EN 10028-6 P690QL1 Boiler And Pressure Vessel Steel Plate

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Overview

As a high-strength and high-toughness special steel for pressure vessels, EN 10028-6 P690QL1 plays an irreplaceable role in critical equipment across fields such as energy, chemical industry, offshore engineering, and construction, thanks to its exceptional comprehensive performance.

Its characteristics of "high strength, lightweight, low-temperature resistance, and excellent weldability" make it an ideal material choice for handling extreme working conditions in modern industries. It is particularly well-suited for large-scale critical engineering structures that demand the highest standards of safety and reliability.

EN 10028-6 P690QL1 represents the pinnacle of performance in the field of engineering steel plates, embodying a perfect synergy of strength and toughness. It is an indispensable key material in the high-end equipment manufacturing industry.

Grade	P690QL1
Standard	EN 10025-6 (Flat products made of steels for pressure purposes - Part6: Weldable fine grain steels, quenched and tempered)
Delivery Conditions	Quenched and Tempered(Q&T)
Approval By Third Party	ABS, DNV, GL, CCS, LR , RINA, KR, TUV, CE
Weldability	The weldability is acceptable, with relatively high carbon equivalent (CEV) and weld crack sensitivity index (Pcm). Specialized welding procedure specifications (WPS) must be followed, including preheating, the use of low-hydrogen welding consumables, and post-weld heat treatment (PWHT). The core risks are cold cracking (hydrogen-induced cracking) and toughness degradation in the heat-affected zone (HAZ).
Machinability	Suitable for flame cutting, laser cutting, and plasma cutting. Heat input must be controlled to avoid embrittlement in the heat-affected zone. Edge grinding may be required after cutting thick plates to eliminate the hardened layer. Cold forming is difficult and may require heating.
Surface Quality	Generally provided as rolled surface, can be processed as required, such as sandblasting, shot blasting, pickling, painting, etc.
Inspection Requirements	Non-destructive testing (e.g., UT ultrasonic testing) and Z-direction property test (Grades Z15/Z25/Z35) can be added as needed.

Key Features and Advantages

1. Extremely High Strength-to-Weight Ratio: While ensuring safety, it can significantly reduce the structural self-weight, which is crucial for mobile equipment (such as cranes, mining trucks) and large structures (such as bridges).

2. Excellent Low-Temperature Toughness: Its impact resistance requirement at -40°C (Charpy V-notch impact energy ≥ 27 J) makes it highly suitable for use in extremely cold environments (such as Arctic regions, high-altitude areas, and low-temperature storage and transportation equipment).

3. Good Weldability: Despite its exceptionally high strength, due to its low carbon content and optimized chemical composition design, reliable welded connections can still be achieved with appropriate welding processes (such as preheating, low-hydrogen welding materials, and controlled heat input).

4. Fine-Grained Microstructure: Through microalloying and thermo-mechanical controlled processing (TMCP), a fine and uniform microstructure is obtained, which serves as the foundation for its high strength and toughness.

Chemical Composition

Grade	P690QL1
Element	C	Si	Mn	P	S	N	B	Cr	Mo	Cu	Nb	Ni	Ti	V	Zr
Content(max, %)	0.20	0.80	1.70	0.020	0.008	0.15	0.05	1.50	0.70	0.30	0.06	2.50	0.05	0.12	0.15

Mechanical Properties

Grade	Thickness (t) [mm]	Yield Strength (ReH) [min, MPa]	Tensile Strength (Rm) [MPa]	Elongation (A) [min, %]	Impact Energy (KV₂) [min]	Brinell Hardness (HBW)
P690QL1	t ≤ 50	690	770 - 940	14	27J (at -40°C, transverse)	220 - 280
	50 < t ≤ 100	670	770 - 940	14	27J (at -40°C, transverse)	220 - 280
	100 < t ≤ 200	630	720 - 900	14	27J (at -40°C, transverse)	220 - 280

Applications

P690QL1 steel plate is widely used in demanding engineering fields due to its high strength, excellent weldability, and low-temperature toughness.

1. Petrochemical Industry

a) Pressure vessels: reactors, heat exchangers, separators, spherical tanks, oil and gas storage tanks

b) LNG/LPG storage and transportation: liquefied gas storage tanks (e.g., large LPG ship tanks), resistant to low temperatures and high pressure

c) Piping systems: high-pressure oil and gas pipelines, resistant to hydrogen/hydrogen sulfide corrosion (corrosion rate ≤ 0.04 mm/a)

d) Offshore platform equipment: wellhead devices, separation equipment, suitable for marine corrosive environments

2. Energy and Power Sector

a) Power plant boilers: steam drums, superheaters, high-pressure water pipes, turbine spiral casings, withstand high-temperature and high-pressure steam

b) Nuclear power equipment: reactor pressure vessels, steam generator support rings, meeting low-impurity requirements

c) Waste-to-energy plants: high-temperature furnace structures, resistant to creep and high-temperature corrosion

