axial thrust failure investigation

Supplier Contact : Rory.Mckay

Pump Type : BB5Pump Model : HPCp 350 - 515 - 5s / 33# Stages : 5Serial # : 9901 - 48296 ACustomer Tag : G- 9001No of Pumps : 1Date : 02-Mar-14

Introduction

Page

* 2

* 3

* 4

* 5

* Hydraulic Clearance Analysis 9

* 10

* Conclusions 10

* Recommendations 10

* Attachments

* Previous Inspection Report

* Current Inspection Report

* Oriface Charts

Brief History

Plant comments

Component Analysis

Customer Engineering comments

Failure Analysis Report - High Axial Load

The above pump has a history of premature failures, with repetitive failure modes, this report is an analysis to establish the root cause of these failures.

Contents

Site / System review

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Brief History (Extracted from past correspondence)

Date

Nov-08

2010/03/02

2010/07/10

2010/08/10

2010/08/10

2010/08/05

16-Dec-13

· Lack of Oil flow at the NDE journal bearing housing

G-9001 pump was added on to an existing pumping system which was originally built in 1991. The original system comprises of 5 machines. Since the first failure after 2 years of operation, this machine has experienced repetitive premature failure.

Started.

Tripped on high NDE bearing vibration. Both NDE bearing and shaft journal were found severely damaged.

· Oil contamination at the NDE bearing

2011/07/01

Description of the events

Successfully commissioned and has a total of 11532 running hours.

NDE seal leak during start-up possibly due to improper pressuring procedure. After replacing the failed mechanical seal and starting up the pump, it tripped on high NDE bearing temperature. Both NDE bearing and shaft journal were found severely damaged. No data available on this trip. The pump cartridge was replaced with a new spare cartridge. The original cartridge was sent to MSSD for repair.

Tripped on DE high seal leakage. DE seal line was unplugging

Client analysis revealed that the bearing exposed to cyclic stresses and recommend finding the cause of these stress or upgrade the existing Babbitt material from soft tin-base metal with Sb and Cu to higher peak stresses copper-lead such as (SAE 48,49,480 and 481) or Aluminum alloy (SAE 770-T10) coating.

· Fitting error / misalignment

Pump was repaired by customer.

As the pump speed increasing, when the flow exceeded 11,500 gpm, all of sudden the axial vibration increased significantly. The thrust bearing temperature also increased significantly and the pump tripped on high axial vibration. Please note that the balance return line pressure could not be noted as the pump tripped suddenly.

Oct-13

Pump was repaired by external workshop.

Pump was shipped to Supplier for repair and Failure Analysis.

However, the balance return line pressure was high. We have installed two pressure gauges, one before the orifice plate and one after the orifice plate in the balance return line. The one gauge reading was pretty much constant around 320 psi (same as suction pressure) but the other one reading was increasing with flow rate / speed of pump. It started from 320 psi (at no flow) to around 600 psi (at 11500 gpm).

Supplier do not believe that there is any mechanical design issues attributed to the NDE Journal bearing (based on post failure operation & operation of the original supplied 5 off units). Supplier recommends that either cartridge is repaired & re-commissioned by Supplier experienced field engineers in light of these two previous failures. All criteria mentioned above can then be checked with original OEM design information. Supplier recommends to refurbish shaft journal by HVOF coating.

The pump started and ran fine up to 11,500 gpm. The axial vibration was around 12 mil. The other parameters were normal.

Supplier issued a report and they cannot identify cause of either failure due to lack of data. Possible factors

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# Actions

1 Client

2 Closed

3 Closed

4 Closed

5 Closed

6 Closed

7 Closed

Figure 1 - Design liquid properties

Check the inter changeability of the radial bearings between GT1-5 and GT9. Can we put GT 1-5 bearing into GT-9?

Reconfirm identical design ; as we noted some changes in the values related to impeller from the two data sheets.

The balance drum is not Tungsten Carbide coated, we observe some wear in the balance drum. Also, the balance drum of G-1-5 is not Tungsten Carbide coated. Comments from UK engineering and recommendation on this.

This is the last stage hub and is not a clearance fit. flow goes from here to the balance drum. this reading is normal.

Double check the data for 5th stage impeller hub clearance as the reading 0.343” is very high.

