Offshore Installation Practice

393 Pages·1988·8.053 MB·English

by  J. Crawford (Auth.)

Offshore Installation Practice
J Crawford CEng, FlMarE
Formerly Principal Surveyor, Lloyd's Register of Shipping
Butterworths
London Boston Durban Singapore Sydney Toronto Wellington
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given by the Publishers in their current price list.
First published 1988
©J.Crawford, 1988
British Library Cataloguing in Publication Data
Crawford, J.
Offshore installation practice.
1. Offshore structures - Design and
construction
I. Title
627'.98 TC1665
ISBN 0-408-01483-0
Library of Congress Cataloging-in-Publication Data
Crawford, J., C. Eng.
Offshore installation practice.
Bibliography: p.
Includes index.
1. Drilling platforms-Design and construction.
I. Title.
TN871.3.C73 1987 627'.98 87-21799
ISBN 0-408-01483-0
Photoset by Butterworths Litho Preparation Department
Printed in Great Britain at the University Press, Cambridge
Preface
Fixed and mobile offshore installations are essentially dealt with as marine
installations, and all equipment essential to the safety of personnel and safe
operation of the installation are to be constructed and installed in
accordance with the classification/certification authority requirements.
The range of equipment and the applications are constantly changing.
New regulations and requirements are constantly being formulated by the
various regulatory authorities both national and international as they
endeavour to seek and ensure maximum safety of installation and
operation. This book endeavours to indicate the main requirements and
applications for the arrangements to be accepted by national and
international classification and certification authorities.
In addition to the general requirements, specific chapters are devoted to
flare systems, fuel gas and crude oil burning, fire protection, fire detection
and extinction and piping design.
The importance of life-support systems is fully recognized by the
inclusion of a section covering submersible and diving systems with special
reference to umbilical (in water) flexible hoses.
This book is intended to be a textbook for the instruction and guidance
of those engaged in the design and installation of offshore units. It will be
useful as a reference work for those who desire a further knowledge of
offshore installation practice. Whilst the book is mainly of a descriptive
and practical nature, it is considered that sufficient theory has been
included to enable the reader to understand the principles involved.
J. Crawford
V
Acknowledgements
The author wishes to express his thanks to his many colleagues at Lloyd's
Register of Shipping, and the following firms and associations for their
help in the preparation of this book and by supplying illustrations and
granting permissions for certain text photographs to be reproduced: AB
Hedemora Verkstader; Argus Ball Valves Ltd; Alfa Laval (GB) Ltd;
Airco Cryogenics Ltd; British Petroleum Ltd; Isaac Bentley and Co. Ltd;
British Standards Institution; Brown Brothers (Offshore) Ltd; David
Brown Gear Industries Ltd; Cameron Ironworks; Department of Energy
(Petroleum Division) UK; Dirivent Ltd; EPOS Ltd; Frank-Mohn Ltd; Gas
Services Offshore Ltd; Gusto Engineering b.v.; Hamworthy Ltd; E. F.
Houghton and Co. Ltd; International Association of Classification
Societies; International Maritime Organization (MODU Code 414A(XI));
Institute of Petroleum; Kaldair Ltd; Krasberg General Diving Systems
Ltd; Thomas Lamont and Co. Ltd; National Air Oil Burners, Inc.;
National Fire Protection Association; Nuove Pignone; Occidental Pet-
roleum (UK), Inc; Peerless Pumps Ltd; Pyroban Ltd; Senrk Heat
Transfer; Shell Ltd; Stothert and Pitt Ltd; Taurus' Hungarian Rubber
Works, Budapest; TK Valves Ltd; Weir Pumps Ltd; Worthington Simpson
Ltd; Yorkshire Imperial Metals Ltd.
vi
Chapter 1
Offshore gas and oil production platforms
1.1 Fixed drilling/production platforms
Drilling platforms are considered as marine units. The items of machinery
which are essential to the safety of the platforms have to be constructed
under Classification Society survey, as in the case of mobile offshore units.
