Page 30: of Offshore Engineer Magazine (Dec/Jan 2013)

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EPIC

Arctic operations at what temperature?

By James Bond and perature comes from the International for Arctic operations applies the wrong

Association of Classifcation Societies numbers, the regulatory guidance will

Dan Oldford, ABS (IACS) Unifed Requirement (UR) S6 for not facilitate safe operations. he concept of temperature seems structural steel intended for service at Before engineering a unit for Arctic simple enough. Everyone knows lower temperatures. IACS UR S6 and operations, a temperature specifcation

T that a thermometer can be used to the ABS Low Temperature Environment has to be established based on measured measure the temperature of a substance (LTE) Guide require that the design data from the work site or from a site as such as air and that by knowing the service temperature (DST) be selected as close to that location as possible. Then, forecast, people can adequately prepare the lowest mean daily average (LMDAT) all of the systems on the unit, including for the day’s outdoor activities. While for the operational window and geo- the equipment to be supplied from ven- it might be marginally problematic to graphical location. The LMDAT, which dors, have to be designed and manufac- be underdressed or overdressed for the has been in use for many years and is tured to operate at that temperature. weather conditions, there are no serious widely recognized in the industry, is The problem lies in answering the repercussions if the forecast is wrong. For easy to calculate using temperature data question, “What is the temperature for

Arctic oil and gas operations, however, for the operational area. the location?” Temperature varies minute poorly developed predictions can have to minute, hour by hour, day by day, and

Prediction and problems catastrophic consequences if the equip- even decade by decade. Often, tempera- ment does not function reliably when the Inaccurate temperature prediction has ture is expressed as an average of all the temperature drops. the potential to impact many operational temperatures ever recorded in a particu-

While some work has been done in elements. If an engineer designing a lar area, the historic average temperature this feld, there is much more to be new support vessel or offshore platform for the day on which operations are done to actually defne the temperature to operate in a specifc location has the expected to take place.

that should be used for design, equip- wrong DST, the designs are wrong. If an To further complicate calculations, ment procurement specifcation, and equipment manufacturer designing and materials vary in their sensitivity to operational risk management for Arctic building equipment for cold environ- temperatures and temperature fuctua- operations. ment applications uses the wrong DST, tion. A sudden drop in temperature for

The most recognized defnition/ the equipment may not be reliable. And a few hours will have signifcantly less selection of a design service tem- if a regulatory body developing guidance effect on the hull material (with its

Temperature plots Temperature plots with StDev 20 10

Barow, Alaska

Barow, Alaska 10 0 3-Nov 23-Dec 11-Feb 1-Apr 21-May 10-Jul 29-Aug 18-Oct 7-Dec 26-Jan 0 1-Apr 3-Nov 23-Dec 11-Feb 21-May 10-Jul 29-Aug 18-Oct 7-Dec 26-Jan -10 -10 -20 -20

Temperature (C°)

Temperature (C°) -30 -30 -40 -40 -50 -50

Lowest Recorded

Lowest Recorded

MDLT

MDAT MDAT - 2 X StDev

MDAT MDHT

Daily Temperature

Daily Temperature

Record Lowest

Lowest Lowest

Record Low = -48.3 Lowest MDAT = -29.1 MIN MDAT - 2StDev = -45.63

Low = -48.3 MDLT = -32.1

MDAT = -29.1 MDHT = -25.51

Fig. 1: Temperature data for Barrow, Alaska, from 1999 to 2011.

December 2013 | OE oedigital.com 32 032_OE1213_EPIC1_ABS.indd 32 11/22/13 4:12 PM