21G86 refurbishment March 2013 - Nov 2015

21G86 Casing defect investigation, seal upgrade and gathering of data that can be trended over time


21G86 - Casing defect investigation, refurbishment, and

double mechanical seal fitment

Defective area of casing

During a routine U/T inspection carried out on 21G86 gasoline pump set in March 2013, a

thickness reading of 6.6mm was measured in one area of the volute casing, which when

compared to a nominal thickness of 20mm, was deemed a cause for concern. The pump

was isolated and removed from situ for further investigative work to be carried out.



Referencing the report Sem 23 provided by Silverwing, (a third party inspection company), it

was suggested that the difference in thickness may be due to a combination of internal and

external corrosion.

The pump hub was removed from the casing in the hope that it would be possible to inspect

the internal surface of the volute, to determine if there was indeed thickness loss in this

area as the UT report suggested.

Unfortunately, due to the design of the casing it was not possible to visually inspect the area

in question:



With the apparent thickness loss being around thirteen millimetres compared to the nominal

thickness of twenty millimetres, an irregularity in the casing of this size should have been clearly

visible if it was external, but this was not the case with only a small external dip of less than two

millimetres in depth. Due to poor access, an endoscope was used to view the casing internally, the

line of thinking being that a dip or hole of around thirteen millimetres should be clearly visible.

Following use of the endoscope, there was little or no sign of such a defect meaning further NDT

would be required.

Following the above inspections, a third party consultancy firm were contacted and details provided

of the findings thus far. In summary, the engineering consultancy firm IDEAS were made aware of

the following; a UT inspection had been performed, an anomaly had been identified within the wall

of the volute, and that there were no large variations visible to the naked eye. Following the

provision of this information, Brian Wilkinson of IDEAS gave some advice and asked some questions:

“I know we did have a conversation about your UT results and whether or not it would be possible to

do anything with the existing casing, but this is an interesting problem so last night I called a

colleague who’s a very experienced Mech Eng and ran through the problem to get some of his

thoughts. The thin-ness in one place only sounds really odd. This prompts you to ask the question are

the results actually correct. Not doubting the competency of the company who did the readings, but

laminations and other defects you can get with castings can throw these readings, especially if, as I

remember you saying, it’s not obvious when you look at it (presumably no obvious metal loss from

corrosion / erosion, or aero-chocolate-bar surface you’d get with prolonged cavitation). Other

techniques could be used to confirm what the report you have is telling you”.

The line of thinking that Brian took, was also the view of Sem Logistics lead technician, although a

reading of six point six millimetres had been measured, this was suspected more and more to be

erroneous, and required further investigation. Upon further consultancy with B. Wilkinson, it was

suggested that further non-destructive testing would help disprove the unusual reading, and give

some more information as to the reason for it.

Third party non-destructive testing specialists IRISNDT were consulted, and advice given in the

senior technician S. Clarks’ opinion, that an X-ray be carried out to provide further knowledge on the

irregularities within the wall of casing. The following image was provided following the X-ray:



The IRISNDT technician provided the following interpretation of the image:

“Area shows signs of repair which could have been carried out at manufacture stage. The area in

question shows a similar thickness to the adjacent area this can be seen due to density of radiograph

being similar, the area adjacent is approx.17-20mm thickness”.

At this point, IDEAS were again consulted, and were informed that an X-ray inspection had been

performed, identifying what was thought to be a weld repair to the volute casing suspected to have

been performed at the time of manufacture.

B. Wilkinson of IDEAS had been gathering information by this point by consulting experts involved in

rotating equipment maintenance. It seemed all were of the opinion that an actual loss in thickness

was looking evermore unlikely.

The consultancy from IDEAS at this point suggested that a ‘phased array’ or ‘shear wave’ UT

inspection be carried out. This is a different type of probe that is a multi-directional UT inspection,

in relation to which, Brian Wilkinson stated: “A shear wave check by a competent technician still

seems to be a useful check; if there is a weld repair, as looks very likely, and the layered weld runs

are properly fused, there is a good probability of attaining useful information”, and forwarded on

the following advice:



“Next step in his view would be to use a UT shear wave technique (different probe, more highly

skilled Tech) at various angles around the suspect area to get a picture of the size / depth of what’s

there. This will also reveal whether or not it is in fact metal loss from the inside wall and not a defect.

People I’ve spoken to have all mentioned that laminations slag etc. in castings like this is not

uncommon and that, gut feel, is what we’ve probably got...but this technique should confirm that.”

