A sanitary weld is required in food processing because a weld that cannot be cleaned thoroughly becomes a contamination point. In a plant, it touches the product and goes through washdown every day. Here is what sets it apart from an ordinary weld, what federal regulations say and how to recognize a weld done right.
Key takeaways
- A sanitary TIG weld in stainless steel is fully penetrated, smooth, back-purged and restored after welding, so it can be cleaned completely.
- Section 53 of the Safe Food for Canadians Regulations requires smooth contact surfaces, free of pitting, crevices and scale. It does not name any welding process.
- TIG remains the process of choice for food-grade stainless steel, because it gives smooth, cleanable, corrosion-resistant and repeatable joints.
- When buying, require written acceptance criteria rather than a process name, and validate them with your quality manager.
What is a sanitary weld?
A sanitary weld is a stainless steel weld that can be cleaned completely, with no cavity where food residue can lodge. Manitoba's guidelines on sanitary equipment design call for smooth, continuous, polished welds to avoid cavities. We explain this principle in detail in our article on polished stainless and fully sealed welds. Four concrete requirements follow.
The four requirements of a sanitary weld
- Full penetration. The molten metal goes through the full thickness, with no void or crack where residue can build up.
- Smooth surface. The bead is continuous, with no porosity or spatter. On a food-contact surface, it is ground and polished so it blends into the sheet.
- Protected back side. On a pipe or tank, the inside of the weld must be as clean as the outside.
- Restored stainless steel. After welding, the heat tint is removed to restore corrosion resistance.
Why a poor weld becomes a risk
A defective weld forms a cavity that cleaning cannot reach. Manitoba lists poor-quality welds among the cavities to eliminate on equipment. It also warns that unsanitary equipment can lead to a foodborne illness outbreak or a product recall. In equipment contaminated by Listeria monocytogenes, the bacteria can leave its harbourage site and reach other surfaces during operation.
Requirements to know in Canada
Federal regulations set the result to achieve, not the welding process. That is the distinction to keep in mind before ordering equipment.
What section 53 of the federal regulations says
Equipment must be designed, built and maintained to prevent food contamination. Its materials must resist corrosion, be durable and withstand repeated cleaning. Food-contact surfaces must be smooth, free of pitting, crevices and scale, and non-absorbent. Section 50 adds that equipment must be kept clean and in sanitary condition. None of these sections names TIG. The weld simply has to make these results possible.
Who these regulations apply to
The requirements of this part apply to food sent from one province to another or exported. They therefore concern businesses that import, export or trade interprovincially. If your plant's products stay in Quebec, confirm with the MAPAQ which requirements apply to you.
Audit programs and shop certification
Depending on your sector, your auditors may apply recognized food safety programs or hygienic design standards specific to your industry. Your quality manager knows which ones apply to your plant. Ask before ordering fabrication.
Why TIG is the standard in food processing
TIG welding is the reference for food-grade stainless steel, because joints must be smooth, cleanable, corrosion-resistant and repeatable. Two characteristics explain this status.
Separate control of heat and filler metal
TIG uses a non-consumable tungsten electrode and a shielding gas, usually argon. The welder controls the heat with one hand and adds filler metal with the other, producing fine, precise beads without spatter, which suits thin stainless steel. The grade matters too: see stainless 304 or 316.
A demanding process
TIG requires a welder experienced with stainless steel, and sanitary welding also demands particular attention to contamination control. Since the regulations do not name a process, another process could be acceptable if it achieves the same result and your quality manager accepts it.
Argon purging: protecting the back of the weld
Argon purging protects the inside of a stainless joint during welding, where nobody will see it once the part is installed. It consists of filling the pipe or tank with an inert gas, argon, to drive the air away from the weld.
An unprotected root takes on colours that can damage the passive layer of the stainless steel; protecting the root avoids or reduces pickling. A smooth, bright back side cleans like the rest of the piping.
Heat tint and passivation: keeping stainless steel stainless
Heat tint is a visible sign that a stainless weld must be restored. These temper colours, which appear during welding, affect the steel's corrosion resistance, which comes from a chromium-rich oxide layer on the surface.
Pickling and passivation are often confused. Pickling removes the layer damaged by heat by taking off a thin layer of surface metal. Passivation then helps the protective layer re-form. To know whether equipment has been properly restored, ask the shop which steps it applies after each weld.
How to recognize a good sanitary weld
A good sanitary weld can be recognized by eye, even if you are not a welder. These criteria follow the spirit of section 53 for food-contact surfaces:
- The bead is even along its whole length, with no holes or bumps.
- The heat tint is light, or it has been removed by pickling and passivation.
- Inside a pipe, the back side is smooth and bright, not grainy.
- There are no sharp corners or slits where the product flows.
- The food-contact surface is smooth, without pitting or crevices.
FAQ: sanitary TIG welding in food processing
What is a sanitary weld?
A stainless weld that can be cleaned completely, with no cavity or porosity where residue builds up. It is fully penetrated, smooth, back-purged and restored after welding.
Does the law require TIG welding?
No. Section 53 of the federal regulations names no welding process. It requires smooth surfaces without pitting or crevices, and equipment that resists corrosion and repeated cleaning. TIG is the most common way to get there.
Why is TIG the standard in food processing?
Because it produces smooth, cleanable, corrosion-resistant and repeatable joints. The welder controls heat and filler separately, which gives fine beads on thin stainless steel.
What is argon purging for?
It fills the inside of the pipe with an inert gas during welding to protect the back of the joint. An unprotected root can see its passive layer deteriorate.
What is the difference between pickling and passivation?
Pickling removes the stainless layer damaged by heat. Passivation then helps the protective layer re-form.
How do you check a welding shop's certification?
CSA W47.1 governs the certification of companies that fusion-weld steel. It covers the company's capability and does not approve a product. The CWB, which administers this certification, publishes a directory of certified companies. See what the standards require of a CWB-certified company, and also ask how the shop handles purging, pickling and passivation.
Can sanitary welding be done in my plant?
Yes. Alliance Maintenance Industrielle offers a mobile service that works directly at the client's site, in addition to its shop work.
Need stainless welding for your plant?
Alliance Maintenance Industrielle performs industrial welding, specializing in food and chemical environments, in the shop or at your site. For a custom part, see our stainless steel fabrication. If production stops, our 24/7 emergency service works everywhere in Quebec. Call 438-357-8800, day or night.
Sources
- Safe Food for Canadians Regulations (SOR/2018-108)
- CWB — Directory of certified companies (CSA W47.1)
- CSA W47.1 — Certification of companies for fusion welding of steel
Photo: Alliance Maintenance Industrielle. This article is for information only; it does not replace the requirements of your quality manager or your auditors.