46920 County Rd E Center, CO Phone: Fax: Pump Rebuild Report. Union/Flowserve 6x8 MQF, 7 stage

Transcription

1 46920 County Rd E Center, CO Phone: Fax: Pump Rebuild Report Union/Flowserve 6x8 MQF, 7 stage April, 2016 Pump Rebuild Report PZE Page 1

2 Contents Page Project Data... 3 Introduction... 4 Basic Pump Discussion... 4 Damage Found... 7 Root Cause... 8 Repairs Made: Impellers... 9 Shaft Casing /2 Interstage Piece Center Bushing Thrust Bushing and Sleeve Packing Sleeves Packing Bearing Housings Bearings Lubrication Oil Pump Recommendations Other Information Pump Rebuild Report PZE Page 2

3 Project Data Customer:...Zelezara Smederevo Customer Purchase Order Number Customer Purchase Order Date Power Zone Work Order Number Repair Start Date Repair Completion Date Equipment... Union Pump 6x8 MQF, 7 stage 1 st Impeller Double Suction inch diameter 2 nd Impeller Single Suction inch diameter 3 rd Impeller Single Suction inch diameter 4 th Impeller Single Suction inch diameter 5 th Impeller Single Suction inch diameter 6 th Impeller Single Suction inch diameter 7 th Impeller Single Suction inch diameter Pump Rebuild Report PZE Page 3

4 Introduction In early 2016, discussions between Power Zone Equipment and Zelezara Smederevo led to the steel mill contracting with Power Zone to rebuild their 7 stage de-scaling pump. The work was to proceed quickly, as the mill has no backup pumps in service. The purchase order was issued on January 14, the pump was shipped to Power Zone, and the down payment was received February 22. Work began immediately. The pump was severely damaged, resulting in an extensive rebuilding effort. The pump rebuild was completed on April 19. Testing took place between April 19 and April 25. The pump was packaged for shipment on April 26. This report contains a complete description of the work performed. In order to provide context to the report, we start with a brief overview of the pump s operations and some of the design issues involved. We then move into an overall description of the damage and our evaluation of the root cause of the failure. Next we discuss the damage found to each individual part and the corrective actions taken. Finally, we discuss recommendations for the future operations and maintenance of the pump. Basic Pump Discussion In order to understand the work performed, we first need to understand some of the basics of a large multi-stage split case pump like this. The first impeller on this pump is a double suction impeller, allowing flow to enter the eye of the impeller from both sides. The flow is directed into the casing with a cutwater and led into the eye of the second impeller. As the flow passes through each impeller, pressure is added and a thrust force is created towards the suction of each impeller. In order to balance the axial thrust on the shaft, the flow direction is reversed after the 4 th impeller, so thrust from impellers 2, 3, and 4 is pushing the shaft to the left, and thrust from impellers 5, 6, and 7 is pulling the shaft to the right. Pump Rebuild Report PZE Page 4

5 The cutwater is the sharp angle that directs the accelerated fluid away from the impeller. In this pump, there is are 2 cutwaters for each impeller, one in the top casing half and one in the bottom casing half. The cutwater sees the most wear in the casing since the fluid impacts it directly. Another important concept in pump design is the clearance between rotating parts and non-rotating parts. Most of these clearances in a pump are controlled by wear rings. We have non-rotating casing rings and rotating impeller rings. Each impeller is equipped with a wear ring around the suction eye and another on the back of the impeller on the hub. There are matching stationary rings in the casing. By carefully machining the diameters of these rings, reasonable clearances can be maintained. Note that the hub rings have the same pressure on both sides: the side towards the back of the impeller and the side towards the next stage. There is no pressure difference to drive fluid between the rings and there is usually little wear. These rings are generally narrower and lighter duty. The casing hub rings are two part rings in this pump. The eye rings see the full pressure difference between the suction and discharge of an impeller. That pressure difference is driving fluid from the front of the impeller, through the Pump Rebuild Report PZE Page 5

6 clearance between the rings, and back into the suction. If the clearance between the rotating eye ring and the casing eye ring is too tight, the rings may touch each other and gall. If the clearance is too large, the fluid will flow faster and wear the rings faster. We used standard API 610 ring clearances to be sure there would be no contact, yet retain reasonable efficiency. This pump has a machined interstage casing ring and shaft sleeve separating the suction of the first stage from the suction of the second stage. This ring works like an impeller eye ring, separating the 1 st stage suction pressure from the 1 st stage discharge pressure/2 nd stage suction pressure. The last set of rotating-versus-statinary parts are the thrust and center bushings. (see diagram on following page). The impeller eye rings resist the pressure generated by one impeller. The thrust and center bushings resist pressure from multiple impellers. The center bushing is located in the center of the pump between the 4 th and 7 th impellers. One side of the bushing sees the discharge pressure from the 4 th impeller, and the other sees the discharge pressure of the 7 th impeller. The pressure across this area is generated by 3 impellers, about 1000 psi. The non-rotating bushing is about 8 inches long and fits tightly into the casing. The rotating wear area is made from extending the impeller hubs from the 4 th and 7 th impellers until they meet. The small gap between the rotating impeller hubs and the heavy non-rotating bushing needs to be very long to provide adequate resistance to the flow being forced through the gap. The throttle bushing is similar. It is located at the non-drive end of the pump and breaks pressure from the suction of the 5 th impeller (discharge pressure of the first 4 impellers, or about 1350 psi) to suction pressure. The large balance line under the pump allows the Pump Rebuild Report PZE Page 6