A Shear wave UT inspection was then arranged, to be performed by IRISNDT. Following this

inspection the following breakdown of the X-Ray was provided:

Analysis of the findings was provided within the Shear wave UT report. M. Williams of IRIS stated:

“An ultrasonic thickness and lamination check was carried out on pump 21G86. The area examined

shows a planar indication at approximately 5-6mm depth. The readings suggest a lamination type

indication 2-3mm in width. Shear wave inspection cannot confirm the quality of the material under

the indication.”

In light of the findings indicating that there was indeed an anomaly of some sort, most likely a weld

repair from new, a specialist cast iron repair company were contacted via email to see if they would

be willing to undertake carrying out a repair to the casing. A senior technician at Shilton Cast Iron

and Welding then contacted site via telephone, the details of which were summarised in further

correspondence to IDEAS by Sem Logistics lead technician in the following bullet points:



Due to the age and supplier, the tech at ‘Shilton Cast Iron and Welding is of the opinion that

the casing is most likely ‘Grey Iron’.

I asked in my original enquiry to them whether a weld repair would be a possibility on such a

casing (should we have to go down this route), and he informed me that they have welded

many such casings.

He was of the opinion that the ‘lamination’ picked up in the shear wave UT was most likely

the interface where the weld repair meets the original material and has been this way since

day one.

He said in his opinion that due to the nature of grey iron, being a naturally porous material,

the interface area may give a UT reading as a lamination, when in fact there is no problem

with the weld repair, and suggested I carry out die pen on the area, (which we have done in

house and found no sign of cracking).

Because of the previous point he informed me that he could not guarantee, even after a new

grind out/weld repair adhering to all applicable standards for welding cast, that a UT

following this may not give a similar result.

In response to the above points, (Wilkinson, 2013) provided the following guidance: “Castings can

and are repaired at foundries and is a specialist task involving preheats, controlled deposition with

high nickel rods and PWHT with very slow cool downs. Welding on anything with 2% carbon in a field

application is like “lighting a blue touch paper” and I would definitely not consider going down this

route for an item that has been in service”.

It was decided following the input from Shilton and IDEAS, that although it was possible to carry out

a weld repair to the area in question, that this may cause further problems. Even if it were to be

performed successfully, it had the potential to lead to a similar UT reading in the future as the

interface between the parent material and the weld repair could be mistaken for a lamination.

Further information provided through the ongoing consultancy with IDEAS also suggested that a

defect of this nature was probably not significantly impacting the ability of the casting to deal with

pressure. (Wilkinson, 2013) stated: “The fact that a visual examination and crack detection has been

conducted internally confirms that the defect is in the metal substrate; its planar and has probably

been there for a very long time. The good news is that this type of defect does not have any

significant effect on the strength required for pressure containment (you can liken this to a laminated

sheet of plywood as opposed to an equivalent size piece of timber)”.



Third party analysis of NDT and decision allowing continued use of unit

under scrutiny Following the NDT and consultancy with rotating equipment and cast iron repair specialists, IDEAS

gave the following information:

A satisfactory static hydro test of the volute casing to 10.3bar was performed, proving its integrity,

and allowing the refurbishment of the unit to progress without having to repair or replace.



Pump refurbishment

Once stripped the condition/dimensions of all pump internals were measured and assessed as

follows:

Shaft components removed and shaft cleaned, measured in all areas for throw, less than 0.001”

measured:



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

2.953” 2.952” 0.001” 0.001” interference fit, no breakdown of area where bearing sits.

Bearing External

Housing bearing sits into

Difference in size

Comments

6.300” 6.301” 0.001” 0.001” clearance, fitted with bush lock to ensure no chance of race turning in housing, no evidence of this happening previously.



Shaft & Bearing Dimensions (Non Drive End)

Shaft External

Bearing internal

Difference in size

Comments

3.149” 3.148” 0.001” 0.001” interference fit, no breakdown of area where bearing sits.

Bearing External

Housing bearing sits into

Difference in size

Comments

5.512” 5.513” 0.001” 0.001” clearance, fitted with bush lock to ensure no chance of race turning in housing, no evidence of this happening previously.

Impellor condition assessed and deemed to be poor, showing signs of excessive wall

thinning on N.D.E:



Also, evidence of cavitation can be seen with porosity clearly visible:

In light of the impellor defects, a replacement was sourced:



The extent of wear to the impellor was clear when the existing wall thickness was compared to the

replacement:

New wear rings installed on new impellor:



Wear ring dimensions

Inner impellor wear ring (D.E)

Pump body wear ring

Diametrical clearance

Comments

12.470” 12.514” 0.044” Above process pump minimum tolerance, see below chart.

Outer impellor wear ring (N.D.E)

Pump casing wear ring

Diametrical clearance

Comments

13.724” 13.753 0.029” 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 = 0.044” (Min is 0.023” for this size wear ring)

N.D.E: Diametrical clearance = 0.029” (Min is 0.024” 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.



