The American Welding Society D18 Committee on Welding in Sanitary Applications was formed to create and revise the welding standards in the fabrication and construction of processing facilities for the food and dairy industries.
The AWS D18.1/D18 Specification for Welding of Austenitic Stainless Steel Tube and Pipe Systems in Sanitary (Hygienic) Applications states that to prevent the formation of crevices, which could trap product and lead to contamination, all welds must penetrate to the inside diameter (ID) of the tube.
The American Society of Mechanical Engineers had worked in parallel on two fronts about requirements for sanitary and pharmaceutical grade applications. In 1997 they produced ASME BPE standard, for bioprocessing applications, and in 2010 they followed it up with the addition of Chapter X, High Purity Piping, in ASME B31.3 Code for Process Piping.
The first standard of this kind, known commonly as ‘3-A Standards’ were introduced in the 1920s for milk pipe fittings. The designation of ‘3-A’ is derived from the cooperation of the three interest groups that cooperated to develop these standards – sanitary professionals, equipment manufacturers, and milk processors.
In this post, we discuss the requirements of a sanitary weld.
What Makes a Weld Sanitary?
A sanitary weld is fully penetrated, which means the weld accesses the ID of the tube and that it creates a 100% structural joint. This type of weld has a smooth surface where it will contact any product, ensuring easy and reliable cleaning with no crevices or oxidation that could possibly harbor bacteria and other contaminants.
To ensure a sanitary design, and be compliant with standards and regulations, all food-contact surfaces, including welds, should be:
- Free of cracks and crevices
- Durable and maintenance-free
When you are creating a sanitary weld with stainless steel tubing or pipe, the weld must be purged with a highly pure inert gas to remove the hazardous gases released and built up during the welding process, which can otherwise pool and cause discoloration, contamination, and oxidation.
The last step in creating a sanitary weld is a final inspection. A borescope is used to verify that the weld is fully penetrated and to identify any defects or contamination. Other NDT methods can also be employed. Weld defects include a lack of fusion to the base metal, root-pass cracking, and incomplete penetration.
Types of Welds
GTAW or TIG Welding
The AWS D18.1/D18 Specification for Welding of Austenitic Stainless Steel Tube and Pipe Systems in Sanitary (Hygienic) Applications establishes that all sanitary welds for austenitic stainless steel tube and pipe are to be done using the gas tungsten arc welding (GTAW) process.
The GTAW process, also known as tungsten inert gas (TIG) welding, is a clean, high-quality welding process, often used when a precision weld is required. GTAW outperforms other processes because it offers greater accuracy over the heat input to the weld area, producing a higher quality weld with a smaller heat-affected zone.
The GTAW process works by creating an arc between a non-consumable tungsten electrode and a metal component to be welded. An inert gas, typically argon or helium, is used to shield the tungsten electrode from oxidation or contamination during the process. GTAW is suitable for most metals, including stainless steel, and produces a high-quality weld with little or no finishing work required.
The food and dairy industries are under increasing pressure to ensure the safety of their products by adhering to higher quality standards than ever before. This mounting pressure has increased industry demand for clean, smooth product contact surfaces, which has, in turn, led to technological advancements for the fabrication of process piping systems.
One of the technological advancements to come from the growing needs of the food and dairy industries is orbital welding, now considered to be the standard for joining stainless steel tubes used for food processing. Orbital welding is an automated process that helps to minimize the risk of operator error in GTAW processes. The method uses a computer-controlled system to direct the arc current, feed, and speed, while allowing the orbital welding head to rotate around the assembly to produce consistent and repeatable weld profiles. At Highland Equipment, our team employs orbital welding to ensure consistent welds whenever possible.
Employ Sanitary Welding Capabilities
The sanitary welding process is thoroughly standardized and codified to ensure the safety of the public. Poor quality welds can create an environment in process piping systems that increase the risk of contamination in food and beverage processing facilities.
Welding is an art that involves a great deal of science and requires a great deal of knowledge and skill. At Highland Equipment, our team of engineers, welders, and technicians are experts in the sanitary welding process. All of our welding procedures as well as welding personnel conform to requirements of 3A, ASME BPE, AWS D18.1/D18 and ASME B31.3, and are qualified according to ASME Section IX Code and registered with T.S.S.A. To learn more about sanitary welding and the capabilities of Highland Equipment, contact us today.