P355QL1 Boiler And Pressure Veseel Steel Plate

What Is P355QL1 Boiler and Pressure Vessel Steel Plate?

Most pressure vessel grades are specified for what happens inside the vessel. P355QL1 is specified for what happens outside it - a cold night, a winter shutdown, a refrigerated transfer. It is the low-temperature branch of the quenched and tempered fine-grain family in EN 10028-6:2017, registered under material number 1.8868, and the L1 suffix moves the guaranteed impact test temperature down to −40 °C where plain P355Q stops at −20 °C.

The reason matters as much as the number. Brittle fracture does not announce itself: a vessel that is perfectly safe at operating pressure can fail during hydrostatic testing in cold weather, or on the first start-up after a winter outage, if the plate has no toughness margin at the metal temperature. P355QL1 buys that margin in two independent ways - through the impact requirement itself, and through tighter phosphorus and sulphur limits in the chemistry.

P355QL1 Pressure Vessel Steel Plate Chemical Composition

Ladle analysis, maximum %, per EN 10028-6:2017:

P355QL1 Boiler Steel Plate Mechanical Properties

Guaranteed minimum values, transverse test pieces:

Elongation is measured on a proportional test piece, gauge length Lo = 5.65·√So. The yield strength steps down with thickness - 355, then 335, then 315 MPa - as section size grows; the tensile range narrows to 450–590 MPa above 100 mm.

P355QL1 Steel Plate Low Temperature Impact Toughness

Charpy V-notch energy, minimum average of three transverse specimens:

P355QL1 Boiler and Pressure Vessel Steel Plate Product Specifications

P355QL1 Boiler and Pressure Vessel Steel Plate Typical Applications

Pressure Vessels and Storage Tanks: Specified for the fabrication of diverse pressure vessels, reactors, heat exchangers, separators, and particularly low-temperature liquid storage tanks (such as LNG storage tanks) and process equipment.

Petrochemical Industry: Widely utilized in high-pressure and low-temperature equipment manufacturing throughout the oil, gas, and chemical processing sectors.

Power Generation and Boiler Industry: Applied in power plant boilers and associated pressure-retaining auxiliary equipment.

Cryogenic Engineering: Engineered for pressure-retaining structural applications in low-temperature environments down to -50°C, providing effective protection against low-temperature brittle fracture.

Why Choose GNEE Steel?

1. Flexible size customization: Cut-to-length, slitting, plasma flame cutting, CNC bending and rolling processing per client drawing requirements
2. Controllable delivery time: standard specifications are shipped within 3-7 days; urgent orders can be prioritized and delivered expedited to ensure no delays to client project schedules.
3. Our exclusive export standard packaging includes: waterproof film + moisture-proof paper + solid wood pallet + corner protectors.
4. Our self-built professional quality inspection team conducts full-process inspection from raw materials, rolling, leveling to finished product delivery, strictly controlling dimensional tolerances and surface quality to eliminate defects such as cracks, slag inclusions, and rust.

Check today's stock in 10–50 mm - send thickness, width × length and quantity, and the quoted price is held for 7 days.

FAQ

Is the −40 °C impact test mandatory, or must it be requested?
It is part of the grade. EN 10028-6 requires impact testing at −40 °C for P355QL1 as supplied; what has to be requested separately is a higher value (40 J) at that temperature.

How much tougher is P355QL1 than P355Q in practice?
At −20 °C, QL1 must reach 40 J against P355Q's 27 J, and QL1 is additionally tested at −40 °C where it must still clear 27 J. The grade also carries tighter phosphorus and sulphur limits, which is what makes that toughness repeatable heat to heat.

Can P355QL1 go below −40 °C?
Down to −50 °C or so, the answer depends on the impact energy agreed at order time, not on the grade name. For a genuine −60 °C design temperature, P355QL2 (1.8869) is the correct branch.

Why are the P and S limits lower than on P355Q?
Both elements harm low-temperature toughness - phosphorus through grain-boundary segregation, sulphur through sulphide inclusions. The standard tightens them for the L grades so the −40 °C guarantee holds across the full thickness range.

Does P355QL1 come with elevated-temperature strength values?
Not by default. Those are specified for the H variant. For QL1 they can be agreed at the time of enquiry and order.

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