Details of most recent NRV strip down as follows, (performed on 17/3/15 in preparation for

re-commissioning of unit):

(A) Hinge pin O.D.

(B) Flap hinge I.D.

Clearance Comments

1.093” 1.127” 0.034” To be monitored periodically for any change in dimensions

(C) Clack central pin O.D.

(D) Central Clack hole I.D.

Clearance Comments

1.696” 1.785” 0.089” To be monitored periodically for any change in dimensions

Mechanical seal upgrade

It was determined that although the use of double mechanical sealing arrangements is not currently

enforced on gasoline pumps, it may be in the future. To pre-empt this, IDEAS were again consulted

to determine what type of double mechanical arrangement would suit this application.

Seal specification and installation instructions, 1695-REPT-SEM-53-0082, were provided following

liaison with IDEAS, this can be found as Appendix 1.

The fitment of the new sealing system was overseen by the supplier:











Rotary drive secured onto shaft and positioning/tensioning tabs removed:

Pump hub inserted into volute casing:



Pressure test of 100PSI performed to prove seal integrity and satisfy IDEAS recommendation to

prove volute casing integrity:

Pump put back in place at pump station 5:



Barrier fluid tank and associated pipework installed by third party:





It was ascertained through consultation with the seal manufacturer that the barrier fluid

pressure should be set at 180 PSI, (12.4 bar), a minimum of 2 bar above the discharge

pressure of the pump. This consultation is referenced below as Appendix 2.

Following the above refurbishment and seal upgrade, alarm parameters were set to ensure

the pump is not run without a sufficient amount of barrier fluid at the correct pressure.

The unit was aligned and test run under the supervision of the seal manufacturer, (AES

Seals), and found to be working correctly at time of writing.



The following guidelines relating to the use of the double mechanical sealing system were

relayed to operations on 11/11/15:

There is a barrier fluid system which must be pressurised between certain parameters

The normal operating pressure of the barrier fluid should be between 180 - 200 PSI on the gauge situated on top of the barrier fluid tank

The system will alarm in the control room if the barrier fluid pressure drops below 165 PSI

The pump will also alarm in the control room if for any reason the barrier fluid level drops below what it should be

If the pump has an active alarm for any reason it must not be started

If an alarm activates during running it should be shut down immediately and maintenance informed

Please inform maintenance if the barrier fluid pressure is not within the correct parameters

Please inform maintenance if there any obvious signs of leakage from the barrier fluid system or seal itself

A PM to drain the barrier fluid tank and inspect all components of the assembly was

put in place on 11/11/15 as stipulated within the manufacturer’s recommendations.

When the pump next comes out of service, whether that be for a seal change or due to an

internal inspection frequency brought about by the ageing plant study, the internal

measurements can be taken again and an inspection frequency worked out based on any

change in wearing part dimensions and/or further losses in thickness, if any, versus time

since last measurements taken.

Manufacturer’s recommendations for a similar unit state the following under the ‘Complete

Overhaul’ section:

‘Frequency of a complete overhaul depends upon the hours of operation of the pump, the

severity of the conditions of service, the materials used in the pump construction, and the

care the pump receives in operation. It is not necessary to open your pump for inspection

unless there is definite evidence that the capacity has fallen off excessively or there is

indication of trouble inside the pump or in the bearings’.

Having taken into consideration the above guidelines in relation to overhaul, it is not

intended that this pump will come out of service for further gathering of data that can be

trended over time, until there is any evidence of the symptoms highlighted above.



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. Further UT thickness assessments of all areas checked in this write up will be carried

out periodically, from this a thickness loss rate can be established and a resulting UT

inspection frequency.

Upon interpretation of the UT inspection reports, other than the defect elaborated upon

within this report, there are no other areas where a significant loss in thickness of isolation

valves body/bonnet, NRV body/bonnet, pump casing and pump body compared to the

nominal thicknesses is a cause for concern. These measurements have been taken in a

repeatable manner to ensure meaningful gathering of data that can be trended over time.

Hard copies of the UT inspection reports are available in the maintenance records office;

also electronic copies are attached within the site CMMS ‘Agility’.

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, (this frequency may be

subject to change based on thickness loss or wear rate data):

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

Visual analysis of barrier fluid, any discoloration may be a sign that the primary

mechanical seal has failed

Condition monitoring to be carried out upon strip down of unit:

Shaft vs bearing dimensions

Condition of impellor (wall thickness, crack, distortion)

Diametrical wear ring clearance measurements repeated



Appendices:

Appendix 1:











Appendix 2:



Documents

21G86 refurbishment March 2013 - Nov 2015