Repair, Overhaul and Upgrade of Vertical Turbine Pumps


Written by:
Dr. Lev Nelik
 

Basically, a repair is the simplest, least-involved way of "fixing" a pump, typically caused by a non-recurring accidental event, such as a broken shaft, failed seal, and so on. An overhaul is more involved. It may include changeover of all the bushings and shafts, reestablishing register fits, restoring impeller clearances, and similar work. An upgrade will include repair and overhaul work, but typically also includes hydraulic modifications to change pump performance - to increase or decrease flow, shift best efficiency point, change materials of construction, etc.

Last month we explored some of the highlights in the repair process of horizontally split pumps. Now let's talk about vertical turbine pumps. First of all, what is the difference between a repair, an overhaul and an upgrade?

Basically, a repair is the simplest, least-involved way of "fixing" a pump, typically caused by a non-recurring accidental event, such as a broken shaft, failed seal, and so on. An overhaul is more involved. It may include changeover of all the bushings and shafts, reestablishing register fits, restoring impeller clearances, and similar work. An upgrade will include repair and overhaul work, but typically also includes hydraulic modifications to change pump performance - to increase or decrease flow, shift best efficiency point, change materials of construction, etc.

Right from the beginning, clearly understanding which of these procedures is called for and why is very important because the extension, quality and price of work vary greatly depending upon what will be done to the pump. Scope of work creates a source of constant misunderstanding and frustration among the pump user community, as well as for repair shops.

For example, a higher-price bidder may lose an order due to simply misunderstanding the expectations of the pump end user. His quote to restore all register fits requires the use of expensive machinery (high price), while all the end user might want is to change a leaky seal and return the pump back to service as quickly as possible.

The need for a pump repair is established essentially from one of the three scenarios:

 

Figure 1. Foundations do not look too good. All you can typically see is a motor and a support head; it is difficult to know what is under it. In this example, note that there are no anchor bolts, and the sole plates do not even have holes for the anchors drilled in it. A spirit alone is holding the pumps down.

a. Problems with a pump (noise, vibrations, leaks, lost performance, etc. or downright failure) - typically (although not always) a "reactive" approach, with run-to-failure mentality being a prevalent culture of the plant.

b. Accumulated run time (10 to 15 years) and gradual deterioration of performance - a more "proactive" approach, typically applied by more reliability-conscious organizations.

c. A combination of (a) and (b) above.

In case (a), a repair shop is called (often on emergency) to pull the pump and fix it. Due to the urgency of the situation, competitive quotes are often either limited or bypassed entirely and repairs are performed by whatever shop performed some repairs in the past.

For vertical pumps, all that is visible is a support head and a motor, with the rest of the pump under the sole plate, as shown in the example photo in Figure 1.

From this, a "rough" quotation is then based strictly on past experience with similar units and typically contains:

  • Disassembly, blast and clean
  • Replacement of (some) bearings (bushings) and packings
  • Replacement (or repair) of mechanical seals
  • Reassembly, paint and delivery back to the customer

The quotation covering the scope of work listed above looks good to a purchasing department seeking a low bid, but it does not address the maintenance concerns of repeated failures. Typically, no repair report, no root cause analysis, and no pre-repair vibrations analysis accompany this sort of expedited repair job and, sure enough, there is little surprise when the same (low bid) repair is repeated again one to three years later.

A more "sophisticated" bidder will get an award based on the minimum amount of quoted work (as listed above), but when the pump is actually reassembled in the shop, the bidder will submit price additions for replacing the broken shaft(s), changing the wear rings, weld repairs, epoxy coat to improve efficiency, and so on.

These additions may dwarf the original quote, but by that time all of the initial competitive bidders are gone. The shop that already has the pump ends up completing the extended scope of work. As many folks know, "bait-and-switch" is an appropriate name for this sort of strategy.

To clarify and unify expectations, a good starting point is to have a 3-level set of specifications prepared for the vertical turbine pump repair/overhaul/upgrade work. These are:

Level 1

Basic repair (a simplified sample is essentially shown above, and each plant can modify for particular needs and specifics). A limited report or documentation of internals, such as clearances, etc. is provided for this level.

Level 2

Extended repair:

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See also:

Upstream Pumping Solutions

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