Chapter 5 Offshore Constructing Operation

CHAPTER 5 Offshore constructing operation 5.1 General Provisions 5.1.1 General 5.1.1.1 The offshore constructing operation of the platform (hereunder called the operation) shall ensure the structural strength of the platform unaffected. A strength check calculation and analysis shall be done for the operation way/method affecting the structural strength. The computer program applied for the calculation and analysis shall be proved reliable and proper through the application in engineering practices or the one approved by the Certifying Survey Agency. Methods used for the analysis and calculation shall comply with the requirements of the applied specifications and standards. 5.1.1.2 Offshore operation shall meet all the technical requirements raised by the technical specification of the operator and specifications & standards for the whole process of operation. 5.1.1.3 If new techniques and means for the fixed platform foundation type and installation method have been used, an effective control and observation shall be taken in the process of foundation construction. 5.1.2 Preparation prior to operation 5.1.2.1 The related regulations for operation safety, construction design report, construction program and emergency measures shall be developed according to the requirements of the applied specifications and standards and those of the government authority. 5.1.2.2 All the vessels to be used in constructing operation shall be on the working state approved by Certifying Survey Agency and suitable for the operation to be done. Any refitment for vessels needed for the operation shall be approved by Certifying Survey Agency prior to the operation. The derrick barge used for operation shall have the operating permit issued by the Safety Office. 5.1.2.3 The system and equipment used for operation shall be disposed and selected according to the operation requirements. Both of the normal operation and emergency condition shall be taken into consideration for the disposition and selection. Prior to the start of the operation, a commissioning shall be carried out for main system and equipment. 5.1.2.4 The appliances and materials to be used in the operation shall be carefully examined to ensure the safety of the operation. 5.1.2.5 Before the loading-out of the jacket, a survey of seafloor topography, geomorphology and submarine structures (if exist) shall be carried out. 5.1.3 The performance of operations 5.1.3.1 The operation shall be performed under the guarantee of accurate and reliable meteorologic and oceanographic forecast. The real operational oceanography shall not go beyond the environment conditions prescribed by the construction design. 5.1.3.2 Emergency plan shall be developed against possible variation of metocean conditions and eventualities, and measures for emergency handling shall be prepared based on the emergency plan. 5.1.3.3 Upon the completion of operations, all temporary members for fastening structures, fitting scaffold and auxiliary structures of operation shall be removed, and such removals shall not cause any damages and impairs to the original structures. A survey for the parts removed shall be carried out after removing. 5.2 Loadout and Seafastening 5.2.1 Two alternatives, either lifting or skidding can be adopted for loading-out the structure. 5.2.1.1 Loading-out the structure by lifting To be implemented in accordance with related requirements of Article 3 of this Chapter. 5.2.1.2 Loading-out by skidding Before loading-out by skidding, a design calculation and analysis shall be done for several major systems, such as skidding way, regulation, measurement and mooring etc. and a program for skidding shall be made up based on them. Also there shall be a well-made plan with sufficient and reliable support for the stand-by equipment and supervising the skidding. During the whole process of skidding onto the barge, the ballast system of the barge shall have sufficient regulating capability and reversibility for variations in tide level and loading, so as to ensure the skidding way on land and on barge aligned and leveled in the process of skidding on. In the same time, appropriate standby ballast pumps shall be provided. 5.2.2 The structure being transported shall be reliably fastened on barge, and the supporting structures such as blocks, supports and braces etc. shall be specially designed. 5.3 Lifting 5.3.1 Lifting analysis shall be carried out prior to the lifting operation, and a lifting program shall be developed based on it. In case two derrick barges are required to operate jointly, the coordination difference and dynamic factor of the two derrick barges shall be considered in design. 5.3.2 The load parameters used for the structure design of lifting eyes shall be taken from the lifting analysis results. The lifting analysis model shall represent the real lifting arrangement. The lifting calculation and the structure design for lifting eyes shall conform to the applied specifications and standards. 5.3.3 The selection of slings and riggings for lifting shall be based on the results of lifting analysis. The safety factor and tolerance of lifting slings and riggings shall comply with the applied specifications and standards. Lifting slings and riggings shall be available with ex-mill certificates of quality, testing certificates and approval certificates issued by Certifying Survey Agency. 5.4 Transportation at Sea 5.4.1 The operation for transporting at sea shall be approved by the maritime authority. 5.4.2 The transportation of the structure could be performed by means of barge carriage or self-floating. 5.4.2.1 Barge carriage The barge to be used for carrying the structure shall be with sufficient loading capacity and structural strength and the barge carriage system (including barge and platform) shall be available with sufficient stability and meet with the requirements in the specification applied. 5.4.2.2 Transportation by self-floating (1) While the structure is transported by means of floating, its floating system shall have sufficient reserve buoyancy. While ancillary buoys being employed, buoys shall be connected to the floating structure through rigid connections, and the whole system shall be with sufficient stability. (2) Prior to towing, the watertightness, strength and rigidity of the floatation system and the operation and control functions of its flooding and draining system shall be inspected. (3) Necessary mooring devices shall be equipped on the self-floating structure for the convenience of temporary mooring and positioning operation. 5.4.3 Towing 5.4.3.1 A towing manual shall be developed for towing operation. The towing manual shall contain: destination of towing, sea route, schedule, meteorological and oceanographical of towing and necessary emergency measures. 