Hydrocarbon leak and fire caused by incorrect seal material used in the assembly of a pipe work clamp connector

Health and Safety Executive - Safety alert

Introduction:

This safety alert describes a serious incident caused by fitting a seal-ring of incorrect material in a proprietary clamp connector used in hydrocarbon service. It outlines the action that should be taken by installation operators.

Background:

The incident occurred on an offshore production platform and involved the failure of a pipework joint resulting in the escape of flammable hydrocarbons and a fire. Gas detection equipment triggered a prompt shut-down and depressurization of the process plant, eliminating the source of fuel. The installation was not normally attended, and no persons were onboard at the time of the incident.

The source of the hydrocarbon leak was a proprietary clamp-type permanent coupling, connecting flowline pipework to a well-head. The coupling has four main parts; hubs, seal-ring, clamps and bolting. All parts are manufactured from metal. When assembled, the seal-ring fits internally between the hubs, which are held together by the two external clamp segments secured with bolting. The seal is metal to metal. During service, the seal is pressure energised.

The clamp and flow line were made from stainless steel. The stainless steel clamp connector had been assembled incorrectly with a carbon steel seal-ring. A stainless steel seal-ring should have been used. The carbon-steel seal-ring deteriorated due to corrosion and the pressure containment integrity of the joint was lost. The reasons underlying the fitting of the carbon steel seal-ring are the subject of a continuing investigation.

Action required:

HSE considers that the emerging findings of this investigation are of sufficient significance to communicate to other installation operators by way of this safety alert. Clamp connectors are in widespread use on offshore installations. They are normally reliable and effective, but this depends on the use of correct parts in accordance with the manufacturer's specification and assembly instructions. Therefore duty holders are advised to:

• Satisfy themselves that their management systems applicable to assembly of pipe work connectors are robust, particularly in respect of ensuring correct seal-rings are fitted. Seal-ring identification markings should be clear and indelible. Hard stamping is ultimately the most definitive method of verifying the material grade and traceability
• Satisfy themselves that their management system provides sufficient information. Before assembling these connectors, the person responsible for making these joints should refer to the piping specifications which will detail the material grade of the different components. In addition, they may need to refer to the manufacturer's product data which will interpret any abbreviations of material grade that may be stamped on the components.

And, as far as reasonably practicable;

• If doubt exists, or as verification to provide confidence, compare assembly records with seal-rings as actually fitted. This may occur on a sample basis and when opportune.

Relevant legal documents:

• Health and Safety at Work etc Act 1974
• Provision and use of Work Equipment Regulations 1998
• Management of Health and Safety at Work Regulations 1999
• Offshore Installations (Safety Case) Regulations 2005

References:

• Section 2.3.2.4 "Specific Seal Rings" - Guidelines for the management of the integrity of bolted joints for pressurised systems. 2nd edition. Energy Institute ISBN 978 0 85293 461 6
• Section 2.4.1. "Identification of Joint and selection of correct component" - Guidelines for the management of the integrity of bolted joints for pressurised systems. 2nd edition. Energy Institute ISBN 978 0 85293 461 6

Further information:

Any queries relating to this Alert should be addressed to:

Team Leader - OSD3.4 Mechanical Systems
Health and Safety Executive
Hazardous Installations Directorate
Offshore Division
5N.2 Redgrave Court
Merton Road
Bootle
Merseyside
L20 7HS

General note:

Please pass this information to a colleague who may have this product/ equipment or operate this type of system/process.