Winterisation – Electrical Heating Mitigation Measures To Counteract Freezing Temperatures
Published 22 Sep 2016
“It is estimated that the Arctic holds around 30% of the world’s undiscovered natural gas and 13% of its yet-to-find oil. This amounts to around 400 billion barrels of oil equivalent, 10 times the total oil and gas produced to date in the North Sea.”
Developing the Arctic could be essential to securing energy supplies for the future, but it will mean balancing economic, environmental and social challenges,” according to Shell.
The search for oil and gas by exploration companies is becoming ever bigger and no corner of our planet is out of reach (or is it?).
Exploration focuses on areas where extreme temperatures are the norm. The Arctic for example has many untapped resources but working in this type of climate poses new challenges to owners and operators with ambient temperatures as low as -60° Celsius.
Manufacturers of equipment for use in these areas have to find solutions which will operate effectively and reliably in such cold weather climates.
Winterisation measures are those which ensure an offshore vessel is prepared for operation in cold climates focusing on the adverse effects and the control of icing, freezing and wind chill. This article has been written as an informative piece about winterisation of offshore platforms, FPSO and FSUs but also focuses on managing onshore process plant through severe weather.
We highlight some of the issues faced by owners and operators when working in cold climates and look at the new DNV Guidelines : DNV-OS-A201 (Winterization for Cold Climate Operations).
DNV GL developed this new offshore standard which came into effect in April 2014 and covers the technical requirements to control the adverse effects of freezing, icing and wind chill on offshore equipment and systems.
T&D are experts in Electrical & Process Heating solutions and our article goes on to focus on how heat tracing cables can be used for some winterisation applications in cold climates.
This introductory article will be a forerunner to a future series of “products and solutions” focused posts.
We shall cover space heating, immersion heaters and anti-condensation heaters. Active measures are those which primarily rely on energy to address adverse effects of icing, freezing or wind chill e.g., heat, physical force and circulation of liquids.
Video: Offshore storm by the moonpool up in the Arctic
The risks posed by extreme temperatures vary but are very real. Obviously humans will be a little “chilly” if temperatures fall to -60°C. Perhaps not so obvious is the fact that the structural integrity of an offshore platform can be compromised with as little as 50mm of ice build up.
Whilst operators and owners are more than aware of the problems and risks, they are not necessarily fully conversant with the complexities involved in designing and specifying solutions for winterisation.
One major design consideration which can easily be overlooked is the amount of energy consumed by the active measures specified.
Although winterisation of mobile units and offshore installations is not a new objective for any oil and gas company, for cold climates, some companies still rely on standards which have been prepared for ships operating in such conditions.
However, a winterisation strategy for ships will not necessarily suit offshore oil and gas platforms. DNV GL standard DNV-OS-A201 defines its objective as :-
“ Ensuring that a vessel is capable of and suitably prepared for operations in cold climates. This is provided for by setting functional requirements to functions, systems and equipment considered important to safety and which are intended to be in operation in cold-climate conditions.”
The standard provides three levels of winterisation requirements: basic, cold and polar. This enables owners to select the correct winterisation strategy based on climate conditions. It should be noted that it is the end users responsibility to specify the correct level.
The guidelines set out provisions for anti icing, anti freezing and de-icing of equipment, plant and exposed areas, explanations of which are below and taken directly from DNV-OS-A201.
- Anti-icing : Measures to prevent ice from forming on surfaces, structures or equipment. The intent of anti-icing is that the surfaces, structures or equipment are immediately available.
- Anti-freezing : Measures to prevent fluids freezing within systems, structures or equipment. The intent of anti-freezing is that the systems, structures or equipment remain functional and are not damaged as a consequence of fluids freezing.
- De-icing : Measures to remove snow and ice from surfaces, structures or equipment. The intent of de-icing is that the surfaces, structures or equipment can be made functionally available within a reasonable time period.
Winterisation : Typical Offshore Installations
It is accepted good practice that where possible, equipment requiring anti-icing should be positioned in enclosed spaces not subject to sea spray or low ambient temperatures. Heating may also be required in these areas depending on the type of equipment being used or stored.
It is not always possible to locate equipment in enclosed areas so other protective measures can include covering with hard removable covers, sheeting or canvas. For storage containers located on the open deck or in unheated spaces the provision of heating blankets or jackets for drum or IBC storage units is recommended.
Finally anti-freeze additives or low temperature fluids are recommended where possible for liquid systems, either with or without supplementary heating dependant on the temperature at which the liquid will freeze.
The challenge faced by owners and operators is finding cost effective solutions which offer long term efficiency and protect process plant, pipework and fluids against low temperatures. Thorne and Derrick specialise in electrical heating equipment and have almost 30 years industry experience.
Plant & Equipment – Just Some Reported Problems
The UK design specification for many items of process plant and equipment is –5° Celsius to –10° Celsius, however much lower levels have been recorded with freezing temperatures plunging down to –15° Celsius for several days in winter. It is considered good practice to develop an Action Plan to assist in prioritising and managing actions identified as necessary to overcome the challenges of freezing conditions and consequent plant failure risks.
Thought it was cold last night? Turning even colder tonight with temps below freezing for a majority of the country pic.twitter.com/2y3zkC3YhM
— Met Office (@metoffice) January 15, 2016
Freezing temperatures can trigger major accidents and should not be underestimated.
