FABRICATION PROCEDURE

Table of Contents

 

1. Purpose -----------------------------------------------------------------    2 of 6
   
2. Applicable Code, Standard and Specification -----------------    2 of 6
   
3. Fabrication Sequence------------------------------------------------    2 of 6
   
4. Material Receiving-----------------------------------------------------    2 of 6
   
5. Nonconforming Material----------------------------------------------    3 of 6
   
6. Receiving of Purchaser Supplied Product-----------------------    3 of 6
   
7. Material Issuing---------------------------------------------------------    3 of 6
   
8. Layout and Cutting-----------------------------------------------------    3 of 6
   
9. Transfer of Heat Number---------------------------------------------    3 of 6
   
10. Fit-up-----------------------------------------------------------------------    3 of 6
    
11. Welding -------------------------------------------------------------------    4 of 6
    
12. Control of Welding Consumable------------------------------------    4 of 6
    
13. Non-Destructive Examination----------------------------------------    4 of 6
    
14. Testing And Inspection -----------------------------------------------    4 of 6
    
15. Painting -------------------------------------------------------------------    5 of 6
    
16. Packing and Shipping preparation----------------------------------    5 of 6
    
17. Manufacturing Data Book (MDR)-----------------------------------    5 of 6
    
18. Appendix A – Fabrication Sequence-------------------------------    6 of 6
    

 

1. Purpose
   

   To describe the method Synco shall adopt for fabrication and assembly of 1440 PSI – TEST SEPARATOR 20' CSC / DNV EQUIPMENT FRAME.
   

   To ensure the products are meet with the referenced fabrication Code and client requisition.
   

   
    

2. Applicable Code, Standard and Specification
   

   All of the equipments shall be fabricated, inspected and tested in accordance with the following related specification :
   

   1. DNV 2.7-1 : 2006
      
   2. EN 12079 : 2005
      
   3. ISO 1496-1 (CSC)
      
   4. AWS D1.1 – Edition 2006
      

 

1. Fabrication Sequence
   
   1. Approval Prototype for Design Calculation and drawing by Third Party comply CSC and DNV Code.
      
   2. The fabrication sequence of 1440 PSI – TEST SEPARATOR 20' CSC / DNV EQUIPMENT FRAME.
      are as per appendix A.
      

 

1. Material Receiving
   
   1. Upon receipt of material, Store man shall spray the material with a yellow paint "hold" to await inspection by QC Inspector.
      
   2. The QC Inspector is responsible for verifying and inspecting all material to be used for Code fabrication against Packing List, P/O and applicable material specification, as follows:
      

• Material has clear identification as required by the Code (e.g., heat number, material specification i.e. grade, type and class if applicable) and traceable to material certificate when required.
  
• Contents of chemical analysis and mechanical test results on material test certificate is in accordance with the respective material specification and P/O.
  
• Material is free from defects and imperfections such as pitting, scaling, lamination, etc. which would affect the safety of the Tank.
  
• Additional examination required by the P/O had been performed (such as Non Destructive Examination, Heat Treatment, Impact Test and Hardness Test) and test certificates are available and in compliance with the Code and client's specification.
  
• Item inspected matches with the "For Construction" drawing.
  

1. All materials that have been checked by Store man and accepted by the QC Inspector shall be painted in accordance with Inspection and Test Status color-coding.
   
2. The Store man and the QC Inspector shall sign Packing List or P/O (green copy) to indicate their acceptance. P/O (green copy) together with Delivery Docket/ Packing List will be forwarded to the Account Officer to match with supplier invoice.
   
3. SYNCO shall give free access to the Authorized Inspector and/ or clients representative to verify material identification if necessary. The QC Inspector shall transmit material test certificate after his review/ acceptance to the Authorized Inspector and/ or client representative for their review.
   

 

 

1. Nonconforming Material
   
   1. The QC Inspector in conjunction with Project Manager shall raise a Material Discrepancy Advice when there is discrepancy in quantity or when material test certificate is not provided with Delivery Docket.
      
   2. The QA/QC Manager shall raise a Non Conformance Report when receiving material with no identification, defective material and material not complying with specification. Nonconformance item shall be identified with hold/ reject tags/ paint in accordance with QM-01 section 7.
      