7 small amount of water flowing past the throttle bushing to return to the pump suction. This keeps the shaft packing at suction pressure. With such a high pressure break, this must be a long bushing to restrict the flow adequately. Damage Found As we opened up the pump, several large pieces of iron debris were present. Below is a list of the issues with the pump that needed correction: 1. First Stage Impeller Both suction eyes were severely damaged. Wear ring on the side towards the secnd impeller was missing. Large pieces or debris were lodged in the impeller. Some of the debris were pieces of the missing impeller wear rings. Severe cavitation damage was found on the outer edge of the impeller vanes. 2. Interstage Bushing Between 1 st and 2 nd Stage (1/2 Interstage Ring) Missing. 3. Interstage Sleeve Severely worn. Sleeve was moved about 2 inches out of position towards the 2 nd impeller. 4. Casing Places where casing rings for first impeller and interstage piece fit severely worn. Cutwaters at first stage shoed severe cavitation damage th impeller Broken shroud. 6. Impellers 2, 3, 4, 5, 6, 7 Debris lodged in impellers. Debris was round iron as well as pieces of the 1st impeller, 5 th impeller and 1/2 interstage ring. 7. Shaft - Bent runout at 2 nd impeller. Severly worn between 1 st and 2 nd impeller. 8. Bearing Housings Split between top and bottom half of housings was not flat. One of the sleeve bearings was held in place by a shim. Mounting surface between bearing housings and pump not true. Oil deflector ring between thrust bearing and sleeve bearing too small. 9. Center Bushing Severly worn. 10. Throttle Bushing Severely worn. 11. Packing Sleeves Severely worn. Pump Rebuild Report PZE Page 7

8 12. Packing Destroyed. No lantern rings found. Two different types of packing were found: one that appeared to be Teflon/graphite with Aramid corners and another that appeared to be metal strand reinforced. 13. Oil Pump Broken off, one pumping screw missing. 14. Normal Pump Rebuild Items Machine existing casing rings, make new impeller rings (both hub and eye) to re-estabish proper clearances. Root Cause We believe that the primary cause of the failure was several large pieces of iron and debris entering the pump. Some of that debris was trapped at the entrance to the first impeller and rotated against the stationary rings, destroying both the eye of the impeller and the rings. As the rings and impeller parts wore, large pieces broke off and were wedged in the first impeller. The flow distrubance from these obstructions caused massive cavitation, which eroded away about 2-3 inches of metal at the cutwaters. Some of the metal pieces and debris made it past the first impeller and into other impellers. We found debris in all 7 of the impellers. Pump Rebuild Report PZE Page 8

9 Repairs Made 1st Impeller Cavitation Damage to Vane Tips Impeller Eye Worn Away Trapped Debris First impeller was replaced with a new impeller. Shown here with new eye wear rings installed. Pump Rebuild Report PZE Page 9

10 5 th Impeller Broken Shroud New Impeller All Other Impellers: All Impellers: Dye Penetrant Tested for Cracks (Small cracks repaired in Impellers 4 and 7) New Eye Rings (inside casing rings) New Hub Rings Equipped with new hub rings and eye rings Hub and eye rings were heat treated to medium Brinell hardness to prevent galling against the un-treated, softer casing rings. Casing rings (both two-piece hub rings and single-piece eye rings) were machined to uniform diameters. Pump Rebuild Report PZE Page 10

11 Shaft Shaft Between Impeller 1 and 2 Severely Worn Original Shaft Being Checked For Runout (Bend) Original Shaft Measured with Runout at 2 nd Impeller New Shaft Shaft Journals Coated with Tungsten Carbide The new shaft was also checked for runout. After the impellers were installed, we measured runout, and we took corrective action to reduce that to maximum indicated runout. Impellers are heat shrunk onto shaft with keys for additional security. Pump Rebuild Report PZE Page 11

12 Pump Casing Cavitation Damage to Cutwater Severe Wear at 1/2 Interstage Saddle Severe Wear at Casing Ring Saddle Cavitation Damage Repaired Worn Saddle Fits Welded and Machined to Size The repair of the saddle fits and the cutwaters involved welding, which always distorts the casing. Following the welding repairs, the top and bottom casing halves were milled flat and then all of the interior saddle fits were re-machined to the correct sizes. Pump Rebuild Report PZE Page 12

