Weight management is necessary throughout operations, decommissioning and removal to facilitate structural integrity management SIM. The provisions of this document are applicable to fixed and floating facilities of all types.
Snow and ice loads are excluded as they are not considered to be part of the facility. Phone: Fax: Email: info document-center. Abstract ISO specifies requirements for controlling the weight and centre of gravity CoG by means of mass management during the engineering and construction of structures for the offshore environment. ISO - specifies quality requirements for reporting of weights and centres of gravity; - specifies requirements for weight reporting; - provides a basis for overall project weight reports or management reports for all weight control classes; - specifies requirements for weight and load budgets; - specifies the methods and requirements for the weighing and the determination of weight and CoG of major assemblies; - specifies requirements for weight information from suppliers, including weighing of equipment and bulk materials for offshore installations.
It can be used: - as a basis for planning, evaluating and presenting the client's, contractor's or fabricator's weight management and reporting system; - as a means of refining the structural analysis or model; - as a contract reference between client, contractor and suppliers; - as a basis for costing, scheduling or determining suitable fabrication method s or location s. Status : Withdrawn.
Publication date : Life cycle Previously Withdrawn. The following tables show the suggested range of design allowances to be applied to dry weights of different disciplines at the various stages of design development. It is dependent on assessed quality of available data - not project phase.
Design change allowance An allowance to account for weight changes that experience shows will be used during normal design development. Fabrication allowance An allowance to account for fabrication tolerances and changes that experience shows will be used from material substitutions, site run materials, and site queries.
Operational Reserve An additional allowance of operating weight expressed as an overall tonnage that is reserved over and above the management reserve to account for additional items added to a platform during its operational life. These would typically include the following. History shows most platforms will have more than 2 in a year operational lifetime. These can amount to increases in excess of 1 tonnes operating. Management reserve An additional allowance of operating weight expressed as an overall tonnage that shall be reserved over and above the factored operating weights to account for any changes made to original contract requirements by the client.
The management reserve shall be released as appropriate by the project Weight Review Panel, or similar body. Primary steel Primary steelwork is usually reasonably well defined at an early stage of a project. A preliminary structural analysis is normally undertaken during the conceptual design to confirm member sizes. As such, lesser individual allowances are justified.
Secondary steel Secondary steelwork is by its nature less well defined and is usually subject to change throughout FEED and detailed design due to revisions made by upstream disciplines. As such, higher individual allowances are recommended. Deck plate and grating Deck plate and grating usually contributes a high proportion of structural dry weight. However, once the area of deck to be plated has been defined and the plate thickness selected, it is normally only subject to weight change in respect of openings and cut-outs for penetrations.
Consequently, only the Fabrication allowance is justified. The value that shall be used is dependent upon: — demonstrated accuracy of weight data previously provided by the design contractor; — demonstrated accuracy of final weights achieved on previous projects.
Design allowances applied to individual items of weight shall not be dependent upon project phase, drawing, or data sheet revision.
This principle gives flexibility to setting of design allowances, produces lower factors, and optimises the platform load carrying capacity at an early stage. It prevents weight conscious designs from being penalised and ensures that full utilization of the available topsides weight capacity is made at the earliest stages of design development.
It is important that the design allowance is understood to be a measure of accuracy of the base dry weight of an item, and not an allowance for omissions. The weight allowance should generally only be applied to the base dry weight of each item, not the contents, as all operating increases should be accurately defined early in the detailed design of a project.
They should be calculated and applied separately to the SI analysis by structural engineers. One is attached below for information. It should be remembered that if it is not modelled, the weight and CoG will not be calculated, e. NOTE 2 Attempts to rationalize drilling loads should be avoided, as these are common conditions. They must be calculated and applied by the Structural Integrity engineer.
The drawings shall include tabulated values for maximum global load, maximum local and concentrated load, and area in m2. Permanent containerised offices, tea shacks, and stores shall not form part of the laydown storage loads. They shall be separately itemised, and reported in the weight database as such.
Figure G. The weight control process involves data gathering from many sources, including discipline weight input from the main contractor, the drilling contractor, the accommodation contractor and equipment vendors see G. Generally, one individual does not have the time, background or skills to single- handedly manage the whole process.
Usually, a team of people, with the requisite skills and background, is needed to implement an effective weight control facility. The engineer or group of engineers involved in the process should be: — familiar with weight control principles and procedures; — knowledgeable about multi-discipline weights; — knowledgeable about CAD extractions and downloads; — familiar with drilling techniques and loads; — familiar with laydown and storage requirements; — familiar with equipment and module weighing requirements; — cognisant of requirements for difference design phases; — familiar with weight control requirements of offshore structural engineers.
Further description of competencies for each aspect of the weight control process is provided elsewhere. Estimated weights for topside units are important input and basis for a number of activities: 1 weight information is one of the main input parameters for cost estimating and planning; 2 weight information is vital for transportation, lifting and installation analyses; 3 weight information is vital for analysis of substructure capacity; 4 weight information is vital for stability analysis, loading conditions and platform operations.
The objective for weight estimation is to predict, from an early stage in concept development, a topside weight as close to the final as-built weight as possible. Weight estimates are established by use of different methods: a Simple analytical models calibrated against relevant previous projects are used in the early stages, especially in screening and feasibility phases.
