Carbon Steel

ts0.250

th0.188 2

ta0.250

Xa0.938

D92.5

H41

Xs1743.588

Ws178149

L558.234

60Lp

Xr209.896

Wr52142

leg 22

leg 1 Wa926

Horz.Vert.App Angle°Dome Rad

0.8D

Ca Rf0.000

Crs 110.0

Crs 210.0

0.500 0.375

Crs 310.0

Crs 410.0

0.300 0.300

Crs 51.0

Crs 6

0.285

Crs 7 Crs 8Crs H

tnom

59245Wt 44434 35547 35547 3377

0.044

Rr.74.000

0 0

RlaOther Shl Wt

lbs

RoofBttm Shell Crs

Angle

Yield Stress430004300043000

MaterialA 662M CA 662M CA 662M C

Mw 5488628

Mpi 1971132

MF 29434165

wa 2190

WDL 10650960

moment about the shell-to-bottom joint from design internal pressure = Pi*(3.1416*D^2/4)*144*(D/2)

overturning moment about the shell-to-bottom joint from horizontal plus vertical wind pressure, Sh Mo =Wp*Ex*H/2) + Rf Mo =lesser of (Wp+Pi*144)*Ex*(D/2) or (Pi*1.6*144*Ex*D/2)

moment about the shell-to-bottom joint from liquid where weight of liquid is wl defined in E.2.2 using a specific gravity of 0.7 and a height of one half the design liquid height H, (see Figure 5-27). =(D/2)*wa*3.1416*D

= 4.67*tb*Fy*H

moment about the shell-to-bottom joint from the weight of the shell and roof supported by the shell, =(Wr+Ws)*(D/2)

1. 5264308 7100640 This condition does not require anchoring2. 6277080 20042563 This condition does not require anchoring

Tank must meet both following conditions, Column "A"must be less than column "B" to not require anchoring:

A B<

<

113894 135044 This condition does not require anchoring

Tank resitance to Sliding

Wind Press. Total Wt (Empty)< Lbs

0.6Mw+Mpi < MDL / 1.5

Mw+0.4Mpi < MDL+Mf) / 2

Wp x Ex < 0.4Tank Wt

tb0.386

D92.75

tba0 106394

WbARW0

lbs/ft^30 in

Ins thickness

0Wi0

Ca Btm0.000

lbs

Ins Wt

Bottom 36000A 36M

Pi

Supported Cone Roof

Floor DataShell Data

Roof Data Top Angle Data

Shell Data RySyAyFy

MPH

File No1

Report No10-278

InitialsGUAM

ClientDCA - GWA

Tank NoMangilao 2

Date 12/7/2010

Temp. °F120

API-650, 5.11 CALCULATIONS

STORAGE TANK WIND LOAD EVALUATION

Where;

ARW = annular floor plate width normal to tank radius, inches (normally 26”)D = tank diameter in ftDlr = roof plates dead load, in lbs/ft^2Ex = exposed area of component under consideration, ft^2Fy = floor material yield stress, psiH = shell height, ftL = roof radius parallel to plate, inchesLP = roof height parallel to tank vertical axis (in) NOTE: std = 0.75 in. per 1 ft, Lr = specified live load, in lbs/ft^2, use 20 lbs/ft^2 if not specifiedMw = wind moment at base of shell [Wp]*[ex]*([h]/2) + Rf Mo =lesser of ([Wp]*[Ex]*([D]/2) or ([Pd]*1.6)*144*[Ex]*([D]/2)Pi = original design internal MAWP, psiPSI = pounds per square inchRla = additional roof dead load, lbs/sqft (i.e., framing, insulation, walkways, et)Rr = dome radius of dome type roofs, fttb = thickness of bottom general plates, inchestba = thickness of bottom annular plates, inchesth = thickness of roof plate, in inches tnom = nominal thickness of component, inchestmin = minimum required thickness of component (tnom-Ca), inchests = top shell course plate thickness, in inches. V = design wind speed per API-650 5.2.1 (f), mph (120mph) or ASCE 7 fig 6-1 or alternately as designated by tank ownerWb = weight of bottom plates, lbswc = inches of water columnWi = weight of insulation, lbsWp = wind pressure, psf [Roof =(30*([V]/120)^2), Shell =(18*([V]/120)^2)]Wr = roof plates total weight, lbsWs = shell plates total weight, lbsWt = total tank weight in the corroded condition resisting up lift (roof, shell, framing, angle), lbsXr = cross sectional area of roof, in^2Xs = cross sectional area of shell crs 1, in^2