13 1/2 Interstage Ring and Sleeve 1/2 Interstage Sleeve Forced Into Eye of 2 nd Impeller 1/2 Interstage Piece Missing New 1/2 Interstage Sleeve Correctly Located New 1/2 Interstage Piece The new 1/2 interstage shaft sleeve was tungsten coated for durability before installation. Pump Rebuild Report PZE Page 13

14 Center Bushing Center Bushing with Signs of Contact Hubs of Impellers 4 and 7 Under Center Bushing Center Sleeve Inside Diameter Restored Hub Rings of Impellers 4 and 7 Coated with Tungsten Carbide for Durability Center Bushing on Rotor Assembly Stand Pump Rebuild Report PZE Page 14

15 Thrust Bushing and Sleeve Thrust Bushing Severely Worn Thrust Sleeve Moderately Worn Thrust Bushing Inside Diameter Restored Thrust Sleeve Tungsten Carbide Coated for Durability Pump Rebuild Report PZE Page 15

16 Packing Sleeves Non Drive End Packing Sleeve Wear Drive End Packing Sleeve Severe Wear Non Drive End Packing Sleeve Repaired and Tungsten Carbide Coated Drive End Packing Sleeve New Sleeve Made and Tungsten Carbide Coated Pump Rebuild Report PZE Page 16

17 Packing Metal Filament Packing No Lantern Ring 100% GFO Packing with Mandrel and Installation Tool Metal filament packing is usually used for valves and other limited motion applications and likely caused the excessive wear. When we disassembled the pump, we did not see any lantern rings. We made new bronze split lantern rings. The 100% GFO (Gore fiber only) packing we utilized is intended for high speed services. We also added lantern rings for the fresh water packing flush. Packing: Sepco ML4002, ½ size The packing was cut on an angle using the white plastic mandrel, and installed into the pump using the 1/3 round tool. The packing is installed like this: Note that the fresh water flush needs to be at a higher pressure than the suction pressure of the pump to ensure that the fresh water is flowing across the packing into the pump. Pump Rebuild Report PZE Page 17

18 Bearing Housings Thrust End Bearing Housing Drive End Bearing Housing Thrust End Bearing Housing Drive End Bearing Housing The bearing housing had two issues to correct: 1. The top and bottom halves were warped and the split line between them did not meet. We suspect there was a significant oil leak. (See oil on split lines in BEFORE photos above). We milled the top and bottom halves of the bearing housings flat, and then need to re-establish the circular fits inside the housings. 2. The surfaces where the bearing housings mount to the pump were not true. We milled those to perpendicular. Pump Rebuild Report PZE Page 18

19 Bearings The sleeve and thrust bearing surfaces were in good condition. However, the outside diameter of the drive end bearing fit loosely into the bearing housing. We added metal to the outside diameter to restore a tight fit between the bearing and the bearing housing without the requirement for a shim. We also refinished the babbit. Lubrication Oil Pump Original Pump Broken Off, One Pumping Screw Missing New Oil Pump We replaced the oil pump with a new pump, IMO pump model D3EIC-95D, part number 3240/245, from Colfax Fluid Handling. Pump Rebuild Report PZE Page 19

20 Recommendations In order to maximize the life of the pump, we recommend the following: 1. Provide a strainer on the pump suction line. The damage to the pump was caused by large solids in the pump system. It is critical to prevent these solids from entering the pump. Clean the suction piping thoroughly before installing the pump again. 2. Be sure the fresh water is flowing in the packing glands. We would recommend some type of very low flow indicator or pressure gages on the packing flush lines to provide visual evidence that the water is flowing. If pressure gages are used, we just need to be sure that the pressure on the flush line is greater than pump suction pressure by more than 15 psi. 3. Provide accurate pressure gages on the suction and discharge lines of the pump. 4. Provide a flow measuring device in the system if possible. 5. Using a laser tool, carefully align the motor to the pump before starting. Check the alignment again after one week of serivce, then again after one month of service. 6. Monitor the vibration of the pump at the bearings on a regular basis (weekly, for example). 7. Monitor the temperature of the following regularly: a) Shaft at the stuffing boxes b) Packing flush lines c) Drive and and non-drive end bearings d) Lubrication oil temperature (should run around degrees F, or degrees C) 8. Use high quality Gore fiber only packing (like Sepco ML4002). Press the packing by hand snugly into the stuffing box with the tools provided. Pump Rebuild Report PZE Page 20

21 Other Information For more information regarding this pump rebuild project, please refer to: 1. Pump Test Report 2. Pump Rebuild Data (showing measurements, clearances and details of the pump repair project) 3. Photos (as-received, during teardown, during assembly, during testing, and asshipped) 4. Pump Curves 5. Rotor Balance Report 6. New lube oil pump data sheet 7. New packing data sheet Pump Rebuild Report PZE Page 21