The Use of 316 SS Socket Weld Fittings in Tube Welding

Tube fittings are critical when creating complex sections of tubing systems for fluid transfer applications. Many fittings are threaded with self-lock ability, while some require welding onto the tube for a permanent fix. Perfectly welded fittings are leak-free and provide excellent structural strength, an advantage when processing highly pressurized fluids. Corrosion resistance is an additional advantage of stainless steel (SS) fittings.

When To Use a Socket Weld Fitting?

When welding a fitting onto a tube, there are two techniques you can use—butt welds and socket welds. Butt welds require two pieces of tubes to be joined end-to-end. In such cases, the weld profile is flat to maintain the surface level with the workpiece avoiding any concavity or convexity of the weld puddle.

Socket welds are also available for tubing or small-diameter pipe transitions within a fluid system.  The tube inserts into the unthreaded fitting (such as t-joints and elbow joints), where it is directly welded to create a stable joint. The advantage of socket weld fittings is that you can connect tubes of different sizes to a configuration.

The socket weld fittings are well defined in the industry codes such as the ASME B16.11– Forged Fittings, Socket-Welding, and Threaded, which covers material and dimensional requirements, pressure-temperature rating, tolerances, and other design parameters required for their production. When all other connection options seem infeasible, manufacturers resort to the use of socket weld fitting.

Among the metals covered in the ASME standard, one widely used in a fluid processing system is 316 stainless steel. The advantage of opting for 316 SS socket weld fittings is that due to its corrosion-resistant ability, it can suitably be used for processes with chemically reactive fluids. With stainless steel tubes being used in many industrial applications for sanitary purposes, the 316 SS socket weld fittings offer material compatibility.

As the welding process is involved to ensure the connection, the operators should be aware of the many challenges of using socket weld fittings for the tubing system. Without proper welding technique:

1. The welds can be prone to cracking and embrittlement.
2. Poor weld quality or change in metallurgical properties at the heat-affected zone (HAZ), due to excess heat, creates a greater risk of leaks and failure due to contamination or oxidation.
3. The irregular surface finish creates multiple entrapment areas where process fluid can collect and cause contamination.
4. Gaps left for thermal expansion can be the source of corrosion due to fluid buildup. 
5. Due to this, socket welds are not preferred for high purity applications.

Installation with quality 316 SS socket weld fittings and proper welding technique is important for criteria during fluid process system assembly. 

Installing 316 SS Socket Weld Fittings: Things to Note

For socket weld fittings to be installed as per the standard, various structural and weld details are essential to note:

1. The tube must be inserted fully into the socket and backed out by 1/16th inch where the welding can be commenced. The recessed length allows for thermal expansion. 
2. Tack weld, when required, should be kept to a minimum. Excessive tack can interfere with the final weld quality.
3. TIG or MIG is the best option for welding 316 SS socket weld fittings to a tube. These processes will require inert shielding and purging gas for ultra-purity results. 
4. The socket weld can be destructively tested by cutting the weld open, examining the weld, and recreating it if it matches the desired quality. Non-destructive methods of testing may involve penetrant testing or magnetic particle testing methods. 

Swagelok’s Socket Weld Fittings and Their Installation

Swagelok provides socket weld fittings with a wide range of dimensions and temperature-pressure ratings to suit your fluid system requirement. Our 316 SS socket weld fittings comply with dimensional, material, and other requirements covered under ASME B16.11. These fittings can be reliably welded with our M200 Orbital Welding System, which offers excellent heat control as required for stainless steel.

With our specialized orbital welding system that offers precision and control and high-quality 316 ss socket weld fittings, it is possible to minimize the fluid system failure rates at your facilities in Northern California. 

To find out more about how Swagelok Northern California can help you in the installation of 316 ss socket weld fittings with its high-quality components and welding system,  contact our team today by calling 510-933-6200.

About Jason Burns | Technical Services Manager

Known to customers and Swagelok Northern California associates as the Swagelok Answer Man. Jason spends his work days answering customers' technical questions about Swagelok products and tools and training customers how to install and use them.