Selection And Procurement Of Pumps For Replacement
Author : Ashish Bhartia
Lot of articles and literature has been published for selection of pumps for industrial uses. It is of note that these normally deal with new procurements while little importance is given to selection of pumps for the purpose of replacing an existing installation. It is generally assumed that the factors for selections remain the same for both the cases. It is of note that while this argument is generally true, still there are some critical points which need to be looked into while going in for a replacement.
Normally a replacement is required for the following reasons:
- 1. Replacement is requested by Maintenance Department
- 1.1. The existing pump is very old and worn
- 1.2. The existing pump is inefficient and a better one is required for energy conservation
- 1.3. The existing pump model is out of manufacturing range of the supplier and spares are hard / expensive to get
- 1.4. The particular pump is very difficult to maintain due to reasons like :
- 1.4.1. Design fault in form of bearing selections, MOC selections etc.
- 1.4.2. The pump was imported and spares are difficult to import or import substitute
- 2. Replacement is required by Production Department
- 2.1. Changes / modifications in process has resulted in revision of specifications
- 2.2. Requirements of operating ease and greater automation for reduction in operational staff requirements.
For Case - 1
Once the requirement for the replacement is felt for a particular pump it is recommended that before finalizing the specification sheet for the requirement the following should be considered:
Though the decision for pump change is based on maintenance department requirements still it is recommended that the maintenance department should involve the production department also at this stage of pump selection. A joint meeting should be organized and following points should be critically examined and care should be taken to ensure that the pump selection takes care of these issues.
The relevance of each of these issues is shown with help of an example (listed in form of table) for each case so that an overview of the, benefits obtained / losses in case of these points not being considered, is highlighted.
- Are there any changes in the process requirements from those stated in the original specification sheet of the pump?
- What were the chronic problems faced by production people in operation of the old pump?
- Is there a plan to modify the process in near future requiring modifications in the specifications of the pump?
For case - 2
Once the maintenance department receives requirement for replacement of the pump, it should then interact with production for the following:
- The nature of change in process and joint study of the specifications provided by the production department.
The other issue which has to be considered for the proposed change is common for all the cases stated above and discussing the same within the Organisation can reap a lot of benefits:
- The problems in operation of the existing pump and benefits expected after change.
After this exercise now a platform is set for finalization of the new specifications. The specifications should be complied in set formats. It is advised that the Organisation should have standard set of formats for equipment specifications and the same should be used for keeping of all specification data. In case such format is not available for pumps then many standard formats are available along with various international standards. API 610 has a very comprehensive format for this purpose and the same can be used.
- Learning Curve of the plant operation persons for the usage and utilization of the pump.
It is highly recommended that after the specification format has been filled, both the production and maintenance departments should again vet it formally and a copy of this document should be kept as a record.
It is possible that no changes have been made in the specifications after all these considerations. In such cases the normal practice is to order a like to like pump if available on the same manufacturer. Though normally this would be the best option but still it is always better to ask for proposals from other vendors also as at times it is found that on evaluation the like to like replacement is not the best of alternatives.
The inquiries can now be floated and after receiving the offers from vendors the selection of the pump has to be done.
The selection procedure and life cycle cost analysis is a very well documented procedure and hence is not dealt in this paper. The paper will concentrate on additional issues that are to be considered for the case of selection of pumps for replacement.
The following points should be studied and should become a part of pump evaluation procedure for effective and optimized selection of the replacement. :
In addition to all these issues some other factors and actions should also be initiated for the purpose of replacement consideration.
- The cost of piping modifications for all the proposals received should be calculated and should be added as fixed cost to the respective proposal.
- The cost of foundation modifications required should be evaluated and should be added to the fixed cost element of the proposals where such modification is required.
- The driver in case requires change (due to specification modifications or due to availability of better efficient pump) the cost of the same should also be become a part of fixed cost element. It is also recommended that in organizations where electrical maintenance is looked after by a separate group, the proposals should be vetted by the electrical group also and there views should be taken for finalization of motor selection and replacement (if required).
It is hoped that the guidelines stated in the article shall be of help to professionals and an effective procedure for procurement of pumps for replacement can be devised by organizations for effective use of resources.
- The moment a proposal is considered for replacement of existing pump and an understanding has been reached on this issue on principle, actions should be taken to block spares procurement for inventory of such pump. This is a factor, which is normally forgotten and results in unnecessary procurement of inventory spares.
- In case piping modifications are required for replacement, actions should be taken to ensure that all required pipe and fittings would be available at the time of installation of the pump.
Table of examples
|Example||Proposal / initiated by||Results of discussion||Benefits|
|1||Maintenance wants to change a pump as it an obsolete model.|| Production wants some capacity enhancements for better operational control.|| Modifications are incorporated in the new specifications.|
|2||Maintenance wants to change a pump as it an obsolete model. ||Production points out that pump has problem of de-priming during plant upset conditions.|| NPSH (A) figure was revised for taking care of plant upset conditions also.|
|3||Maintenance wants to change a pump as it an obsolete model. ||A modification is under consideration where by it would be required to double the capacity of the pump. ||The decision for procurement was deferred by 3 months and was done after finalization of the modification proposal with revised specifications.|
|4||Process requested to procure a pump with reduced NPSH (R) requirements. ||The pump was a water pump (in Cast Iron construction) but due to process changes proposed the fluid would be Aqua Ammonia Solution. ||The MOC was also revised to Cast steel.|
|5||Production requested to replace the wastewater pump by a non-clogging type pump. The reasons stated were the fine strainer provided around the foot valve got frequently choked due grit and muck present in waste water and frequent cleaning was required, resulting in loss of machine availability and wastage of manpower resources. A non-clogging type pump was requested so that the mesh size of the strainer could be increased for reduction in the frequency of cleaning. ||On discussions it was found that a problem of foot valve passing was also present for this pump though it was less frequent. ||The proposal was finalized to procure a self-priming pump (hence eliminating the use of foot valve) with suction strainer (along with a standby parallaly installed strainer). Hence both the problems were taken care off and also a more efficient pump could be selected as compared to the efficiency of non-clogging type pump available.|
|6||Maintenance wants to change the washing water pump as it an obsolete model. There were 2 pumps, of 10 m3 / hr capacity each, installed and one of them had to run continuously for providing washing water at various points at all times.||It was found that except for 2 hours every day (when full 10m3 capacity was utilized) the plant requirement was for about 4 to 5 m3 / hr. ||Proposal was finalized to procure 3 pumps of 5 m3 / hr capacity each and run the second pump for the required time only. The 3rd was kept as standby. The result was substantial savings in energy costs.|
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Revised: Thursday, 08-Oct-2015 11:54:29 AEDT