APPENDIX B PHOTOS



Mangilao Tank Photos


Mangilao 2 Water Tank Reservoir Photo No. 1

Mangilao 2 Water Tank Reservoir Photo No. 2

Mangilao Tank Photos 2

ENGINEERING (CIVIL, STRUCTURAL, MECHANICAL, ENVIRONMENTAL) * CONSTRUCTION MANAGEMENT * SURVEYING ENVIRONMENTAL SERVICES * PLANNING * DEVELOPMENT CONSULTATION * GEOGRAPHIC INFORMATION SYSTEMS GUAM P.O. Box 8900, Tamuning, Guam 96931 / 155 ET Calvo Memorial Parkway, Suite 200, Tamuning, Guam 96913 / Tel: (671) 646-7991 / Fax: (671) 646-6315 SAIPAN Caller Box PPP, Suite 164, Saipan, MP 96950 / Chalan Pale Arnold, Pacific Plaza Bldg., Unit 5, South Garapan, Saipan 96950 / Tel: (670) 234-9017 / Fax: (670) 234-3842

Tank Identification Plate Photo No. 3

Corrosion at Base of Exterior Tank Floor Plate Photo No. 4







Exterior Tank Shell with Corrosion at Welded Joint Photo No. 7

Base of Interior Column Support with Surface Corrosion Photo No. 8



Base of Interior Column Support with Isolated Corrosion Photo No. 9





Severely Corroded Interior Tank Ladder Photo No. 12







Surface Corrosion on Interior Wall Shell Plates Photo No. 15








Surface Corrosion at Roof Shell Plate & Roof Framing Photo No. 19









Corrosion at Roof Shell Plate & Roof Framing Photo No. 24












Corrosion at Base of Interior Tank Wall Shell Photo No. 30



Corrosion at Base of Interior Tank Wall Shell Photo No. 31

Through Hole at Interior Tank Floor Base Plate from Corrosion Photo No. 32



Corrosion Pit at Interior Tank Floor Base Plate Photo No. 33




Corrosion Pit at Interior Tank Floor Base Plate Photo No. 35






APPENDIX C CALCULATIONS (ETABS)



ETABS v9.7.0 - File: Mangilao 2 - January 21,2011 15:503-D View - Kip-in Units

Duenas Camacho & AssociatesETABS - Finite Element Model

Mangilao 2 Smax Combo Course Note

Water Tank ksi

Water @ 38', t=0.449" 25.6 AWWA1 1 Stresses from actual thickness exceed AWWA

Wind/Seismic @ 38', t=0.449" 26.7 AWWA2 1 Stresses from actual thickness exceed AWWA

Water @ 24', t=0.449" 14.3 AWWA1 1 AWWA calculated fill height

AWWA allows 15ksi stresses in steel tank shell for Dead + Live Load

AWWA allows 20ksi stresses in steel tank shell Wind & Seismic Combinations

Combo AWWA1 = 1.0DL+1.0LL+1.0H20

Combo AWWA2 = 1.0DL+1.0LL+1.0H20+1.0WIND

Combo AWWA3 = 1.0DL+1.0LL+1.0H20+1.0QUAKE

ETABS v9.7.0 - File: Mangilao 2 - January 21,2011 15:513-D View Stress SMAX Diagram (AWWA1) - Kip-in Units

Duenas Camacho & AssociatesETABS - DL + LL COMBO AWWA1, H = 38ft

0.0 2.2 4.4 6.6 8.8 11.0 13.2 15.4 17.6 19.8 22.0 24.2 26.4 28.6

ETABS v9.7.0 - File: Mangilao 2 - January 21,2011 15:493-D View Stress SMAX Diagram (AWWA2C2A) - Kip-in Units

Duenas Camacho & AssociatesETABS - Wind Combo AWWA2, H = 38ft

0.0 2.4 4.8 7.2 9.6 12.0 14.4 16.8 19.2 21.6 24.0 26.4 28.8 31.2

ETABS v9.7.0 - File: Mangilao 2-reduced - January 21,2011 15:523-D View Stress SMAX Diagram (AWWA1) - Kip-in Units

