Repeat Failures of Boiler Feed Water Pumps

The low lubricity of boiler feed water, combined with operational challenges, can lead to pump seizures. This case study examines how two 1.2 MW boiler feed water pumps experienced repeat failures immediately after commissioning — and how specifying Vespel® CR-6100 could have prevented every one of them.

Background

A refinery commissioned two new 1.2 MW boiler feed water pumps fitted with metal wear parts, running at 2980 rpm. The pumps experienced failures immediately after commissioning. The low lubricity of boiler feed water along with operational challenges led to repeated pump seizures.

The pumps were fitted with metal wear parts, ran at 2980 rpm, and experienced failures immediately after commissioning.

Failure History

Here is a brief summary of the sequence of failures the site faced:

The first failure was due to pump seizure. The original failure analysis suggested the pumps failed due to sand or debris lodging into the close clearance between rotating and stationary wear parts. The filters on the suction strainer were changed to a finer mesh to limit particle size which could enter the pump.
Soon after, one of the pumps seized again — this time, the metal parts had galled before start-up and the pump could not be rotated by hand. The clearances at the wear rings, centre bushing, and throttle bushing were increased.
The pumps seized again.
Repeated start-up attempts against seized pumps had also damaged the pump motors.

The failure analysis led the engineers to re-check the entire design and installation of the pumps:

Re-checking the design basis of the pumps
Re-checking the materials of construction
Re-checking assembly and rotor run-out
Re-balancing the rotor
Performing a new pump rotordynamic analysis
Verifying soundness of foundation and pipe strain within limits
Evaluation of operational practices and function of the minimum flow control valve

Root Cause & Solution

Ultimately, the site realised the minimum flow valve was not functioning properly, leading to low flow rates at start-up. The low flow rates caused localised flashing inside the pump and the metal parts would seize.

Their corrective action was to:

Change the minimum flow valve
Increase the clearance at the centre bushing, throttle bushing, and wear rings
“Upgrade” to a “non-seizing” metal alloy

Because they increased the clearance at all internal parts, they ran a new rotor dynamic analysis to verify that the rotor would remain stable.

What Did It Cost?

Between repeated pump repairs, motor overhauls, and engineering resources to troubleshoot and re-verify the design, the problem undoubtedly cost hundreds of thousands of dollars. If start-up was delayed or the site lost production, the losses were probably in the millions.

The solution was also extremely expensive. The clearance at the pump wear parts was permanently increased. Assuming a generous 2% efficiency loss and a power price of $0.12/kW-hr, this loss of efficiency will cost approximately $50,000 per year. Over the life of the pumps, the site will lose another million dollars or more.

Between pump repairs, motor overhauls, and lost production, the problem cost hundreds of thousands of dollars — and the permanent efficiency loss will add another million over the pump’s lifetime.

How It Could Have Been Avoided

If the site had specified Vespel® CR-6100 wear parts when the pump was ordered, the pump would not have seized. Most likely, the pumps would have made it through the low flow transients without issue and all of the efforts above could have been avoided. The motors would not have been damaged, and they would not have had to increase the internal clearances.

Even after the first seizure occurred, they could have converted to Vespel® CR-6100 and saved time, effort, and cost. The small adder to specify Vespel® CR-6100 would have saved several hundred thousand dollars at a minimum.

Furthermore, because Vespel® CR-6100 does not seize, clearances at the wear rings, centre bushing, and throttle bushing could have been reduced, resulting in an efficiency gain instead of an efficiency loss. So, instead of losing $50,000 per year in operating costs, the site could have saved at least $50,000 per year — a net $100,000 annual saving from using Vespel® CR-6100.

Combined with the Boulden PERF-Seal® design, the pump would be more reliable, easier to operate, and more efficient than a pump with metal parts and increased clearance.

Conclusion

If you are buying or overhauling a boiler feed water pump, specify Vespel® CR-6100 for all of the stationary wear parts (the rotating parts will remain metal). You’ll have a better pump that is easier to operate with a lower life cycle cost due to higher efficiency.

If you have an existing pump that seizes, contact Soletec today. We can help you solve this problem in just about any pump service. If you simply have an urgent repair and need a great material fast, we have a large inventory of material in stock and can supply raw material or machined parts with very short lead times.