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

Department Name:
Hazardous Installations Directorate (Offshore Division)

Bulletin No:
HID 5-2010-2

Issue Date:
24 May 2010

Target Audience:
Offshore oil and gas production industry, Chemical processing and production

Key Issues:
This safety alert describes a serious incident caused by fitting an incorrect seal-ring in a proprietary clamp connector used in hydrocarbon service and outlines the action that should be taken by offshore installation operators.


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.


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:

And, as far as reasonably practicable;

Relevant legal documents:


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
L20 7HS

General note:

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