The most essential safety system on a fixed platform is the fire-fighting
equipment, including sensors, alarms and cutouts. Since this equipment is
essentially electrically operated, it follows that the generators, their prime
movers and ancillary equipment, must also be considered essential and,
therefore, should be constructed under survey. However, as only a small
amount of power is required for the essential service in relation to the total
amount of power available, construction under such survey is not insisted
upon, provided the generators and prime movers are constructed to
nationally recognized standards.
When planning the piping system, consideration should be given to the
location of various items of machinery in relation to hazardous areas,
referred to as 0, 1 and 2 areas.
Division 0 area: An area in which a dangerous atmosphere could
continually be present.
Division 1 area: An area in which a dangerous atmosphere is likely to
occur under normal operating conditions, e.g. crude
oil-mud pump room, drill area, etc.
Division 2 area: An area in which a dangerous atmosphere is likely to
occur only under abnormal operating conditions, e.g.
due to pipe failure.
All materials used in gas/oil production systems should be suitable for the
specified service having due regard to the temperature and working
pressures involved. The nature of the restricted area and the resulting
possible congestion of equipment also should be taken into account. The
process systems and associated equipment and piping for these, which is
within the boundary of the offshore installation, should conform to the
relevant national and international standards which for the UK is BS 3351,
Code of Practice for petroleum refinery installations and, internationally,
ANSI, Β 31 3.
Piping external to the offshore installation must be in accordance with
1
2 Offshore gas and oil production installations
the recognized national and international standards for oil or gas
transportation piping. These standards are ANSI Β 31 4 and Β 31 8.
Boilers or other fired appliances must be located in safe spaces, and
special attention given to their location with regard to the above classified
areas. Access to both machinery spaces and safe spaces must be from the
open deck. There should be no direct intercommunication between the
safe and dangerous spaces (accommodation and mud rooms, etc.).
Audio-visual alarms should be provided to indicate the pressure of low
flashpoint vapours at the air inlets to the diesel and gas turbine units.
Provision should also be made to prevent the oil engines from
overspeeding in the event of accidental ingestion of low flashpoint vapour.
Whilst this can be dealt with for diesel units, it is not always practicable in
the case of gas turbines. However, it is essential that the air intake for these
units is led from a safe space and preferably overhung from the platform.
Gas detectors/alarms should be provided on the external length of the air
trunking to indicate the presence of gas in order that suitable precautions,
such as the shutdown of the unit, can be taken (see Figures 1.1 and 1.2).
dJ Turbine exhaust
Generator room (safe area)
Turbine enclosure
vent inlet
Turbine enclosure
(extraction)
vent outlet
/
Turbine
Turbine enclosure
combustion
(negative pressure)
air intake
Figure 1.1 Basic arrangements of gas turbine venting (offshore installation)
1.1.1 Gas and oil production systems
All materials used in gas and oil production systems should be suitable for
the service intended, having due regard to the temperatures and working
pressures involved. In this respect, having due regard to the nature of
restricted area and thus the resultant congested equipment areas, the
process systems and associated equipment should conform to the
applicable national and international standards for petroleum refinery
installations, i.e. BS 3351, Code of practice for petroleum refinery
installations or the equivalent ANSI Β 31 3 in so far as the piping system is
located within the boundary of the offshore installation. Piping external to
the offshore installation to be in accordance with recognized national and
Fixed drilling/production platforms 3
Inlet
/turbine^
LT
'Safe' module
Gas turbine combustion air inlet and exhaust
to be led to safe area on open deck
Figure 1.2 Gas turbine arrangements
international standards for oil and gas transportation piping, i.e. ANSI
Β 31 4 and Β 31 8 as applicable.
