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Oleh:Oleh:Ir. Murdjito, MSc.EngIr. Murdjito, MSc.Eng
Dosen Jurusan Teknik KelautanFakultas Teknologi Kelautan
Institut Teknologi Sepuluh Nopember (ITS)Surabaya
MATERIALS & MATERIAL GRADE
SELECTIONS
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Structural Material
Carbon Steel
most important material for offshore & marine material used for: pile, tubular and cans, rolled beam and plate girders,
flat plate, etc
Stainless Steel
Quite expensive material Restricted used as roof and wall cladding, fastener, plating in
splash zone
Common type AISI 304 & 316, yield: 180 200 MPa
Grout A structural material for steel designer
Application: grouting of annulus between pile sleeve and pile,internal grouting of tubular joint
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Continue..
Glass fibre reinforced (GFRP) Very strong but lack stiffness, the fatigue resistant is excellent
Not corroded excellent marine environmental stability
Jointing techniques is particularly important, welding is not an option Repair & inspection procedure will yet require considerable effort to obtain
offshore acceptance
Offshore applications:
Furniture and internal cladding of LQM
Grating, Life boats
Ducting, Small covers and enclosed, Piping for water GRFP gives weight saving over carbon steel of 40 70%
Cost: CAPEX level : 100 150%,OPEX level lower
Cast steel For offshore application has progressed by effort of the industry in UK,
Germany and japan Aluminum
Major application: helideck, roof and wall cladding, platform bridges, stairsand platform, telecommunication mast, cable trays, walkway, hand railing etc
Development to be considered as platform deck flooring
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STEEL PROPERTIES
Yield and tensile strength
Ductility
Through thickness properties
Fatigue strengthSuitability for fabrication (welding,
forming)
Corrosion resistance
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YIELD STRENGTH AND TENSILE
STRENGTH
Tensile strength is required to be not too close to the yieldstrength
Material selection specify: y/ tAPI/AISC
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DUCTILITY & THROUGH THICKNESS
PROPERTY
Ductility
phenomenon of failure after considerabledeformation
the risk of brittle fracture is influenced by speed of straining
temperature of material
thickness of material amount of strain and reliability of its prognosis
basic tools for providing ductile behavior are: fracture mechanics analysis
fracture mechanics test Through thickness properties
problem in welded structures: lamellar tearing occurs in fabrication
lamellar tearing can be very costly to repair
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FABRICATION PROCESS
impact of fabrication process to material
properties: thermal cutting
hot or cold forming
welding
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PROBLEM OF STEEL MATERIALS
Fabrication process:
Weldability of material
Cutability
Corrosion resistance Fatique resistance
Stiffness according to the temperature
change lamellar tearing, fracture Quality control & assurance
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MATERIAL GRADE SELECTION FOR
OFFSHORE STEEL STRUCTURES
extreme importance to the fitness of the
structure
material selection procedures:
the material selection of each member orcategory members is justified in the design
report
the material grade is precisely specified onthe drawing
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API RP 2A WSD
Section 8: Material
Minimum strength level, group and class
specified by designer
Mill test report provided by fabricator inaccordance with ASTM A6 or A20
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Steel Group
Grouped according to strength level and weldingcharacteristics:
Group I: mild steel with yield strength 0.45%
Require the use of low hydrogen welding processes
Group III
Yield strength > 52 ksi Each application is investigated with regard to:
Weldability and special welding procedures required
Fatigue problem
Notch toughness fracture control
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Steel Classes
Class C steel Applicable to primary structural members involving limited
thickness, moderate forming, low restraint, modest stressconcentration, quasi static loading and redundancy
For piling, jacket braces & legs, deck beam, etc
Class B steel Suitable use where thickness, cold work, restraint, impact loading,
lack of redundancy the need for improved notch toughness
Charpy V-Notch energy: Group I: 15 ft-lbs (20 J)
Group II: 25 ft-lbs (34 J)
Charpy test temperature: 10 0OC)
Impact test in accordance with ASTM A 673, Frequency H
Class A steel Suitable for use at subfreezing temperatures Charpy test temperature: (-)20 (-)40OC
Impact testing in accordance with the specification under whichsteel ordered
Heat lot testing may be used
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table 8.1.4-1
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Table 8.1.4-2
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Steel for Tubular Joint
Underwater joint Notch toughness criteria:
NRL Drop-Weight Test no break performance
Charpy V-notch energy:
Group I: 15 ft-lbs
Group II: 25 ft-lbs
Group III: 35 ft-lbs
Above Water Joints Expose to lower temperatures and possible impact from
boat or critical connections at any location: Class A steelconsidered
Critical Joints: use steel having improved throughthickness (Z-directions) properties e.q: API Spec2H, Suplements S4 and S5
Brace ends: same class as joint cans or one class
lower
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DNV-OS-B101: METALLIC MATERIALS
rolled steel for structural application
requirements for weldable normal strength,high strength and extra high strength hot
rolled structural steel plates and sections,
seamless steel tubes and pipes intended forstructural application
applicable to steel products with a thickness
not exceeding 150 mm.