5.4.3.2 The ability and towing facilities of tug boats employed for towing operation shall be capable for ensuring efficient control of the structure being towed and to maintain an appropriate voyage speed. 5.4.3.3 Towing hawser system shall be with sufficient strength and provided with sufficient spare parts. 5.4.3.4 In addition to the safest sea route, an alternate sea route shall be chosen. For a long-distance towing, one or several shelter harbors shall be pre-selected. 5.4.4 Towing analysis The towing analysis includes strength check for the structure towed, barge and fastening structures, as well as stability check of the structure — barge system. 5.4.4.1 The strength check can be done on the basis of the theory of rigid body. The relative rigidity effect between the structure and the barge shall be taken into consideration, if necessary. 5.4.4.2 Various possible drafts, loading and ballasting conditions shall be considered during stability check. 5.4.4.3 Import of fatigue, vortex vibration and action of wave slapping force on structures shall be considered, if necessary. 5.5 Launching and Positioning of the Jacket 5.5.1 Launching The removal of jacket from the barge is generally accomplished by either lifting with a derrick barge or skidding. 5.5.1.1 Removal of the jacket by lifting To be performed in accordance with the related provisions of Article 3 of this Chapter. 5.5.1.2 Removal of the jacket by skidding (1) A calculation analysis shall be done for skidding off launching, and an operation program shall be developed accordingly. (2) The barge shall be equipped with a rocking arm with sufficient strength and appropriate length. (3) The barge shall have sufficient stability and strength during launching operation. (4) After the jacket launched, the clearance between the lowest point of its moving track and the seafloor shall conform to the requirements. (5) The jacket shall have sufficient buoyancy, so as to keep a satisfactory self-floating after the launching, the jacket shall also have sufficient reserve buoyancy for an unexpected event. (6) Upon the completion of the launching operation, it is necessary to check whether all the states of the jacket is consistence with that calculated. If there is not any abnormal phenomena, the uprighting operation shall be carried out immediately. 5.5.2 Uprighting The uprighting operation of the jacket can be accomplished by either self-uprighting or with the aid of a derrick barge. The uprighting operation shall meet with the following requirements: 5.5.2.1 Prior to the uprighting operation, a computer analysis shall be performed, and a uprighting operation program shall be developed accordingly. 5.5.2.2 The control system of valves for flooding and exhausting used for uprighting operation shall be clearly marked to avoid misoperation. Standby systems shall be provided for flooding, filling and exhausting. 5.5.2.3 During the uprighting, the clearance between the lowest point of jacket and the seafloor shall conform to the requirements. 5.5.2.4 If the uprighting is accomplished with the aid of a derrick barge, the barge shall be moored and positioned reliably. 5.5.3 Positioning and landing of the jacket 5.5.3.1 The jacket can be positioned with an anchor wire system or (and) by means of other ships. 5.5.3.2 The landing operation of the jacket shall be progress according to the ballast order made certain in advance. The ballast system shall be reversible. 5.5.3.3 The jacket shall be of sufficient stability in the process of lowering. When the jacket is approaching to the seafloor, its lowering speed shall be controlled to avoid excessive impacting. 5.5.3.4 While there is a pre-drilled subsea template, reliable guide device shall be equipped and the sheathing speed shall be controlled. 5.5.4 Leveling 5.5.4.1 After landed on the seafloor, the jacket shall be leveled prior to piling. Once leveled, the jacket shall maintain its levelness during the later operations. When all the piles have been installed, leveling shall be avoided, if it is possible. However, if necessary, the jacket may be leveled after a minimum number of piles have been driven, and some measures shall be taken to minimize the bending stress in the piles. 5.5.4.2 To keep the levelness of the jacket, the position and area of the mudmat of the jacket shall be determined based on the actual loads. 5.6 Pile Driving 5.6.1 Prior to the piling, pile driveability analysis shall be carried out in aid of selecting appropriate piling hammers and other tools. 5.6.2 To decrease piling resistance, piling operation shall have as less interruption as possible. 5.6.3 Ending the piling shall not be based on pile driving refusal. While the pile has met the specified pile driving refusal, it shall remain to be driven to the design depth by the use of other methods. 5.6.4 When jetting or drilling are used for piling, the load-supporting capability of soil in pile tip shall not be destroyed by the operation. Otherwise, the soil plug removed shall be replaced by grouting cement slurry or concrete. 5.6.5 The welding of add-on pile and the welding of pile and the jacket shall comply with the related provisions of 3.10 of the . 5.7 Grouting 5.7.1 If it is specified in the design, the annular space between piles and jacket legs shall be grouted with cement slurry. For the jacket with primary piles, the grouting operation shall be performed after the completion of welding connection between the piles and the jacket legs. 5.7.2 The strength of the consolidated cement slurry and the specific gravity of the slurry shall meet the design requirements. 5.7.3 The grouting system shall have ability for continuously grouting and the necessary method shall be provided to ensure a designed grouting result. Some standby grouting pipes shall be provided. 5.7.4 The grouting shall be stopped in case of loss of grout in the process of grouting. Measures shall be taken to prevent the loss of grout, and the grouting can be continue only after the successful plugging. 5.7.5 Artificial disturbance shall not be permitted to occur in the process of consolidation of cement slurry. 5.8 Top-side Installation 5.8.1 To ensure the elevation and levelness of the topside in accord with the design requirements, the height of the transition shall be adjusted prior to the installation. 5.8.2 The stabbing and positioning guide shall be installed to ensure the correct position of deck or module. The stabbing and positioning guide shall have proper strength to prevent damages of primary structures. 5.8.3 Once the topside is in place, it shall be fixed to provide necessary supports and be well connected as required in the design. 5.8.4 The installation of topside by lifting method shall comply with the related provisions of item 5.3 of this Chapter. 5.8.5 All welding activities shall comply with the related provisions of Item 3.10 of the . 5-7