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Design to Avoid Danger: 8 Steps for Building Safer Fluid Systems

safe fluid system design

Industry is inherently complex and only becoming more complicated. Today there are deeper wells, new drilling techniques, and more sub-sea equipment and controls, together with higher temperatures and pressures in more corrosive environments. There also are increased health, safety, and environmental concerns as well as more demanding standards, regulations, and other forms of liability. Where seizing opportunity means assuming more risk, how can operators minimize safety concerns for rig, refinery, and plant personnel? When it comes to the reliable operation of fluid systems, there is a real answer: Safe working conditions start with careful design considerations.

As a provider of fluid system components and training, Swagelok understands the pain customers feel when downtime, lost revenue and legal responsibilities add up due to inattention to details. Strict adherence to design standards and documented procedures can go a long way towards preventing costly errors.

Before you replace parts or put a completely new system in place, brush up on these best practices.

1. Never mix components from different manufacturers.

Leak-tight seals that will withstand high pressure, vibration, vacuum, and temperature changes depend on exacting tolerances, meticulous quality control, and time-tested design principles. Though components from different suppliers may look alike, there is no assurance they are manufactured to the same rigorous standards, meaning they may not perform properly when used with other manufacturers’ components.

2. Choose your alloys carefully.

Material chemistry is a major consideration in most environments. Component compatibility, if not controlled properly, can result in serious issues, including chloride stress corrosion cracking (crack formation in pipework and tubing in a chloride-rich environment). Numerous alloys have been used or have presented themselves as candidates for use in installations that require resistance to seawater corrosion. The most frequently used alloys have been the 300-series austenitic stainless steels , mainly 316 and in some cases 317. Alloys with at least 6% molybdenum, the so-called “6-moly ” alloys, have performed well in offshore systems. Typical 6-moly alloys include 254SMO, AL6XN and 25-6Mo.

More recently, alloys with slightly more than 6% molybdenum have been introduced: 654SMO, AL6XN Plus, 27-7Mo and 31. The published properties of these alloys suggest that they would perform well in chloride environments. Meanwhile, nickel alloys such as 825, 625 and C-276 are more frequently used for their performance in sour gas applications.

3. Minimize opportunities for mistakes.

Consider how better labeling and safety-minded system design can reduce opportunities for mistakes to happen. For instance, be sure to place tags on your equipment to indicate what an operator is viewing. Try to color-code handles, tubing, and pipe to make it clear at a glance what types of fluids or gases are flowing through them, even in processes where hydrocarbons are not present. Also take care to orient components in a way that avoids accidental contact with moving objects or people passing by.

4. Only use ideal materials for the job.

It may be tempting to make a price-based decision, but where the stakes are highest it is rarely worth the risk, and you should only rely on products with a proven reputation. The market has become saturated with counterfeit and substandard inventory that can harm your operation. Only purchase through trusted partners and authorized channels.

Also important is knowing the difference between similar-sounding parts and being precise when deciding which to use. For instance, a safety valve (which opens fully at a set pressure) is not the same as a relief valve (which opens gradually as pressure increases). While these terms might sound similar, always be sure to understand exactly which part to use.

5. Remove complexity wherever you can.

Reduce system complexity where possible to minimize potential complications, and never stop looking for opportunities to make improvements. Simplifying systems also helps down the line, as it will be easier to troubleshoot problems when there are not as many components to analyze. Consult an expert who can make recommendations for making fewer connections. Ultimately, this reduces the number of parts that could potentially fail.

6. Always follow manufacturer instructions carefully.

Failure to follow documented assembly and disassembly procedures might seem like a minor mistake but it can lead to major consequences. Common errors include:

  • Under-tightening fittings, creating opportunities for leaks and blowouts
  • Overtightening fittings, limiting the potential number of remakes
  • Not ensuring tubing rests firmly on the shoulder of the tube fitting body before tightening
  • Not following proper protocols for tube insertion depth or not “bottoming out” the tube
  • Failing to properly check tubes for ovality, defects or scratches that can compromise a seal

Swagelok’s Tube Fitter’s Manual contains the most comprehensive tube fitting guidelines you will find.

7. Factor for vibration and motion in your designs.

When assembling a de-energized system (something you must always do, because working on a pressurized system is dangerous), it can be easy to forget about the effects of machine vibration. Be sure you have the proper supports in place to ensure tubing and fittings will not be unduly fatigued or dislodged during high-pressure usage. The constant strain placed on a system by vibration can also gradually wear away at connection points, so specifying proper materials from the start and allowing for a proper range of motion are important.

In some circumstances, switching to hose can eliminate certain vibration concerns. Keep in mind, however, that hoses can wear quickly and will need to be replaced over time. Some elastomers also have a limited shelf life—know the age of the hose you will be installing. 

8. Account for material hardness when making tubing systems.

It is important that component materials be compatible with each other and have the appropriate hardness to stay connected. Metal tubing materials should be softer than fitting materials to allow the fitting to grip and collet the tube well.

When fluid systems perform flawlessly day after day, it is easy to forget the dangers even one improperly installed component can present. Keeping best practices in mind will keep your operation on guard. These steps sound simple but are often overlooked. There are many ways to design for safety, and with extra care, you can avoid unexpected issues.