   3. The non-conforming material shall be segregated from fabrication area.
      

   
    

2. Receiving of Purchaser Supplied Product.
   
   1. Upon receipt, purchaser supplied materials or items shall be subject to exactly the same level of inspection as SYNCO purchased items using packing list and material test certificates provided.
      

 

1. Material Issuing
   
   1. Responsibility is given to the Workshop Manager or his delegate and the Store man to dispatch and receive accepted items from secured storage area.
      
   2. Materials for specific jobs are collectively located in job areas. The Workshop Manager or his delegate shall ensure that only the intended material is used in Code fabrication. He shall check to ensure the material has been checked by the QC Inspector with appropriate color-coding and check with the drawing for correct sizes and specification.
      

 

1. Layout and Cutting
   
   1. Plate's layout for cutting accordance with the actual drawing.
      
   2. Dimension shall be verified diagonally to ensure the square ness.
      
   3. Plates, shape structural and other parts should be cut by oxygen cutting. Beveling shall be in accordance with construction drawing.
      
   4. After oxygen cutting, all slag and detrimental discoloration of material which have been molten shall be removed by grinding.
      
   5. Before cutting QC inspector shall inspect for correct material, sizes and heat number are properly transferred.
      
   6. After cutting, QC inspector shall visually inspected the cut edges for possible for laminations, shearing cracks and other imperfections.
      

 

 

1. Transfer of Heat Number
   
   1. The Workshop Manager or his delegate is responsible for transferring heat number of plates or pipes before cutting. The method of transferring heat number shall use low stress die stamping except if prohibited by client's specification or by the Code. The remaining material to be returned to stock shall be identified with material specification and heat number marked. The QC Inspector is responsible to ensure that all material is clearly identified. Material with no identification shall not be used.
      

 

 

1. Fit-up
   
   1. Items/ material that are being welded shall be fitted, aligned and retained in position during welding.
      
   2. Bars, jacks, clamps and tack welds may be used to hold the edges of parts in alignment.
      
   3. Tack welds, which are to be incorporated into the final weld, shall be visually examined for defects. If a defect is detected, tack weld shall be removed. The start and stop ends shall be properly prepared prior to continuing welding.
      
   4. Alignment during fit-up shall be maintained not to exceed Code requirements.
      

 

 

1. Welding
   
   1. Welding Procedure Map and the WPS(s) to be used for production shall be transmitted to Workshop Manager and put on the notice board in fabrication shop for easy access to the welder and welding operators.
      
   2. The Workshop Manager is responsible for assigning and supervising welders for Code fabrication. He shall ensure that the assigned welders are qualified or make arrangements for their qualification. The welder and welding operator shall ensure inspection clearance status, i.e., color coding "GREEN" before embarking on any production welding.
      
   3. Welding may be performed from single side or double side. For double side welding second side may be prepared by grinding or carbon arc gouging and finished by grinding. In-house MT/ PT are required after back grinding or back gouging.
      
   4. After completion of the weld, the QC Inspector shall examine them visually. Any comment shall be marked with chalk or felt pen on location requiring subsequent work, i.e., grinding, touch-up weld, etc. After he is satisfied with his visual examination he shall initial and date in "Welding Traceability Records" form. The QC Inspector shall also use this form to record welder no, weld/ joint no. and NDE results.
      
   5. QC Inspector shall verify weld reinforcement and undercut are not exceed Code requirements. Fillet sizes shall be in accordance with the drawing.
      

 

1. Control of Welding Consumable
   
   1. Electrodes and welding consumable receiving, storage and issuing shall be in accordance with procedure WCP-01 "Welding Consumable Control Procedure".
      
   2. Welding consumables (electrodes, wire and flux) shall be stored at temperature and humidity recommended by the electrode manufacturer.
      
   3. Covered low hydrogen electrode shall be baked/ re-dried from its original packing at temperature and period as per manufacturer recommendation.
      
   4. After baked/ re-dried covered low hydrogen electrode shall be kept in holding oven at a temperature recommended by manufacturer.
      
