Specifying steel for sour service environments and high-pressure containment leaves no room for error. Whether you are procuring material for global Oil & Gas refineries and Nuclear facilities. Understanding the exact metallurgical properties and testing requirements is critical to ensuring long-term safety and structural integrity.

In this hub, the technical experts at Brown McFarlane answer the most critical questions regarding HIC (Hydrogen Induced Cracking) and Pressure Vessel boiler plates. From navigating complex ASME and EN 10028 standards to understanding strict NACE testing protocols, this guide is designed to support engineers and procurement teams in making data-driven material selections.

Explore the FAQs below to learn more about specifying premium grades—including CarElso HIC Premium+ and Super Duplex stainless steel, and discover how our advanced in-house processing capabilities, such as precision water jet cutting and press braking, can streamline your fabrication supply chain.

Core Definitions & Material Selection

What is a HIC plate?

A HIC (Hydrogen Induced Cracking) plate is a highly specialised carbon steel manufactured specifically to resist degradation in “sour service” environments, typically within the Oil & Gas sector where hydrogen sulphide (H2S) is present. To ensure maximum safety, we supply CarElso HIC Premium+ plate, which is engineered with exceptionally low sulphur and phosphorus levels to prevent hydrogen atoms from forming gas blisters within the steel matrix.

What steel is used for pressure vessels?

Pressure vessels require materials that can withstand immense internal pressures and extreme temperatures. The most common choice is high-quality carbon steel, such as ASME SA516 Grade 70 and EN 10028 boiler plates. For more volatile or highly corrosive environments, such as those in the Nuclear sectors—high-end stainless steels like Duplex and Super Duplex are often utilised.

What is the best material for a pressure vessel?

The “best” material strictly depends on the operating environment. For standard high-pressure containment, ASME SA516 Gr 70 offers good balance of strength and weldability. However, based on our processing expertise, if the vessel will be exposed to high corrosion, high temperatures, or abrasion, Super Duplex stainless steel is far superior due to its high chromium and molybdenum content.

What is the difference between HIC and SSC?

While both occur in sour service environments, they are fundamentally different mechanisms:

• HIC (Hydrogen Induced Cracking): Occurs internally. Hydrogen atoms permeate the steel, form gas molecules, and build internal pressure that leads to blistering and cracking. No external stress is required.
• SSC (Sulphide Stress Cracking): Occurs on the surface and requires the combination of tensile stress and a corrosive environment (hydrogen embrittlement).

Standards, Equivalents & Technical Specifications

What is the difference between SA 516 Gr 60 and 70? 

The primary difference lies in their tensile and yield strengths. SA 516 Gr 70 has a higher carbon content, offering greater tensile strength (70 to 90 ksi), making it ideal for lower ambient temperature applications. SA 516 Gr 60 has slightly lower tensile strength (60 to 80 ksi) but offers superior ductility and weldability.

SA 516 Gr 70 vs SA 516 Gr 485: What is the difference? 

There is no physical difference; these are two naming conventions for the exact same material. SA 516 Gr 70 is the imperial designation (indicating a tensile strength of 70 ksi), whereas SA 516 Gr 485 is the metric equivalent (indicating a tensile strength of roughly 485 MPa).

What are the requirements for HIC-resistant steel? 

To be certified as HIC-resistant, the steel must undergo rigorous metallurgical control during the manufacturing process. The essential requirements include:

• Ultra-low sulphur content (typically <0.002%) to reduce sulphide inclusions.
• Vacuum degassing to remove residual hydrogen during casting.
• Calcium treatment used in some instances to modify the shape of any remaining inclusions, rendering them harmless. However, CarElso has such a low P & S content that it is not required.

What is the British standard for pressure vessels? 

Historically, the UK relied on BS 1501. However, this has now been fully superseded by the harmonised European standard EN 10028 (specifically EN 10028-2 for non-alloy and alloy steels with specified elevated temperature properties).

Testing, Safety & Lifecycle

What is the HIC test for steel? 

To guarantee safety in sour environments, steel must be tested strictly in accordance with NACE TM0284. The testing protocol involves:

1. Extracting sample test blocks from the mother plate.
2. Immersing the samples in a saturated hydrogen sulphide (H2S) solution for 96 hours.
3. Removing the samples and sectioning them.
4. Inspecting the sections under a microscope to measure the Crack Length Ratio (CLR), Crack Thickness Ratio (CTR), and Crack Sensitivity Ratio (CSR).

Why do pressure vessels fail? 

Pressure vessel failures are catastrophic and are typically caused by three main factors: material fatigue, unmitigated corrosion (such as HIC or SSC), and poor fabrication. Selecting the correct grade of steel and utilising precise processing methods—such as our in-house water jet cutting and press braking facilities—ensures the structural integrity of the steel is perfectly maintained prior to final welding and assembly.

How often do pressure vessels need to be inspected in the UK?

 In the UK, inspection frequencies are strictly governed by the Pressure Systems Safety Regulations 2000 (PSSR). The frequency is dictated by a “Written Scheme of Examination” drawn up by a competent person. Generally, minor vessels require inspection every 12 to 24 months, while major, high-risk vessels may require continuous monitoring and NDT (Non-Destructive Testing).