Agreed, the wear materials follow technology of the early 1990's, Duplex versus Stellite. This is known to be a good combination in clean SWI applications, but is prone to accelerated wear if sand is present in any quantity. If sand is known to exist then today's material combination of choice would be Tungsten Carbide coatings on all wear surfaces. This provides greatly reduced rates of material loss so gives extended pump run life.Note that there was no mention of sand in the fluid at the time of the additional pump order (Job No 48296) - see figure 1 - so no reason for Supplier to alter the original materials of construction.

Yes, bearings are interchangeable.

We re-confirm all hydraulic components were manufactured to the same drawings.

Check with engineering in UK for the hydraulic running of the pump.

Check with UK what is “normal” for balance return line pressure. Get comment on our observation during the test / start up; the suction side pressure 300 psi equal to suction pressure and discharge side pressure vary as the flow increases ; upto 7500 gpm, it was 300-350 psi, from 7500 to 11500 gpm, it increases from 350 to 600 psi, beyond 11500 gpm, the pump tripped on high thrust.

Plant Comments

GT-9 was not performance tested as there was no casing avalaible. Performance would not change however as all clearances are identical.

Normal process condition is <41 PSI, with range of 0-90PSI . The balance line orifice for both the original (11231) and recent (48296) jobs is the same - 39mm orifice in a 2" NB line. On this basis, back pressure in the balance line should be similar for all pumps, given similar internal clearances. Differential pressure across the orifice will vary as flow squared - so if we've got a worn pump it'll show a higher delta-p.

PMI of all wearing parts radial side including impeller eye & hub sides, balance drum sleeve and bushing sides to verify material wear resistance.

Comment Supplier Response

To be conducted by Client.

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# Actions

1See

Recommendations

2 Closed

3See

Recommendations

4See

Recommendations

5 Closed

6 Info

7 Open

With the additonal axial load, we would expect to see a corresponding temperature increase on the thrust pads.

Does the piping configuration make this pump sees more sand than others GT-1-5?

Please refer to site visit detail below.

The wearing parts material need to be upgraded from Duplex A890 1C/A743 CF3M+Stelite 12 (as per data sheet) to Tungsten Carbide coating by qualified HVOF vendor to improve the wearing resistance to sand erosion.

Agreed, see preliminary recommendation.

Excessive impeller hub side clearances while the eye side are acceptable !! 5th stage impeller hub clearance reading is very high 0.343”. The data need to be verified.

This phenomenon of accelerated wear on hub side w/rings is quite common. One reason for this is that the hub rings see a higher % concentration of sand than both the eye rings and balance drum. This is clear just by consideration that the flow to the eye and drum comes from the impeller tip - only a small % of any solids in the fluid will be carried in the return flow down the shrouds - the majority is 'centrifuged' through with the main flow. By contrast, the flow that leaks across the hub rings is at full concentration - see Figure 2, below.

Why the thrust temperature did not increase? There was previous recommendation (attached email) to modify the existing spring loaded thrust bearing temperature probes with RTD’s. Also, relocate the temperature element at the thrust pad from the middle to loaded area at 75% of the pad. Both of the existing temperature probes are connected to the active side of the thrust bearing. They read max. of 150 deg. F and they did not protect the thrust bearing from catastrophic failure. Relocate one of these elements to the inactive side.

Order pump coupling hub for GT-9 similar to GT-1-5 to ease interchangeability and send it to Supplier for lapping to ensure contact is ≥ 85%.

Noted

Verify orifice sizes and flow rates to all the bearings to ensure adequate flow rated as per vendor requirements.

For reference, attached oriface charts for G1-5 and G9.

Client technical Department Comments

Comment Supplier comment

Excessive balance drum clearances compared to as shipped readings in AMCO Weir repair record. This can explain why the pump experienced high differential pressure on the balance line and high axial displacement.

Agreed. For the recorded clearances we'd expect greater leakage flows, therefore higher delta-p across the orifice and higher loads on the thrust bearing (balance chamber pressure will affect axial thrust load).

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# Action

8 Info

9 Info

10 Info

Figure 2 - Erosion wear in pumps

Request operation to collect periodic measurement of differential pressure across balance line orifice to monitor balance drum wear as short term. Also, consider to install differential pressure transmitter and connect it to DCS as a long term.

