P690QH is a high-strength quenched and tempered steel plate manufactured in accordance with the European standard EN 10028-6. It is primarily used for the fabrication of pressure vessels, especially in applications requiring high yield strength, good high-temperature stability, and excellent weldability. The use of this material typically enables significant weight reduction in design, but strict quality control must be implemented throughout the manufacturing chain, particularly in welding procedures.

Key Features and Advantages

1. Exceptionally high strength: Yield strength ≥ 690 MPa, tensile strength ranging from 770 to 940 MPa, suitable for high-pressure environments. This allows components to be designed lighter and thinner while carrying high loads.

2. Good toughness: Despite its high strength, it maintains excellent impact toughness at low temperatures (typically tested at -40°C or -60°C) through quenching and tempering treatment and strict chemical composition control. This is crucial for pressure vessels and low-temperature applications.

3. High-temperature stability: Can maintain high strength below 350℃.

4. Weldability: As a low-alloy high-strength steel, its weldability is acceptable but more complex than ordinary structural steel. The carbon equivalent (CEV) and weld crack susceptibility index (Pcm) are relatively high, meaning strict measures are required during welding.

5. Chemical composition: Based on low carbon content (typically ≤ 0.20%), alloying elements such as manganese, chromium, molybdenum, nickel, vanadium, niobium, and boron are added to enhance hardenability, strength, and toughness.

Due to the ultra-high strength, good toughness, and excellent high-temperature stability of P690QH Steel Plate, it is widely used in the following fields:

1. Petrochemical Industry

High-pressure reactors, heat exchangers, separators

Liquefied petroleum gas storage tanks, nuclear reactor pressure vessels

2. Power Industry

Power plant boiler drums, steam turbine components

High-pressure pipelines, hydroelectric station steel pressure pipes, spiral casings

3. Marine Engineering

Offshore platforms, oil drilling platforms

High-pressure and corrosion-resistant marine equipment

4. Other Fields

Critical load-bearing components of high-rise buildings and bridges

Engineering machinery, lifting equipment

Aerospace components (due to their high strength-to-weight ratio)

Processing and Welding Precautions

1. Cutting: Suitable for flame cutting and plasma cutting. However, after cutting thick plates, edge grinding may be required to eliminate the hardened layer.

2. Forming: Cold forming is relatively difficult and may require heating.

3. Welding: This is the most critical step. It is essential to follow a dedicated Welding Procedure Specification (WPS).

a) Preheating (150–250°C) and post-weld heat treatment (PWHT) are generally required to avoid cold cracks.

b) Use matching low-hydrogen electrodes.

c) Strict control of heat input is necessary during welding.

The Differences Between Grades Within The Same Series

* 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