Difference between S355G7+N and S355G8+N steel plate - Knowledge

S355G7+N is a normalized offshore structural steel certified under EN 10225 for fixed marine structures, offshore platforms, and wind turbine foundations . It has a minimum yield strength of 355 MPa (for thickness ≤50mm) and tensile strength ranging from 470 to 630 MPa, with a minimum elongation of 22% . The "+N" suffix indicates the normalized delivery condition, which refines grain structure to improve toughness and weldability . This grade is impact tested at -40°C with a minimum energy requirement of 50 Joules (longitudinal) . It is widely used for offshore platforms, terminal equipment, and marine structures in cold environments .

S355G8+N is also a normalized offshore structural steel certified under EN 10225, sharing the same minimum yield strength of 355 MPa and tensile strength range of 470-630 MPa . Like G7, it is impact tested at -40°C and requires a minimum of 50 Joules . However, S355G8+N offers enhanced low-temperature toughness compared to G7, achieved through stricter chemical composition controls including lower carbon (≤0.14%) and sulfur (≤0.01%) limits . The higher "G" number (G8 vs. G7) signifies more stringent requirements for toughness and impact strength, making it more suitable for critical offshore applications in extreme environments .

Both S355G7+N and S355G8+N are normalized offshore structural steels under EN 10225 with identical strength (minimum yield 355 MPa) and delivery conditions (+N) . Their primary difference lies in the G number designation, with G8 representing a higher specification grade that offers superior low-temperature toughness and fracture resistance for the most demanding offshore roles, while G7 serves broader structural applications . Both grades are impact tested at -40°C with 50J minimum, but S355G8+N employs stricter chemical composition controls to achieve enhanced ductility and safety margins for critical marine structures . The selection between them depends on whether the project requires standard offshore performance (G7) or enhanced toughness for extreme conditions (G8) .

S355G7+N Steel plate Chemical Composition

S355G7+N Chemical Composition
Grade	The Element Max (%)
Grade	C	Si	Mn	P	S	Al	N
S355G7+N	0.14	0.15-0.55	1.0-0.01	0.02	0.01	0.0055	0.01
	Nb	V	Ti	Cu	Cr	Ni	Mo
	0.04	0.06	0.025	0.3	0.25	0.5	0.08

S355G8+N Steel plate Chemical Composition

S355G8+N Chemical Composition
Grade	The Element Max (%)
Grade	C	Si	Mn	P	S	Al	N
S355G8+N	0.14	0.15-0.55	1.0-0.01	0.02	0.01	0.0055	0.01
	Nb	V	Ti	Cu	Cr	Ni	Mo
	0.04	0.06	0.025	0.3	0.25	0.5	0.08

S355G7+N Steel plate strength property

S355G7+N high strength property
Grade		Mechanical Property			Charpy V Impact Test
Grade	Thickness	Yield	Tensile	Elongation	Degree	Energy 1	Energy 2
S355G7+N	mm	Min Mpa	Mpa	Min %	-40	J	J
	t≤50	355	470-630	22%		50	50
	50＜t≤63	355	470-630	22%		50	50
	63＜t≤100	325	490-630	22%		50	50
Note: Energy 1 is transverse impact test, Energy 2 is longitudinal

S355G8+N Steel plate Mechanical Properties

Grade	S355G8+N Mechanical Properties (min)
	Tensile Strength		Yield Strength						Elongation A
	Thickness (mm)		Thickness t - mm						Elongation A
	≤100	>100	≤16	16<t≤25	25<t≤40	40<t≤63	63<t≤100	100<t≤150	%
S355G8+N	470/630	460/620	355	355	345	335	325	320	22