Transcript Slide 1

Excursions Challenges!
13th March 2013
Arnfinn Anfindsen
Diving Manager-Norway
• Background/History
• Excursions as per Norsok U100
• Various scenarios
Agenda
•
•
•
•
A – Working in a trench
B – Welding Habitat/H-Frames
C – Subsea Manifold
D – X-Tree Protection cover
• An Offshore Managers Frustration
• UK Unlimited Excursion Table
• References
7-Jul-15
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History/Background
Facts:
Vessel : DSV Seven Pelican
Operation: B11 Bypass Project
preparatory work (German Sector)
When: May 2012
Seabed dept: 32ms before excavation
Operational issue: Limited excursions for
given depth
Safety issue: Diving bell, stage and clump
weights located minimum 2 meters above
seabed
Deviations: Norsok U-100 section
8.2.3.4, and to Subsea 7 Saturation Diving
Manual Chapter 10
7-Jul-15
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Norsok U100 8.2.3.4 Excursions
• Procedures for
excursions shall be
prepared. If excursions
are extended compared
to Table 8, longer stays
at living depth prior to
start of decompression
should be considered.
Decompression shall not
start with an upward
excursion. There shall
be a minimum 8 h hold
at living depth prior to
decompression after an
excursion.
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As a minimum, the procedures shall
define;
• a) living depth,
• b) working depth,
• c) limitations of excursion after change
of living and/or working depth,
• d) maximum rates for compression and
decompression during excursion,
• e) maximum pressure increase and
decrease during the excursion.
It is of special importance to restrict
the use and distance of upward
excursions.
The maximum ascent rate during
excursion is 10 msw/min.
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Selection of Excursion Types and Distances – Norway
• Usually, it will be possible to select one of
several different storage depth/excursion
scenarios for carrying out a specific job. As a
general rule, choose the storage depth
which minimises ascending excursion
distances during the dive operation. Thus,
prefer:
• Descending excursions rather than
ascending excursions.
• Storage depth as close to the working
depths as practical. In order that operational
excursion distances are not affected by the
distance between the two, they should be as
close as practical.
• Planning of the dive is essential!
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Diving Excursions – Table 8
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Diving Excursion - Working in a trench
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Page 8
Bell door
-27 msw
Min 3 m
Bottom of clumpweight
-30 msw
Excursion
needed
9m
5m
Norsok U100 5m excursion
based on LD 27m
Min 2 m
4m
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Diving Excursion – Umbilical Length
Umb. length: ~28m
Bottom of bell: ~28m
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How to obtain consensus for proposed solutuion
Involvement of the
following personnel is
essential;
• Diving Responsible
Doctor -Contractor
• Health Department–
Contractor
• Offshore Manager
• Safety Delegate Divers
• Contractors HSE
Department
• Contractor Diving
Manager
• Company Responsible
Diving Doctor
• Company Diving
Advisor
• Company HSE Dep
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Excursion - solution
• Divers maximum in water time 4 hours (vs normal 5,5 hours) to
avoid Jo-Jo effect during break for rest break, and to reduce total
time at maximum excursion depth
• Increase hold period from 8 hours to 12 hours prior to final
decompression
The diving procedure for extended downward excursion will
include following:
• Storage dept 27 MSW
• Working depth, from 32 to 36 MSW
• There is no changes in divers living or working depths
• The maximum ascent rate during excursion is 10 msw/min.
• Maximum pressure increase and decrease during the excursion is within following
window: 3.7 to 4.6 ATA.
• There is no plan to use upward excursions and should this be necessary there will be no
changes to limitations as described in NORSOK U-100.
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Client B – Welding Habitats/Lifting Frames
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Client C – Subsea Manifold
Bell door
-109 msw
Min 3 m
Bottom of clumpweight
-112 msw
Min 3 m
Excursion
needed
12 m
Top of
manifold
115m
6m
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Client D – X-Tree Protection Structure
Min
3m
Excursion
needed
15 m
11m
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An Offshore Managers frustration
“I am fully aware of all this and more, which is my whole point. The best way to deal with a
hazard is to remove the hazard. We could effectively do this by raising the bell, i.e. changing
the excursions.
With the current restrictions we only have 1.7 metre vertical separation, it is not often in the
North sea that the sea state is less than that. Everyone keeps quoting “set up for drift off“ etc.
etc. No one has mentioned drive off, which can be in any direction.
The simple solution is to allow some tolerance in the excursions. There is as you are aware a
precedent for this as both Norsok U100 and our Subsea 7 diving Excursion tables has tested
that.
Why can’t we get a similar decision to enhance safety? I am having safety, safety, safety
pointed out to me time and time again, yet time and time again beach support is “safetying” us
into less safe situations.
“No one seems to want to listen to the people who are doing the work.”
«NN»
Offshore Manager
Subsea 7 DSV
7-Jul-15
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UK «Unlimited» Excursion Tables
Standard
Standard
Maximum
Maximum
Storage
Descending
Ascending
Descending
Ascending
Depth
Excursion
Excursion
Excursion
Excursion
Ranges
Ranges
Ranges
Ranges
10-17 m
3m
2m
Forbidden
Forbidden
18-19 m
4m
4m
Forbidden
Forbidden
20-22 m
4m
4m
8m
Forbidden
23-29 m
5m
5m
10 m
Forbidden
30 m
6m
6m
12 m
Forbidden
31 - 33 m
7m
7m
14 m
Forbidden
34 - 39 m
7m
7m
14 m
14 m
40-59 m
8m
8m
16 m
16 m
60-79 m
9m
9m
18 m
18 m
80-99 m
10 m
10 m
20 m
20 m
100-119 m
11 m
11 m
22 m
22 m
120-139 m
12 m
12 m
24 m
24 m
140-179 m
13 m
13 m
26 m
26 m
180-350 m
15 m
15 m
30 m
30 m
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• Subsea 7 has wide operational
experience in shallow saturation
diving on the Southern part of the
UK, Dutch and German sectors in
the North Sea using Subsea 7 Sat
Diving Manual UK Excursions (USNavy).
• Subsea 7 has not experienced
any decompression sickness or
other injuries from the high
number of dives performed from
dives performed on this table.
References
• Norsok U100 section 8.2.3.4 Excursions
• Subsea 7 Group Diving Manual Vol 2 – Diving Techniques
clause 2.8.2 Excursion Limits
• OD 91-88 (Eng) Comparison of Saturation diving tables
and preparation of Framework for standardisation of tables
• OD 91-12 (NO) Rapport om sammenligning av
metningsdyddetabeller og utarbeidelse av
rammebetingelser for standardisering
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seabed-to-surface
www.subsea7.com
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