Work carried out on 21G62 between Nov 2015 - Feb 2016
1. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
20160126: Joe
Edwards
Maintenance
Supervisor, Sem
Logistics Milford
Haven
FULL REFURBISHMENT OF
DOUBLE ENDED CLASS 2
HYDROCARBON PUMP SET
21G62, INCLUDING
DETAILED ANALYSIS OF
WEARING PART
DIMENSIONS & CONDITION
2. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Executive Summary
Following an HSE investigation into the sites approach to ageing plant condition monitoring
in December 2012, it was deemed that there were shortcomings in regard to the approach
taken to proving that the sites rotating equipment was safe to use, as it was most likely
operating beyond its intended design life.
At the time of the investigation, the majority of the pumps had been in service for circa 45
years, albeit in reduced capacity when compared to the period when the site was a running
refinery.
In order to prove the ageing centrifugal hydrocarbon pump sets fitness for service, there
were a number of changes implemented with effect January 2013, with further condition
monitoring methods being implemented periodically, as follows:
Seal failure rates were documented from this point onwards, the aim being to help
better predict when a seal failure may occur, and take steps to prevent loss of
hydrocarbon due to such failures.
An ultrasonic thickness inspection regime was commenced, the aim being to build up
thickness loss data on: pump casings, pump set non-return valves and isolation
valves. This data can be trended over time to build up thickness loss data and
develop a resulting inspection frequency.
A programme to refurbish all hydrocarbon pump sets was implemented, the aim
being to gather dimensions of all internal wearing parts so that these could be
analysed and a future refurbishment regime based on the wear rate seen.
Further condition monitoring methods have since been implemented, such as
vibration monitoring and thermography, which also help to build up a picture of a
pumps’ internal condition and justify its use whilst it awaits full refurbishment.
Table of Contents
Executive Summary.............................................................................................................................2
Removal from situ and strip down of unit..........................................................................................3
Findings of strip down.........................................................................................................................9
Gathering of data to be trended over time ......................................................................................10
Manufacturers guidelines.................................................................................................................13
Wear ring dimensions.......................................................................................................................14
Rebuild of unit...................................................................................................................................16
Conclusions .......................................................................................................................................18
3. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Work carried out on 21G62 between Nov 2015-Jan 2016
Removal from situ and strip down of unit
To progress the site wide pump refurbishment programme, 21G62 was removed from situ
complete to undergo full refurbishment.
4. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
To progress the ongoing condition monitoring programme on ageing plant, the pump was
completely stripped to assess condition of all internals.
5. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Seal flush pipework, and bonnet bolts removed:
6. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
7. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
8. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
The shaft was then removed complete:
9. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Findings of strip down
As was the case with a similar units, (21G87X & 21G50X), the area of shaft that the seal runs
on has developed surface corrosion, causing interference on the R.S.R. internal diameter, in
turn preventing it from moving up the shaft to meet the S.S.R. as the faces wear over time.
This has the potential to allow seal seepage in the future if not addressed.
Surface corrosion on shaft
10. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Gathering of data to be trended over time
Once stripped the condition/dimensions of all pump internals were assessed and measured
as follows:
Shaft measured in all areas for throw, less than 0.001” measured.
Areas of shaft that R.S. R runs on coated and machined, (see Appendix 1)
11. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Impellor wall thickness measured:
Readings were taken from 5 points on each side of the impellor, (clockwise from point 1):
Drive End:
Measurement point Thickness
1 0.412”
2 0.336”
3 0.431”
4 0.411”
5 0.380”
Average thickness = 0.394”
Non Drive End:
Measurement point Thickness
1 0.427”
2 0.429
3 0.413
4 0.395
5 0.418
Average thickness = 0.416”
12. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Replacement 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
2.752” 2.750” 0.002” 0.002” interference fit, bearing warmed to
shrink fit onto shaft.
Bearing
External
Housing
bearing sits
into
Difference in
size
Comments
5.909” 5.911” 0.002” 0.002” clearance fit into bearing housing,
fitted with bushlock to ensure outer race
doesn’t turn. Correct thickness gasket
used on bearing retaining cover to ensure
size for size fit of bearing into recess.
Shaft & Bearing Dimensions (Non Drive End)
Shaft
External
Bearing
internal
Difference in
size
Comments
2.752” 2.750” 0.002” 0.002” interference fit, bearing warmed to
shrink fit onto shaft.
Bearing
External
Housing
bearing sits
into
Difference in
size
Comments
5.909” 5.911” 0.002” 0.002” clearance fit into bearing housing,
fitted with bushlock to ensure outer race
doesn’t turn. Correct thickness gasket
used on bearing retaining cover to ensure
size for size fit of bearing into recess.
A third party inspection company are used to carry out U/T thickness checks of any parts
that have been identified as an area that could potentially deteriorate over time, eventually
leading to a loss of containment, analysis and graphing of this data can be found within the
‘Asset Integrity System’.
13. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Manufacturers guidelines
When the pump next comes out of service, the internal measurements can be taken again
and an inspection frequency worked out based on the further loss in thickness or wear, if
any, versus time since last measurements taken.
The manufacturer’s guidelines state the following under point 3 of the ‘Recommended
Inspection Schedule’ section:
‘Wearing parts – Check by periodical inspection and simple hydraulic test. A simple
hydraulic test is at suction lift not exceeding 10 ft., and at a specified speed, close discharge
valve and take reading on pressure gauge on pump side of valve. Drop in pressure against
reading when pump was new indicates excessive clearances in the pump.’
Having taken into consideration the manufacturers inspection guidelines, it is not intended
that this pump will come out of service for another overhaul until there is any evidence of
the symptoms highlighted in the above paragraph, eg. drop in outlet pressure, unless future
procedures implemented to address the issue of ageing plant deem the manufacturers
inspection recommendations insufficient.
In addition to the measurement of bearing versus shaft dimensions and impellor wall
thicknesses detailed above, all other pump internals were inspected for wear, see below
wear ring dimension table:
14. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Wear ring dimensions
Wear ring dimensions (Drive End)
Inner impellor wear
ring (D.E)
Pump body wear ring Diametrical
clearance
Comments
11.000” 11.025” 0.025” Above process pump
minimum tolerance,
see below chart.
Outer impellor wear
ring (N.D.E)
Pump casing wear
ring
Diametrical
clearance
Comments
11.000” 11.025” 0.025” 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
7.000 - 7.999 0.018
8.000 - 8.999 0.019
9.000 - 9.999 0.020
10.000 - 10.999 0.021
11.000 - 11.999 0.022
12.000 -12.999 0.023
13.000 -13.999 0.024
14.000-14.999 0.025
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 = 0.025” (Min is 0.022” for this size wear ring)
N.D.E: Diametrical clearance = 0.025” (Min is 0.022” 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.
15. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
The condition of the impellor was assessed to see if there were any cracks or distortion and
none were found:
On other similar units, in addition to the measuring and documenting of thicknesses,
bearing interferences and wear ring dimensions, additional work was carried out on the seal
to pump casing joint, although this was not required in this case:
16. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
Rebuild of unit
The shaft was reassembled and refurbished seals set to the compression stipulated in the
manufacturers recommendations:
For future reference, approx. 40mm gap between the rear of the spring carrier and the
outer edge of the impellor securing nut gives the correct spring compression:
17. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
The latest NRV strip down to obtain sizes and clearances between moving parts was
performed on 27/1/2015, details and analysis of which can be found within W/O:1027326.
The strip down of the NRV will be performed 2 years from the date of the units’
reinstatement following this refurbishment, this is based on analysis of wear rate data
showing very little change in internal clearances when on an annual inspection.
In addition, the NRV, isolation valves and pump casing of all in service hydrocarbon pump
sets are subject to annual U/T thickness checks also. Details of the latest UT inspection can
be found within W/O:1026382, no areas are considered a cause for concern, analysis and
graphing of this data can be found within the ‘Asset Integrity System’ also.
The bonnet was put back into place using an in-house made 0.75mm thickness gasket,
which is the same thickness gasket in place when the pump was removed, and end play of
the shaft compared to when it came out still measured at 0.002”.
A satisfactory pressure test at 100psi was performed upon reassembly of the unit:
The unit was reinstated at pump station 5, 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 in the maintenance records office and is also attached to the
work order relating to this unit on Agility, and the ‘Asset Integrity System’.
18. 21G62 Overhaul and gathering of data that can be trended over time.
21G62 Overhaul and gathering of data that can be trended over time.
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 data that can be trended over
time, helping to establish a future inspection frequency.
Further external UT thickness assessments of all areas checked in this write up will be
carried out on an annual basis. During future strip down of the unit, internal
thickness/clearance and wearing part dimension measurements repeated.
Upon interpretation of the latest UT report, there are no areas where a significant loss in
thickness of isolation valves body/bonnet, NRV body/bonnet or pump casing when
compared to the nominal thicknesses, is a cause for concern. These measurements have
been taken in a repeatable manner to ensure gathering of meaningful data that can be
trended over time has been obtained.
Hard copies of the Silverwing reports are available in the maintenance records office, also
electronic copies are attached to the UT PM work order on the site maintenance scheduling
system ‘Agility’, and logged within the ‘Asset Integrity System’.
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, (or 2 yearly in the case of the
NRV, this may be further adjusted based on the wear rate seen):
UT thickness checks of inlet isolation valve body and bonnet
UT thickness checks of outlet isolation valve body and bonnet
UT thickness checks of non-return valve body and bonnet
UT thickness checks of pump casing
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 dimensions and condition
Condition and wall thickness of impellor
Diametrical wear ring clearance measurements repeated