Resolving a 7 year recurring pump failure

Customer	India Power Major
Location	Central Eastern India
Industry	Power Generation
Key Services	Site evaluation Root cause analysis Re-engineering Retrofit OEM-X line service

PUMPS RETROFITTED

WITH 8 IN PROGRESS

MTBF FROM

4 to 18 months

TURNKEY DELIVERY WITHIN

6 months

PARTS RE-ENGINEERED

50++

THE IMPACT

Peace of mind with regained reliability for critical application via re-engineering solution with minimal physical and carbon impact

Condensate extraction pumps (CEPs) at one of the company’s power stations in central eastern India were failing at an unusual rate.

Every pump was failing within four months of scheduled maintenance. Some were even failing after no more than 25 days of scheduled maintenance.
The plant had been grappling with these issues for nearly seven years, the OEM was unable to suggest any changes that would help the pumps last longer.
The failures took two forms:
- Catastrophic shaft failures at the muff-coupling section of the pump, either on the torsional plane or due to crushing
- Leakage through a bottom column weld joint.
An OEM report concluded that the shaft had failed as a result of weld buildup.
But the sample that had been tested at the lab by the OEM had been from a shaft which had failed previously and undergone urgent repairs. The OEM hadn’t tested any of the brand-new pumps with no weld buildup – even though these pumps were also failing.
Report didn’t accurately account for the real conditions on site at the power plant, explain why brand-new pumps were continually failing and didn’t address the leakage through the bottom column weld joint.
It was clear that the solution to this conundrum wouldn’t be found by examining the pumps in isolation. They needed an expert assessment of their entire setup.
They called us in to help.

Gallery

We conducted investigations to find out:

Were they operating under the conditions for which they were designed?
Were they being used within their preferred operating range?
If the correct materials had been used. Was there a mismatch between the material of the pump and the material of the shaft?
If the shaft geometry, coupling, key sizing, and column pipe wall thickness had been designed according to best practices.

During this process, we uncovered a few important weaknesses.

Uneven stress distribution on the key along with uneven distribution of bending and crushing forces on key and shaft caused failures.
Thin column wall thickness was lower than required while bottom column was missing additional stiffeners.
This resulted in bottom column weld joints withstanding increased stress and would crack over time, which in turn caused.
Below-grade structural vibration.
Misalignment of bearing spiders during operation.
Eventual pump seizure.
Original design of bearing spiders follow best engineering practice.
The alignment of the line bearing would largely depend on assembly skills and would risk damage to the sealing O-rings.

Our team designed and began implementing the following modifications to the pumps:

A new shaft design with a closed-end keyway and a split ring with a wider diameter.
Changing the MOC of the shaft from 1.4313.09 to 17-4 PH steel to improve the safety margins of the pump.
A new muff-coupling design with a large split-shoulder ring and two separate keys, removing the need for one key to pass between different shafts.
Increasing the wall thickness of column pipes and adding additional stiffeners on the bottom column pipe to prevent leakage.
Adding a centralizer feature to make it easier for the team to assemble the pump and dismantle it from the barrel.
A new bearing spider design to seal the column and ensure the line bearing remained aligned.
A new design for a line shaft bearing and sleeves

All the above were done on existing pumps, negating CAPEX with high capital outlay

OEM-X Line
Outages and downtime are costly. Even worse, rotating machinery and pumps face numerous specific challenges, many of which are hard to isolate. Choosing the right supplier is vital when you factor in high maintenance levels and running costs of critical equipment.
Retrofit
Retrofitting your critical assets with the latest technology will maximize performance, minimize costs, and improve reliability.

The new pumps will have a minimum one-year warranty, an improvement with significant impact on the productivity and costs of the power station.
By November 2022, the MTBF had already increased from 4 to 11 months.
To date, the pump’s operating parameters – including vibration and bearing temperature – remain well within limits.
At the time of writing, the modified pump has been running for more than 18 months without a single failure, an impressive improvement on the original MTBF of four months.