If you work with steel, you know that not all steel surfaces are the same. One of the key choices buyers face is whether to purchase pickled and oiled (P&O) steel or dry (mill scale) steel.
While both types serve different purposes, many industries prefer P&O steel for its cleaner surface, improved corrosion resistance, and better workability. But why exactly do some industries favor pickled and oiled over dry steel?
Let’s break it down.
What Is Pickled and Oiled (P&O) Steel?
Pickled and oiled (P&O) steel undergoes a chemical treatment to remove mill scale, followed by a light oil coating to prevent rust.
🔹 Pickling – The steel is immersed in an acid bath to remove oxides, rust, and mill scale.
🔹 Oiling – A thin layer of protective oil is applied to prevent oxidation during storage and transport.
This results in a clean, smooth surface that’s easier to work with.
What Is Dry (Mill Scale) Steel?
Dry steel, also called hot-rolled steel with mill scale, comes directly from the rolling mill without additional surface treatment.
🔹 Mill Scale – A dark, flaky coating of iron oxides that forms during hot rolling.
🔹 No Protective Oil – This makes it prone to rust when exposed to moisture.
While mill scale provides some temporary protection, it can cause adhesion issues for coatings and needs removal for many applications.
Why Some Industries Prefer Pickled and Oiled Steel
While both types of steel have their uses, certain industries choose P&O steel for its advantages in fabrication, painting, and long-term performance. Here’s why:
1. Easier Welding and Fabrication
Many manufacturers prefer P&O steel because it welds, cuts, and bends more easily than dry steel. Mill scale on dry steel can cause porosity in welds, leading to weaker joints.
✔ Who benefits? Metal fabricators, machinery manufacturers, and structural engineers.
🔹 Example: A company making steel frames for heavy equipment prefers P&O because it reduces prep time before welding.
2. Better Paint and Coating Adhesion
P&O steel provides a clean surface that holds paint, powder coatings, and adhesives much better than mill scale. Dry steel requires extra surface preparation (sandblasting or grinding) before painting.
✔ Who benefits? Automotive, construction, and appliance manufacturers.
🔹 Example: A truck trailer manufacturer uses P&O steel to ensure smooth and even paint coverage, preventing premature corrosion.
3. Improved Corrosion Resistance
While the oil coating on P&O steel is temporary, it still offers more protection than dry steel, which rusts quickly when exposed to moisture.
✔ Who benefits? Industries storing steel for extended periods before use.
🔹 Example: A construction supplier storing steel beams outdoors chooses P&O to prevent early rust formation.
4. Smoother Surface for Precision Applications
Certain industries require steel with a more uniform surface finish for tight tolerances in machining or forming. P&O steel’s scale-free surface reduces defects in precision parts.
✔ Who benefits? Aerospace, automotive, and precision manufacturing.
🔹 Example: A hydraulic cylinder manufacturer uses P&O steel to ensure a smooth inner surface for sealing and performance.
When Is Dry Steel the Better Option?
While P&O steel has many advantages, dry steel is still widely used in applications where surface quality is less critical or where cost savings are a priority.
1. Structural Applications
For steel used in non-visible structural components, the presence of mill scale isn’t a major concern.
✔ Who benefits? Large-scale construction projects.
🔹 Example: A steel beam inside a building’s framework doesn’t need a smooth finish, making dry steel a cost-effective choice.
2. Cost-Sensitive Projects
Dry steel is usually cheaper than P&O since it skips the additional pickling and oiling process.
✔ Who benefits? Budget-conscious manufacturers.
🔹 Example: A manufacturer making steel pallets might choose dry steel because finish and appearance aren’t a priority.
3. Applications That Remove Mill Scale Anyway
If the steel will undergo blasting, grinding, or coating treatments that remove mill scale, there’s no need to pay extra for P&O.
✔ Who benefits? Industries that process steel before final use.
🔹 Example: A company making galvanized steel parts removes mill scale before applying zinc, making dry steel a suitable option.
Which One Should You Choose?
The decision between P&O and dry steel depends on your industry, application, and budget.
FactorPickled & Oiled (P&O) SteelDry (Mill Scale) Steel
Surface FinishSmooth, clean, and uniformRough, flaky, with mill scale
Welding & FabricationEasier to weld and bendRequires cleaning before welding
Paint & Coating AdhesionExcellentRequires prep work (blasting/grinding)
Corrosion ResistanceHigher (with oil coating)Prone to rust
CostSlightly more expensiveMore affordable
Best forPrecision work, welding, paintingStructural steel, budget projects
Final Thoughts
Industries that require cleaner surfaces, better workability, and superior paint adhesion prefer pickled and oiled steel. Meanwhile, dry steel remains a cost-effective choice for projects where surface finish isn’t a major concern.
If you need steel that’s ready to use with minimal prep work, P&O is the better option. But if cost savings or post-processing is your priority, dry steel might be the way to go.
Which type do you prefer for your projects? Let us know in the comments! 🚀
