Abrasive Selection Guide for Steel Structures

By Pritam Singh, QC Coating Inspector

In my 11 years of experience in oil & gas coating inspection, I have seen many surface preparation failures that were not caused by poor blasting technique — but by wrong abrasive selection.

Abrasive choice directly affects:

• Surface cleanliness
• Surface profile (anchor pattern)
• Production speed
• Coating adhesion
• Long-term corrosion protection

Selecting the correct abrasive is critical for steel structures in industrial, marine, and offshore environments.

This guide explains how to select the right abrasive for steel structures based on field conditions and coating requirements.

Why Abrasive Selection Is Important

Abrasive blasting serves two main purposes:

1️⃣ Remove contamination (rust, mill scale, old coating)
2️⃣ Create the correct surface profile for coating adhesion

If the abrasive is too fine → profile too low
If abrasive is too coarse → profile too high
If abrasive is contaminated → coating failure

Correct abrasive selection ensures both cleanliness and profile compliance.

Key Factors to Consider Before Selecting Abrasive

Before approving abrasive for site use, I always verify:

✔ Required cleanliness grade (Sa 2½, Sa 3, etc.)
✔ Required surface profile range (µm/mils)
✔ Type of coating system
✔ Environmental exposure (marine, immersion, atmospheric)
✔ Steel thickness and hardness
✔ Recycling system availability

Types of Abrasives Used for Steel Structures

Abrasives are generally classified into:

• Metallic abrasives
• Non-metallic abrasives
• Natural abrasives
• Synthetic abrasives

1️⃣ Metallic Abrasives

Steel Shot

Shape: Spherical
Profile Produced: Dimpled/peened surface

Best for:

• Shot blasting machines
• Structural steel fabrication
• Recyclable systems

Advantages:
✔ Durable
✔ Reusable multiple times
✔ Consistent cleaning

Limitation:
❌ Produces lower angular profile compared to grit

Steel Grit

Shape: Angular

Best for:

• Heavy-duty industrial structures
• Offshore components
• High-build coating systems

Advantages:
✔ Produces sharp anchor profile
✔ High cleaning efficiency
✔ Recyclable

Common for oil & gas yard blasting.

2️⃣ Non-Metallic Abrasives

Garnet

Very popular in oil & gas projects.

Advantages:

✔ Low dust
✔ Good cutting ability
✔ Minimal embedment risk
✔ Suitable for field blasting

Commonly used for:

• Maintenance work
• Pipeline blasting
• Tank external surfaces

Aluminum Oxide

Very hard and aggressive.

Best for:

• Heavy corrosion removal
• Tough coating removal

Limitation:
❌ Higher cost

Copper Slag / Coal Slag

Used in some regions for open blasting.

Advantages:
✔ Good cutting performance
✔ Economical

Limitations:
❌ Higher dust
❌ Environmental concerns in some countries

3️⃣ Natural Abrasives

Silica Sand (Not Recommended)

Previously common but now restricted in many countries due to health hazards (silicosis risk).

Avoid unless specifically permitted and controlled.

How Abrasive Shape Affects Surface Profile

Angular Abrasive (Grit, Garnet)

• Produces sharp, deep anchor pattern
• Better for epoxy and high-build coatings

Rounded Abrasive (Shot)

• Produces peened surface
• Lower profile
• Suitable for thin coatings

Abrasive Size vs Surface Profile

Larger abrasive particle size → Higher profile
Smaller abrasive particle size → Lower profile

Example:

• 50–75 µm profile → Medium grit size
• 75–125 µm profile → Coarser grit

Always verify actual profile using replica tape or depth gauge.

Never assume based on abrasive size alone.

Abrasive Selection Based on Service Environment

🔹 Atmospheric Exposure

• Medium profile (50–75 µm)
• Garnet or steel grit suitable

🔹 Marine / Offshore

• Higher profile (75–100 µm)
• Angular abrasive preferred
• High cleanliness grade (Sa 2½ or Sa 3)

🔹 Immersion Service

• Strict cleanliness
• Controlled abrasive
• No embedment
• Often Sa 3 required

Common Mistakes in Abrasive Selection

❌ Using same abrasive for all projects
❌ Not checking abrasive cleanliness
❌ Ignoring chloride contamination in abrasive
❌ Excessive recycling leading to size reduction
❌ Mixing incompatible abrasive types

Abrasive Quality Control Checks

Before approving abrasive, I verify:

✔ Supplier approval
✔ Sieve analysis (particle size distribution)
✔ Chloride contamination test
✔ Oil contamination check
✔ Moisture content
✔ Recyclability condition

Abrasive Recycling Control

In recycling systems:

• Fine particles increase over time
• Profile reduces
• Dust level increases

Regular sieve analysis is required to maintain profile consistency.

Practical Field Recommendation

For most oil & gas steel structures:

✔ Garnet (good quality) for field blasting
✔ Steel grit for yard blasting with recovery system
✔ Angular abrasive for high-build epoxy systems
✔ Avoid silica sand

Final selection must align with coating manufacturer recommendation and project specification.

Conclusion

Abrasive selection directly affects:

• Surface cleanliness
• Surface profile
• Coating adhesion
• Long-term durability

From my experience, wrong abrasive selection is one of the top hidden causes of coating failure.

Surface preparation quality begins with selecting the right abrasive — not just blasting technique.

📌 Related Articles

• Common Sandblasting Defects and How to Avoid Them

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