In recent years, the number of large-scale oil and gas processing plants sited in remote locations such as the Arctic regions has increased significantly. As well as exceptionally low temperatures, the extreme environmental conditions in such areas include snow, ice and high wind speeds, often with moving sea ice. The complexity and risks of operating in these arduous conditions is considerable. Outdoor instrumentation is a case in point; special winterization measures need to be adopted to adequately protect control and measurement equipment, to ensure continued plant safety and reliability.
The dramatic drop in oil prices over the past few months has, if anything, further focused attention on equipment winterization: with a number of future projects put on hold, many companies are now looking to improve the efficiency and reliability of existing plant. Parker brand products such as A-Lok fittings and tubing have proven their reliability over the years in low temperature environmental conditions. However, due to ambient temperature differences, customers pay more attention to the special materials and solutions that are necessary to avoid corrosion issues and loss of equipment.
The need for efficient equipment winterization is not limited to greenfield sites. Heat loss due to poor insulation is also often an issue at existing plants, resulting in unnecessarily high energy usage and additional operating costs. Many of the refineries in Eastern Europe, for example, were constructed 50-60 years ago in the times of the Soviet Union, and are now outdated and require upgrading.
Nearly all process plants have some outdoor instrumentation. The winterization measures that will be needed depend on a number of factors, such as the location of the plant, the worst-case environmental conditions and the type of heating (electrical or steam) that is employed. Parker offers a complete range of winterization products – including special manifolds, heaters, insulated enclosures and heat traced tubes – that enable instrumentation engineers to implement the optimum solution for every type of application.
Parker manifolds with contact heater
Parker’s instrumentation manifolds are available in special versions that are designed specifically for base or rear mounting inside protective enclosures. These manifolds offer unrestricted access to process/vent connections and eliminate internal tubing connections to minimise potential leak points. They also provide adequate free surface area for attaching a contact block heater.
Fig. 1 This five-valve base-mounting manifold provides sufficient space for a block heater.
A contact block heater dissipates heat by conduction (which is much more efficient than convection) and needs to be mounted on the flat surface of a conducting material, such as metal. One bolt is generally sufficient to attach the heater. Parker’s base and rear mounting manifolds accept steam tracing blocks or electrical heater blocks and conduct sufficient heat to prevent freezing or to maintain the process temperature of the contained fluid or gas media. These types of manifolds also help to conduct heat to the instrumentation, as well as to the process and vent connections.
One point worth mentioning concerns the type of material used for sealing rings. There is a potential threat with grafoil seals between the manifold and transmitter. This appears to be due to the risk of seal material expansion caused by frozen liquid, which may lead to a break of the seal. Tests have shown that at a temperature of -55˚C, the sealing rings leaked. Subsequent visual inspection showed that the damage was caused by low temperature liquid/ice, rather than incorrect assembly or a faulty part. If the temperature allows, replacing the graphite seals with PTFE seals will eliminate the problem. Although PTFE seals can potentially be damaged by fire or high temperatures, they are far less susceptible to material change at low temperatures.
Fig. 2 A scratch on the graphite sealing ring near the location of the bolt hole where the leak appears.
Protective enclosures for extreme cold
Specifying an enclosure for field-based instrumentation is not a trivial task – the enclosure must have a robust structural integrity and a long service life – preferably with little or no maintenance requirements of its own. The costs of maintaining some types of outdoor enclosures and the fitted components, especially in remote or difficult-to-access locations, can be considerable. Even greater effort is needed when the environmental conditions are challenging, such as when protection is required against extreme cold, frost and condensation.
Insulation makes a big difference to enclosure performance. To maintain the same internal temperature, insulated enclosures typically require just one-sixth of the heating power of uninsulated enclosures. If components need to be protected against low temperatures, a contact heater is an ideal means of keeping the enclosure warm and it is more cost-effective than other forms of heating. Parker and its distributors offer a comprehensive range of steam tracing and electrical models, to best suit the application.
The main criteria of any enclosure designed to protect instrumentation from severe cold is its thermal conductivity – the higher the conductivity, the greater the heat loss to the external ambient. The bigger the difference between internal and external temperatures, the higher the running costs, mitigated only by the thermal insulation qualities of the enclosure. Even heavily insulated metal connections act as thermal shortcuts, which effectively couple the inside of the enclosure to the external environment. Parker has a vast experience of providing the fully fitted enclosure with the pre-installed components that is more reliable and easy to assemble in proper manufacturing plant conditions rather than on site in a cold environment. Optimal thermal insulation saves a lot of energy.
Prefabricated tube bundles
Tube bundles comprise one or more process tubes, steam or electric tracing, insulation and a jacket. They are typically used to prevent viscous materials from freezing, to avoid gas condensation and to maintain process temperatures in applications such as instrument sampling and impulse lines.