We also would recommend monitoring balance line flow to use as an indicator of wear rate.

Comment Supplier comment

Provide operation history of GT-9 cartridge B for review.

Serial # for one cartridge is 9901 - 48296 A - which is dissasembled one, serial # for other cartridge is 9901 - 48296. This would enable us to reconcile wear rates.

Request Previous repair record for GT-9 cartridge B for review.

This would be useful, Serial # for one cartridge is 9901 - 48296 A - which is dissasembled one, serial # for other cartridge is 9901 - 48296. A comparison with repair records for the original cartridges (S/No 11231) may also help.

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Journal Bearings

Thrust Bearing

There were no visible signs of damage or heat to the bearings and dimensional checks confirmed that the bearings are suitable to be re-used to rebuild the pump.

There were no visible signs of damage or heat to the pads or thrust disc and dimensional checks confirmed that the bearing is suitable to be re-used to rebuild the pump.

Component Analysis (related to failure)

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Wear Rings

Sl # Location Stationary Ring ID Impeller Eye Wear Ring OD

Clearance mm / Inches

Design Clearance (Inches)

Comments

1 1st Stage 376,2 375,450.75 mm /

0.029"

2 2nd Stage 356,07 355,50.57mm /

0.022"

3 3rd Stage 356,12 355,520.62 mm /

0.024"

4 4th Stage 356,12 355,450.67 mm /

0.026"

5 5th Stage 356,15 355,480.67 mm /

0.026"

Sl # Location Stationary Ring ID Impeller Hub Wear Ring OD

Clearance mm / Inches

Design Clearance (Inches)

Comments

1 1st Stage 277,33 275,71.60 mm /

0.064"

2 2nd Stage 277,24 275,51.74 mm /

0.068"

3 3rd Stage 277,26 275,6 1.66 / 0.065"

4 4th Stage 277,17 275,51.67 mm /

0.066"

5 5th Stage 285,02 275,559.47 mm /

0.372"

Impeller Eye Wear Ring Clearances

NEW: 0.021 (+/- 0.0013)

WORN: 0.043 (+/- 0.0013)

WORN: 0.047 (+/- 0.0014)

NEW: 0.023 (+/- 0.0014)

Impeller Hub Wear Ring Clearance

Very High wear - 3 times New.

Relatively low Damage, between

10-20% wear.

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Balance Drum & Liner

Sl # Location Balance Drum Liner ID (mm) Balance Drum OD

(mm)

Clearance mm/inches

Design Comments

1 0 Deg 362,55 360,98 1.57 / 0.061"

O/B 90 Deg 362,55 360,97 1.58 / 0.062"

0 Deg 362,55 360,92 1.63 / 0.064"

90 Deg 362,6 360,98 1.62 / 0.064"

0 Deg 362,74 360,87 1.87 /0.073"

90 Deg 362,74 360,87 1.87 /0.073"

0 Deg 362,78 360,83 1.95 / 0.076"

90 Deg 362,89 360,92 1.97 / 0.077"

5 0 Deg 362,85 361,3 1.55 / 0.061"

I/B 90 Deg 362,85 361,3 1.55 / 0.061"

Note that the pattern of wear on the Balance Drum Liner again shows clear sign of solids. The pattern in the bore local to each swirl brake hole reflects the disturbance in the flow stream.

Balance Drum Clearances

NEW: 0.02 (+/-0.0014)

WORN: 0.039 (+/-0.0014

2

3

4

Very High wear - 3 times New.

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# As Received As Shipped As Received Difference Specification376,03 376,03 376,2 0,17375,30 375,43 375,45 -0,02

