The papers range from a review of ‘mega-furrows’ in the deepwater Gulf of Mexico (essentially, similar to sand dunes, and up to 8 m high and over 100 m in length), to the threat posed by lightning strikes on pipelines, and the affect of February’s Chilean earthquake on the gas pipeline infrastructure in the worst hit areas. The difficulties created for pipeline operators by landslips are also examined, along with a review of the ways pipelines can be protected during subsea operations.

The lightning threat to pipelines and coatings

by Joseph Pikas, Schiff Associates, Sugar Land, TX, USA, and William Shoaf, Williams Gas Pipeline – Transco, Princeton, NJ, USA.

The US Pipeline Hazardous Material Safety Administration (PHMSA) regulators require that pipelines with external coatings for which there is a threat of weather-related conditions, such as lightning, should be assessed by external corrosion direct assessment, in-line inspection, hydrostatic testing, or other methods to ensure the integrity of the pipeline system. Managing the threat posed by lightning requires sufficient historical data on the number or density of lightning strikes, condition of coating, distance from AC tower grounding and pipe investigations. Therefore, a need is required for an auditable and systematic process by which the threat of lightning can be assessed adequately. This paper describes an approach to monitor, integrate outside data, and analyse this information in order to identify whether outside force damage by lightning is a threat for a given pipeline segment.

Design of deepwater HP/HT pipe-in-pipe flowlines crossing mega-furrows in the Gulf of Mexico by Dr Tianxi (Andy) Tang, Jacob Chacko, Mengjuan (Jane) Zhou, and Gabriel O Omonoji, Technip USA, Houston, TX, USA, and Uwa Eigbe, representative for Petrobras America, INTECSEA, Houston, TX, USA.

Two 21 km long pipe-in-pipe (PIP) high-temperature/high-pressure flowlines were recently designed for the Chinook offshore oil field in the Gulf of Mexico. The Chinook flowline routes cross continuous mega-furrows at water depths ranging from 2,660–2,860 m. The design temperature and pressure of the flowlines were 120 degrees Celsius and 875 bar, respectively.

Detailed finite-element analysis was performed to predict flowline in-place behaviour. The strain-based criterion of API RP 1111 was used where stresses were greater than ASME B31.8 allowable limits, and found to be satisfactory. Fatigue analysis of the pipe spans subjected to vortex-induced vibration (VIV) showed the need for VIV-mitigation measures, and it was decided that the entire length of the flowlines crossing the mega-furrows should be straked. The analysis of the straked flowlines resulted in a fatigue life greater than the required 25-year service life.

Further analysis was performed on the PIP system to optimise the centraliser spacing to sufficiently limit the buckling of inner pipe under operational conditions, and prevent crushing of the insulation in the annulus. J-lay installation analysis determined the amount of the inner pipe pre-tensioning that was required to eliminate locked-in stresses in the inner and outer pipes. The 2010 Chilean earthquake: gas distribution system resilience by Enrique Acuna C, Dandilion Ingeniería Ltda, Santiago, Chile.

This paper provides a quick review of the gas distribution pipeline systems’ behaviour during and after the Cobquecura earthquake, the fifth biggest earthquake since 1900 and the seventh (by magnitude) ever recorded in human history.

Modern transmission and distribution piping systems endured the earthquake with no fatalities, serious injuries, or property damage related to gas pipe failures. Some marginal supply loss occurred due to customers’ decisions to cut-off the gas supply and some under-pressure protection actuation. Gas service was restored within two to three weeks.

In the city of Concepcion and the port of Talcahuano, the areas most affected by the Cobquecura earthquake and the following tsunami, an old cast iron gas network collapsed because of earth settlement and subsequent flooding. Service restoration and cast iron pipe insertion took between 7 and 11 weeks to get maximum penetration; however 97 km were impossible to rehabilitate, and 500 customer services have had to be converted to LPG.

There are no available official figures and evaluation of the effect of the Cobquecura earthquake on gas transmission and distribution systems. Information is not available either from companies or authorities. The figures presented in this paper include general information acquired from public sources and unofficial discussions, and are not from an official damage report. Deep subsea oil and gas infrastructure development: some challenges and solutions

by D.K. Das and Jose Gonzalez, Universal Pegasus International Inc., Houston, TX, USA. This paper first describes some of the challenging seabed characteristics that are increasingly encountered during exploitation of oil and gas from deepwater locations. These include sandwaves, outcrops, pockmarks, and steep slopes. Thereafter the paper focuses on some of the equipment and accessories currently available in the global market, their capabilities to handle specific seabed problems, and the owners of such equipment.

Custom-designed equipment able to level undulating seabeds at depths surpassing 1,000 m, are also presented. Working procedures, concurrent survey requirements, as well as equipment-monitoring systems and acceptable disposal methods for dredged materials, are discussed briefly. Finally, the paper mentions some projects where such equipment has been put into use.

The role of FEM in the operation of pipelines in unstable soils

by R Bruschi, Saipem SpA Project Execution Centre, Fano, Italy, and S Bughi and M Spinazzè, Saipem Energy Services, Fano, Italy.

During the operation of complex gas pipeline networks, it may be necessary to cross mountainous regions including those possibly affected by hydrogeological instabilities. Unfortunately, soil instability might be manifested through minor and slow down-slope movements, which are hardly recognisable in the short term and, are difficult to predict in the design phase. The interference of soil settlements or down-slope movements with the pipeline can give rise to unacceptable pipe deformations over time.

The role of mathematical modelling, involving both slope and pipeline for simulation of the above-mentioned conditions is introduced and analysed in the paper. Numerical modelling is a tool for integrating and supporting a global structural integrity-monitoring system. In particular, it is shown how the numerical model must include consideration of the physics involved (sliding or settlements due to unexpected or excessive rainfall or seasonal snow melting, soil-pipe interaction in the trench, etc.). Relevant hydro and geologic parameters, characteristic of the site, must be addressed and qualified through field measurements and laboratory testing.