Prefabricated tube bundles are generally regarded as more secure and reliable than handmade solutions, but some users believe that they are more expensive because of material costs. However, prefabricated bundles can be installed much more quickly. This reduces the amount of work that needs to be performed in the field, which means that even when material costs are taken into account, prefabricated tube bundles result in lower overall project costs.
Although not so obvious, corrosion is another threat that needs to be considered when applying handmade insulation. A typical scenario is when corrosion progresses underneath a loose wrap of insulation layer. The ‘gas/oil/chemical pockets’ that can form due to leaks between the handmade insulation and the tubes can also cause corrosion issues.
The main advantages of prefabricated tube bundles compared to handmade solutions are:
- Application-specific design ensures reliable and predictable performance
- Extruded outer jacket provides superior weather protection
- Easier handling reduces risk of compromised performance due to installation mistakes
- More cost-effective due to shorter installation time
Parker’s prefabricated tube bundles offer the additional advantage that they are available with a choice of cabled or parallel construction (many manufacturers only offer the latter). The main advantages of cabled tube bundles are:
- Reduced stress on tubing when bending is required
- Requires less space in tube or cable tray
- Tubes will not separate in bends
- Ideal for projects involving multiple long runs and multi-plane bends
The system needs to be connected safely to transmit fluids and gases, to keep a process warm or above dew point and to protect personnel from hot pipes/tubes, as well as to protect tubes against corrosion. For this purpose, heat traced tube bundles are typically used for manifold and relief valves, and pre-insulated tubing is used for large pipe tracing and condensation return lines/systems. The insulation is usually designed for extremely cold environments and can typically withstand cryogenic temperatures down to -180˚C. However, it is not always obvious how to choose the correct insulation, especially in cases where the temperature needs to be maintained over some distance in a cold environment. The heat loss will obviously be smallest in the centre of the bundle and largest at the insulation’s periphery.
Fig. 3 Cross section of heat distribution from centre outwards.
The main criteria that instrumentation engineers need to consider before specifying the insulation are the distance that the fluid or gas needs to be transmitted, the ambient and fluid temperatures and the outside diameter and material of the tubing. In the case of electrical tracing, the operating voltage of the heating cable is also an important consideration.
Nowadays there are many different types of tube bundle technology for instrumentation winterization, providing system designers and installers with a wide range of options. Parker’s product range includes pre-insulated tubes and prefabricated versions of all the main categories of heat traced tube bundles, with a choice of eight different types of tube jacket materials to best suit the application.
Fig. 4 Types of tube bundles.
Parker manufactures each tube or tube bundle using a proprietary insulation process, in which the first layer is wound in one direction with an overlapping layer and then the next layer is wrapped in the opposite direction and overlapped. If a third insulation layer is required, this is wound in the opposite direction to the second layer. This construction process means that installation engineers are able to pull the insulated tube or tube bundle direct from a reel – through the cable or tube support trays in the plant and with turns and bends in any direction – without the possibility of the tube or heater cable popping out through the insulation layers. This helps to prevent any ‘hot spots’ or ‘cold spots’ forming along the length of the installation run, which occur with handmade insulation.
One especially critical aspect concerns the end-sealing of prefabricated insulated tubes or tube bundles; it is essential that the insulation material is kept dry to ensure long term performance. The installer must exercise due care when carrying out this procedure, and use the correct sealing products and techniques.
As operators move into increasingly hostile environments, ensuring the safe and reliable long-term operation of oil and gas process plants is becoming even more challenging. The need for efficient equipment winterization has never been more acute, and demands innovative thinking and field-proven solutions. Sourcing the various application-specific manifolds, insulated enclosures and heat traced tubes that you require does not need to be onerous.
Although corrosion seems a minor threat in cold conditions, one needs to consider temperature gradients: a number of fields (e.g., Kashagan in Kazakhstan) feature extreme cold winters (minus 50 deg C) and extremely hot summers (up to 40 deg C). At Parker we provide products manufactured from corrosion resistant alloys (e.g., 6Mo, 625) in addition to standard stainless steel materials, and have gained wide experience of producing non-standard solutions. One such solution is Shell TAMAP 2 start valves that can operate over a temperature range of minus 50 deg C to plus 150 deg C, which is a key advantage compared to standard valves that have certain temperature limits.
To summarise: nowadays more customers choose Parker Hannifin because it has the expertise and product breadth to help at every stage of equipment winterization, from one-off items through to complete parts kits or fully assembled systems. If you need further help on the subject of equipment winterisation we are here for your support and service, and have a broad network of experts specialising in various products and solutions.
Alexander Patskov is specification manager - Central Europe & CIS, Parker Hannifin, Instrumentation Products Division Europe