Product Overviews: P690Q and P690QL1 High Strength Pressure Vessel Steel Plate
P690Q and P690QL1 are both quenched-and-tempered fine-grained high-strength pressure vessel steel plates complying with European pressure vessel steel standard EN 10028-6, tailor-made for heavy-load pressure-containing equipment. They have fundamental differences from S690Q/S690QL structural steel to EN 10025-6, which are not eligible for pressure vessel certification.
Grade Designation Breakdown:
- P: Steel designated for pressure vessel service
- 690: Minimum yield strength of 690 MPa for plates with thickness ≤ 50 mm
- Q: Quenched and tempered delivery condition (heat treatment applied to balance strength and toughness)
- L1: Upgraded grade for enhanced low-temperature toughness, certified to pass Charpy V-notch impact test at -40 °C, while standard P690Q only meets impact toughness requirements at -20 °C
Founded in 2008, GNEE Steel (Tianjin) Co., Ltd. is a professional high-strength pressure vessel steel integrated supplier integrating steel stock, precision processing, technical consultation and global export service, with 18 years of experience in EN10028 series vessel steel supply for overseas pressure vessel, petrochemical and offshore engineering clients.
What is the core difference between P690Q and P690QL1 Steel Plate?
The key distinction lies in impurity element control and low-temperature brittle fracture resistance. P690QL1 features stringent limitation on detrimental impurities (phosphorus and sulfur) to eliminate cold brittle fracture hazards under low-temperature service conditions. P690Q is an economical base grade suitable for pressure equipment operated at ambient temperature and mild low-temperature environments. Both grades deliver ultra-high yield strength, enabling reduction of vessel wall thickness, lightweight design of equipment structures and cut-down of overall fabrication costs.
If you have uncertainties regarding grade selection for low-temperature pressure vessel projects, please send parameters including operating temperature, design pressure and plate thickness to our technical engineers for free optimized material selection consultation.
Why is Toughness Critical for the Operational Safety of Pressure Vessels?
Pressure vessels are subjected to cyclic internal pressure, welding residual stress, localized stress concentration at nozzles and openings, along with thermal shock resulting from temperature fluctuation during unit startup and shutdown. Insufficient low-temperature toughness of the base material will directly result in catastrophic brittle fracture accidents, which has been validated by classic brittle cracking failure cases of vessel heads in the global petrochemical industry.
Prevention of Cold Brittle Fracture during Low-Temperature Startup and Shutdown
Conventional high-strength steels exhibit a ductile-to-brittle transition at temperatures below 0°C. P690Q (impact tested at -20°C) is applicable to equipment running under constant indoor temperature; P690QL1 with validated toughness performance at -40°C can avoid brittle cracking caused by abrupt temperature drop of outdoor equipment in severe winter or low-temperature medium working conditions.
Alleviation of Weld Notch Sensitivity
Hardened brittle regions will inevitably form in the Heat-Affected Zone (HAZ) of welded joints. Excellent toughness can absorb stress concentration at weld seams, openings and structural transition areas, so as to inhibit crack initiation and propagation.
Resistance to Cyclic Fatigue Failure
Pressure vessels run under alternating pressure for long-term service. High toughness delays the growth of fatigue cracks, thereby lengthening the overall maintenance cycle and service life of pressure-bearing equipment.
Safety Buffer for Abnormal Operating Conditions
In cases such as emergency overpressure, water hammer shock or external collision, high-toughness steel absorbs energy through plastic deformation rather than instantaneous fragmentation and explosion, which greatly upgrades the inherent safety performance of the equipment.
P690Q P690QL1 High Strength Pressure Vessel Steel Plate
| Name | P690Q P690QL1 High Strength Pressure Vessel Steel Plate |
| Thickness | 2-300mm,as you request |
| Width | 1000-3000mm,as you request |
| Length | 1-12m,as you request |
| Surface Treatment | clean, finishing, blasting and painting according to your requirement |
| Standard | EN 10028-6 |
| Material |
P690Q,P690QL1 |
P690Q vs P690QL1 High Strength Steel Plate Chemical Composition
| Element | P690Q (1.8880) | P690QL1 (1.8881) |
|---|---|---|
| C | 0.20 | 0.20 |
| Si | 0.80 | 0.80 |
| Mn | 1.70 | 1.70 |
| P | 0.025 | 0.020 |
| S | 0.015 | 0.010 |
| Ni | 2.50 | 2.50 |
| Cr | 1.50 | 1.50 |
| Mo | 0.70 | 0.70 |
| V/Nb/Ti | V≤0.12, Nb≤0.06, Ti≤0.05 | V≤0.12, Nb≤0.06, Ti≤0.05 |
| B | 0.005 | 0.005 |
| Cu | 0.30 | 0.30 |
| Zr | 0.15 | 0.15 |
| N | 0.015 | 0.015 |
P690Q vs P690QL1 High Strength Steel Plate Mechanical Property
| Performance Item | Thickness Range | P690Q | P690QL1 |
|---|---|---|---|
| Yield Strength ReH (MPa) | t ≤ 50mm | 690 | 690 |
| 50＜t ≤100mm | 670 | 670 | |
| 100＜t ≤150mm | 630 | 630 | |
| Tensile Strength Rm (MPa) | t ≤100mm | 770~940 | 770~940 |
| 100＜t ≤150mm | 720~900 | 720~900 | |
| Elongation A (%) | All thickness | ≥14 | ≥14 |
| Charpy V-notch Impact Energy (KV, J) | Test Temperature | ≥27J @ -20℃ | ≥27J @ -40℃ |
| Delivery State | - | Quenched & Tempered (Q&T) | Quenched & Tempered (Q&T) |
Welding and Machining Procedure Specification for P690Q and P690QL Plate
Welding Technical Requirements (Applicable to Both Grades)
Applicable Welding Processes
SMAW (Shielded Metal Arc Welding), SAW (Submerged Arc Welding), GMAW (Gas Metal Arc Welding), and GTAW (Gas Tungsten Arc Welding for root pass welding).