   5. Low hydrogen electrode shall be issued to the welders from holding oven to their individual quiver.
      

 

1. Non-Destructive Examination
   
   1. NDE shall be performed in accordance with approved "NDE Map and NDE Procedure" and ITP.
      

 

1. Testing and Inspection
   
   1. On completion of fabrication, the QC Inspector shall perform final dimensional check and visual examination of welds and all surfaces before Load and Proof test. Synco will invite Authorized Inspector and Client Inspector for final inspection before proof test for final visual and dimensional inspection.
      
   2. The Authorized Inspector shall make his final visual inspection before proof test. He shall sign and date ITP package, when he is satisfied that the 1440 PSI – TEST SEPARATOR 20' CSC / DNV EQUIPMENT FRAME meets the applicable Code requirements. The QA/QC Manager shall ensure that all NCRs are properly closed before proof test.
      
   3. Testing shall be conducted in accordance with CSC / DNV requirement
      
   4. Prototype testing include:
      
      1. 4 Lifting points test
         
      2. 2 Lifting points test
         
      3. Drop Test
         
      4. Longitudinal and lateral inertia test
         
      5. Longitudinal restraint test
         
      6. Transverse Racking
         
      7. Stacking Test
         
      8. Top Corner ISO Lifting Points Test
         
      9. Bottom Corner Lifting Points Test
         
      10. Lifting Test – Forklift Pockets
          

   
    

2. Painting
   
   1. Surface Preparation and Painting shall be conducted in accordance with approved procedure.
      

 

1. Packing and Shipping preparation
   
   1. Packing and shipping preparation shall be in accordance with procedure
      

   
    

2. Manufacturing Data Book (MDR)
   
   1. All material test certificates and inspection reports shall be compiled progressively by QC Inspector.
      
   2. The contents of MDR shall be in accordance with "Manufacturing Data Report Index - Table of Content".
      

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

   
    

Appendix A – Fabrication Sequence

Arctic SteelsCriteria for safe materials utilisation

Arctic Steels

Criteria for safe materials utilisation

by

 

Christian Thaulow

Norwegian University of Science and Technology (NTNU), Trondheim, Norway

christian.thaulow@ntnu.no

 

Jack Ødegård and Erling Østby

SINTEF Materials and Chemistry, Trondheim, Norway

 

Abstract

The development of arctic oil and gas fields will require new low temperature High Strength Steels, including welding, and integrity management capable of significantly reducing the probability of failure in critical extreme environments. In addition to low temperatures, also larger strains must be accounted for because of iceberg scours ,thaw settlement and landslides . In order to allow for a high utilisation of the new arctic steels and at the same time increase the level of safety ("zero-leakage" and "maintenance-free" solutions), relevant material test methods and acceptance criteria must be available. Constraint corrections and direct calculations based on linespring technology opens up for realistic quantitative assessments of failures. One example is the calculation of probability of failure based of probabilistic fracture mechanics methodologies

 

1. INTRODUCTION

Back in the 80-ties large thematic programs were conducted on steel research and development in order to meet the new challenges brought forward by the oil and gas exploration and production on the Norwegian Continental Shelf.

Oil and gas exploration in Arctic regions puts new and harsh requirements to competence and technology development as new materials will be introduced into new environments. In order to meet the standards for safe exploration and operation, new step changes have to be made. The most reliable and robust technology have to be developed as "zero-leakage", and "maintenance-free" solutions must be sought and qualified.

The development of arctic oil and gas fields will require new low temperature High Strength Steels, including welding, and integrity management capable of significantly reducing the probability of failure in critical extreme environments.

 

Special Arctic environment conditions

Air temperature – Steels are susceptible to brittle fracture at low temperatures. In general the materials are qualified at so-called "design temperatures", which typically lies 20°C below minimum expected service and/or ambient temperature. The lowest ambient temperature on the Norwegian continental shelf is about -20°C, and the design basis for the Snøhvit project is -23°C. In the Arctic regions, minimum ambient temperatures well below -40°C must be expected. Consequently minimum design temperatures down to - 60°C must be accounted for.