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STEEL GRADES
The steel grades strength groups:
normal strength steels (NS) high strength steels (HS)
extra high strength steels (EHS)
Parallel series of steel grades steels of normal weldability
steels of improved weldability.
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DnV STEEL GRADES
Table A1 Definitions of steel grades
A - -
B2) BW DW 0 235
D DW -20
E EW 40
A AW 0 27 265D DW 20 32 315
E EW 40 36 355
F - 60 40 390
A - 0 420 420
D DW 20 460 460
E EW 40 500 500
F - 60 550 550
620 620
690 6901) For steels of improved weldability the required minimum yield stress is reduced
for increasing material thickness.
2) Charpy V-notch tests are required for thickness above 25 mm but is subject to
agreement for thickness of 25 mm or less.
Strength
group
Omit-tedNS
HS
EHS
Impact testing
Symbol x
Tens ile properties
Minimum yield
stress(N/mm2)Symbol y
Test
tempera-
ture (C)
Improved
weldability
Normal
weldability
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Normal Strength Steel
T a b le B 3 C o n d i t io n o f s u p p ly f o r n o r m a l s t r en g t h (N S )s t e e l
G rade Th ickne ss , t (m m ) C ond ition o f sup p ly 1 )
N V A t ? 5 0 A n y
5 0 < t ? 1 5 0 A R 2 ) C R , N , T M
N V B t ? 5 0 A n y
5 0 < t ? 1 5 0 A R 2 ), C R , N , T M
N V D t ? 3 5 A n y
3 5 < t ? 1 5 0 A R 3 ), C R , N , T M
N V E t ? 1 5 0 A R 3 ),C R 3 ),N , T M1) C ond i tion of supp ly :
A R : A s ro l led .
N : N orm a lised .
C R : Con t ro lled ro l led .
2 ) G r a d e s N V A a n d N V B m a y b e s u p p lie d a s r o lle d ( A R )
sub jec t to spe-c ia l con s idera t ion.3) Su bjec t t o spec ia l con s ide ra t ion , sec tions in g rade N V D m ay
b e su p -p lied a s ro lled (A R ) p ro v id ed sa tisfa c tory resu lts a re
cons i s ten t ly ob - ta ined f rom C harpy V -notch im pac t te s ts .S im i la r ly, sec t ions in g rade N V E m ay b e supp li ed a s ro l led
(A R ) or con t ro l led ro lled (C R ) .
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Mechanical properties
Table B4 Mechanical properties for normal strength (NS) steel of normal weldability
Averageimpact energyJminimumt 50 50 < t 70 70 < t 150
Grade
YieldstressReH
minimum(N/mm)
Tensilestrength
Rm(N/mm)
ElongationA5
minimum(%)
Testtem-
perature(C)
Longitudinal
Transverse
Longitudinal
Transverse
Longitudinal
Transverse
NV ANV B
NV DNV E
235 400-520 223)
+200
-20-40
-271)
2727
-201)
2020
342)
34
3434
242)24
2424
412)41
4141
272)27
2727
1) Charpy V-notch impact tests are generally not required for grade NV B steel with thickness of 25 mm or less. 2)Impact tests for grade NV A over 50 mm thick are not required when the material is produced using fine grain practiceand furnished normalised or thermo-mechanically controlled processed. 3) For full thickness flat test specimens with awidth of 25 mm and a gauge length of 200 mm the elongation shall comply with the following minimum values:
Thickness, mm t 5 5 < t 1010 < t
15
15 < t
20
20 < t
25
25 < t
30
30 < t
40
40 < t
150Elongation 14 16 17 18 19 20 21 22