This notice is to highlight a recurring problem with the fasteners holding together either side of Barton Differential Pressure Gauge Indicators (Model 227). Information on other, similar, failures to this item of equipment can be found on the Step Change in Safety Incident Alerts Database (previously known as SADIE - Safety Alert Database and Information Exchange).
The investigation of a serious gas release at an onshore gas reception terminal showed that the release had occurred following the fracture of the fasteners holding together the two sides of the differential pressure gauge pressure input blocks. On the reverse of the gauge, two blocks, incorporate threaded fittings to connect to the two pressure lines. These blocks are located on either side of a central block; the sandwich being held together by four socket headed fasteners. The fasteners pass through countersunk holes in one block and are threaded into the other block.
The identified mode of failure was due to brittle mode fracture - in particular there was evidence of hydrogen induced cracking on the stainless steel fasteners. A metallurgical examination of the failed fasteners shows they were manufactured from 15Cr/5Ni stainless steel - a grade unsuitable for use in a marine or coastal environment.
In addition to the above, discussions with the manufacturers have identified earlier failures of this type of fasteners, with the failures being attributed to the presence of H2S.
HSE's experience is that these differential pressure gauges are in use in the offshore oil and gas industries and at the onshore reception terminals. It is also likely that these gauges are used in other processing environments.
Dutyholders should identify where this type of differential pressure gauge is in service, inspect the fasteners with the aim of identifying any signs of corrosion, and take action that ensures the fasteners remain serviceable. Dutyholders should also check with the supplier that the fasteners are made from a material that is suitable for the environment in which the device is located.
As an indication an appropriate grade of steel for this type of fastener being used in a marine or coastal environment and operating at between 500psi and 3000psi is;
This is a precipitation hardening austenitic stainless steel material with a high Ni content that provides high temperature resistance. It is a corrosion resistant material with increased strength compared to 316 stainless steel.
Where gauges are being operated in a marine or coastal environment in excess of 3000psi specific advice from the supplier or manufacturer on the appropriate type of fastener should be sought.
Where gauges are of a similar design but not manufactured by Barton, it is recommended that the same checks should be undertaken.
The relevant legal requirements are:
Any queries relating to this information sheet should be addressed to:
Health and Safety Executive
Hazardous Installations Directorate
Lord Cullen House
Aberdeen AB25 3UB
This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice