Centrifugal Pump – Case Study

Introduction

Berg Engineering was requested by the client to carry out a detailed condition assessment on the E-10X23 DVSHF pump.

This pump had been running for 408 days and had been removed due to loss of performance.

This particular pump housing Berg Engineering had manufactured in 2013.

Equipment Assessed – Radially Split Centrifugal Horizontal Shaft Pump

Manufacturer: United Pumps Australia (OEM)

Model: E-10X23 DVSHF

Suction Size: 14″ NB

Discharge Size: 10″ NB

Stages: 1

Speed (RPM): 1350

Rated Flow (LPM): TBA

Rated Head (m): TBA

Details of Assessment

The following inspections were carried out to assess the conditions of the items delivered to Berg.

Visual Inspection

A visual inspection was undertaken on the as received condition of the rotating assembly.  Some key items are as follows:-
• Impeller was found to have severe erosion of vanes
• Impeller rings almost worn through
• Welds on auxiliary piping noted as looking too small (undersize)
• Minor scratches along shaft journals
• Mechanical seals not delivered, not in scope
• Coupling hub not delivered, not in scope

T.I.R Checks

As the impeller and impeller rings were already agreed to be replaced due to the poor condition and the coupling hub was not sent with the job a TIR check of the assembled rotor was not required. However a TIR check was carried out after removal of the impeller and locking nuts. The acceptance criteria for the shaft TIR was measured against API 610 table 17. The total acceptable TIR over the length of the shaft is to be within 0.035mm.

The TIR check was carried out by setting the shaft on rollers located on the two sleeve bearing diameters.  The bearing and coupling diameters where all within acceptable limits. The shaft showed excessive runout in the middle of the shaft though on the impeller and impeller nut diameters. The cause of this has not been investigated but we believe this can be resolved by shaft straightening cold with a hydraulic press.

Pump Strip Down and Component Visual Inspection

The pump was stripped down and cleaned to carry out a more detailed assessment of the pump. After an attempt to remove the impeller locking nuts failed it was agreed that the nuts and impeller would have to be machined off in order to save the shaft.

After the components were stripped down and pressure cleaned the major components were abrasively blast to carry out further inspection. After blasting we found the following after a visual inspection:-
• The volute area of the pump only sustained minor erosion, this was more evident on the cut waters
• Casing rings were not delivered
• Cavitation/erosion damage to the DE end cover
• Cavitation/erosion damage to both end cover inner discs where the casing rings are located

Non-Destructive Examination

The following NDE (Non-Destructive Examination) was carried on the components.

Positive Material Identification

A PMI (Positive Material Identification) test was conducted to ascertain the material of the pump components.

It was found at the time of the PMI test that the inner discs of the end covers where manufactured from AISI 4140 rather than the original cast material of ASTM A487 CA6NM class B. We believe this may have been done on a previous refurbishment by another contractor.

Dye Penetrant Inspection & Ultrasonic Inspection of Shaft

A DPE (Dye Penetrant Inspection) and UT (Ultrasonic Inspection) was carried on 100% of the shaft to check for any discontinuities or cracking.

The UT inspection was carried out in accordance with AS1065 level 1. No unacceptable reflectors detected.

The DPI was carried out in accordance with AS2062 table B1 & B2 class 2. No relevant indications detected.

Dye Penetrant Inspection of Housing & End Covers

DPI was carried out on nominated critical stress points of the castings as well as 100% of all nozzle welds to check for any relevant indications. No relevant indications found.

Thickness Measurements of Housing

Wall thickness measurements were taken of the main housing for records.

Component Dimensional Check

The housing, end covers and pump shaft was checked dimensionally to record all critical clearances and fits.

The shaft dimensions were found to be within acceptable limits on all sizes however the impeller diameter will require verification after receiving the new impeller.

The bearing sleeves are oval and oversize which will require having the white metal recast and machined back to the original tolerances. The corresponding diameter on the shaft has some minor wear marks but will be acceptable for re-use. These diameters will most likely require hard chroming on the next overhaul.

The locating diameter clearances of the end covers into the housing are fit for purpose. The pocket depth for the location of the spiral would gaskets are all within tolerance.

REBUILD REPORT

Overhaul Scope

• Weld repair of pump bowl volute in accordance with ASME VIII & IX

• Removal and replacement of end cover plate with ASTM A487 CA6NM

• PWHT end covers

• Machining of new end cover plate

• Re-metal bearing sleeves

• HVOF of volute area of pump bowl with Tungsten carbide at 0.25mm thick

• HVOF inner disc face with Tungsten carbide at 0.25mm thick

• Balance shaft assembly in accordance with ISO 1940 G1

• Hydro testing of pump assembly with blanking plates

• Straighten shaft to ensure compliance with API 610

• Supply all new studs and fasteners

• Painting of pump externals

• Assembly of pump

• Carry out leak test of assembled pump

Casing Volute HVOF

Casing Volute HVOF

Impeller Machining Reference

Clocking of Seal Housings

Impeller Direction

Clocking of Seal Housings