Fluid system leaks do not occur without cause. Paths have origin points, and failures have causes. What may seem like a minor oversight early in the process of engineering and installing a gas-handling system can cause major future headaches in the form of hazardous leaks and production interruptions.
The right foundational practices will help ensure your fluid system’s tubing and fittings are up to the task of safe and efficient transport and containment.
Leak prevention actually begins with careful system design and tubing handling. For example, tubing placed where it may be used as a footrest or a handrail – purposefully or not – will be more susceptible to damage. During system assembly, avoid dragging or dropping tubing. Bumping and scraping can cause scratches, gouges, dents, and nicks, all of which can interfere with proper seals, especially in gas-handling applications.
Other layout considerations include stacking tubing vertically when running multiple lines together in order to prevent dirt, corrosives, and other contaminants from collecting between the tubes; and providing proper support to limit the effects of vibration.
The frequency of supports should be determined by fluid density and tube size, and all tubes should be clamped on both sides of a bend as close to the bend radius as possible. Supports are also especially important around elbows, tees, and heavy in-line objects like valves – the tubing shouldn’t bear the weight of these components.
Focusing on fittings
Tubing connections are equally important in preventing leaks, and some of the most common causes of fitting failure can happen even before the first fitting is tightened.
When it comes to making up tube fitting assemblies, proper tube preparation is critical, starting with tube cutting. When using a tube cutter, always use a sharp wheel to minimise burring and work hardening. If you’re cutting with a hacksaw, use a blade with at least 24 teeth per inch and use a sawing guide to ensure a square cut and keep the tube from flattening.
In either case, deburring the tube is the next step, since tube cutters push burrs to the inside diameter (ID) of the tube, and hacksaws burr both the ID and outside diameter (OD). Removing these burrs helps ensure proper fitting and a clean, leak-free system. Burrs left on the OD can keep the tube from being fully inserted through a fitting’s nut and ferrules or against the shoulder of the fitting body. ID burrs can also break off and scratch valve seats or soft seals like O-rings, or they can lodge in holes or vents.
Consider the components
Remember: Not all fitting components are the same, even if they seem similar or are marketed as compatible. Missteps such as combining metric components with fractional components, using the wrong-sized fitting for the tubing, and intermixing or interchanging parts from different manufacturers can all lead to leaks, which could have been avoided.
© Swagelok
Intermix occurs when fitting components like nuts, ferrules, and bodies from two or more manufacturers are assembled into a complete fitting. Interchange is when a tube fitting from one manufacturer that has been installed on a piece of tubing is taken apart and then reassembled into a tube fitting body from another manufacturer.
The risks of intermix and interchange are due to the fact that each results in an untested fitting design. Manufacturers have differing standards and procedures, and their products may vary significantly in aspects such as material composition, electroplating, and surface hardening. When components haven’t been engineered to work together, intermixing and interchanging can lead to an increased risk of compromised performance and fatigue failure, and incompatible or inconsistent sealing due to differences in geometry, tolerances, and material properties.
Keys to effective installation
The installation process is full of potential pitfalls that can introduce leak paths into a system, and the best way to avoid them is through a comprehensive tube fitting installation training program, preferably from the manufacturer. But even before you bring in training experts, you can spread awareness of several basic best installation practices.
For example, one universal tip is to inspect any length of tubing that’s going into a fitting for proper roundness: out-of-round tubing can scratch the fitting’s ID, endangering the seal’s effectiveness. Installers should also avoid springing tubing into position and instead utilise additional elbow fittings. This will allow for expansion, prevent side-load stress, and ease maintenance.
Another point to remember is that when installing tube fittings located near bends, a minimum length of straight tube is necessary for the tube to be bottomed in the fitting. The deformed section of tubing at the bend should not enter the fitting. And when connecting a section of bent tubing, be certain the tube is in correct alignment before doing any tightening.
Use added elbow fittings instead of springing tubing into position | © Swagelok
Other leak-prevention installation tips include:
- Avoid disassembling tube fittings before installation, which can introduce contaminants and the possibility of error in reassembly (such as an inverted ferrule).
- Watch for under-tightening and improper tube bottoming, two of the most commonly found leak causes.
- Before tightening the fitting nut, make sure the tubing is resting firmly on the shoulder of the tube fitting body.
- Never turn the fitting body: Hold the fitting body and turn the nut.
- Use a gap inspection gauge to ensure sufficient pull-up.
- When marking up tubing to gauge bottoming, use pens with a low-chloride ink on stainless steel components — some permanent inks contain chlorides, which can cause stress corrosion cracking in austenitic stainless steel.
In all aspects of tube preparation and fitting installation, manufacturer training is a foundational best practice, and will equip technicians with the most applicable insights for their particular application. Pairing the right knowledge with the right tools and experience sets up your fluid system for safe and efficient operation.
