Brewery Weld Inspection: How to Spot Bad Welds (AWS D18.1 & ISO 5817)

Read Time: ⏱️ 9 minutes | By: Luca

Key Takeaways: Sanitary Welding Standards

• Surface Roughness: Must be Ra ≤ 0.8µm (32µin). If a cotton ball snags, bacteria will grow.
• Zero Tolerance: No sugaring (granulation), undercutting, or cracks are permitted in product-contact zones.
• Global Codes: We inspect AWS D18.1 (USA) and ISO 5817 Level B (Global/Europe) standards.
• The Golden Rule: Never trust a polished exterior. Always inspect the internal weld root with a borescope.

Introduction: The “Shiny Tank” Trap

A polished exterior means absolutely nothing if the inside of your tank looks like volcanic rock.

Brewery owners often focus on shiny, mirror-polished jackets. But bacteria don’t live on the outside of your tank. They live inside, hiding in microscopic cracks and rough patches that your CIP machine cannot reach.

If you’re buying equipment, checking the welds is the only way to protect your beer. You don’t need to be a certified welder to do it. You just need to know what a “sugared” weld looks like and why it ruins beer.

Below is a quick checklist of what we look for when auditing a factory.

A sanitary weld is a joint smooth enough for your CIP system to clean without scrubbing.

In the United States, The industry standard is AWS D18.1 (Specification for Welding of Austenitic Stainless Steel Tube and Pipe Systems in Sanitary Applications). This standard dictates exactly how smooth a weld must be to prevent microbial growth.

The key metric here is Ra (Roughness Average).

• The Rule: A sanitary weld needs an Ra finish of 0.8µm or better.
• The Test: Imagine running a cotton ball over the weld. If it snags, shreds, or catches, that weld is a bacterial harbor. It fails.

Whether you are sourcing complex brewing machinery or a simple spool piece, the physics of bacteria remains the same. If the surface isn’t smooth, the bugs survive.

Whether you are brewing in Munich, Melbourne, or Minnesota, bacteria doesn’t care about your local code. It cares about surface roughness.

While we reference American standards heavily, a bad weld is a bacterial trap anywhere in the world. If you are sourcing equipment internationally, use this cheat sheet to make sure your factory understands what “Sanitary” means in your region.

Region	The Standard	What to Specify in Your Contract
USA	AWS D18.1	The primary standard for sanitary tube and pipe. Focus on Ra < 0.8µm.
Europe	EHEDG (Doc 35) & ISO 5817	EHEDG is the bible for hygienic design. Defects like “Sugaring” violate Doc 35 explicitly.
UK / Global	ISO 5817 (Quality Level B)	Specify that all product-contact welds must meet Quality Level B (Stringent). Level C or D is for structural steel, not beer.
Asia / China	GB Standards (Export Grade)	Top-tier Chinese factories manufacture to Western standards (AWS/ISO). Make sure your contract specifies Export Grade finishing, not domestic standard.

 

The Universal Language: No matter where you are, specify Ra < 0.8µm. This number works in every country and every language.

Visual inspection is your first line of defense. Here are the five specific defects you need to look for inside any brewing equipment you purchase.

1. Sugaring in Stainless Steel Welds

What it is:

Sugaring happens when the welder fails to purge the back of the weld with inert gas (like Argon). The hot metal reacts with oxygen, creating a dark, crusty, “sugar-like” texture on the inside of the pipe or tank.

The Danger:

This is a deal-breaker. That rough surface is impossible to clean. Yeast and beer stone (calcium oxalate) will build up in the pores, leading to persistent infections that ruin batch after batch.

2. Undercutting (The Groove)

What it is:

An undercut is a groove melted into the parent metal right next to the weld bead. It usually happens when the welding heat is too high.

The Danger:

This groove creates a weak spot. Over years of thermal cycling, going from hot CIP cycles to cold crash temperatures, these grooves turn into cracks. A crack in the jacket of a fermenter can lead to glycol leaking into your beer.

3. Lack of Penetration

What it is:

This happens when the welder doesn’t fuse the metal all the way through. It leaves a microscopic crevice between the sheets of steel.

The Danger:

This gap is a “dead leg” for bacteria. Your CIP fluid flows over it, but it cannot penetrate deep into the crack to kill the spoilage organisms hiding there.

4. Heat Tint (The Rainbow)

What it is:

If you see blues, purples, or golds on stainless steel, that is “heat tint.”

The Danger:

While it looks pretty, heat tint indicates that the chromium oxide layer (the part of the steel that prevents rust) has been thickened and chemically altered. If this isn’t removed via passivation, that colorful spot will eventually rust.

5. Misalignment

What it is:

This is when the two pipes or sheets of metal don’t line up perfectly flush, creating a “step” or ledge.

The Danger:

In a brewhouse system, liquid needs to drain completely. A misalignment creates a dam where hop trub and wort get trapped, preventing a full drain.

 

Never trust the photos of the tank’s exterior alone; demand to see the inside.

