4-Transocean

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Transocean Spitsbergen
Summary failure in anchor line no 7,
02.08.2012
Failure in anchor line 7, 02.08.2012
Broken link no 740 appr 10 m above fairlead
2
Findings from investigation report after the failure in
anchor line 7

Anchorline 7 consisted of 4 x 500 m segments of 84 mm NV R4,
studded anchor chain

The inner segment, was produced as chain production no 241 in
the period from 06.09.2007 to 08.09.2007 by Jiangsu Asian Star
Anchor Chain Co., Ltd, China and certified by DNV, Certificate
SHA-07-3409, issued 05.01.2008

Chain production no 241 consists of a total of 1487 links and the
broken link no 740 is located close to the middle of this segment.
3
Findings from investigation report after the failure in
anchor line 7
4
Arrangement of thermocouple of heat treatment
Furnace no 3
5
Heat treatment parameter curve figure
Furnace no 3 , ref MRB
6
5-link length checking record for mooring chain proof
load test, ref MRB
7
Dimensioning checking record of mooring link , ref
MRB
8
Findings from investigation report after the failure in
anchor line 7

The failure was caused by corrosion fatigue exposed to high
stress and propagated with fast overload fracture

The underlaying cause was improper heat treatment resulting in
hard material in a ”train” of 18 links

It was identified corrolation between high hardness measured in
the broken link and the surface hardness

On this background, hardness measurements were initiated on
each link (1009) in the broken chain segment and 20% in
remaing segments of 8 anchor lines.

No links with high hardness values were observed during the
measurement performed by DNV
9
Summary after hardness measurements of all chain
Transocean Spitsbergen.

In segment that failed: 100% hardness measured by Brinell,
1009 links (336 m) Measured in both link ends

Rest of chain: 20% hardness measured by Brinell, 8326 links
(14154 m)

Total measured 9335 links (14 490 m)

No link with high hardness was observed

All 8 anchorlines are certified for 5 years
10
ASAK testing heat treatment Furnace no 3
Test of 30 links,
stopped in
cooling water
and run through
tempering
tower with max
speed.
19 links were
measured with
higher hardness
than
recommended
352 HB
11
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