Exploring Pressure Vessel Steel Plate
Pressure vessel tanks dot the landscape of countries all across the globe. These pressurized containers play important roles in the chemical and energy sectors, as they safely store potentially volatile liquids, such as fuel, gas and chemicals.
Pressure vessels are defined as closed containers that hold gases or liquids at a pressure substantially different than the ambient pressure. Since reliability and safety are so critical to pressure vessels, their production is regulated and tested for quality.
Pressure vessels are used for a variety of applications, most often in energy and transportation sectors. Common applications include:
- Aboveground storage tanks to store chemicals and fuels, including oil, gas and petrochemicals.
- Belowground storage tanks to store chemicals and fuels, with the contents partially stored underground.
- Pressurized railroad tank cars to transport chemicals, fuels and liquids from production locations to storage and usage locations.
What is PVQ Steel Plate?
Pressure vessel quality (PVQ) steel plate is used to produce pressure vessels due to its tensile strength, notch toughness, ductility and fatigue characteristics.
Before examining the properties of PVQ grades, here are a few terms used to describe the properties of steel, defined:
- Strength: the load the steel can bear. Steel strength is determined by yield point and tensile strength. A yield point is the point at which a material is stressed to the point where it deforms but does not break. Tensile strength is the amount of stress needed for the material to break.
- Notch Toughness: the level of impact steel can absorb before denting, typically measured by a Charpy Impact test.
- Ductility: the capability of a material to be stretched out before it becomes weak or brittle. Ductility is measured by elongation, which is the percent the length of a stretched material increases before it breaks.
Each of these properties impacts the applications and use of PVQ plate, and their influence on the use of primary PVQ grades will be explored below.
Properties of Primary PVQ Grades
ASTM A516 is a low-to-medium carbon steel that boasts high strength relative to weight, high ductility and high machinability. It is available in four grades of varying strength: 55, 60, 65 and 70.
Compared to other grades, A516 is a highly machinable PVQ steel grade, making it ideal to produce welded vessels where materials are manipulated to form the curved shape of a storage tank or boiler.
To increase strength while keeping carbon levels low, other elements are added to harden and strengthen, such as manganese, phosphorus, sulfur and silicon. Each grade has varying levels of each element, which are detailed in the chart below.
|ASTM A516||Grade 55||Grade 60||Grade 65||Grade 70|
A516 can be supplied in two conditions:
- As-rolled: the plate is supplied without heat treatment. As-rolled plate is typically not as strong as heat-treated plate because heat treatment alters the grain structure of steel plate, increasing strength, hardness and ductility.
- Normalized: the plate receives a heat treatment in which plate is heated to an extremely high temperature and held at that temperature for a sufficient time (typically up to an hour minimum for every 1” of thickness). After holding this high temperature, the plate is then cooled to room temperature. Normalizing a plate increases its hardness.
A516 grades have a relatively high yield and tensile strength, allowing the steel to endure high levels of stress, energy and weight without breaking or changing shape. Yield and tensile strength are important in PVQ steel to ensure the vessel does not break or deform, risking the leakage of materials inside the vessel. Below is a chart detailing the yield point, tensile strength and elongation of each grade of A516.
|A516||Grade 55||Grade 60||Grade 65||Grade 70|
|Elongation (200 mm)||23||21||19||17|
ASTM A537 Heat-Treated PVQ Steel
ASTM A537 is heat-treated, carbon steel typically used to produce boilers and pressure vessels for oil, gas and petrochemical products. A537 has similar machinability and ductility to ASTM A516, but its strength and hardness are significantly increased by heat treatment.
Like A516, A537 can be normalized, but it also can also be quenched and tempered, another type of heat treatment. Quenching and tempering is a two-part process in which steel is brought to an extremely high temperature and rapidly cooled with water (quenching), then re-heated to a below-critical temperature and cooled in room temperature.
In addition to the strength given by its chemical composition, heat treatment gives A537 steel grades greater yield and tensile strengths than the A516 grades. As a result, A537 steel can endure extremely high stress, weight or energy before deforming or breaking.
High yield and tensile strength are particularly important for use in the energy sector – a broken, leaking tank holding oils or gases could have significant, negative environmental impacts. Below is a chart detailing the yield point, tensile strength and elongation of A537.
Less Common PVQ Grades
While A516 and A537 are common PVQ grades and can be used in a variety of applications, other PVQ grades can be used for more specific pressure vessel applications.
A high-strength carbon steel used to produce pressurized railroad cars and is regulated by the Association of American Railroad.
|ASTM A612||A high-strength carbon steel used to produce pressure vessels for moderate and lower temperature use.|
|ASTM A285||A carbon steel intended to be used in the production of fusion-welded pressure vessels.|
Sourcing PVQ Steel Plate
When considering a steel supplier for your PVQ plate, it is important to look for a supplier who is reliable, knowledgeable and carries a large inventory of PVQ plate. This will ensure you get the right plate for the pressure vessel you are producing.
As North America’s leading steel plate supplier, Leeco® Steel is experienced in supplying pressure vessel plate to a variety of customers. Our 11 fully-stocked warehouses have a wide inventory of PVQ plate, making it easy for you to source plate for project and get the plate you need, when you need it.