Petrell has performed an analysis of the SFP segment at Statoil's processing plant at Kårstø. Scope of work included to determine temperature profiles in the segment during cold blowdown, and to calculate time to rupture in case of fire exposure, and advise on PFP requirements.
Teekay Petrojarl has contracted to Petrell to review passive fire protection on the Knarr FPSO. Work includes review and update of fire scenarios and blowdown.
There is an increasing interest for VessFire in Malaysia but also in other countries in the region. To make sure both current, new and prospective users are up to date on the possibilities of VessFire 1.4 we are now organizing a course in Kuala Lumpur. Dr. Geir Berge of Petrell will lecture on topics such as the physics and process of blowdown, including application of ISO 23251/API521 with a special focus on the issues related to simulation. Topics also include heat transfer, material properties, rupture criteria and the use of VessFire 1.4 including modelling and presentation of results. Program – Day 1 (9 am – 5 pm)
- Registration (from 0830)
- Introduction to the subject
- Blowdown calculation procedure
- Heat load and duration
- Acceptance criteria
- Theoretical basis
- Example on calculation results
- VessFire user interface
- Familiarization with the case
- Clarify the limiting conditions
- Get hold of the technical information
- Set up a matrix of required simulations
- Run the simulations
- Analysis and reporting
There are numerous modifications to offshore oil & gas installations due to e.g. tie-in of new fields and wells. When an existing production system is considered host for a tie-in there are a number of issues that need to be considered; the composition is different, and there is probably also different pressure, temperature and flow rates. A design that once was deemed fit may be severely challenged. Fire loads may also have changed, and corrosion and wear & tear may have taken away capacity. So what do you do if the flare capacity is too low? Doing modifications to the flare system is normally not an option. More or less feasible alternatives include changing the size of the segments by i.e. introducing another segment, replacing weaker piping and flowlines with better materials or larger wall thickness, or adding passive fire protection (PFP). Example of planned modification A modification to a platform located in the North Sea was planned. The modification had impact on several process segments, including 53 flowlines and pipe spools, whereof 19 were exposed to fire. These belonged to four process segments, with operating pressures ranging from 3 to 33 barg. The inventory was a multiphase fluid. Cost saving alternatives for PFP The peak fire load varied from 250 to 350 kW/m2 with a background fire load of 100 kW/m2. The initial analysis, using VessFire, revealed that 9 flowlines and piping spools with Nominal Pipe Size (NPS) (as shown in the table) would rupture. In order to possibly avoid costly PFP, we applied different pipe schedules and wall thicknesses; the heat-stress curves for the steel qualities were already available in VessFire. The results are shown below. With the revised schedule and wall thicknesses there were no unacceptable ruptures and hence no need for PFP. The fire insulation in this example is 40-50 mm cellular glass with a 15 mm alkaline earth silicate (AES) wool and 0.7 mm steel mantling. Huge cost saving potential With an estimated effort of 10 man-hours/meter pipe (including bends and support) for offshore application at 180 USD/mhr, the saving in PFP work was about 475.000 USD. Painting of pipes (if necessary) and scaffolding are not included. Then there is the saving in insulation costs; the results showed an estimated saving in PFP of 4.65 tons at the expense of an additional net weight increase of 3.52 tons of steel due to increased wall thickness. The piping and flowline surface area that would otherwise have been provided with fire insulation was about 263 m2. The additional 8.2 tons of steel represents a minor cost increase. In addition to savings in installation cost and reduced offshore work, benefits include reduced risk of corrosion under the PFP on piping and flowline, reduced cost of inspection and re-application, as well as reduced cost of repair of PFP on piping and flowlines. Multi-discipline tool In addition to documenting blowdown capacity and fire integrity, the analysis also contributed to reduced installation cost and reduced inspection, maintenance and repair costs. This is actually the beauty of VessFire: It is truly a multi-discipline tool where Piping & Layout, Process, Safety and Material disciplines can meet, test and explore consequences of options before they conclude on mitigations. Learn more about the possibilites of VessFire now
Petrell launches version 2.0 of VessFire. Version 2.0 makes dynamic calculation possible for all processes involved in depressurisation. In most situations, this means more precise results and thus even better safety for process systems, with better utilisation of the flare system as a result.
VessFire 2.0 calculates multiphase flow in pipe networks and treats different vessel types. A new and improved interface provides a better description of the process systems. It also allows data stored in Excel to be pasted into the user interface. It is easy and it is fast.
New thermodynamic library
Certain constraints in version 1.0 have been eliminated and new features added. For example: there is no limit to the number of vessels, blowdown valves and pressure relief valves in the process segment. Petrell has also developed a new thermodynamic library (ThermoProp), implemented in version 2.0. ThermoProp handles water/oil mixtures and CO2.