3. Offshore Engineering and Shipbuilding

a) LNG/LPG carriers: Type C independent cargo tanks, design pressure 19 barg, resistant to -35°C low temperatures

b) Offshore platforms: columns, support structures, resistant to wave impact and seawater corrosion

c) Specialized vessels: high-strength hull structures, reducing weight while enhancing safety

4. Construction and Infrastructure

a) Large bridges: main beams, piers, withstand heavy loads and wind forces, reducing steel usage by over 30%

b) High-rise buildings: structural frames, load-bearing walls, resistant to earthquakes and wind loads

c) Stadiums: large-span roof support systems, reducing structural self-weight

5. Engineering Machinery and Special Equipment

a) Lifting machinery: crane booms, excavator chassis, withstand high stress and fatigue loads

b) Mining machinery: mining dump truck frames, derricks, resistant to heavy loads and harsh environments

c) Wind power generation: towers, foundations, resistant to wind loads and atmospheric corrosion

d) Hydraulic equipment: hydropower station high-pressure water pipes, turbine spiral casings

Other Information

Precautions for Processing and Welding

1. Cutting: Suitable for flame cutting, plasma cutting, and waterjet cutting. After flame cutting, grinding of the hardened layer is required.

2. Cold Forming: Cold bending is possible, but significant springback occurs, necessitating greater forming force.

3. Hot Forming: If the heating temperature exceeds the tempering temperature of the quenching and tempering treatment (typically >580°C), it will compromise the quenched and tempered condition, leading to a decline in performance. This process should be conducted with caution and may require re-quenching and tempering treatment.

4. Welding: Strict adherence to the Welding Procedure Specification (WPS) is mandatory. Common requirements include:

a) Using low-hydrogen or ultra-low-hydrogen electrodes/welding wires.

b) Applying appropriate preheating based on plate thickness and joint type (typically in the range of 100–200°C).

c) Controlling interpass temperature and heat input to prevent softening or embrittlement in the heat-affected zone (HAZ).

d) Post-weld heat treatment (PWHT) or hydrogen removal treatment may be required.

The Differences Between Grades Within The Same Series

Grade	Nominal thickness (mm)	Impact Energy (KV₂) [min, transverse]
Grade	Nominal thickness (mm)	-60℃	-40℃	-20℃	0℃	+20℃
P690Q	≤ 200	-	-	27 J	40 J	60 J
P690QH	≤ 200	-	-	27 J	40 J	60 J
P690QL1	≤ 200	-	27 J	40 J	60 J	-
P690QL2	≤ 200	27 J	40 J	60 J	80 J	-

* The P690QH is a high-temperature variant of the P690Q, with its chemical composition and heat treatment process placing greater emphasis on strength retention and creep resistance at elevated temperatures.

* If the project involves low-temperature environments, P690QL1 (-40°C) or P690QL2 (-60°C) should be selected.

* All grades (Q / QH / QL1 / QL2) have a lower limit of yield strength of 690 MPa, but differ in toughness and temperature adaptability.

International Equivalent Steel Grades

Grade	Standard	Yield Strength (ReH) [min, MPa]	Tensile Strength (Rm) [MPa]	Elongation (A) [min, %]	Impact Energy (KV₂) [min]
P690QL1	EN 10028-6 (European)	690	770 - 940	14	27J (at -40°C, transverse)
Q690E	GB/T 16270 (Chinese)	690	770 - 940	15	34J (at -40°C, longitudinal)

Technical Documentation

FAQ

Q1:

What is the main difference between LR Grade AH32 and LR Grade AH36 shipbuilding steel plates?

A:

Both are high-strength hull structural steels certified by Lloyd’s Register (LR). The key difference lies in their yield strength grades: LR AH32 has a minimum yield strength of 315 MPa, while LR AH36 has a minimum yield strength of 355 MPa.

Therefore, LR AH32 is suitable for conventional-tonnage vessels and general offshore engineering projects, offering better cost-effectiveness; LR AH36, on the other hand, is intended for applications requiring higher strength, such as ultra-large vessels and high-load-bearing offshore structures.

Q2:

Does your LR Grade AH32 shipbuilding steel plate support third-party inspection?

A:

Yes. All of our LR Grade AH32 shipbuilding steel plates support inspections by internationally recognized third-party organizations such as SGS, BV, and DNV. They come with complete official LR certification and original mill test certificates, ensuring full quality traceability.

Q3:

What processing services can you provide for LR Grade AH32 shipbuilding steel plates?

A:

We offer one-stop value-added processing services, including precision cutting, bending, drilling, beveling, surface derusting, shot blasting, anti-corrosion treatment, and heat treatment, to meet all custom manufacturing and installation requirements for offshore engineering projects.

Q4:

Does LR Grade AH32 shipbuilding steel plate require special welding procedures?

A:

LR Grade AH32 shipbuilding steel plate offers excellent overall weldability, stable material properties, and a low carbon equivalent. It is suitable for all conventional shipbuilding welding processes and does not require complex preheating or special protective measures.