Preheating Temperature
For plates with thickness above 20 mm, maintain a preheat temperature of 150–200°C to remove diffusible hydrogen and prevent hydrogen-induced cold cracking.
Interpass Temperature Control
The maximum interpass temperature shall not exceed 250°C, so as to avoid grain coarsening and consequent toughness deterioration caused by overheating.
Matching Welding Consumables
Low-hydrogen high-strength welding consumables (e.g., E11018-G) shall be used to match the strength grade of the base metal.
Post-Weld Heat Treatment (PWHT)
Stress relief tempering shall be performed at 580–620°C after welding. The soaking time is determined according to plate thickness, with furnace slow cooling adopted to eliminate welding residual stress.
Post-Weld Inspection
After the weldment cools to ambient temperature, non-destructive testing including MT (Magnetic Particle Testing) and UT (Ultrasonic Testing) shall be carried ou
Hot and Cold Forming Processing
Cutting
CNC flame cutting and plasma cutting are the standard processing methods. For plates thicker than 80 mm, preheating shall be applied to the cutting edges to prevent edge cracking.
Bending and Rolling
Hot rolling forming is recommended for dished heads. Sharp-angle cold bending is prohibited to avoid surface microcrack generation.
Surface Treatment
For equipment placed in long-term storage or deployed for outdoor service, surface treatment shall consist of shot blasting followed by anti-rust primer coating.
P690Q vs P690QL1 Pressure Vessel Steel Plate Typical Application
P690Q Typical Applications
- Petrochemical high-pressure heat exchanger cylinder, reactor barrel for normal-temperature process;
- Thermal power plant high-pressure boiler steam drum, steam buffer tank;
- Indoor nitrogen, compressed air high-pressure storage tank for industrial park;
- Hydraulic power station high-pressure pressure cylinder, heavy hydraulic equipment pressure housing.
P690QL1 Typical Applications
- Offshore oil & gas platform high-pressure water injection separator, production manifold pressure vessel;
- Northern alpine area field oil and gas gathering pipeline pressure ballast tank;
- LNG gasification station cryogenic buffer tank, liquid ammonia low-temperature pressure storage vessel;
- Mobile cryogenic tank truck cylinder for cold-region road transportation;
- Wind power offshore booster station high-pressure fire water pressure vessel.
Supporting Services by GNEE Steel
Precision Machining Services
We provide full precision processing including CNC cutting, edge beveling, dished head rolling, drilling and shot blasting pretreatment for rust removal, delivering finished semi-finished pressure vessel components directly for assembly.
Custom Export Packaging & Global Logistics
We offer seaworthy moisture-proof packaging and steel frame reinforcement, with worldwide port delivery solutions applicable to FOB, CIF and DAP incoterms.
After-Sales Quality Traceability & Support
Full lifecycle traceability is guaranteed via steel plate heat numbers. A 24-hour rapid response service is available for all quality-related issues on overseas projects.
For bulk orders of P690 series steel plates, we provide free pre-cut test coupons for welding procedure qualification prior to mass production, effectively mitigating trial production and engineering risks.
FAQ
Can P690QL1 be used for hydrogen-containing medium pressure vessels?
Yes, P690QL1 (a quenched and tempered fine-grain structural steel under EN 10028-6 with a minimum yield strength of 690 MPa) can theoretically be used for pressure vessels, but using it for hydrogen-containing service requires extreme caution and strict engineering evaluation.
What are the equivalent grades of steel to P690Q steel?
P690Q steel (EN material number 1.8879) is a weldable, quenched and tempered high-strength fine grain steel defined under EN 10028-6 for pressure purposes, featuring a minimum yield strength of 690 MPa. Its closest international equivalents include ASTM A517 Grade Q (and ASME SA517 Gr. Q) in the United States, Q690 (such as Q690D/E or Q370R-related high-yield variants) in China, and structural counterpart S690Q (EN 10025-6) for load-bearing frameworks.
What are the advantages of P690QL1?
P690QL1 is a high-strength, quenched and tempered fine-grained structural steel designed for pressure vessels. Its main advantages include a high minimum yield strength of 690 MPa, excellent low-temperature impact toughness down to -40°C, good weldability, and the ability to reduce structural weight through thinner plate designs.