Version 2.0 is more stable and precise. Users familiar with version 1.0 will find major improvements to the user interface in terms of modelling and result presentation.
During the development of the 2.0 version, Petrell identified calculations that took the most time. Improved algorithms, the new thermodynamic library and smarter implementation have resulted in an increased calculation speed.
Dynamic analysis of flare system
Design of process systems for oil and gas has traditionally been based on a stationary approach. This applies to flare system design as well. When gas is discharged into the flare header, the pressure rises and then gradually decreases as the segments are emptied. In flare analyses, a fixed backpressure is traditionally used, because the dynamic pressure profile is not known. VessFire 2.0 calculates backpressure dynamically based on the properties and condition of the gas released into the flare system from various segments. A process system should be dimensioned for actual conditions and what is dynamic should be dealt with dynamically. That's what VessFire 2.0 is designed to do.
Pipes and vessels
Previous versions of VessFire is based on the condition that the vessel is the dominating object in the segment. If the segment contained more than one vessel, the additional vessels were modelled as pipes. In version 2.0, all vessels are recognised as vessels and pipes as pipes. All components constitute a network interconnected by the flow between the components. Segments without vessels (or pipes) are of course permitted. As in version 1.0, users can select steel quality and materials for passive fire protection, and if the material is not listed, new types can be added.
Figure 1 Screen shot showing how pipes and vessels etc. are defined. The list can be export as an Excel file or the list can be prepared in excel and inserted in VessFire using copy/paste.
Figure 2 Screen shot showing a graphical representation of a process segment. Heat load and low temperatures
Heat load and low temperatures
There is no limitation on defining heat loads – peak and background loads can vary over time as before, and if required, a fire load can be allocated for each vessel or pipe.
Version 2.0 provides better support for analysis of low temperatures in connection with e.g. cold depressurisation, through a much broader spectrum of reporting options. For example: temperature fluctuations during a given period for a given pipe section can be extracted.
Licenses available 1Q 2017
Licenses will be made available to existing and new customers in 1Q2017. Until then is VessFire 2.0 available through consultancy services from Petrell.
Fact box on process systems and depressurisation:
The blowdown and flare system is the most important process safety system as their purpose during an accidental event or emergency situation is to reduce the pressure in process segments in order to reduce the risk of rupture and subsequent release of flammable substances that cause fire and explosion. Once overpressure occurs in a process system, getting the pressure down as quickly as possible is important, by diverting the contents to the flare header. Blowdown is a challenging process, even more so in a situation where parts or all of the system are exposed to fire. The blowdown and flare system must handle both scenarios.
Fact box, VessFire:
VessFire is a multi-physics simulation system for blowdown analysis, treating the thermo-mechanical processes interacting with each other. VessFire meets the requirements for advanced depressurisation analysis as outlined in the 2014 edition of API 521 (ISO 23251). Blowdown analysis in VessFire takes into account external heat sources, heat transfer from the outside and through vessel and pipe walls, and through the fluid and gas phases. Evaporation and condensation take place inside vessels and pipes causing the composition of phases to change over time. When a blowdown valve (and/or pressure release valve) opens, mass is removed from the segment, reducing pressure. If the pressure is reduced too slowly in a fire case, rupture can result. VessFire calculates time to rupture. Parameters such as wall thickness, flow orifice diameter, material quality etc. can be varied to see the effect on time to rupture.
Teekay Petrojarl Production is executing modifications of the FPSO Petrojarl 1 for deployment at the Atlanta field offshore Brasil. The Atlanta field is characterised by heavy oil. Petrell has performed a depressurisation and fire integrity analysis of the process systems, by use of VessFire. Work included optimization of depressurization with regards to flare capacity. T
We wish to congratulate Nazanin Jahani with her PhD degree on Coupled Fluid Flow and Elasto-plastic Damage Analysis of Acid Stimulated Chalk Reservoirs. The doctoral thesis has been carried out at Petrell AS and the Department of Engineering Design and Materials at the Norwegian University of Science and Technology (NTNU), under the supervision of Dr. Geir Berge (Petrell AS), Associate Professor Bjørn Haugen (NTNU) and co-supervision of Professor Rune Martin Holt( NTNU and SINTEF Petroleum). An abstract of the thesis: Coupled Fluid Flow and Elasto-plastic Damage Analysis of Acid Stimulated Chalk Reservoirs
BP Norge AS has awarded a contract to Petrell for modelling and simulation of unignited flare (flame out scenarios) at Valhall.
Geir Berge presented "Computer-aided fire integrity analysis of pipe flanges" at the 2014 Tekna Process Safety in Oil and Gas Conference. The presentation was well received by the attendees. The presentation is available for download here.