 

Larger deformations – Present pipeline design rules are stress-based, and only limited strains are allowed for, typically up to 0.5%. However, larger deformations/strains are expected in the Arctic for a range of reasons: thaw settlement and frost heave, landslides, iceberg scours (up to 10 meters deep), strains far beyond the yielding limit of the materials are out of range of today's design rules, Figure 1. Steel constructions in arctic marine regions are exposed to heavy wind and ice-loads, which must be taken into account. In combination with extreme low temperatures this puts the toughest requirements to the structures and their functionality and lifetime integrity.

 

 

 

 

 

 

 

 

 

 

 

Figure 1 Range of deformations for pipelines

2. Steel research at NTNU/SINTEF for the Norwegian continental shelf

There has been a continuous development and application of new materials coupled with fundamental understanding of the material properties and development of predictive tools. Before 1980 the materials used in offshore industry were based on materials qualities from the ship industry and general structural engineering. Nothing was developed or specified with respect to the extreme and harsh conditions that are characterizing the North Sea.

 

In 1980 there was a break through for new steels developed to meet the demands from the offshore industry. The fabrication yards had for some time demanded more fabrication friendly materials with respect to weldability and fracture toughness. The result was the so-called low carbon micro alloyed steels, which were standardized in 1984.

 

The first full-scale application of the steel was for the Odin platform. But, surprisingly, areas of the heat affected zone showed low toughness, and large research projects were carried out in order to understand the problem of "local brittle zones". The Norwegian Petroleum Directorate was very concerned about the safety, and a long lasting cooperation with SINTEF/NTNU was established. This resulted in the so-called NPD testing procedure. More than 30 steels were tested and the development in welding/fracture toughness could be compared and commented upon.

 

Norway, with very limited domestic steel manufacturing industry, negotiated with the international steel manufacturers in order to find the balance between what is possible to manufacture (to an acceptable price) and what is needed for a fabrication friendly and safe offshore structure. Other countries often have to take special considerations in order to "protect" or help their national steel industry and are therefore more limited in their choices.

 

One example of this unique situation is the cooperation with Japanese steel industry. This industry has for a long time been very innovative, and they have delivered steel to a range of offshore structures and pipelines. In 1990 a Norwegian-Japanese Cooperation was established between the five large Japanese steel manufacturers, Norwegian oil companies and fabrication yards, Osaka University and SINTEF/NTNU. The aim with the project was to qualify the new high strength steels (yield strength 420-500 MPa) for offshore application and to develop realistic acceptance criteria. It was for the first time that so many Japanese steels works cooperated, and it was created a "win-win" meeting place between manufacturers and users. The cooperation included exchange of researchers for longer periods, up to two years, and numerous seminars, workshops and joint papers in international journals.

 

The driving force for introducing high strength steels has been the potential for weight reductions and the gains have been so high that the offshore industry continuously has asked for material qualities that have not yet been standardised. In order to qualify the steels and their weldments, and to prepare for future standardization, the industries have sponsored both basic and applied R&D programs, Table 1. These programs are usually organized to bring steel manufacturers, welding companies, fabricators, engineering companies and the oil companies together.

 

Table 1. Research projects at NTNU/SINTEF on Fracture Control for Offshore Applications.

CAOS "Crack Arrest Offshore Steels" (1986-1990). SINTEF/NTNU. Joint Industry Project (JIP), with one Japanese and one European steel-manufacturer and offshore industry.

 

Norwegian-Japanese cooperation program (1990-1994), Osaka University and SINTEF/NTNU.
JIP with 5 Japanese steelmakers and Norwegian industry, supported by NRC (Norwegian research council).

 

ACCRIS "Acceptance Criteria and Level of Safety for High Strength Steel Weldments" (1994-1997). SINTEF/NTNU. JIP, supported by ECSC (European Coal and Steel Community) and NRC

 

PRESS "Prediction of Structural Behavior on the Basis of Small Scale Testing." (1998-2002). SINTEF/NTNU. JIP, supported by ECSC and NRC

 

Fracture Control Offshore Pipelines (2002-2006). SINTEF/NTNU. JIP, supported by NRC

 

 

As a result of this kind of research new steel qualities with low alloying content and high weldability has been developed, and a high level of safety has been maintained despite for the increased strength level (which will generally increase the stresses and thereby reduce the critical defect sizes).

