Case Studies: Surge Analysis

North Tees Ethane Import Terminal

As part of Sabic UK’s major project to upgrade the Wilton cracker to take US shale gas, Spectrum has been carrying out surge analysis for the liquefied ethane unloading line and 10 km cross country pipeline. A full range of transient scenarios was considered, including controlled start up and shut down, pump trip events and valve trip events including unloading arm PERC operation. Confirmation of acceptable valve closure times was provided together with detailed predictions of transient forces to enable the client to carry out full dynamic stress analysis for the pipelines.

Canvey Island Terminal Firewater System

Spectrum provided a surge study for the new Firewater System at Canvey Island Terminal storage facility operated by Oikos Storage. Water velocities in firewater systems are typically much higher than normal pipeline velocities resulting in much larger potential surge pressures in the case of pump start up, pump trip and valve operations. A range of planned and unplanned events including testing was considered to identify potential risks to the system both from excessive pressures and large unbalanced forces. A mitigation strategy was developed so the client could clearly understand the recommendations and evaluate the response required.

Toamasina Ammonia Line Surge

Ambatovy in Madagascar has had an Ammonia unloading and transfer facility constructed to provide liquefied ammonia to the large new nickel and cobalt refining plant near Toamasina. Spectrum were asked to carry out surge analysis for both the ammonia ship unloading line and the transfer line. A full range of transient scenarios was considered and recommendations provided relating to controlled start up and shut down, pump trip events, valve trip events and PERC operation. Operating procedures were reviewed in detail to identify potentially hazardous sequences involving liquid and vapour to advise how the risks could be controlled.

Ineos EDC Road Loading, Runcorn, UK

Spectrum carried out a surge study for a road loading line equipped with breakaway couplings at the road tanker connection. The client needed to understand and quantify the effect of the extreme transient event when the coupling valve closes over 30 milliseconds. Large shock forces and pressures on the road loading line were predicted. Spectrum also considered the automated sequences finding that the fast opening valves at the loading bay could lead to vapour cavity formation and collapse during the proposed start up sequence and recommending slower opening times.

GDF Suez/Storengy Stublach Gas Storage Facility, Cheshire, UK

Spectrum provided surge studies for all the major piping systems required for the solution mining of the Stublach gas storage caverns. When complete, Stublach will be the largest UK onshore underground gas storage facility. The surge studies addressed the usual issues of cross country piping systems but in this case the new high pressure cavern mining system was supplied with water boosted from an existing water supply network operating with much lower pressure constraints. A combination of surge vessels and diverter valves was used to provide the necessary protection.