Companies have reported incidents including freezing of coolant lines to a chemical reaction vessel resulting in a rise in reaction temperature and pressure; and failures of primary containment after freezing and subsequent thaw.
Snow and ice loading on tank roofs, warehouses and buildings are also factors that have resulted in structural failures and roof collapse caused by snow build-up. Plants can install gutter heating to counteract the real risk of falling icicles, ice and thawing snow onto pedestrians from roof overhangs in production areas or staff entrance points to buildings.
On the ground, melting snowfall accumulation away from critical access pathways and loading bays can be achieved by the installation of a ramp heating system to ensure snow clearance in winter weather.
Bunds can crack caused by ‘heave’ from freezing ground. Again, these outcomes should be factored into risk assessments when considering plant winterisation.
Pipes – Freezing, Fracturing & Bursting
Water and other ‘wet’ pipelines freeze – this leads to flanges, valve bonnets and other joints failing. In some cases even wet hydrocarbon lines or effluent lines with higher salt concentration have frozen. Damaged pipelines can inflict disruptive knock-on effects – for example, loss of boiler feed water lines that froze and fractured have led to consequent process shutdowns due to boilers being out of action.
HAZOP assessments have identified safety critical plant that may be especially vulnerable – for example the HAZOP guide phrase ‘lower temperature’ may prompt the provision of lagging or trace heating to prevent frost damage to pipework and maintain cold weather operationality of process plant.
- HAZOP: a hazard and operability study is a structured and systematic examination of a complex planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment.
Pneumatic control systems can also be affected. For instance, if instrument air is not dried adequately, water can condense and freeze leading to line blockages preventing plant controls (including potentially safety critical controls) from working.
Extra attention should be devoted to plant emergency mitigation systems exposed to extreme cold weather – this could include fire mains, remote monitors, hydrants, fusible tubes in fire detection systems, water deluge and emergency safety showers.
T&D, The International Electrical Heating Specialists
Thorne & Derrick work in partnership with the worlds leading Electrical Heating Equipment manufacturers such as Thermon, EXHEAT, Hazloc, Eltherm and Chromalox who are continually pioneering new technologies for winterisation solutions. The article will now explore heat tracing and how it can be used for winterisation applications.
Passive Measures v Active Measures
It should be said at this point that passive measures for anti-icing and anti-freezing are usually the most cost effective and should be considered as the first option. Passive measures do not rely primarily on energy to address the adverse effects of icing, freezing or wind chill; e.g. shielding, enclosures, insulation and building-in areas or equipment.
Passive measures are not always possible and active measures such as electrical heating or heat tracing provide the only solution.
Probably the most common and widely known, heat tracing is used across many industries to provide frost protection of pipework. Some common heat tracing applications in the oil and gas industry include loading and unloading lines, gas/vapour return lines, fuel oil lines, fire protection lines and storage tanks/vessels.
Heat tracing can also be used for other winterisation problems associated with cold climates such as:-
Door Seals & Hatches : water tight doors require sufficient heat to prevent icing of the seals
Platforms & Walkways : heat tracing can be installed under walkways for anti-icing or de-icing of walkways to maintain a safe access route for personnel.
Helidecks : anti-icing or de-icing of helicopter decks can be achieved with heat tracing. Different deck designs and materials of construction should be considered to ensure a reliable and efficient solution is specified. Companies such as Thermon can provide such design analysis.
Anti-Icing or De-icing Stairs : heating cables are installed to the underside of each tread along with thermal insulation to prevent or melt snow/ice build up.
“We have found that the winterisation rules for ships do not work for oil and gas platforms,” said Steven Sawhill, Principal Consultant, Arctic Operations & Technology, Maritime Advisory at DNV GL technical consultancy.
As well as ice being less of an issue for vessels moving from place to place, Steven said that these standards were “too prescriptive” and prevented designers from coming up with new solutions to the challenges faced in the Arctic.
“Standards are blocking innovation,” commented Stevenl, adding that the overall situation “did not leave oil and gas owners and operators in a very comfortable position.”
Pictured : Heat Tracing Cables can be specified and installed in both safe and hazardous areas to prevent frost damage to pipework, vessels, drums, tanks, walkways, emergency fire escape stair cases and helidecks.
HAZARDOUS AREA Electrical Heating
Electric heating can be used to provide frost protection and reduce viscosity in order to improve flow of heavy oils in a pipeline or within a storage tank in the production, transportation and refining processes of heavy crude oil. EXHEAT heaters are ATEX and IECEx certified to provide safe explosion protected electrical heating in Zone 1 and Zone 2 hazardous areas.
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The impact of frozen process plant and pipelines as potential causes of major accidents cannot be underestimated or overstated but can be prevented.
Preventative steps can be taken and mitigation measures enacted to prepare for prolonged periods of sub-zero temperatures to maintain business continuity, avoid plant shutdowns and improve site safety.
Any winterisation plan should be robust and reviewed.
To discuss any of the points raised above or to obtain assistance with your sites winterisation plan please do not hesitate to contact Thorne & Derrick
HAZARDOUS AREA ELECTRICAL & PROCESS INSTRUMENTATION EQUIPMENT
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