Preparing pumps for duties in the tropics
01 September 2014
Amarinth's Oliver Brigginshaw offers some insights into the issues that must be addressed when preparing oil and gas duty pumps for the extreme heat and humidity of tropical environments.
Exploration and production of oil and gas is taking place in ever more remote regions. Some of the world's most promising deposits lie deep beneath the earth’s tropical zones; for example, Papua New Guinea, Malaysia and even the Amazon rain forests. With oil at historically high prices, the incentive to develop these resources has never been greater.
This poses new challenges for manufacturers to design equipment that can operate reliably in high temperature and high humidity environments.
Pump manufacturer, Amarinth, supplies pumps into just such environments and has extensive experience of tropicalising equipment for these applications. In this article, I draw from some of the lessons my own company has learned to ensure its pumps operate reliably in these testing conditions.
In Papua New Guinea, Amarinth pumps operate in temperatures exceeding 35°C and humidity of 80 percent; in Sabah Malaysia they are subject to temperatures of 40°C with humidity frequently reaching 100 percent. In Iraq, temperatures around our pumps reach 55°C with humidity levels of 70 percent, and in the United Arab Emirates we have designed pumps for operation in temperatures as high as 87°C under the blazing sun and humidity levels as high as 95 percent.
All equipment suppliers have their own definition of a tropical environment and as can be seen from the above examples of pumps that were classed as tropicalised, the definition of temperatures varies widely. As a guide, temperature extremes of -5°C (at night) to over 55°C (in direct sunlight) and a relative humidity of 70 to 100 percent could be considered as tropical environments.
For the oil and gas industry, technical specification API 610 (relating to centrifugal pumps) is widely used to ensure that equipment is capable of performing reliably in the conditions in which it is used. However, when it comes to equipment that has to work in hostile tropical climates, the API 610 datasheet has just a tick box indicating that tropicalisation may be required and there isn’t any clear definition for tropicalisation – nor, indeed, any further guidance for material selection or design considerations to assist customers or manufacturers.
In the absence of any industry standard definition of what tropicalisation actually means in relation to pumps and how equipment should be prepared in order to achieve it, Amarinth has drawn up its own list of special measures necessary to ensure that its pumps operate reliably in tropical conditions.
Materials selection - selection of materials is related to the prevention of corrosion, oxidisation and the potential build-up of growth on the pump. Type 316 stainless steel is usually the minimum choice of material, though the fluid being pumped will often govern ultimate material selection, with duplex stainless steel and exotic alloys often required.
Lesser grade materials are an option for some components but if used would require appropriate covering (paint specified to prevent material oxidisation and mould/bacterial growth).
Base-plates - the frame arrangement and sizes will follow the API sizing and design unless specified by the purchaser. Surface finish should be to Sa 2.5 (equivalent to ISO 8501) and it is recommended that an acrylic top coat or equivalent is used. The industry usually follows the Shell DEP specifications. It is also important to ensure that there are no water traps in the design that would harbour the growth of moulds and bugs.
Seals and seal support systems - the main manufacturers of seal systems make no reference to any major differences or special requirements for tropical environments other than that the material selection is generally duplex stainless steel and the top coating for the reservoir should prevent growth on the surface.
However, in environments where the maximum temperature exceeds 55°C, air cooled heat exchangers may be required around the equipment or increased in size as appropriate, and sun shades should be included for all instrumentation.
Material finish - in order to prevent growth on the surface a smooth finish is desirable that is water and microbe resistant. The surface finish of any castings should be to Sa 2.5 (equivalent to ISO 8501) and blast cleaned to remove all millscale, rust, paint and foreign matter to achieve near white metal. If painting, a rust inhibiting primer should be applied and top coatings are normally silicone based, polyurethane or epoxy.
Motors and drives - in a tropical environment heat generated by the motor will create condensation regardless of usage (intermittent or long periods). Condensation within the motor will eventually damage the windings. Thicker silicone based varnishes should therefore be applied to protect the windings from oxidisation.
There should also be additional condensate drainage holes within the motor housing. The use of anti-condensate thermostatically controlled heaters within the motor housing is recommended in very high humidity environments.
To prevent the possibility of dust and water ingress IP65 is the standard often requested for motors unless the pump is being used offshore or around other specific water hazards in which case the specified protection rating may be higher.
Stainless steel is usually the minimum choice of material for all main motor components. Fixings (bolts, nuts, etc) are preferably of stainless steel but if carbon steel fixings are used then a zinc based anti-corrosion compound must be applied.
Oil sight glass - condensate can often build-up within the bearing bracket housing as a result of temperature fluctuation and humidity and so the use of an oil sight glass in tropical regions is recommended. This can be fixed to the lowest point of the bearing bracket on a horizontal pump and any condensate from the bearing bracket will sink to the bottom of the oil-filled glass, thereby allowing for maintenance drainage. The glass is normally constructed of an acrylic bodied vessel resistant to temperatures up to 110°C (glass is not allowed in an ATEX zone).
Instrumentation - monitoring instrumentation should be placed under sun shades for dial reading and rated IP65 as a minimum. The minimum material specification should be type 316 stainless steel.
Shipment, storage and installation - there are various storage and preservation procedures recommended to ensure the integrity of the equipment between shipment, storage and installation/start-up. For example, storage of rotating equipment should be between 15°C and 26°C and less than 75 percent relative humidity to avoid microbe build-up and prevent corrosion.
Humidity levels can be controlled during shipment and storage using vacuum packed bags and desiccants. Seals may also require turning every three months. If this is the case and the pump is not to be commissioned for some time it is better to store the seals separately.
In conclusion, I would stress that these recommendations are based on Amarinth’s interpretation of tropicalising industrial centrifugal pumps and have been compiled from data and information received from various parties we have worked with in designing and manufacturing pumps for tropical regions.
The list is by no means exhaustive but illustrates some of the design considerations for operating pumps in high temperature and humidity environments. Further technical details are available on the Amarinth website in its Tropicalisation Technical Bulletin.
Oliver Brigginshaw is managing director of Amarinth
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