Sample Pump Rebuild Report - Power Zone Equipment, Inc. · Pump Rebuild Report PZE 10625 Page 5 The...

Pump Rebuild Report PZE 10625

46920 County Rd E Center, CO 81125

Phone: 719-754-1981 Fax: 719-754-1982

Pump Rebuild Report

Union/Flowserve 6x8 MQF, 7 stage

April, 2016


Contents Page

Project Data ........................................................................................ 3

Introduction ........................................................................................ 4

Basic Pump Discussion ........................................................................ 4

Damage Found .................................................................................... 7

Root Cause .......................................................................................... 8

Repairs Made:

▪ Impellers ...................................................................................... 9

▪ Shaft ........................................................................................... 11

▪ Casing ......................................................................................... 12

▪1/2 Interstage Piece ................................................................... 13

▪ Center Bushing .......................................................................... 14

▪ Thrust Bushing and Sleeve ......................................................... 15

▪ Packing Sleeves .......................................................................... 16

▪ Packing ...................................................................................... 17

▪ Bearing Housings ....................................................................... 18

▪ Bearings ..................................................................................... 19

▪ Lubrication Oil Pump .................................................................. 19

Recommendations ............................................................................ 20

Other Information ............................................................................. 21


Project Data

Customer: .............................................................Zelezara Smederevo

Customer Purchase Order Number ................................... 4500036132

Customer Purchase Order Date .......................................... 14.01.2016

Power Zone Work Order Number ............................................... 10625

Repair Start Date .................................................................. 22.2.2016

Repair Completion Date ........................................................ 18.4.2016

Equipment ............................................ Union Pump 6x8 MQF, 7 stage

1st Impeller – Double Suction – 13.00 inch diameter

2nd Impeller – Single Suction – 13.00 inch diameter

3rd Impeller – Single Suction – 13.00 inch diameter

4th Impeller – Single Suction – 11.00 inch diameter





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 4th 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.


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


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 1st stage suction pressure from the 1st stage discharge pressure/2nd

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 4th and 7th impellers.

One side of the bushing sees the discharge pressure from the 4th impeller, and the other

sees the discharge pressure of the 7th 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 4th and 7th 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 5th impeller (discharge pressure of the first 4 impellers, or

about 1350 psi) to suction pressure. The large “balance line” under the pump allows the


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 1st and 2nd Stage (1/2 Interstage Ring) – Missing.

3. Interstage Sleeve – Severely worn. Sleeve was moved about 2 inches out of

position towards the 2nd impeller.

4. Casing – Places where casing rings for first impeller and interstage piece fit

severely worn. Cutwaters at first stage shoed severe cavitation damage.

5. 5th 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, 5th impeller and 1/2 interstage ring.

7. Shaft - Bent. 0.008” runout at 2nd impeller. Severly worn between 1st and 2nd

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.


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.


Repairs Made

1st Impeller

Before:

Cavitation Damage to Vane Tips Impeller Eye Worn Away

Trapped Debris

After:

First impeller was replaced with a new impeller.

Shown here with new eye wear rings installed.


5th Impeller

Before: After:

Broken Shroud New Impeller

All Other Impellers:

Dye Penetrant Tested for Cracks (Small cracks repaired in Impellers 4 and 7)

All Impellers:

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.

New Eye Rings

(inside casing rings)

New Hub Rings


Shaft

Before:

Shaft Between Impeller 1 and 2 Severely Worn Original Shaft Being Checked For Runout (Bend)

Original Shaft Measured with 0.008” Runout at 2nd Impeller

After:

New Shaft Shaft Journals Coated with Tungsten Carbide

The new shaft was also checked for runout. After the impellers were installed, we

measured 0.002” runout, and we took corrective action to reduce that to 0.001”

maximum indicated runout. Impellers are heat shrunk onto shaft with keys for additional

security.


Pump Casing

Before:

After:

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.

Cavitation Damage to Cutwater

Severe Wear at Casing Ring Saddle

Severe Wear at 1/2 Interstage Saddle


1/2 Interstage Ring and Sleeve

Before:

After:

The new 1/2 interstage shaft sleeve was tungsten coated for durability before installation.

1/2 Interstage Piece

Missing

New 1/2 Interstage Piece

1/2 Interstage Sleeve Forced

Into Eye of 2nd Impeller

New 1/2 Interstage Sleeve Correctly Located


Center Bushing

Before:

Center Bushing with Signs of Contact Hubs of Impellers 4 and 7 Under Center Bushing

After:

Center Sleeve Inside Diameter Restored Hub Rings of Impellers 4 and 7 Coated with

Tungsten Carbide for Durability

Center Bushing on Rotor Assembly Stand


Thrust Bushing and Sleeve

Before:

Thrust Bushing Severely Worn Thrust Sleeve Moderately Worn

After:

Thrust Bushing Inside Diameter Restored Thrust Sleeve Tungsten Carbide Coated

for Durability


Packing Sleeves

Before:

Non Drive End Packing Sleeve Wear Drive End Packing Sleeve Severe Wear

After:

Non Drive End Packing Sleeve Drive End Packing Sleeve

Repaired and Tungsten Carbide Coated New Sleeve Made and Tungsten Carbide Coated


Packing

Before: After:

Metal Filament Packing 100% GFO Packing

No Lantern Ring 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.


Bearing Housings

Before:

Thrust End Bearing Housing Drive End Bearing Housing

After:

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.


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

Before: After:

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.


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 170-180 degrees F, or 75 – 82

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.


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 as-

shipped)

4. Pump Curves

5. Rotor Balance Report

6. New lube oil pump data sheet

7. New packing data sheet

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