0,73 0,60 0,75 0,15356,01 356,01 356,07 0,06355,34 355,40 355,5 -0,10

0,67 0,61 0,57 -0,04356,01 356,01 356,12 0,11355,34 355,41 355,52 -0,11

0,67 0,60 0,6 0,00356,05 356,05 356,12 0,07355,37 355,46 355,45 0,01

0,68 0,59 0,67 0,08356,01 356,01 356,15 0,14355,33 355,43 355,48 -0,05

0,68 0,58 0,67 0,09Comments

# As Received As Shipped As Received Difference Specification277,03 277,03 277,33 0,3276,25 276,48 275,7 0,78

0,78 0,55 1,6 1,05277 277 277,24 0,24

276,21 276,45 275,5 0,950,79 0,55 1,74 1,19277 277 277,26 0,26

276,16 276,42 275,6 0,820,84 0,58 1,66 1,08

277,05 277,05 277,17 0,12276,25 276,47 275,5 0,97

0,8 0,58 1,67 1,09Comments

# As Received As Shipped As Received Difference Specification361,29 361,29 360,98 0,31362,06 362,06 362,55 0,49

0,77 0,77 1,57 0,8361,4 361,4 360,92 0,48

362,04 362,04 362,55 0,510,64 0,64 1,63 0,99

361,4 361,4 360,87 0,53362,04 362,04 362,74 0,7

0,64 0,64 1,87 1,23361,4 361,4 360,83 0,57

362,04 362,04 362,78 0,740,64 0,64 1,95 1,31

361,4 361,4 361,3 0,1362,04 362,04 362,85 0,81

0,64 0,64 1,55 0,91Comments

ImpellerClearance

ClearanceCasing

ClearanceCasing

ImpellerClearance

CasingImpeller

ClearanceCasing

Impeller

NEW: 0.021" / 0.53 mm

1

2

3

4

5

NEW: 0.023" / 0.58 mm

WORN: 0.047" / 1.19 mm

Weir10-Dec-10

Supplier16-Dec-13

Impeller Eye Wear RingsLocation

CasingImpeller

WORN: 0.043" / 1.09 mm

4

Wear is too high to recover clearance with coating. Wear rings need replacement - upgrade to Tungsten Carbide coating. It is also noted that the wear on stationary rings is lower than that of the rotating ones, which leads to the question of the hardness of the rotating ring surface.

ClearanceCasing

ImpellerClearance

Impeller Hub

CasingImpeller

ClearanceCasing

Impeller

1

Location

2

3

ClearanceCasing

Impeller

DrumLiner

3

4

5

Wear is too high to recover clearance with coating. Balance Drum & Liner need replacement - upgrade to Tungsten Carbide coating.

Balance DrumLocation

DrumLiner

ClearanceDrum

Clearance

DrumWORN: 0.039" /

0.99mm)Liner

ClearanceDrumLiner

Clearance

Taken ByDate

Hydraulic Clearance Analysis

Liner

Clearance

Wear is at an acceptable level.

1

NEW: 0.02" / 0.51mm)2

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Site System Review

1

2

Conclusions

Recommendations

1

2

3

4

5

During next shut down, open blanked flange on Suction Header to check for accumulated sand. Investigate possibility of sand trap to flush sand out of system during operation.

Develop a maintenance plan to inspect the other pumps and upgrade wear parts in all pumps.

A site visit was conducted on the 17 Feb 2014, the following was observed :

As per the sketch below, the suction piping to G-9001 has a end piece for future expansion. This would provide a "dead" spot where it is possible for sand to accumulate.

The recirculation system was also looked at, as this pump is run mostly in recirculation mode :

From the above sketch, it is reasonable to assume that accumulated sand at G-9001, when operated in recirculation will also enter the other running pumps to a certain extent.

Potential Sand Accumulation

The high axial thrust trip can be attributed to excessive erosion wear in the pump, which is caused by the presence of sand in the sea water, and it appears that G-9001 is being exposed to higher quantities of sand than the other 5 pumps, however it must be noted that there must still be a fair % of sand that goes through the other pumps due to the re-circulation system.

Existing wear materials follow technology of the early 1990's, Duplex versus Stellite. This is known to be a good combination in clean SWI applications, but is prone to accelerated wear if sand is present in any quantity. If sand is known to exist then today's material combination of choice would be Tungsten Carbide SA coatings on all wear surfaces. This provides greatly reduced rates of material loss so gives extended pump run life.

Change stationary wear ring profiles from serrated to straight profile wear surfaces to reduce turbulance in wear area's.

Remove the 3x deep grooves in the Liner bore - these just cause turbulence and create localised erosion on the Drum OD. by removing the grooves will improve wear rate.

Technical Sales ManagerRory McKay

48 "Suction Header

48" Suction Header

Recirculation Header

G 9001

G 9001

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The suction header was opened some months after this report - see the findings below :

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axial thrust failure investigation

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