Valves for use in hydrocarbon systems must be of an approved and
fire-tested type. Valves incorporating non-metallic seatings may be used in
hydrocarbon systems providing that a prototype valve has been subjected
to a recognized fire test with satisfactory results. This test should conform
to BS 5146 or equivalent standard in relation to soft-seated ballvalves.
For hydrocarbon systems it is usual to limit acceptance to a range of
valve sizes to the diameter of the test valve multiplied or divided by 2, i.e. a
test carried out on a valve of, say, 200 mm diameter would be accepted for
a range of valves between 2 x 200 mm = 400 mm, and 200 mm -f- 2 =
100 mm. Any alteration to the original design would invalidate the original
approval of the valve. Similar restrictions may also be applied in regard to
the pressure rating (class) of the valve.
Lubricating oil and fuel systems should be in accordance with the
Classification Society's Rules for steel ships. All oil pumps and cargo oil
pumps are to be capable of being stopped from outside the area in which
they are located, in addition to any local manual control. Further, all such
pumps should be fitted with relief valves in closed circuit. In the case of
offshore units, this also includes those pumps which are used in
conjunction with the drilling and production systems.
Occasionally, dispensation may be requested with regard to the fitting of
the relief valve in close circuit and this is acceptable subject to:
(1) The piping system being suitable for the maximum discharge pressure
of the pump.
(2) An audio-visual thermal alarm and cutout, or equivalent, i.e. a
minimum flow return bypass system being provided at the pump. The
thermal alarm and cutout device should be located at the pump casing
and not in the suction or discharge branch on the pump.
The pressure vessel, i.e. gas separators, dryers, etc. should be provided
with a safety device. The arrangements are to be such that the relief valve
and relief devices cannot be isolated from the pressure vessels or piping
4 Offshore gas and oil production installations
systems. Safety valves on boilers or other fired pressure vessels should be
provided with eating gear capable of being operated from a readily
accessible position.
If blocking valves are to be fitted in conjunction with safety valves, not
less than two safety valves should be provided. The blocking valves must
be suitably interlocked in order that both safety valves cannot be isolated
simultaneously. Figure 1.3 shows an acceptable interlock arrangement.
INTERLOCK SYSTEM
Position No. 1 valve
maintenance/removal
V1 closed but not locked can
be opened to remove A
V4 L.O. cannot be closed without C
V2 L.C. cannot be opened without A
V3 L.O. cannot be closed without Β
Position No. 2 normal operation
V1 L.O. cannot be closed without A
V4 L.O. cannot be closed without C
|V2 L.C. cannot be opened without A
V3 L.O. cannot be closed without Β
PRESSURE VESSEL/SYSTEM RELIEF VALVE
ARRANGEMENT Position No. 3 intermediate
V1 L.O. cannot be closed without A
V4 L.O. cannot be closed without C
V2 L.O. cannot be closed without Β
V3 L.O. cannot be closed without Β
Bleed and vent line
valve locked shut Position No. 4 normal operation
(Alternative)
-D><r- ©-ι V1 L.O. cannot be closed without A
V4 L.L. cannot be closed without C
-A
V2 L.O. cannot be closed without Β
|V3 L.O. cannot be opened without C
V1 operated by one lock and key A
V2 operated by two locks and two keys A and Β
VV34 ooppeerraatteedd bbyy otwneo lloocckk sa nadn do ntweo k ekye yCs Β and C ? Vd V, > mln taenPiaonscieti/oren mNoov.a 5l v(Aallvteer native)
V1 L.O. cannot be closed without A
V4 closed but not locked can be
opened to remove C
•4 V2 L.O. cannot be closed without Β
ι &—I V3 L.C. cannot be opened without C
Vessel or line
^ Valve closed [><^]Valve open
] Key trapped [X] Key free
Removal of a key from a valve locks valve in position at which key
removed. Key can only be removed when valve reaches position
showing key free.