 

During the last ten years mathematical modelling and FE calculations have developed from research tools to be used in practice. The predictive capacity has improved as new material qualities and strength levels are introduced. The development from steel grade 350 to 460 has continued, and the Grane platform was recently built with 500 steel. This progress has been made possible through the research projects over the years. And the development continues in various directions. One example is the research project PRESS where steel grade 700 has been examined. Such high strength steels were applied in the Siri platform.

3. Criteria for safe materials utilisation

For safe materials utilisation the brittle fracture phenomena is a focused area. The state-of-the-art today is represented by a micromechanical approach to model the initiation of cleavage fracture. A new approach in quantifying the constraint effect, e.g. the fracture toughness dependency on geometry, loading and material mismatch, is the so-called JQM Approach (1, 2).

 

Much of to-days methodologies for Crack Arrest relates back two the Battelle approach which was first presented by Maxey in 1974. The approach is based on empirical relationships and simplified equations, and has proved to be robust to date, even when stretched far beyond the empirical basis. However, the operational characteristics currently being considered for future pipeline designs range far beyond any conditions that have been investigated in the past (higher pressure, higher strength materials/welds, rich gas, lower operating temperatures, frost heave, thaw settlement….). There is also a strong need to improve current gas-decompression models to account for the future pipeline designs.

 

To account for large deformations, Figure 1, a framework for strain-based design of pipelines is now under development (3-7).

 

4. Constraint based design and direct calculations

Today's practice in fracture mechanics testing is to ensure a conservative approach by recommending the use of test specimen geometries with high constraint (deeply notched bend- or compact tension specimens). This approach, however, can put severe limitations on the application of high strength steels. By applying constraint corrections, e.g. the T-stress or the Q-parameter, more accurate predictions can be achieved, and the safety aspect can then be managed by introducing safety factors, Figure 2. The thick line represents the fracture toughness (eg. the material property), while the thin lines represents the applied crack driving force. The structure is expected to fracture when the applied force exceeds the material resistance.

 

Figure 2 also includes a pipe subjected to bending load. The pipe-geometry exhibits typically much lower constraint than the fracture mechanics SENB-specimens, and revisions of the rules have recently been published in favour of including the SENT specimen geometry for engineering critical assessments of installation of pipes (8). SENT specimens have not yet been qualified for operational conditions, due to limited information about the effect of biaxial loading (internal pressure). But results from SINTEF shows that internal pressure has no influence on the fracture toughness for ductile materials, which means that SENT specimens can be used for establishing fracture properties also under conditions of operation (7).

 

The procedure of constraint correction works well theoretically, and many papers have demonstrated a sound physical basis. A major drawback for the practical application is, however, the need for detailed FE calculations or detailed knowledge of the theories. So, new methodologies where high accuracy can be maintained without introducing complex or costly calculations are needed. Direct calculations of components based on a combination of shell- elements and linesprings, LINKpipe, has demonstrated to meet this challenge (9-13).

 

LINKpipe is a state-of-the-art software-tool for analysis of the criticality of cracks and defects in pipelines and piping systems. The program simulates external and internal surface cracks in pipelines under tensile, bending and internal/external pressure. In LINKpipe the geometry of an elliptical surface crack is represented by so-called linespring elements. The linespring is implemented in a co-rotated kinematical finite element formulation, i.e. accounting for large displacements and rotations. The program also accounts for plastic necking of the ligament and non-proportional loading. The linespring calculations have been verified by 3D FE calculations and full scale testing of pipes, with and without internal pressure.

 

 

 

 

 

 

Figure 2 Schematic representation of fracture toughness as a function of constraint for three test specimens and a pipe-geometry.

 

In Figure 3a we compare the result of the linespring/shell-elements with 3D large strain FE calculations for a pipe . The results are very similar, except for the time of calculation: LINKpipe is 600 times faster.

 

Shown in Figure 4 are the results obtained from the tensile loading of a surface cracked pipe with additional internal pressure. The magnitude of pressure is marked as the ratio of hoop stress caused by the internal pressure to the initial yield stress. As the internal pressure increases, the unstable tearing begins at lower values of deformation. In other words, the deformation capacity of the cracked pipe is significantly reduced under biaxial loading.

