Page 308 - Offshore Electrical Engineering Manual

P. 308

CHAPTER
3
Environmental Protection

INTRODUCTION
The environmental conditions for most electrical equipment offshore are generally
more onerous than those onshore. Environmental problems may be divided into three
main categories:

1. those associated with sea and weather,
2. those associated with oil and gas,
3. those due to mechanical shock and vibration and the structural limitations of the
installation.

WEATHER AND SEA PROTECTION

The salt-laden air and salt spray mists produced during bad weather have a searching
corrosive effect on unprotected metal, as electrolytic cells are set up at these loca-
tions. Therefore, any protective coatings used on metal equipment offshore should
remain impermeable, and preferably contain a sacrificial metal such as zinc.
A variety of different enclosure and support structure materials have been tried
offshore, with varying results, but experience suggests that the following materials
are suitable.

STAINLESS STEEL
This tends to be an expensive solution and needs to be carefully specified so as to
avoid problems such as susceptibility to cracking. Stainless steel cable ladder and
tray is more difficult to manufacture than that fabricated from the more common
structural steels and may be delivered with some deformity. This should be checked
by normal quality control procedures, as even a small out-of-true error will make the
installer’s life very difficult. Stress corrosion in stainless steel takes place in the pres-
ence of chlorides, and related failures occur well below the normal tensile strength
of the metal involved. The stresses during the deformation processes involved in the
manufacture may remain locked up until ‘season cracking’ occurs in the presence
of sodium chloride (salt spray). However, good-quality low-temperature-annealed
stainless steel products will provide long-term resistance to corrosion and are highly
resistant to incidental damage.

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