• ByRouging Solutions Editorial Team  ·  28 October 2026

Solid Oral Dosage Equipment: Cleaning and Passivation Guide

It often starts with a small brown spot. A QA officer checks a granulator bowl during a batch changeover and finds a mark that will not wipe off. The bowl is stainless steel, so how can it rust? This guide covers how to clean solid oral dosage equipment, where rust and residue hide, and when passivation helps.

Tablet and capsule lines handle mostly dry powder, but several steps use water, solvents or coating liquids. And every step uses steel. So the state of that steel matters to the pharma teams who run these lines.

What Does Cleaning Solid Oral Dosage Equipment Involve?

It means removing the last product and the cleaning agent from each part that touched it, down to your set limits. That covers blenders, granulators, dryers, tablet presses, coating pans and capsule fillers. Each one is cleaned to a written method, then dried, checked and stored clean. FDA expects all of this to be on record.

The US rule is clear on procedures. 21 CFR 211.67 asks for written procedures and cleaning schedules. It also asks for "Inspection of equipment for cleanliness immediately before use." So a look inside the bowl before each batch is part of the rule.

The EU adds rules on design and storage. Chapter 3 of the EU GMP guide says equipment "should be designed so that it can be easily and thoroughly cleaned." It should be "stored only in a clean and dry condition."

Each machine leaves its own kind of residue:

Why Does Steel Condition Matter on a Tablet Line?

Because worn or rusty steel can shed metal into the product. US rules say surfaces that touch drug products "shall not be reactive, additive, or absorptive". The EU's rule 3.39 uses nearly the same words. Rust spots, loose metal and scratches that trap powder all work against that rule. Clean, smooth and passive steel does not.

A real case shows what is at stake. In June 2013, Hong Kong's Department of Health reported a recall of potassium chloride tablets made in Canada. The maker found the tablet coating solution "may have contained metal particles". It traced them to "a piece of mixing equipment used for the preparation of the coating solution."

The notice adds that the particles "were confirmed to be stainless steel". No tablet was found with a metal particle in it. Even so, three batches were recalled worldwide as a safety step.

The notice does not say why the mixer shed metal. On any line, worn or damaged parts need repair first. Passivation then helps sound steel keep its guard layer, so it is less likely to rust.

Which Solid Oral Equipment Is Hardest to Clean?

The parts with soft materials, tight gaps and wet residues. FDA names one directly. Its guide to cleaning validation says "Fluid bed dryer bags are another example of equipment that is difficult to clean". It adds that they are "often dedicated to a specific product". So many plants keep a set of bags for each product.

Coating pans come next. The film dries onto spray guns, nozzles and baffles, and some coating polymers resist plain water. Our guide to cleaning Eudragit coating polymer covers one widely used polymer.

Granulators trap wet mass around the impeller and chopper seals. Blender valves and press feed frames hold fine powder in small corners. FDA's guide gives one advantage of swabbing the steel directly: "areas hardest to clean and which are reasonably accessible can be evaluated". Pick these spots for your swab samples. Your results then show the worst case on each machine, which is what an auditor wants to see.

Wear makes cleaning harder over time. Bowls, chutes and hoppers rub against powder every day, which leaves scratches where powder lodges and stains begin. Where wear is deep, mechanical polishing can bring back a smooth surface that is easy to clean.

How Do Wet Steps Put Tablet Line Steel at Risk?

Water and time are the main risks. Granulation, drying and coating put moisture on the steel, and so does washing. If water sits in a bowl, valve or hose, it can mark the steel and let germs grow. FDA says "equipment should be dried before storage". It adds that stagnant water should never stay in equipment after cleaning.

Time matters for residue, too. FDA says "the drying of residues will directly affect the efficiency of a cleaning process." A granulator left dirty over a weekend can be much harder to clean on Monday. Many plants set a hold time for this, so that each bowl is cleaned within a set number of hours.

Cleaning agents can add risk if they are left behind. FDA says residues from the cleaning process itself "also have to be removed from the equipment." A final rinse with purified water helps remove them, and a full dry stops water from standing.

When Should Solid Oral Dosage Equipment Be Passivated?

At four points: when it is new, after a repair that cuts or welds the steel, after polishing and when rust spots appear. New steel can carry free iron, the loose iron specks left by tools. Welding, grinding and mechanical polishing strip off the steel's guard layer. Passivation removes that free iron and helps the chromium-rich layer form again.

Here is how the four points usually play out:

• New equipment. If the maker passivated it, ask for the record before you sign it off. If not, passivate it before first use.
• After a repair or weld. A new weld on a blender or a dryer bowl needs its guard layer restored.
• After polishing. Mechanical polishing leaves freshly cut steel, so passivate it before the part goes back in use.
• When rust spots appear. Clean the spot, find the cause, then passivate. Rust that keeps coming back points to a deeper problem.

ASTM A967, a widely used US passivation standard, includes citric acid methods. Our citric acid passivation service can treat bowls, chutes and parts at your site. For sprayed or wiped work on large items, we can use CitriSurf 77 Plus, a ready-to-use citric product that we supply. Our ASTM A967 guide explains the tests that prove a part is passive.

A Simple Steel Care Routine for a Tablet Line

A routine works best when it is written down and kept short. Use these steps as a starting point. Then adjust them with your QA team to fit your own products, hold times and cleaning methods. The aim is clean, dry and passive steel at the start of every batch.

1. Inspect before each batch. The US rule asks for it, so make it a signed line on the batch sheet.
2. Clean within the hold time, starting soon after the batch ends and before residues dry hard.
3. Rinse off the cleaning agent with purified water as the last rinse.
4. Dry fully, then store covered. Take special care with bowls, valves and hoses, where water can sit unseen.
5. Log any spot or stain. Note the machine, the place and a photo, then raise it with QA.
6. Plan passivation after repairs by booking it with the repair, so the part does not go back in use untreated.
7. Review the log every quarter. A spot that keeps coming back on one machine needs a closer look.

Can Tablet Line Steel Be Treated at Your Site?

Rouging Solutions cleans, descales and passivates solid oral equipment at your site or at our premises. Our inspection team uses imported, fully calibrated instruments to check the steel first. We also polish worn parts, and our cleaning service covers glass-lined vessels too. Every job comes with all the relevant documents for your QA file.

Our three directors bring 60+ years of combined industry experience. Here is a made-up example of how a job can run. Say a tablet plant in Baddi finds rust spots on two granulator bowls in October, ahead of an audit. The plant traces the spots to bowls left wet over a weekend and changes its drying step. Our team cleans the spots and passivates both bowls on site. The plant gets a record with the method, the chemical, the contact time and the test result for each bowl.

Where to Start

Remember one thing: clean, dry and passive steel helps keep metal out of your product. This week, walk your tablet line with a flashlight. Look inside each bowl, valve and hopper for spots, stains or any water left after cleaning.

Write down what you find, with a photo for each spot. Then share the list with QA and plan the fixes, starting with the machines you use most. If you need help, our team can check the steel with you on site. We reply within 24 hours.

Frequently Asked Questions