 

Concluding remarks

In order to allow for a high utilisation of the new arctic steels and at the same time increase the level of safety ("zero-leakage" and "maintenance-free" solutions), relevant test methods and acceptance criteria must be available. The application of constraint corrections and the introduction of direct calculations pave the way for quantitative assessments of failure. One example is the calculation of probability of failure based of probabilistic fracture mechanics methodologies (6).

 

 

 

 

 

Figure 3 CTOD vs. strain for a pipe with an elliptical surface crack. The pipe dimensions are OD=400mm, WT=20mm. The crack is halfway through the thickness. The computation times for the 3D and linespring calculations are indicated.

 

 

Figure 4 The effect of internal pressure, combined with ductile tearing, on the applied CTOD vs. global strain. Surface cracked pipe under tension load.

 

References

1. Zhang, Z.L., Hauge, M. and Thaulow, C.: "Two Parameter Characterisation of the Near Tip Stress Fields for a Bi-Material Elastic-Plastic Interface Crack", Int. Journal of Fracture, 79:65-83, 1996.

 

2. Thaulow, C., Zhang, Z.L., Ranestad, Ø. and Hauge,M., "J-Q-M approach for failure assessment of fusion line cracks: two material and three material models". ASTM STP 1360, Fatigue and Fracture Mechanics: 30^th Volume. St.Louis. June 1998

 

3. Bruschi, R., Torselletti, E., Vitali, L., Hauge, M., Levold, E. Fracture Control – Offshore Pipelines: Current Status of Fracture Assessment for Pipelines Limitations and the Need for Development. Proceedings of OMAE2005, 24th International Conference on Offshore Mechanics and Arctic Engineering (OMAE 2005), June 12-16, 2005, Halkidiki, Greece

 

4. Østby, E., "Fracture Control – Offshore Pipelines: New Strain-Based Fracture Mechanics Equations Including the Effects of Biaxial Loading, Mismatch and Misalignment", Ibid

 

5. Thaulow C, Skallerud B, Jayadevan KR, Berg E, Fracture Control – Offshore Pipelines: Advantages of Using Direct Calculations in Fracture Assessments of Pipelines. Ibid

 

6. Sandvik A, Østby E, Naess A, Sigurdsson G, Thaulow C. Fracture Control – Offshore Pipelines: Probabilistic Fracture Assessment of Circumferentially Surface Cracked Ductile Pipelines Using Analytical Equations, Ibid

 

7. Nyhus B, Østby E, Knagenhjelm HO, Black S, Røstadsand PA. Fracture Control – Offshore Pipelines: Experimental Studies On The Effect Of Crack Depth And Asymmetrical Geometries On The Ductile Tearing Resistance, Ibid

 

8. Wästberg, S. Pisarski, H. and Nyhus, B., "Guidelines For Engineering Critical Assessments for Pipeline Installation Methods Introducing Cyclic Plastic Strain", Proceedings of OMAE04, 23rd International Conference on Offshore Mechanics and Arctic Engineering, June 20–25, 2004, Vancouver, British Columbia, Canada

 

9. Skallerud B, Holthe K and Haugen B., (2005). "Thin shell and surface crack finite elements for simulation of combined failure modes". Comput. Methods Appl. Mech. Engng. 194, 2619-2640

 

10. Thaulow C, Østby E, Nyhus B, Zhang Z L and Skallerud B (2004). "Constraint correction of high strength steel: Selection of test specimens and application of direct calculations". Engineering Fracture Mechanics, 71, 2417-2433

 

11. Skallerud B, Berg E, and Jayadevan KR (2006), "Two-parameter fracture assessment of surface cracked cylindrical shells during collapse", Engineering Fracture Mechanics 73, 264-282

 

12. Jayadevan, K.R., Thaulow, C., Østby, E., Berg, E., Skallerud, B., Holthe, K., Nyhus, B., (2005). "Structural Integrity of Pipelines: T-stress by line-spring". Fatigue Fract Engng Mater Struct, 28, 467-488.

 

13. Jayadevan K R, Berg E, Thaulow C. ,Østby E. and Skallerud B. (2006) "Numerical investigation of ductile tearing in surface cracked pipes using line-spring". Int. J. Solids and Structures, 43, 2378-2397