Page 17 - Offshore Electrical Engineering Manual

4 CHAPTER 1 The Offshore Electrical Dimension

HAZARDS OFFSHORE

GAS
Accumulation of combustible gas can occur on an offshore installation from various
sources, including the following:

1. Equipment and operational failures such as rupture of a gas line, flame out of an
installation flare, a gland leak, etc.
2. Gas compressor surge/vibration causing failure of pipe flanges, loss of compres-
sor seal oil, etc.
3. Drilling and workover activities.
4. In concrete substructures, the buildup of toxic or flammable gases due to oil
stored in caisson cells.

CRUDE OIL AND CONDENSATES
1. Equipment and operational failures such as the rupture of an oil line, a gland
leak, etc.
2. The high pressures involved in some cases could cause spontaneous ignition
because of the electrostatic effects.

OPERATIONAL HAZARDS

1. Apart from the fire and explosion hazard of process leaks, there is a hazard to
personnel purely from the mechanical effects of the leak jet and the sudden
pressure changes caused by serious leaks in enclosed compartments.
2. Care must be taken in the siting of switchrooms, generator sets and motor drives
to minimise the risk of damage due to crane operations, especially if sited near
drilling equipment areas where heavy pipes and casings are being frequently
moved.

ELECTRICAL SYSTEM DESIGN CRITERIA
The purpose of any offshore electrical supply system is to generate and distribute
electricity to the user such that

1. power is available continuously at all times the user’s equipment is required to
operate,
2. the supply parameters are always within the range that the user’s equipment can
tolerate without damage, increased maintenance or loss of performance,
3. the cost per kilowatt hour is not excessive taking into consideration the logis-
tical and environmental conditions in which generation and distribution are
required,