work carried out on 21g80 between october 2014 - mar 15

21G80 Overhaul and gathering of data that can be trended over time


Work carried out on 21G80 in between Nov 2014 and March 2015

Following the work order 1022235, raised on 15/2/14, 21G80 pump was removed complete

from situ and brought to the main workshop.



Under the site wide pump refurbishment project, aimed at addressing ‘ageing plant’

condition monitoring, the pump was completely stripped to assess condition of internals.



Drive end bearing assembly removed complete:



Drive end mechanical seal removed:



Non-drive end casing bolts removed:



Pump up-ended and jacking bolts used to seperate:

Scale build up required substantial force to separate casing from main body of pump,

wedges needed in addition to jacking bolts:



Shaft and impellor removed complete:



Non-drive end bearing assembly stripped:



Drive end white metal bearing assembly stripped also:

Mechanical seal assembly removed both ends:



Pump shaft now separate from assembly:



Shaft set up in lathe:

Impellor positioning/locking sleeves were worn in localised areas, possibly due to fretting of

seal assembly:



Area of shaft under locking sleeves also in poor condition:

Metal spraying technique used to repair damaged areas of shaft and locking sleeves, see

appendix 1 for metal spraying/machining report performed by 3rd party:



Impellor checked for signs of damage and overall condition found to be very good

It was difficult to measure the impellor wall thickness as the external surface sloped away

from the impellor edge, but no major variations were apparent, and thicknesses varied

between 8mm – 10mm.



New wear rings fitted, (see table later in write up for clearances):

All components were cleaned and their condition assessed:



The condition of the seal plate to casing gasket face was assessed and machining was not

deemed necessary.



Once all components were clean and prepared:

The pump was set up for reassembly:



Casing painted prior to reassembly:

Impellor, spacing collars and shaft sleeves installed on shaft:



Ensuring the impellor was located in the same position as prior to dismantling:



Rebuilt shaft inserted into pump body using an in-house made 0.75mm thickness gasket,

which is the same thickness gasket in place when the pump was removed, end play of the

shaft compared to when it came out still measured at 0.001”

Drive end bearing and seal assembly installed once shaft centralised:



Followed by installation of non-drive end of assembly:



And drive end bearing and seal assembly:



Following full reassembly of unit:

A pressure test was performed:



At this point, it was found that there was a problem with both seal assemblies leaking,

meaning the pump had to be dismantled to investigate. As nothing was obviously incorrect

with the installation of the seals, a seal manufacturer visited site to provide guidance. It was

suggested by the AES Seals representative, (Steve Salter), that the reason for the seals not

performing correctly was most likely due to porosity in the metal sprayed coating on the

shaft sleeves, and upon further investigation this did appear to be the case:

With an area of the coating seemingly cracked, as well as porous:



Following identification of the above defects, the shaft sleeves were sent to AES seals where

they were recoated with a Chrome Oxide coating, see Appendix 2, difference in appearance

as below:

The pump was again reassembled and pressure tested:

And seals inspected for leakage, none found, proving that the initial shaft sleeve coating was

the problem as suspected.



Bearing internal diameters measured, (drive end and non – drive end) and compared to

external measurements of shaft, see tables below for measurements:

Shaft & Bearing Dimensions (Drive End)

Shaft External

Bearing internal

Difference in size

Comments

1.875” 1.877” 0.002” 0.002” clearance fit between shaft and ID of white metal bearing.

Bearing External

Housing bearing sits into

Difference in size

Comments

4.330” 4.332” 0.002” 0.002” clearance fit into white metal bearing housing.

Shaft & Bearing Dimensions (Non Drive End)

Shaft External

Bearing internal

Difference in size

Comments

1.574” 1.573” 0.002” 0.002” interference fit, bearing warmed to shrink fit onto shaft.

Bearing External

Housing bearing sits into

Difference in size

Comments

4.330” 4.332” 0.002” 0.002” clearance fit into bearing housing, fitted with bush lock to ensure it doesn’t turn.

When the pump next comes out of service, the bearing vs shaft diameter measurements

can be taken again to establish a wear rate and resulting inspection frequency. As this is a

water pump only, a UT inspection of the pump set was not performed.



In addition to the measurement of bearing vs shaft dimensions detailed above, wear ring

dimensions following their replacement can be seen below:

Wear ring dimensions (Drive End)

Inner impellor wear ring (D.E)

Pump body wear ring

Diametrical clearance

Comments

6.980” 7.010” 0.030” Above process pump minimum tolerance, see below chart.

Outer impellor wear ring (N.D.E)

Pump casing wear ring

Diametrical clearance

Comments

6.980” 7.010” 0.030” Above process pump minimum tolerance, see below chart.

Wear Ring Diameter in Inches Minimum Diametrical Clearance Recommended by API 610 Standards, (in inches”)

1 - (Anything under 2” diameter has same minimum clearance by API 610 standards)

0.010

2 - (Anything under 2” diameter has same minimum clearance by API 610 standards)

0.010

2.000 – 2.499 0.011

2.500 – 2.999 0.012

3.000 – 3.499 0.014

3.500 - 3.999 0.014

4.000 - 4.999 0.016

5.000 - 5.999 0.016

6.000 - 6.999 0.017

If a comparison of the wear ring clearances is taken it can be seen that the minimum

diametrical clearances, D.E & N.D.E, adhering to API 610 are above the lowest tolerance:

D.E: Diametrical clearance = 0.030” (Min is 0.017” for this size wear ring)

N.D.E: Diametrical clearance = 0.030” (Min is 0.017” for this size wear ring)

Although there are no maximum wear ring tolerances documented, a ‘rule of thumb’ is to

change wear rings for new if diametrical clearance doubles the minimum, meaning that D.E.

& N.D.E. of this unit are currently within minimum and ‘maximum’ tolerances.



A strip down of the non – return on the discharge to obtain sizes and clearances between

moving parts was carried out, see Appendix 3, and a function test was carried out by means

of opening the discharge valve and the casing drain, no significant amount of water flowed

from the drain proving the NRV is working as it is intended to.

The unit was put back into position at pump station 24, alignment was carried out and the

motor was shimmed and adjusted via jacking bolts to bring within correct tolerances, a hard

copy of the alignment report is available within the ‘Asset Integrity System’, in the

maintenance records office and is also attached to the work order 1024195 within CMMS

Agility.

Conclusions

The pump has been refurbished to a high standard, taking into consideration condition of all

internals and measuring all areas that will be able to provide wear data that can be trended

over time.

Methods that will be used to monitor condition of this pump unit over time:

Condition monitoring to be carried out in line with annual PM:

Alignment of unit.

Visual oil analysis and change.

Strip down of internals of non-return valve and measurements taken to establish

whether there is a change in the tolerances since last measurements were taken,

also visual inspection of seats to identify any damage.

Additional condition monitoring to be carried out upon strip down of unit:

Shaft vs bearing dimensions and condition

Condition and wall thickness of impellor

Diametrical wear ring clearance measurements repeated



Appendices:

Appendix 1:



Appendix 2:



Appendix 3:

work carried out on 21g80 between october 2014 - mar 15

Documents