Figure 1.3 Interlock arrangements (safety valves)
Fixed drilling/production platforms 5
With the use of blocking valves in conjunction with safety valves or,
indeed, any safety device, a hidden danger may be incorporated into the
system. For example, it is not unnatural to utilize a lower class of piping
and valve standard on the discharge (downstream) side of the safety valve
or device or pressure control unit on the basis that a lower pressure exists
in this system. However, should the downstream (discharge) isolating
valve be closed and the safety device come into operation, this should
result in the lower rated sections of the safety device up to and including
the downstream isolating valve being subjected to full relief pressure
conditions. This could be a possible hazard to personnel or equipment in
the vicinity (see Figure 1.4). In view of the above, all pressure ratings on
the downstream side, including the safety device outlet, up to and
including the isolating valve, must be rated for the full relief pressure.
Vent
Code break
Figure 1.4 Interlock arrangement
Where fuel gas firing arrangements are provided, these are to comply
with the Classification Society's Rules for fuel gas burning in so far as they
are applicable.1,2
Offshore units also include single-point mooring buoys (SBMs), flare
stacks and storage spares, all of which require individual attention. In the
case of submerged piping, consideration must be given to structural
strength and collapsing pressure, since such units can operate in depths up
to 152 m and over. In the case of SBMs for loading/discharging oil tankers,
consideration must be given to outside loading forces in addition to any
pressure forces. Adequate lubrication of the turntable and central pipe
swivel is essential if the units are to operate without recourse to constant
overhaul and repair.
1.1.2 Location of oil- and gas-fired power units
1.1.2.1 Diesel and turbine units
Diesel and turbine units should be located in safe areas, and venting
systems are to be led from outlets located in safe areas.
6 Offshore gas and oil production installations
It may be pertinent to add that similar requirements are indicated in the
Classification Society Rules since: 'oil engines are not to be situated within
pump rooms, cofferdams, or other spaces liable to contain petroleum or
other explosive vapours, or in spaces or zones immediately adjacent to cargo
oil or slop tanks'.3
1.1.2.2 Diesel engines for use in hazardous areas
With the increasing use of diesel-powered units for use in conjunction with
offshore cranes, compressors, fire pumps, forklift trucks, etc., the area for
potential incidents from accidental release of flammable vapours and gases
is greatly increased.
It is only within the last decade or so that serious consideration has been
given and special precautions taken in relation to diesel units operating in
potentially hazardous areas. Whilst spark ignition systems are not present
on a diesel unit, a number of potential ignition sources can be identified,
e.g.:
(1) The compression-ignition cycle makes overspeeding possible when
inhaling a flammable vapour or gas.
(2) A direct flame path exists between the combustion chamber and the
external environment during valve overlap which can result in ignition
of entrained gas via the induction system.
(3) On full load, ingestion of flammable gas can also produce a substantial
increase in exhaust temperature with corresponding increase in surface
temperature.
(4) The emission of flame and/or incandescent particles from the exhaust
provides another source of ignition.
(5) Further additional hazards exist from static-producing fans and belts or
frictional sparks.
In the case of offshore units, consideration could be given to the use of
suitably protected engines in Zone 2.
1.1.2.3 Open deck areas
Such units must be installed in accordance with recognized national and
international Standards. In this respect it is considered that the following
minimum requirements should be complied with:
(1) Exhaust manifold to be watercooled.
(2) Maximum exposed surface temperature at full rated power of engine
not to exceed 200° C.
(3) Efficient flame arrester to be provided in air intake.
(4) Efficient flame trap and spark arrester to be fitted in exhaust system.
(5) Aluminium fittings are not acceptable unless suitably coated as a
protection against incendive sparking.
(6) Pneumatic/hydraulic starting arrangements to be provided. Electric
starting arrangements are not acceptable.
(7) Minimum flame length not to be less than 13 mm.
(8) Provision to be made to prevent overspeeding in the event of
accidental ingestion of low flash vapours/gases.
(9) Air intake and exhaust to be led from and to safe areas.
(10) All belts to be of antistatic type.