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Preventing bolted flange joint failure

Posted by Alan Hillier on Apr 6, 2016 11:12:09 AM


    

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Are you doing enough to prevent the failure of flange joints at your industrial plant or installation? In this post we cover some of the reasons why bolted flange joints can leak and take a look at what steps you can take to prevent this from happening.

The consequences of flange joint failure

The old saying that ‘prevention is better than cure’ certainly applies within the oil and gas industry. One incident illustrating this happened just a couple of years ago in North Sea when a four bolt hub joint on an offshore oil and gas platform passed the operator’s leak test, but failed three years later causing an explosion and a hefty $30 million in damage costs.  Following an investigation, the cause of the failure was found to be galvanic corrosion, due to the incorrect use of a carbon steel seal ring between the two stainless steel hubs when a stainless steel ring should have been used.

Whilst the above may represent an extreme example, some operators claim that that even when just one leaking flange at a major plant needs repair work the manpower and material costs can sometimes amount to a six figure number.

Reasons why bolted flange joints fail

Corrosion is just one of the reasons why pipeline failures occur. One report into the causes of oil and gas pipeline failures in Nigeria’s Delta Area also identified mechanical failure, operational error, 3rd party activity and natural hazards as other key causes.

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Download the Complete Guide to Managing Flanges

 

Gaskets for bolted flange joints

Choosing the correct joint gasket type is vital, and these continue to evolve with new designs materials resulting in more reliable seals.

However, according to Garlock Sealing Technologies, choosing the correct gasket is just half of the battle, as the installation process is equally as important as the correct specification of the gasket itself. A study carried out by Garlock examined returned gaskets from leaked flanges and found that 82% of these showed signs of problems with compression and 14%  attributable to the wrong product being chosen.

Improper compression can arise from incorrect installation procedures, warped or misaligned flanges, the wrong flange finish and flanges that are too thin. An additional preventative measure is to use a flange facing machine on-site, to eliminate any flange distortion, pits, dents or scratches and to create the optimum surface finish.

Results from a study featured 0n pump-zone.com in May 2008 highlighted the importance of training and management of maintenance personnel.

  • From 100 failed gaskets, 68 were attributed to under compression, and 14 to over compression
  • 58% of respondents who outsourced maintenance to external contractors had bolted joints that leaked.
  • 29% of respondents who did not outsource maintenance had bolted joints that leaked.

The above figures should not be interpreted as outsourcing being the root cause of the problem, what they do demonstrate is that regardless of whoever carries out the job, training and procedures need managing properly. This may include installation guidelines, bolt tightening sequences and torque tables being issued.

 

Joint Integrity Programs

With the consequences of flange joint failure being so high, many leading industrial plants and facilities operate a ‘Joint Integrity Program’ (JIP), which standardizes their management systems and processes to help meet or exceed the requirements of quality, environmental and health and safety legislation.

The essentials of a Joint Integrity Program

According to Neil Ferguson, in the March/April issue of Inspectioneering Journal, there are three key elements to a JIP:

  • Quality products fit for a specific purpose and correctly and accurately designed and calibrated.
  • Well trained, competent operators and technicians.
  • An effective management control process, including the collection and storage of vital information.

The assembly of bolted joints does not solely rely on the physical tools required to tighten the joint. Software for bolt load calculation and flange integrity system management is now readily available.

The 9 areas of JIP assurance management

The article then also goes into more detail explaining the 9 areas of JIPs from a management perspective which we have summarised below;

  • Ownership – Assign a JIP “owner” to become an expert and to rollout the necessary processes and procedures.
  • Best industry practices and procedures – Benchmark compared to industry peers and associations.
  • Assess criticality, set rules - Categorize flanges as low, medium or high risk.
  • Training and competency management – Ensure technicians are sufficiently trained, experienced and qualified.
  • Joint identification and tagging – noting the level of risk, the status, and relevant operator.
  • Comprehensive data tracking – ASME now stipulates 3 levels of data tracking; short form, medium form and long form. These should cover traceability of the technician who carried out the work, materials and the procedures followed.
  • Inspection and compliance – including checking for flange damage. This cannot be retroactive and should therefore be ingrained into the process at the assembly stage.
  • Leak management – despite the introduction of a robust JIP, leaks can still occur and managing the investigation process correctly will help to prevent re-occurrence.
  • KPI, analysis and improvement – analysis of key performance indicators and formal reviews of the management system. The results should fuel ideas for continuous improvement. Other spin off benefits include contractor performance and visibility of the return on investment gained from the program.

Find out more about flange machining by downloading our free document The Complete Guide To Managing Flanges

 Download the Complete Guide to Managing Flanges

If you need any advice for a machining project please click here to email us. 

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Disclaimer

This article is intended to provide brief overview only. Readers must ensure products and procedures are suitable for their specific application by referring to the relevant manufacturer or service provider and should refer to locally applicable compliance requirements.

Sources:   https://inspectioneering.com   http://www.iaeng.org  http://www.pumpsandsystems.com

Topics: flange facing, flanges

   

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