Things to Remember Before Setting Up an Acid Bath for Pickling

Setting up an acid bath isn’t just about mixing acids — it’s about controlling corrosion, safety, and process stability. Small mistakes in setup often lead to high rejection rates or poor surface finish later. Here are the essential things to keep in mind:

1. Bath Material and Lining

Never compromise on tank material. Rubber-lined MS tanks or FRP (Fiber Reinforced Plastic) are standard for HNO₃ + HF mixtures. Stainless steel tanks are not suitable for acid pickling — they corrode quickly.

2. Chemical Composition

Maintain the right acid ratio. For stainless steel pickling, nitric acid (HNO₃) acts as an oxidizer, while hydrofluoric acid (HF) removes oxides and scales. Typical concentration lies between 8–15% HNO₃ and 0.5–3% HF, depending on grade and surface condition.

3. Temperature Control

The bath temperature directly affects pickling rate and surface quality. Excessive temperature accelerates metal loss and increases fuming. Ideal range: 45–55°C.Always include a heat exchanger for temperature regulation.

4. Ventilation and Fume Extraction

Pickling emits NOx and HF fumes — both hazardous. Proper exhaust systems and fume scrubbers with alkali neutralization are mandatory for worker safety and compliance.

5. Bath Life and Regeneration

Track bath life through regular chemical analysis. Overused baths cause pitting or dull surfaces. Implement a regeneration plan or acid recovery system to minimize waste and cost.

6. Water Quality

Hard water introduces unwanted ions like calcium and magnesium, forming insoluble salts on the surface. Use softened or demineralized (DM) water for rinsing.

7. Safety and SOP

Acid handling must always follow SOPs — from acid addition order to PPE usage.Golden Rule: Always add acid to water, never water to acid.

Takeaway:A well-set acid bath isn’t about guesswork — it’s controlled chemistry. The right setup gives uniform finish, reduces rework, and extends bath life.