Duenas Camacho & AssociatesETABS - DL + LL COMBO AWWA1, H = 24ft

0.0 1.2 2.4 3.6 4.8 6.0 7.2 8.4 9.6 10.8 12.0 13.2 14.4 15.6

Yigo 1 Astumbo 1 Mangilao 2 Mangilao 2

H 38.5 38.5 38.5 38.5 Current Fill Height, ft

S 15000 15000 15000 15000 psi

E 0.85 0.85 0.85 0.85 n/a

t 0.08 0.555 0.449 0.074 Shell Thickness, in

D 48 66 92 5 92 5 ft

AWWA D100 Allowable Fill Heights

D 48 66 92.5 92.5 ft

G 1 1 1 1 n/a

H* 8.17 41.24 23.80 3.92 Maximum Fill Height, ft

H* = SEt/(2.6DG)

Derived from:Derived from:

t = 2.6DHG/(SE) (Equation 3‐19) AWWA D100

AWWA D100 Standard allows 15ksi stresses

Yigo 1 Astumbo 1 Mangilao 2 Mangilao 2

API‐653 Allowable Fill Heights

H 38.5 38.5 38.5 38.5 Current Fill Height, ft

S 23500 23500 23500 23500 psi

E 0.85 0.85 0.85 0.85 n/a

t 0.08 0.555 0.449 0.074 Shell Thickness, in

D 48 66 92.5 92.5 ft

G 1 1 1 1 n/a

H* 13 80 65 60 38 29 7 15 Maximum Fill Height ftH* 13.80 65.60 38.29 7.15 Maximum Fill Height, ft

H* = SEt/(2.6DG) + 1

Derived from:

t = 2.6D(H ‐ 1)G/(SE) API‐653 Addendum 2

API 653 Standard allows 30ksi stresses

GWA Water Tanks - Mangilao 2 Seismic Calculations

Tank DimensionsUniform Shell Thickness, t,

t = in = mWater Height, H

H = ft = mTank Radius, r

r = ft = mH/r =

Calculated Masses and Centers of Gravity

0.380 0.00966

38.5 11.73

46.25 14.100.832

Calculated Masses and Centers of GravityMass of water in tank, ml

ml = kgMass of tank wall, mw

mw = kgHeight of Tank Wall Center of Gravity, hw

hw = mMass of Tank Roof, mr

mr = kg

7.33E+06

7.38E+04

5.46

2.30E+04mr kgHeight of Tank Roof Center of Gravity, hr

hr = mImpulsive & Convective Masses, mi & mc

mi = kgmc = kg

Material PropertiesYoung's Modulus, steel

12.19

2.30E+04

3.47E+047.29E+06

Young s Modulus, steelE = ksi = Pa

Density of Fluidrho = lb/ft3 = kg/m3

Calculated PeriodImpulsive Coefficient, Ci

Ci =Convective Coefficient Cc

29,000 2.0E+11

62.4 1000

6.70Convective Coefficient, Cc

Cc = s/m^0.5Implusive Natural Period, Ti

Ti = Ci*(H/rho^0.5)/((E*t/r)^0.5) = sConvective Natural Period, Tc

Tc = Cc*r^0.5 = s

Seismic Responses `Impusilve Acceleration Si

1.56

0.212

5.87

Impusilve Acceleration, SiSi = g

Convective Acceleration, ScSc = g

Total Base Shear, QQ = (mi+mw+mr)*Si+mc*Sc = N = kips

Overturning Moment above the base plate, Mhi = m hi = mM = (mi*hi+mw*hw+mr*hr)*Si+mc*hc*Sc = Nm = kip ft

1.24E+03

9 29E+03

1.17

0.06

5.52E+06

4.8 6.931 26E+07M = (mi*hi+mw*hw+mr*hr)*Si+mc*hc*Sc = Nm = kip-ft

Wave Sloshing Height, dd = r*Sc/g, where g acceleration due to gravity m = ft

PROJECT: SHEET

BY DATE CHECKED BY DATE SUBJECT: OF

2.32

9.29E+031.26E+07

0.79

GWA Water Tanks 1

DAL TPC M il 2 S i i C l l ti 3DAL TPC Mangilao 2 - Seismic Calculations 3

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