Next in our series of Troubleshooting Leaks in tube fitting and adapter connections is leaks that are coming from O-Ring Face Seal (ORFS) braze sleeve connections. In this post, we investigate the probable causes of these types of leaks and how to avoid them.
In our first post, Troubleshooting Fluid System Connection Leaks, we identified the following as the probable causes for a leak coming from a ORFS brazed sleeve joint:
How do you figure out which of the above is the root cause? With braze sleeve joints, it is extremely hard to figure out what the root cause is, especially if you were not the one who performed the braze initially. A new tube connection will need to be created at this point, and, if you chose to braze it, it is important to avoid the issues listed above.
Alternatively, mechanically flanging tube ends is quicker than brazing and creates a more consistent and reliable high-quality, leak-free tube end connection for ORFS fittings.
Note: Parker offers several machines for flanging tube ends – Parflange Equipment Comparison Guide. Additionally, these machines are also available for rent from your local Parker Distributor for short-term projects.
Below we have detailed each of the ORFS brazed sleeve joint probable leak issues and discuss how to avoid these when you remake the tube connection.
In addition, tube brazing can be done with clearance or interference joints, however, for this blog post we will only consider clearance joints designed for “silver” brazing and for single or low volume production.
The wrong braze ring can cause a bad braze, leading to a leak. There are two errors that can be made when selecting braze rings, the wrong material or poor quality.
When brazing a sleeve to a tube, you will want to choose a braze material that is designed for the tube material you are using. Steel tube can use either a braze material designed for steel or stainless steel. Stainless tube, on the other hand, requires a braze material designed for stainless steel. Any materials, whether for steel or stainless steel, need to be selected for clearance joints.
Care should be taken when selecting a braze ring. If a preformed ring is selected, the ring will provide the correct amount of braze material without over or underfill. There are significant disadvantages to not using a preformed ring, the primary one being that the amount of braze material and the precise application of heat become more critical, requiring more expertise to make a quality joint. Preformed rings provide the exact amount of braze material required for a clearance fit joint. In the case of those used for high-pressure hydraulics, they fit inside the joint helping visualize adequate material flow through the clearance gap, ensuring the quality of the finished braze connection. It is best to contact the manufacturer of your braze fitting to see which braze ring they recommend.
If an incorrect, low-quality or inappropriate material braze ring is selected, a leak path may be formed.
Note: Parker’s SBR and SBR-SS braze rings have been carefully selected and sized to match the design capabilities of SAE J1453 face seal fittings. SBR-SS also has a small percentage of nickel which is essential for preventing interface corrosion. Interface corrosion can cause separation of stainless-steel brazed joints when exposed to corrosive media, creating leaks.
A complete 360-degree fillet at the smaller end of the sleeve (see figure 2) is a good sign of full braze flow and a proper braze. Figure 1 shows a lack of a braze fillet, which may be caused by inadequate heat on the joint. If there isn’t a 360-degree fillet, a leak will eventually occur at this joint. When brazing, the key is to apply just enough heat to melt the braze ring completely and draw the braze material through the joint to fully wet all the surfaces, resulting in a smooth 360 degree fillet. When heating, a dull red color of the tube and sleeve is a good sign of an adequate brazing temperature. Also when using preformed braze rings, the sleeve will drop suddenly when the correct temperature is reached to melt the ring.
Figure 1. No braze fillet indicates a poor braze joint.
Figure 2. 360 degree braze fillet is a good sign of complete braze flow.
If too much heat was used during brazing, you may see bubbling in the braze fillet, scorching of the sleeve or tube, or a poorly formed fillet with excess braze material on the tube surface outside the sleeve. All are caused by too much heat which results in poor joint quality and eventually leads to leaks. Figure 3 shows an example of what a braze fillet could look like if too much heat is used.
As mentioned above, when applying heat for brazing, a dull red color of the tube and sleeve is a good sign of an adequate brazing temperature.
Figure 3. Too much heat
Properly preparing the tube and sleeve before brazing is important for ensuring a proper braze connection. If the braze area is not cleaned properly before the flux is applied, there may be impurities trapped in the joint area that will cause incomplete or inadequate flow of the braze material, which could eventually lead to a leaking connection. When preparing tubes for brazing, it is important to clean the tube thoroughly before brazing by sanding with aluminum-free 100 grit emery paper to remove all dirt, rust, burrs, paint, etc. and then washing with a petroleum-free solvent. The sleeve should also be inspected for rust, sanded as needed and washed in a solvent to remove any debris or oils before using.
Braze sleeves are designed to achieve a joint clearance of 0.003”- 0.008” when using typical hydraulic tubing. Proper tube preparation is critical when brazing, measuring the tube OD and sleeve ID will ensure specified clearances. The sleeve should easily slip on and off the tube end without binding. See our post and video - Tube End Preparation Best Practices for Leak-Free Hydraulic Tube Fitting Connection – for details on proper tube end preparation.
Tube material which is different from that of the braze sleeve can affect the joint clearance at brazing temperature due to the differences in their thermal expansion rates. While brazing is an excellent way to join dissimilar materials, typical braze sleeves are designed for same material joining. Therefore for maximum joint strength always use carbon steel sleeves with carbon steel tube and stainless-steel sleeves with stainless steel tube.
Figure 4 shows what good and bad joint clearance looks like. It will not be easy to spot this difference, so it is best to get out calipers to check the OD of the tube and ID of the braze ring. As stated before the difference should lie between 0.003” and 0.008”, any more or less may result in a bad braze.
Figure 4. Good vs. bad joint clearance
For step-by-step instructions for brazing ORFS sleeves, please see the Assembly and Installation section of the Tube Fittings, Adapters, and Equipment Catalog 4300.
If the root cause of your leak is the braze sleeve joint, it is best to have the connection remade following the tips in the article. That said, if you are starting over, it may be worthwhile to consider mechanically flanging the tube instead as previously noted.
Leaks cost a lot of downtime, and finding the root cause is not always obvious. But with the details included in this post, you should be able to avoid the same braze sleeve leak issue from happening again.
If you are unsure about a leak cause or what you should do about a leak once you find one, feel free to reach out to our techConnect engineering team. We’ve often seen the issue before and can get you pointed in the right direction. We are here to help.
The next post in our troubleshooting leaks series is: Troubleshooting Leaks: Understanding a Circumferential Tube Crack.
Have you had any tube connection leaks where the source was not what you anticipated? Share your story below with what happened and how you determined what was really going on.
If you have any questions or comments, please post them, and we will respond if warranted. To talk to our techConnect engineer team directly, they can be reached at Parker Tube Fittings Division, 614.279.7070. See Parker Tube Fittings Division's full line of tube fittings and hose adapters.
Did you find this post helpful? Subscribe to TFD techConnect posts by email. TFD techConnect is a technically-focused monthly blog written by engineers for engineers specifically around motion and control engineering challenges.
Do you want to receive new product announcements and technology updates from Parker Tube Fittings Division? Subscribe today and stay informed.
Article contributed by Emily Alexander, senior design engineer, Parker Tube Fittings Division
and Ted Amlng, senior project engineer, Parker Tube Fittings Division
Additional related content about hydraulic tube, hose and port fitting connections: