Pipeline inspection

1. Pipeline inspection Generally, Offshore Subsea Pipeline inspection contains following: • Pressure tests • External pipeline inspection (Direct Assessment) • Internal pipeline inspection (in-line inspection)

2. Internal Inspection Comparison External Inspection Direct Assessment Coating Coating Lining CP Leaks Intelligent Pigs Steel Pipe Geometric anomalies Corrosion Cracks

3. External Pipeline Inspection (Direct Assessment) • Coating Survey • CathodicProtection • Manual or automated external inspection • Soil Modeling

4. Internal Pipeline Inspection Application of pigs and in-line inspection tools Free swimming tools • Intelligent pigs • Cleaning, batching and sealing pigs • Cable tools • Pumped tools • Crawler tools

5. Internal Pipeline Inspection Application of pigs and in-line inspection tools Free swimming tools • Intelligent pigs • Cleaning, batching and sealing pigs • Cable tools • Pumped tools • Crawler tools

6. Pipeline Coatings The purpose of pipeline coating is to reduce the necessary CP-current. Bare Pipe would draw to much current. Today’s external coating types are usually either from Fusion Bonded Epoxy (FBE) or three-layer (Polyethylene) PE. Internal coating is used for different circumstances. • Gas lines: Reduction of gas friction • Oil Lines: Prevention of internal corrosion

7. Internal Coatings The primary reason of applying internal coatings is to reduce the friction and therefore enhance flow efficiency. Besides, the application of internal coatings can improve corrosion protection, pre-commissioning operations and pigging operations. An effective coating system will provide an effective barrier against corrosion attack.

8. External coatings Oil and gas pipelines are protected by the combined use of coatings and CathodicProtection. The coating systems are the primary barrier against the corrosion therefore highly efficient at reducing the current demand for cathodic protection. However, they are not feasible to supply sufficient electrical current to protect a bare pipeline. Cathodic protection prevents corrosion at areas of coating breakdown by supplying electrons.

9. Coatings are selected based on the design temperature and cost. The principle coatings, in rough order of cost are: • Tape wrap • Asphalt • Coal tar enamel • Fusion bonded epoxy (FBE) • Cigarette wrap polyethylene (PE) • Extruded thermoplastic PE and polypropylene (PP)

10. Inspection Technology Pigs as an instrument for non-destructive testing For inspection, intelligent pigs are used. They contain • odometer-wheels, • IDOD-sensors, • data recording part, • sensor carrier, • battery section • and propulsion. The pig has to carry out its inspection task without damaging itself or the line.

13. Underwater Visual Inspection General Visual Inspection (GVI) Does not normally require cleaning, and allows either diver or ROV to carry out a visual inspection of a component or components. However due to marine growth coverage, only major defects may be observed such as, dented, buckled or missing members, gross cracks and any recent abrasions. Close Visual Inspection (CVI) This type of inspection requires marine growth to be removed from a component, and in most cases to bare metal. This will enable either a diver or ROV to establish any visible corrosion, pitting, weld damage and areas of previous grinding. Detailed Visual Inspection (DVI) This type requires minimal cleaning, and can normally be achieved using either hand wire brush/scrapers or HP water jetting. Bear in mind that certain types of hard marine growth will remain. It does however allow either divers or ROV to access the condition of, protective coatings, surface corrosion, clamp/flanges, relative movement and localized damage. This type of cleaning is also sufficient for Eddy Current Inspection.

14. Flaws and defects • Flaw: an anomaly or imperfection in the pipe wall which does not as yet impair the integrity of the pipe. • Defect: a flaw in the pipe wall which has grown to a significant size and requires action. • Failure: a failure has occurred when the pipe can no longer fulfill its intended function. Flaws are always present: • Despite taken greatest care in the planning, design, construction and operation of a pipeline, a flaw canal ways occur and is usually present in a latent state. • From a materials perspective there is no perfect or flawless material. In engineering terms the material or component is considered as long as it can fulfill its function: fit-for-purpose and defects have not exceeded a specific critical size.

15. Types of Flaws • Indirect flaws: Flaws not directly in the pipe wall, but which can lead to direct flaws if not controlled. Examples: Coating flaws, faulty or insufficient cathodic protection. • Direct Flaws: Flaws directly in the pipe wall, which can lead to failure of the pipe. Examples: Corrosion, cracks, dents etc.

16. Types of Flaws They can be summed into 4 main categories: • Geometric Flaws: Any significant change to the ideally round cross section of a pipe. • Metal Loss: Metal loss leads to wall thinning. • Cracks: Material separation. Tip causes stress singularity. • Leaks: Flaw which has grown through the pipe wall.

17. Requirements Regarding Pipeline Maintenance The maintenance process must ensure that: • The pipeline is always operated safely • The pipeline is operated efficiently and economically • The pipeline is compliant • The pipeline is available. A typical inspection and monitoring system includes: • Polymer monitoring: online, offline, topside and subsea; • Annulus monitoring: vent gas rate, annulus integrity; • Riser dynamics: tension, angle and curvature; • Steel armor: inspection method, magnetic or radiographic; • Use of existing sensors, pressure and temperature sensors.

18. For commissioning, this specification defines the minimum requirements for pigging and gauging, hydrostatic pressure testing and pre-commissioning for the development of offshore gas, condensate and oil production facilities. It describes the selection and preparation of a test section, the safety and environmental precautions, the test medium and test equipment requirements, the specific parts of a pressure test and the documentation of the work. The operation covered by this specification includes the following: • Filling • Cleaning • Gauging • Hydro testing • Dewatering • Vacuum drying • Nitrogen filling and nitrogen packing

19. Marine Growth Introduction The differing types of marine organisms that attach themselves to platforms are commonly known to most of use as, marine growth or marine fouling. From an engineering and technical view, information on marine growth coverage, thickness and type is essential for structural engineers. As they can analyze information collected offshore and calculate loading, drag, deterioration and possibly failure. All information collected is stored in a baseline database for assessment. From an engineering point of view, the two type of fouling are expressed as, • soft marine growth: density is equivalent to that of seawater • hard marine growth: density is thereabouts 1.4 times greater than seawater.

20. Reasons for Removal Experience has shown that growth rate, of marine fouling has proved greater than originally anticipated. In certain cases marine fouling has significantly exceeded the structural design parameters. This has lead to great concern amongst structural engineers and installation operators. Effects of Marine Growth Important structural features are obscured, making visual inspection impossible. Increases mass, without changing stiffness. Increases static load and drag factors. Distorts the structures natural designed frequencies. Increases 'Slam effect' within the splash zone, leading to premature failures and stress related cracking. Reduces efficiency service inlets or outlets. Accelerates internal corrosion, on control equipment used to supply firewater and cooling water etc. Possible effect of accelerating the structure corrosion rate. Hard Marine Growth Species Tube Worm Casts The most stubborn form of hard marine fouling to remove, casts leave calciferous white patterns almost all metal surfaces.

21. CLEANING TECHNIQUES HAND CLEANING MECHANICAL CLEANING (PNEUMATIC)

22. MECHANICAL CLEANING (HYDRAULIC) HIGH PRESSURE WATER JET CLEANING

23. GRIT ENTRAINED

24. HYDRODYNAMIC LOADS 1. Waves Loads Wave load is one of the most important effects we should consider for offshore structural analysis. Wave can be represented analytically using different theories. Several wave theories are available in ocean engineering, such as Airy, Stream Function, and Stokes, cnoidal, Solitary, trochoidaltheory depending on three dimensional parameters, d, H, and T. Or the validities of these theories could be described in terms of two dimensional parameters, H/T2 and d/T2. .

25. To calculate wave forces, one must select a proper wave theory first to compute the water particle velocities and acceleration Linear Airy theory, the sea surface elevation, water particle velocity and accretion for the regular wave, which could be expressed as:

27. The natural sea state is a stochastic process. Several wave spectrum functions are proposed to describe the sea state. The most frequently used spectra for wind generated seas are the Pierson- Moskowitz (PM) spectrum for a fully developed sea, and the JONSWAP spectrum for a developing sea. The formula for the JONSWAP spectrum is written as follows: (10) Where the significant wave height, Hs, and the peak period, TPare the required parameters to define a wave spectrum, γis the Peak-shape parameter. The Pierson-Moskowitz spectral density function may be regarded as a special case of the JONSWAP spectrum with γ =1.

28. Given the significant wave height and peak spectral period for a single simulation, the wave spectrum is calculated first and then a random, stationary sea surface elevation process composed of irregular, long-crested waves is generated. Irregular random waves, representing a real sea state, can be modeled as a summation of sinusoidal wave components. The wave profile is computed as: with Hydrodynamic loading resulting from the interaction between waves and structural members is known as a key factor in the design of offshore structures.

29. A vertical cylinder representing an offshore substructure can be considered as a slender structure in waves. For the slender structure, the diameter D of the cylinder is small compared with the wavelength λ, or the diffraction parameter D/λ is less than 0.2 (figure). In this case, the forces on the structure can be calculated from the drag and inertia components using Morison’s equation. The drag and inertia components are calculated from the water particle kinematics aforementioned. The force per unit length of member is: Where uwand uware the water particle velocity and acceleration, respectivelyusis the structure acceleration, the first term in Eq. is referred to inertia force, second one is the water added mass force, and the third one is drag force.

30. The total shear force on a slender member elevating from z1 to z2 could be found as: The coefficients Cd and Cm are determined by structure shape, the Keulegan–Carpenter number, Reynolds number and surface roughness. From Morison’s equation, hydrodynamic loads depend on the forms of the structure and the current, and inertia and drag forces. The marine growth increases the member’s diameter, surface roughness and mass of the structure, and therefore affects the hydrodynamic loads.

31. For the offshore space frames, which do mainly consist of tubular elements jointed together with different members, such as jacket structure, Morison’s equation could be also used. For the cylinder member which is oriented along a unit vector I withdirectional cosines (l, m, n), the force per unit length on the elementmay in general be written as a vector sum of the inertia or massforce Fm the drag force Fd and a transversal lift force Fl, that is:

32. EFFECTS OF MARINE GROWTH ON LOADING Marine growth has number of effects on loading of offshore structure that may among others be listed as the following: (a) increase in structural diameter and displace volume, (b) increase in force coefficients, (c) increase in structural weight, (d) increase in mass and hydrodynamic added mass, (e) increase flow instability, (f) conceal the member's outer surface and (g) cause physical obstruction. Generally, these effects cannot be overlooked if accurate estimation of the response of the structure is required.

33. Welds discontinuities • Gas Pores (Πόροι αερίου) • Slag inclusions/entrapments(Εγκλείσματα σκουριάς/Παγίδευση) • Incomplete fusion and penetration(Ατελής τήξη και διείσδυση) • Cracks(Ρωγμές) • Elongated • Transversal • Asteroid

34. FLOODED MEMBER DETECTION Flooded member detection is an inspection method which is utilized for analyses of offshore steel structures, where pipe sections are used. These structural elements (Members) are analysed for possible lack of water resistance which may indicate water leakage at the weldings, which are then selected for closer inspection. The method today is mostly undertaken by the use of ultrasound, if and when divers are used. This however requires a "living" A-scan in order to be useful and so a radioactive source is instead used when ROV (Remote Operated Vehicle) are used for inspection purposes. Through development of the inspection equipment it will be possible to also use ultrasound for ROV. This entails the improvement of safety and handling of ROV in comparison with the use of radioactive sources. The interest in such equipment which uses ultrasonic waves for ROV purposes is significant among many international underwater equipment operators. The result of the project will be presented to all interested parties at a seminar organized by Force and OCD.

35. To assess the integrity of the pipe and casing an ROV deployed flooded member detector is deployed. This device has a small radioactive source and Geiger counter mounted on a fork. The counts are proportional to the average density of whatever is between the forks and thus interrupts the radioactive beam. See Figure. Flooded Member Detector. The detector is calibrated on the west flowline, which is believed to be dry.

36. NDT INSPECTION • Visual Inspection • Liquid Penetrant Inspection • Ultrasonic • Straight beam • Angle beam • Magnetic Particles Inspection • Radiographic Inspection For the below type of defect-imperfection which type of NDT method is suitable to complete tests. Fill the below matrix with the indication (0) to (3). (0)= Does not detect (1)= Not indicated (2)= Indicated (3)=Ideal for implementing

37. Two dimensional surface Three dimensional surface Two dimensional close to surface Two dimensional close to surface and parallel to it Type of defect – imperfection Internal two dimensional vertically to surface Three dimensional close to surface Internal two dimensional parallel to surface Internal three dimensional

39. (0)= Does not detect (1)= Not Indicated (2)= Indicated (3)= Ideal for implementing