Foreseeing the unforeseen... tough operating conditions trigger second opinion on integrity assessment

When the retrieval of oil and gas combines bleak Arctic temperatures, with extraordinarily high fluid pressures and velocities, and oil containing high concentrations of hydrogen sulphide any operator knows its work will command a particularly rigorous schedule of preliminary design.

So when one of TWI's oil and gas related Industrial Members, operating in the Kazakh sector of the Caspian Sea completed its front end engineering design (FEED) stage of a key project it turned to TWI for confirmation of its integrity assessment. The scope of the project embraced all onshore and offshore refining equipment namely topsides, refinery and pipeline installation.

The work had three objectives:

• To carry out an integrity assessment of the field development, based on FEED information, with respect to all damage mechanisms
  
  
• To produce a criticality ranking of the process and production units/areas by undertaking a risk-based assessment of pressure equipment
  
  
• To identify any pressure system integrity issues that may have been missed during the FEED.

The integrity assessment was conducted at a global level, between the conceptual and detailed design stages. It was conducted in four phases; familiarisation, initial screening, criticality ranking; and design and fabrication hazards analysis (DAFHA).

The so-called DAFHA was conducted interactively with TWI engineers and its client's project personnel, by evaluating the questions and concerns identified by TWI during the previous stages.

Six conclusions were reached relating to vibration fatigue, corrosion resistance, brittle fracture, the use of flanged bolted joints and internal pipe erosion.

As a direct result of these TWI made 10 detailed recommendations to its client on a wide range of issues related to containment of hydrocarbons while operating in such hostile conditions, namely; fracture control, vibration fatigue, corrosion fatigue, internal erosion, flange connection integrity, dissimilar metal cracking, ice damage, flare stack integrity, adoption of a risk based inspection system and a quality management system.