Small Bore Fitting (or small bore connection) failures are amongst the highest causes of hydrocarbon releases in the oil and gas industry.   

Oil and gas facilities have hundreds of SBFs, including instrumentation tubes, measurement points and thermowells. Failure occurs when flow or structural excitation causes an SBF to vibrate out of sync with the main pipe.   

The risk to safety is well understood: an ignition source near a gas leak can cause a major accident event.  

Operators have told SVT that an SBF failure can cost anywhere between A$1 million and AU$10 million due to lost production and repairs.   

The Offshore Petroleum and Greenhouse Gas Storage Act 2006 regulates safety, environmental protection and well integrity for petroleum facilities in Australian waters.  

The Act requires that operators of petroleum facilities reduce risks to health, safety and the environment to a level that is as-low-as-reasonably practicable (ALARP). ALARP is the point where the cost (in terms of time, money and effort) of further risk treatment is grossly disproportionate to the reduction in risk that would be achieved.  

The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) is charged with regulating the Act. Due to an overall increase in the number of reportable hydrocarbon release incidents and the discovery of SBF failures by NOPSEMA inspectors, the enforcement of ALARP requirements around SBFs has increased.

Why SBFs fail

Design

Operators expect vibration vulnerability to have been designed out of their SBFs.  However, design studies only consider a limited operating envelope. Whenever process rate or conditions change, there is the possibility of newly excited resonances that cause SBFs to fail. Additionally, changes in personnel and responsible entities between project phases may result in the recommendations of SBF design studies not being captured in final designs.

Installation

Installation can introduce additional vulnerabilities.  Small bore piping runs are often not documented in detail, which means that the installer has significant latitude to decide the as-built condition. SBF installers may not have management processes in place to ensure that SBF installations are fit for purpose with regard to vibration vulnerability.

Process change

Acoustic and flow-induced SBF vibration is strongly dependant on process conditions.  Small changes in gas composition, pressure or flow velocity can move the peak frequencies of these sources too close to an SBF resonance.  The resulting step change in vibration level significantly increases the risk of failure.

What you should do about your SBF risk

SBF Risk Register

Maintaining a register of your SBFs is the best way to assess and manage your risk. Identify all SBFs and where they are and then rate them using your risk matrix. By documenting the risk of failure thoroughly, you can go some way to demonstrating the management of risk to ALARP.

Visual Assessment

It is possible to identify some vibration issues by visual inspection.  SBFs that are visibly moving are almost certainly vibrating in excess of the acceptable level.  

Vibration measurement

Most SBF vibration issues can only be identified by measuring the vibration level.  Including vibration surveys on high-risk SBFs in your condition monitoring program should be low cost relative to the reduction in risk achieved.  If that is the case on your facility, it should form part of your ALARP position.

Bracing

Often the first action taken with a vibrating small bore fitting is to brace it. This works in the majority of cases, provided it is done in the right way. Planes of vibration need to be considered carefully by a specialist if the fix is to work and the element to which you brace the SBF needs to be selected properly, otherwise the risk of fatigue can be increased.  

Contact our integrity team to find out more.