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Ensuring the safety of instrumentation

24th June 2019


In critical applications such as those found in the oil and gas industry, there are many factors that can help deliver the successful installation of instrumentation tube and fittings systems. Here Deborah Pollard, Specifications Manager, North Sea, Instrumentation Products Division Europe, Parker Hannifin explains.

Safety, simplicity and effectiveness all feature highly, and with good reason. Any failure in this regard can increase the risk of outcomes such as leaks, which are likely to prove dangerous, costly and time-consuming to repair. With this in mind, finding the optimum balance between quality and cost is challenging but paramount if projects are to succeed.

One of the principal causes of leaks in an instrumentation tube and fittings system deployed in the oil and gas sector is poorly executed design. As a result, taking technical advice from the manufacturer at the front-end engineering design (FEED) stage will help promote best practice; a factor that especially applies to oil and gas projects where high pressures and high standards of safety are prevalent.

Consultation with the manufacturer also ensures that the most efficient and cost-effective design is chosen. Last-minute design changes frequently lead to further expense and delays. A comprehensive review of design and installation will deliver a safer system, and limit potential leaks and situations hazardous to installers and operations personnel.

Costs can also be reduced by taking advice. For instance, traditional designs for oil and gas applications feature long tubing runs with multiple fittings along the route. Current best practice, however, is to make use of direct mounting and close-coupled solutions wherever possible, thus saving on the cost of both equipment and installation.

Standardisation is another factor that needs to be considered at an early stage in the project as it enables the engineering team to work more closely with the selected supplier so that multiple design revisions can be avoided. Together with good design, standardisation can improve system lifetime and, where required, engender a safer, faster and easier maintenance procedure.

The advisable next step is leak-path reduction, which is of clear importance in oil and gas projects. Industry has largely reached the conclusion that the use of NPT threads is an outdated method for the connection of fittings to valves, manifolds and instruments due to over or under tightening, as well as stress corrosion cracking. In contrast, close-coupled solutions are far more effective as they remove potential leak paths. The direct mounting of transmitters and gauges to manifolds and monoflanges eliminates the necessity for NPT threads in most oil and gas applications.

Another tip is to use an integrated double block and bleed valve solution, along with a suitable monoflange, as this compacts multiple valves into a single integrated unit. The latest tube fittings, especially those offering two-ferrule compression, further reduce the potential for leaks.

After performing leak-path reduction measures, quality control, testing and certification should be applied. Consulting with the manufacturer before specifying the design, inspection and testing requirements, such as HCT traceability, PMI testing and 3.1 certification, will ensure the correct tests are incorporated into the supply chain, and that they are suitable and necessary for the application. Over or incorrect specification of the testing requirements can introduce unnecessary costs and delays to a project.

Next, assess the importance of the temperature and pressure rating. Again, consultation with the manufacturer regarding the tube and fittings necessary to meet the required design pressures and temperatures will save time and cost. Ideally, tubing system components should be of the same material and pressure rating. The tube must be the lowest-rated component, which thus determines the pressure rating of the system as a whole. Only use annealed, high-quality seamless tube.

For all applications in the oil and gas sector, derating will be applied to the material based on the system, process and ambient temperatures. Pressure and temperature ratings should be considered for tube and fittings, as well as valves and manifolds.

Another important step is selecting the correct material, which should be based on factors such as corrosion resistance, process fluid, temperature and cost. It is advisable to discuss this task with a highly experienced metallurgist at the manufacturer to ensure optimum choice. Material selection is particularly critical when hydrogen sulphide is present within the process – as it commonly is on oil and gas work sites – as this can exacerbate stress corrosion cracking.

When it comes to instrumentation tube and fittings systems, the mixing of materials can exacerbate corrosion or reduce operational lifetime. However, when mixing materials is the sole option, then attention must be given to their differing temperature and pressure ratings, and how these will likely impact system integrity. The material and positioning of tubing clamps should be carefully considered during the design phase to ensure that the clamps are corrosion resistant, cause no abrasion to the tube and are positioned such that water is free draining.

Fugitive emissions (FE) should also form part of a safe installation plan. When oil and gas applications require the use of FE valves, the customer should ensure that the requirement for TAMAP 2 is written into the specification at an early stage. In addition, as hydrogen sulphide can promote embrittlement, single-piece FE valves that avoid the use of welded connections will provide added system security.

Designs, where fugitive emissions are critical, need additional consideration with respect to the reduction of potential leak paths. Once again, integral fitting technology can be deployed to eliminate NPT connections, which are subject to stress corrosion cracking and embrittlement within the threads.

So, what of the correct handling and storage of tube prior to installation? After all, if the tube is stored externally or dragged around, it may compromise product integrity. The tube may pick up water or contamination, become corroded or scratched, or even lose its roundness. Tube should always be stored inside, on racks, to remove these potential issues.

To ensure optimum tube installation in oil and gas applications, a full process assessment must take place, covering cutting, deburring and bending. The tube should be cut with a hacksaw featuring a high-quality blade. In addition, a suitable vice will be required; it is recommended to use a specific tube cutter. Any visible burrs must then be removed inside and out using a tube deburring tool. Once complete, the cut should be wiped clean, making sure no swarf has entered the tube by purging with dry air. If required, some suppliers can provide pre-cut tube lengths.

Tube benders should be procured from the fittings manufacturer to ensure optimum bending quality and accuracy. The tube bender should be of 316SS material, as carbon-steel tube benders are likely to leave a residue of material on harder tube compounds, which could be a starting point for corrosion. A gap gauge is recommended to check correct installation of the tube into the fitting prior to system testing.

As a final point, the importance of appropriate training should not be underestimated. It is advised that site installers undertake at least basic training on the installation of tube and fittings from a company approved by the fittings supplier. Safety-first training for oil and gas professionals should cover both theoretical and hands-on procedures for the correct installation of fittings and all connection aspects, as well as best-practice tube bending procedures.

For all installations of instrumentation tube and fittings systems, using a trusted, experienced product supplier has significant value. Parker has worked in the oil and gas sector for over five decades and is able to supply a number of key technologies and services for this application; everything from the latest twin-ferrule compression tube fittings, double block and bleed manifolds, and monoflanges, through to FE valves and graded tubing. The company can also offer expert advice and applications support relating to material selection, the supply of pre-cut tube lengths and the provision of comprehensive training.

Ultimately, safety-first is the primary aim when installing instrumentation tube and fittings systems. The consequences of poorly installed systems can endanger the safety of personnel and the environment, while simultaneously increasing costs and project delays. In short, there can be no compromise in the quality of the selected products or services.

 

 







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