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Shortcuts Can Lead to Disastrous Outcomes

Design flaws cause catastrophic failure in a geothermal power station hotwell in New Zealand.

Written by: Chandra Verma (Hydro, Inc.)
Publisher: Pumps & Systems / August 2016

 

Despite well-documented pump system standards and basic requirements, omission of certain crucial design steps remains a problem in the industry, often causing disastrous outcomes for the end user. When suppliers, manufacturers and/or contractors take shortcuts, technical and commercial risk can present serious ramifications for a large project.Communication failures between the end user’s staff, suppliers and contractors can intensify problems, especially when pumps that may not be appropriate for a given job are commissioned and put into service. Without the end user’s knowledge, a facility may install pumps that have not been properly tested for the application, were fabricated to inferior standards or subject to other shortcuts that adversely affect performance.Sometimes the end user becomes aware of shortcut-derived flaws during the commissioning stage. Other times, problems in equipment or system design might not be evident immediately—they surface during subsequent plant and equipment maintenance that reveals potentially dangerous, hidden conditions. The ensuing problems can lead to tense project politics and expensive rectification, including hiring independent consultants.

Suppliers, manufacturers and contractors take shortcuts for various reasons. These shortcuts can be attributed to a lack of experience with how a pump might be deployed in the field. There may be miscommunication of technical details from both the user and supplier or between the user and contractor.

Budget constraints and concerns can also result in omissions; commercial reality can cause a manufacturer or supplier to make a project’s bottom line cheaper by reducing the cost of equipment and cutting corners.

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Figure 1. The velocity distribution of the original (left) and modified geometries (right)

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How Root-Cause Analysis Solved a Vertical Turbine Pump Failure

A comprehensive approach to reverse engineering helped to establish the differences between the stainless steel and original bronze impellers.

Written by:  Hydro, Inc.
Publisher: Pumps & Systems / March 2016

 

When a severe pump failure involving one of three installed circulating water makeup pumps happened, facility personnel grew concerned about the root cause. The subject pump failed just 40 days after its commissioning.
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Image 1. A crack in the discharge head flange that involved fatigue failure of the weld of a pump.

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Image 2 (right). The pump’s impeller wear ring landing shows heavy scoring.

The equipment in question consisted of three-stage vertical turbine pumps running either in standalone or in parallel operation as required. The failure manifested itself through high vibration and caused severe scoring of the pump shaft and wear ring landings, leading to fatigue failure of the weld on the discharge head flange (see Images 1 and 2). The commissioned pump was refurbished and rebuilt by another company’s service center with spare impellers supplied by an original equipment manufacturer. No changes to the geometry had reportedly been made, although the impeller material had been upgraded from bronze to stainless steel.

The plant initiated its internal root-cause analysis process, and the failed pump required emergency repair. The station sought a company to conduct the repair, and the firm reviewed the customer-supplied documents and background providing the possible causes of the failure. Continue reading