What Is Macro Examination of Steel Plate? A Practical Guide for Pressure Vessel Steel
When reviewing a steel plate specification, buyers usually look at chemical composition, tensile strength, yield strength, and impact toughness. But what about the internal soundness of the plate?
Some pressure vessel steel specifications include macro examination. It is different from ordinary mechanical testing, and it provides information about the internal condition of the steel.
This guide explains what macro examination is, what it can reveal, and why it matters for grades like SA516 Gr.70.
1. What Is Macro Examination?
1.1 What Does "Macro Examination" Mean?
Macro examination is the visual inspection of a prepared steel section to evaluate large-scale internal features. "Macro" means relatively large-scale observation — not individual grains.
- ✔ A section is cut from the steel plate
- ✔ The surface is prepared by grinding and polishing
- ✔ The surface is etched to reveal macrostructural features
- ✔ The prepared surface is examined visually or at low magnification
💡 Key distinction: Macro examination is not the same as microstructure examination. Macro examination looks at the overall internal condition; microstructure examination looks at the metallurgical structure at microscopic scale.
2. What Can Macro Examination Reveal in Steel?
Segregation
During solidification, alloying elements can concentrate in certain areas. Severe segregation can affect internal uniformity and may be visible in macro examination.
Porosity and Shrinkage
- ✔ Porosity
- ✔ Shrinkage cavities
- ✔ Internal voids
These features can affect internal soundness and are worth checking in critical applications.
Cracks and Discontinuities
Macro examination can reveal larger-scale cracks or continuity anomalies that may not be visible on the surface.
Inclusions and Internal Imperfections
Macro examination can help observe certain obvious non-metallic inclusions or abnormal internal areas. However, it is not a method for detecting every type of inclusion — that would be an overstatement.
3. How Is Macro Examination Performed?
Step 1: Sampling
A sample is taken from the steel plate. The exact sampling location and method depend on the applicable material specification or supplementary requirement.
⚠️ Important: Do not assume a universal sampling position. It must be specified by the applicable standard or purchase requirement.
Step 2: Cutting the Sample
The sample is cut to a suitable size for surface preparation and examination.
Step 3: Surface Preparation
- ✔ Cutting
- ✔ Grinding
- ✔ Polishing or suitable surface preparation
Step 4: Etching
Etching (also called macroetching) makes macrostructural features visible on the prepared surface.
Step 5: Visual Examination and Evaluation
The prepared surface is examined visually or at low magnification to determine whether any specified internal defects or anomalies are present.
💡 Key point: Acceptance criteria come from the applicable specification, standard, or supplementary requirement — not from the inspector's own judgment.
4. Macro Examination vs. Microstructure Examination
5. Is Macro Examination the Same as Ultrasonic Testing?
No — they are different methods, and they serve different purposes.
- Macro Examination — observes the internal macrostructure and defects through a prepared cross-section.
- Ultrasonic Testing (UT) — uses ultrasonic waves to detect internal discontinuities in steel plates.
💡 Key point: They are complementary inspection methods rather than interchangeable tests. Some projects may require both.
6. Why Is Macro Examination Important for Pressure Vessel Steel?
6.1 Pressure Vessel Applications Require Reliable Internal Quality
Pressure vessel steel plates are subject to pressure, temperature, and cyclic loading. Internal quality is a concern for buyers and engineers.
6.2 Mechanical Properties Do Not Show Everything
A plate can meet its specified tensile and impact requirements, but mechanical testing alone does not describe every aspect of its internal structure.
6.3 Specification Requirements Matter
Different projects may have different requirements for base material, supplementary requirements, customer-specific inspection, and classification/third-party inspection. Do not assume that "SA516 Gr.70" means the same inspection scope for every project.
7. Macro Examination Requirements for SA516 Gr.70
Does Every SA516 Gr.70 Plate Require Macro Examination?
Not necessarily.
Whether macro examination is required depends on:
- ✔ Applicable edition of the specification
- ✔ Purchase specification
- ✔ Supplementary requirements
- ✔ Customer requirements
- ✔ Project requirements
⚠️ Important: For an SA516 Gr.70 order, the purchase specification may include additional inspection requirements beyond the basic grade designation.
8. Macro Examination and Supplementary Requirements
Buyers often see a standard designation followed by S2, S3, S5, or S12. These are supplementary requirements.
- ✔ Basic specification
- ✔ Supplementary requirements
- ✔ Additional testing
- ✔ Acceptance criteria
📌 Note: A supplementary requirement should always be read together with the base material specification.
9. What Should Steel Buyers Check in a Macro Examination Report?
- ✓ Material grade — SA516 Gr.70 / SA516M Gr.70
- ✓ Heat number — traceability to the corresponding heat
- ✓ Plate identification — plate number, thickness, dimensions
- ✓ Sampling information — position and direction
- ✓ Examination method — how the test was performed
- ✓ Acceptance criteria — what standard or requirement was used
💡 Key point: Don't just look for "Macro examination: Qualified." Confirm what standard or requirement the acceptance was based on.
10. Frequently Asked Questions
❓ What is macro examination in steel?
Macro examination is the visual inspection of a prepared and etched steel section to evaluate large-scale internal features such as segregation, porosity, cracks, and inclusions.
❓ What is macro etching of steel?
Macro etching is the process of applying an etchant to a prepared steel surface to make macrostructural features visible for examination.
❓ What is the difference between macro and micro examination?
Macro examination observes large-scale internal features visually or at low magnification. Micro examination uses a microscope to examine the metallurgical structure at microscopic scale.
❓ Is macro examination the same as ultrasonic testing?
No. Macro examination observes a prepared cross-section. UT uses ultrasonic waves to detect internal discontinuities. They are complementary methods, not interchangeable.
❓ Is macro examination required for SA516 Gr.70?
Not necessarily. Whether it is required depends on the applicable edition of the specification, purchase specification, supplementary requirements, and project requirements.
❓ Can macro examination detect internal cracks?
Macro examination can reveal larger-scale cracks and discontinuities visible on the prepared surface. It is not a substitute for UT or other NDT methods for detecting all internal defects.
❓ Why is macro examination used for pressure vessel steel?
Pressure vessel steel requires reliable internal quality. Macro examination provides information about internal soundness that mechanical testing alone does not cover.
❓ Does every steel plate need macro examination?
No. Macro examination is typically specified by the applicable standard, supplementary requirement, or project specification. It is not a routine test for every steel plate.
11. Final Thoughts
When buying pressure vessel steel, the grade is only one part of the specification. Chemical composition, mechanical properties, impact testing, UT, and macro examination may each provide different information about the material.
For this reason, buyers should always review the complete material specification and purchase requirements rather than checking the steel grade alone.
💡 Our view: If you are sourcing SA516 Gr.70 or other pressure vessel steel plates with specific inspection requirements, send us the full specification — including any supplementary requirements — and we'll confirm the applicable testing and documentation.
📚 Further Reading & Related Content
- 🔗 Q345R vs SA516 Grade 70 – Comparison Guide
- 🔗 Ultrasonic Testing (UT) for Steel Plates – Buyer Guide
- 🔗 How to Read a Steel Plate Mill Test Certificate (MTC)
- 📄 ASTM A20/A20M, ASTM A516/A516M, ASME SA-516/SA-516M, GB/T 713.2-2023
Need Pressure Vessel Steel Plates with Macro Examination?
CEHE STEEL supplies SA516 Gr.70 and other pressure vessel steel plates with full inspection documentation. Send us your specification, including any supplementary requirements — we'll confirm the testing scope and provide a quotation.