Standard marine welding operating procedures ensure consistent weld quality, effectively reduce construction difficulties, and improve project efficiency.

Q5:

What is the application of LR Grade AH32 shipbuilding steel plate?

A:

LR Grade AH32 shipbuilding steel plate is primarily used in the construction of commercial vessels, conventional offshore platforms, coastal marine infrastructure, and the maintenance of marine equipment. It is suitable for various marine engineering applications that require high strength and stable overall structural performance.

Q6:

What is the weldability of LR Grade E shipbuilding steel plates?

A:

The weldability is good, and the carbon equivalent (CEV) is typically controlled at ≤ 0.40% (depending on the specific thickness).

For thicknesses of 40 mm or less, preheating is generally not required at ambient temperatures (≥0°C), but low-hydrogen electrodes must be used.

For plates thicker than 40 mm or highly constrained joints, preheating to 50°C–100°C is recommended to reduce the cooling rate and prevent cold cracks.

Important Note: Welding consumables approved by the classification society and compatible with LR Grade E must be used.

Q7:

What is the main difference between LR Grade D and Grade E marine steel?

A:

The basic strength parameters of the two grades are the same; the key difference lies in low-temperature impact resistance and application scenarios.

LR Grade D must pass an impact test at -20°C and is suitable for conventional cold-water regions; LR Grade E must pass an impact test at -40°C and offers superior low-temperature toughness and resistance to brittle fracture, making it suitable for polar and extremely cold marine environments.

Q8:

What is the application of LR Grade E shipbuilding steel plates?

A:

LR Grade E shipbuilding steel plate is a high-performance, ordinary-strength marine structural steel plate with exceptional impact toughness at ultra-low temperatures of -40°C. It is primarily used in polar icebreakers, polar research vessels, ultra-cold ocean-going vessels, extremely cold offshore structures, and high-end marine infrastructure requiring resistance to brittleness at extremely low temperatures. It serves as an upgraded replacement for LR Grade D shipbuilding steel plate in polar and extremely cold marine environments.

Q9:

What are the delivery conditions for LR Grade D shipbuilding steel plates?

A:

The standard delivery conditions for LR Grade D shipbuilding steel plates are as follows:

1) Hot-rolled (HR): Suitable for thin plates with a thickness of ≤12 mm; this is the standard supply condition.

2) Thermomechanically Controlled Process (TMCP): The primary delivery condition for medium- and thick plates; grain refinement ensures compliance with impact toughness requirements at -20°C without the need for additional heat treatment.

3) Normalized (N): Suitable for thick plates with a thickness of ≥50 mm; used for critical components with stringent low-temperature toughness requirements.

All delivery conditions must pass LR third-party inspection prior to shipment.

Q10:

What processing services do you offer for LR Grade D marine steel plates?

A:

We provide one-stop value-added processing services, including precision cutting, bending, drilling, beveling, surface derusting, shot blasting, anti-corrosion treatment, and heat treatment, to meet all custom manufacturing and installation requirements for extreme-low-temperature offshore engineering projects.

Q11:

Does your LR Grade D shipbuilding steel plate support third-party inspection?

A:

Yes. All of our LR Grade D shipbuilding steel plates are fully compatible with inspections by internationally recognized third-party organizations such as SGS, BV, and DNV. They come with complete official LR certification and original factory test reports, ensuring comprehensive quality traceability.

Q12:

What is the difference between LR Grade B and Grade D marine steel?

A:

The key difference lies in low-temperature impact resistance. LR Grade B is tested at 0°C and is suitable for temperate and mildly cold waters; LR Grade D is subject to a mandatory -20°C low-temperature impact test, offering greater cold resistance and making it suitable for cold waters and extremely cold marine environments. Both grades have the same basic tensile strength and yield strength.

Q13:

Do you provide official certification for your LR Grade D marine steel plates?

A:

Yes. All of our LR Grade D shipbuilding steel plates hold valid official certification from Lloyd’s Register (LR) and EN 10204 3.2 mill test certificates. These certificates are internationally recognized and fully support global project bidding, high-standard engineering acceptance, and cross-border customs clearance requirements.

Q14:

What is the range of available dimensions for your LR Grade B marine steel plates?

A:

Thickness: 5 mm - 150 mm (thicknesses ≥ 40 mm: require normalizing or TMCP heat treatment)

Width: 1,500 mm - 4,000 mm

Length: 6,000 mm - 18,000 mm

We offer custom flame-cutting or plasma-cutting services based on shipyard drawings, with cutting tolerances meeting LR rules requirements.

Q15:

Does your LR Grade B shipbuilding steel plate support third-party inspection?

A:

Yes. All of our LR Grade B shipbuilding steel plates are subject to inspection by internationally recognized third-party organizations such as SGS, BV, and DNV, and come with complete official LR certification and original Mill Test Certificate (MTC) to ensure full quality traceability.