Weights are then estimated from assumed functions and capacities, and scaled based on earlier project experiences. This method is normally used in feasibility and concept phases, and also in FEED. Different ways to use the MEL information to establish weight estimates are given in 1 and 2. Based on this, weight for bulk and structural can be estimated based on experience factors for bulk and structural per system. Weight allowance should then be added to account for items not yet identified.
This method is applicable for some disciplines in FEED in combination with experience factors. Reported weights based on WTO must always be verified by experience factor estimates. The equipment list and the 1. Weight estimate to be based equipment layout should be basis for equipment layout should be basis for on experiences from earlier, compa- the topside weight estimate. Weights should be distributed 2. Weights should be split in on areas construction units. Weights in each area should 3.
Split between topside and be split in equipment, structural and be split in equipment, structural and substructure should be defined. Weights should be calculated for both substructure and topside and 4. Bulk should be split on dis- 4. Bulk should be split on dis- be given separately.
Weight accuracy and confi- 5. Structural should be split in 5. Structural should be split in dence level for the established weight primary, secondary and outfitting. WTO for designed structure 6.
If possible, piping material chosen estimating method and level should be prepared, based on 3D models. May 7. WTO for piping should be pre- 7. Split between topside and be verified by statistical simulations. Material substructure should be clearly defined. Weights should be calculated for both 5. SI-units should be used. Weight allowance should be separately. Centre of gravity should be 9. Split between topside and calculated.
Weights should be calculated for both 9. Weight accuracy and confi- substructure and topside and be given dence level for the established weight separately. Centre of gravity should be of details i. May Lift weight for each lifting item be verified by statistical simulations. Layout drawings and coordi- Source of weight data should be nate system should be given.
Weight accuracy and confi- dence level for the established weight estimate should be given, based on the chosen estimating method and level of details i.
May be verified by statistical simulations. Layout drawings and coordi- nate system should be given. Irrespective of chosen weight estimation method, MEL is the main input and basis for the weight estimate. Weight allowances should be used and clearly stated in the equipment list. Weight allowance should be added based on concept development and maturity. MEL must also include temporary equipment needed for any defined temporary operation. These items should be marked as temporary. The amount of weight allowance should be determined based on experience, judgment of concept maturity and development of engineering.
The amount of weight allowance added should always be specified. When weights are estimated by comparative methods, scaling or by experience factor estimates, no weight allowance is needed as the basis for these methods are determined from existing, complete facilities, and the estimated weights are considered to be expected values. The executive summary varies from project to project depending on the risks and concerns for the project or customer. A good executive summary will use point font for all text and should be something that is posted on project status boards.
An example is shown in Figure I. Figure I. The CoG s that are plotted vary from project to project, based on the issues. For a module or topside the CoG envelope may be presented. For a ship or submersible hull the KG curve may be presented.
Each trend chart should have a bold limiting curve or line, with one or two trend lines shown. A future weight and CoG point should be plotted for each trend line that shows the impact of the potential changes on the currently reported weight. It presents the weight budget by discipline structure, piping, outfitting, equipment and electrical , current weight allowance, and current gross weight. The loading conditions are a limited set of all the conditions developed by the naval architect.
Typically the loading conditions used to establish the WLB, construction and extreme operating conditions are used. The construction conditions may include launch, integration, tow out, commissioning and inclining experiment. The extreme conditions are those that are close to the edge of the KG limit or CoG envelope. It compares the gross weight to the not-to-exceed limits to determine the amount of management reserve. A description, weight impact and CoG information should be provided for each change.
Potentials include the impact of weight changes of drawing calculations that have not been completely checked, design changes that have not been completed, rumoured weight changes from vendors, etc. The disciplines are usually those identified on the organization chart or upon customer request by their definition of disciplines. These are not usually the same.
The weight should be rounded to the nearest whole number. It is quantified by its standard deviation and its weight result uncertainty, called the standard uncertainty, denoted u. As the GUM requires that the coverage factor is given together with the measurement uncertainty one can easily recalculate the expanded uncertainty to any wanted value of k. Calibration is a documented act of observing and documenting the output of a measuring device when it measures a physical quantity at a set of values having known uncertainty.
The set of quantities should be large enough to enable reasonable assessment of the measurement uncertainty and should cover the whole range for which the measuring device is intended used. Standard uncertainty is the standard deviation of the measurement uncertainty, denoted u. Expanded uncertainty is the standard uncertainty multiplied by the coverage factor, denoted u.
Coverage factor is the factor used to multiply the standard uncertainty to obtain the expanded uncertainty, denoted k. Drawing number: The drawing number Drawing number: The drawing from which the weight has been identified number from which the weight has or calculated. Drawing revision: The revision of the Drawing revision: The revision of drawing from which the weight has been the drawing from which the weight identified or calculated. The girder M10— shown on a struc- data field is a text field.
The data field is a text field. Number off: Number of identical pieces. Only integer numbers shall be used. Size: The size of each piece, e.
Dry weight: The dry weight of each Dry weight: The dry weight of each piece in kg, that is the product of Number piece in kg. Content: The weight of the content in kg Content: The weight of the content in a piping line, vessel, tank etc.
Weight status code: A coding to identify Weight status code: A coding to the level of accuracy of the weight data of identify the level of accuracy of the each piece number. Weight phase code: A coding to identify Weight phase code: A coding to during which phase a piece number will identify during which phase a piece be installed and present.
Date: The date when a piece number was Date: The date when a piece number entered or revised in the weight control was entered or revised in the weight database.
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