Cheap factories focus on what you can see. They will polish the outer jacket to a mirror finish because that’s what sells. But the interior welds, the ones that actually touch your beer, might be left raw.

The Solution:

Before you sign off on shipping, ask for borescope photos. A borescope is a small camera snake that goes inside sanitary piping and tank ports. It shows you the “root pass” inside the pipe, the part you can’t see from the outside.

 

The Invisible Shield: Brewery Tank Passivation Standards

Stainless steel isn’t naturally rust-proof. It needs chemical treatment to stay that way.

After welding, a tank must undergo passivation. Factories use an acid bath (usually citric or nitric) to remove free iron from the surface and restores the protective chromium oxide layer. This applies to everything from large tanks to malting machines.

The Test:

If you receive a tank that looks dull and matte grey on the inside welds, that is actually a good sign, it likely means it has been pickled and passivated properly. If the weld looks shiny but colorful (heat tint), it might have skipped this important step.

You don’t need expensive gear for a basic check. If you are visiting a factory or inspecting a tank upon delivery, bring these tools:

1. High-Lumen LED Flashlight: Shine it sideways across the steel (raking light). This highlights pits that overhead lights hide.
2. Inspection Mirror: Use a telescoping mirror to look behind baffles, spray balls, and under manway rims.
3. Your Fingernail: The simplest test of all. Run your fingernail across the weld. If it “clicks” or catches, the finish is likely too rough for sanitary standards.

If you suspect your tank wasn’t passivated properly, you can perform a quick field check using a Copper Sulfate Test Kit (ASTM A967 Practice D).

• The Method: Apply a drop of copper sulfate solution to the surface. Keep it wet for 6 minutes.
• The Result: If the liquid turns pink/copper color, Free Iron is present (FAIL). If it stays clear, the surface is passivated.

⚠️ COMPLIANCE WARNING: This is a field spot-check only. It is excellent for verifying new equipment upon arrival, but it does not replace a formal lab-verified passivation report for official certification. Always rinse the area thoroughly with water after testing, as copper sulfate is toxic.

 

Decision Matrix: Can It Be Fixed?

You found a defect during your brewery weld inspection. Now what? Use this decision matrix to decide if you should accept repairs or reject the tank.

Defect Found	Can it be fixed?	The Required Action
Heat Tint	✅ Yes	Clean with pickling gel (Acid) + Re-passivate.
Rough Grind	⚠️ Maybe	Polish with fine grit to < 0.8µm Ra.
Sugaring	❌ NO	REJECT. Must be cut out and re-welded.
Cracks / Undercut	❌ NO	REJECT. Structural integrity is compromised.

Conclusion: Don’t Gamble on Quality

A bad weld costs more than a premium tank because it costs you batches of dumped beer and a damaged reputation.

Buying tanks is expensive. You shouldn’t have to guess whether your tanks are safe. We source equipment that actually meets international standards, including ISO 5817 and AWS D18.1.

Don’t want to fly overseas to inspect welds yourself? We have engineers on the ground who perform Borescope Inspections on every tank we source, from canning machines to reverse osmosis machines.

Contact Us For Consultation

 

Frequently Asked Questions (FAQ)

What does a brewery weld inspection involve?

A sanitary inspection involves checking the product-contact surfaces of tanks and pipes for defects. Inspectors look for sugaring (oxidation), undercutting, and lack of penetration. They use tools like borescopes and profilometers to Make sure the surface roughness (Ra) meets AWS D18.1 standards (usually < 0.8µm).

What does a “sugared” weld look like?

A sugared weld looks like dark, grey, granulated rock or rough sandpaper. It happens when the back of the weld is exposed to oxygen during the welding process (lack of purge gas). It is never acceptable in sanitary brewing equipment.

Can you fix a bad stainless steel weld?

Sometimes. Minor heat tint can be cleaned with pickling gel. However, deep sugaring or severe undercutting usually requires cutting out the defective section and re-welding it properly. Simply grinding it down often weakens the tank wall too much.

Does this apply to dry hopping equipment?

Absolutely. Even equipment for raw materials, like hop dry kilns, should be free of crevices where mold or organic dust can accumulate.

Why is my stainless steel tank rusting?

Stainless steel rusts if its “passive layer” is damaged. This is often caused by Heat Tint from welding that wasn’t properly passivated (acid cleaned) at the factory. It can also happen if you use chlorine-based cleaners, which strip the protective layer.

Do bottling machines need sanitary welds?

Yes. The liquid path of a bottling machine is a critical control point. Since beer is packaged cold and won’t be boiled again, any bacteria hiding in a bad weld in the filler bowl will go directly into the bottle.

Also Read:

Brewery Lab Equipment on a Budget: Essential Quality Control Tools for Startups

The Commercial Pilot Brewhouse Guide: Why Every Brewery Needs a 1 BBL System

Why Most Homebrewers Mess Up Volumes (And How to Fix It Fast)

Evolution of Brewing Technology: From Clay Pots to Modern Brewery Equipment

How to Tap a Keg Like a Pro: Bar Secrets for Smooth Pours Every Time