How to Weld Underwater

Underwater welding is a process whereby metals are melted together underwater to either repair a structure or create a new structure. Used on oil wells, ships, and other underwater structures, underwater welding is done by one of two methods. The first is hyperbaric welding, in which a structure is created around the weld and a pressurized environment created. The second is arc welding, in which the welding electrode contains a flux coating that releases gases to preserve the integrity of the weld. Because of the dangers of shock, explosion and poisoning, underwater welding is only performed by professionals with both diving and welding certifications.

Hyperbaric Welding Method

1. Identify the site and material of the joint to be welded as most underwater welds involve steel, but metals may vary.
   
   
   
2. Prepare a chamber to place around the joint (each joint should have a separate chamber).
   
   
   
3. Introduce gas into the chamber.
   A typical gas mixture uses helium and oxygen, but requirements vary based on the specific joint to be welded. The pressure of the chamber should be slightly above that of the surrounding water.
   
   
   
4. Run a power supply to the chamber and set up a port for your electrodes.
   Multiple electrodes will likely be required, and should be placed in advance in front of the area of the joint to be welded.
   
   
   
5. Dive to the weld site.
   
   
   
6. Turn on the power supply and weld the joint from outside the chamber.
   
   
   
7. Turn off the power supply as soon as the welding is done.
   
   
   

Arc Welding Method

1. Investigate the joint to be welded and identify the types of metals involved.
   
   
   
2. Prepare the adequate electrodes, plan out the order of welding and dive to the weld site.
   
   
   
3. Weld the joint, ensuring that the flux coating of the weld is coming off as expected, and that too much hydrogen is not approaching the joint.
   
   
   
4. Turn off the power supply as soon as the welding is done.
   
   
   

Source :

http://www.wikihow.com/Weld-Underwater

Subsea Tie-in Systems

SUBSEA TIE-IN SYSTEM

Subsea flowlines are used for the transportation of crude oil and gas from subsea wells, manifolds, off-shore process facilities, loading buoys, S2B (subsea to beach), as well as re-injection of water and gas into the reservoir. Achieving successful tie-in and connection of subsea flowlines is a vital part of a subsea field development.

Vertical Tie-in System
Vertical connections are installed directly onto the receiving hub in one operation during tie-in. Since the Vertical Connection System does not require a pull-in capability, it simplifis the tool functions, provides a time effiient tie-in operation and reduce the length of Rigid Spools.
Stroking and connection is carried out by the the Connector itself, or by the ROV operated Connector Actuation Tool (CAT) System.

Vertical Tie-in assisted by V-CAT

Horizontal Tie-in System
Horizontal Tie-in may be used for both first-end and second-end tie-in of both flowlines, umbilicals and Jumper spools. The termination head is hauled in to the Tie-in point by use of a subsea winch. Horizontal Tie-in may be made up by Clamp Connectors operated from a Tie-in tool, by integrated hydraulic connectors operated through the ROV, or by non-hydraulic collect connectors with assistance from a Connector Actuation Tool (CAT) and ROV. Horizontal connections leave the flowline/ umbilical in a straight line, and is easy to protect if overtrawling from fishermen should occur.

Horizontal Tie-in

Considerations related to choice of connector can be seen in the table below

Connector

• Collect connector
  Collet connectors consist of collet-style “figer” design which fimly locks around a mating hub. Collet connectors are used for both vertical and horizontal jumper spool connections and are available in both integral hydraulic and mechanical (with separate actuation tool) confiurations.
  
  

  

  Collect connector

• Clamp connector
  Clamp connectors consist of a two piece segmented clamp design and are particularly well suited for larger bore, lower pressure horizontal connection applications.
  

  

  Clamp connector

  
  
• Bolted flange
  A bolted flange connection utilizes a metal gasket which is compressed to seal between two flanges. The bolts axis has the same orientation as the pipeline. When the bolts are tightened the metal gasket is deformed between the two flanges. The gasket allows the flanged connection to have some initial misalignment, but it is very vulnerable to rotational misalignment about z-axis due to the flanges respective bolt hole orientation.
  
  

  

  Bolted flange

Source :
Sletteb, Espen, 2012, Master's Thesis : Tie-in SPools - A Verification Study, University of Stavanger
Subsea Tie-in System brochure by FMC Technologies

Horizontal Directional Drilling

Didalam melakukan pengeboran suatu formasi, selalu diharapkan pengeboran dengan lubang yang lurus/vertikal, karena pengeboran dengan lubang yang lurus/vertikal selain dalam operasinya lebih mudah, juga pada umumnya biayanya menjadi lebih murah. Namun karena kondisi-kondisi tertentu, pengeboran lurus/vertikal tidak bisa dilakukan oleh karenanya perlu dilakukan pengeboran yang bisa diarahkan sesuai kondisi-kondisi tersebut. Pengeboran yang dilakukan dengan cara mengarahkan lubang biasa disebut dengan pengeboran berarah atau pengeboran horisontal (Directional and Horizontal Drilling). Beberapa faktor-faktor penyebab dilakukannya pengeboran berarah atau horizontal (Directional and Horizontal Drilling) adalah geografi, geologi dan pertimbangan ekonomi. Di bawah ini beberapa contoh alasan dilakukannya pengeboran berarah atau horizontal (Directional and Horizontal Drilling).

1. Inaccesible Location Drilling
   Beberapa reservoir dengan kondisi di permukaan yang tidak memungkinkan untuk dilakukan pengeboran lurus/vertical akan sangat cocok untuk dilakukan pengeboran berarah atau horizontal (Directional and Horizontal Drilling). Teknik ini adalah salah satu dari teknik pengeboran berarah yang paling umum dilakukan untuk mencapai lapisan yang tidak dapat dicapai dengan cara yang biasa, sebagai contoh reservoir yang terletak di bawah kota, di bawah lahan pertanian/perkebunan, dll. Gambar dibawah memperlihatkan formasi yang berada di bawah perkotaan sehingga dilakukan pengeboran berarah atau horizontal (Directional and Horizontal Drilling).
   
   
   
2. Multiple Well DrillingBila suatu lokasi pengeboran memiliki keterbatasan area pada permukaan sehingga tidak mungkin dilakukan pengeboran banyak sumur dengan letak yang berbeda. Hal ini bisa diatasi dengan melakukan pengeboran multiple well. Yakni mengebor pada satu lokasi dengan banyak sumur yang dibuat, untuk itu dilakukanlah pengeboran berarah atau horizontal (Directional and Horizontal Drilling). Multiple well drilling ini sering dilakukan pada pengeboran lepas pantai dari suatu platform tunggal atau dari suatu tempat yang terpencil. Gambar dibawah  memperlihatkan suatu platform yang melakukan Multiple well drilling.
   
   
   
3. Salt Dome DrillingPada daerah yang didapati kubah garam (salt dome) yang letaknya berada di atas reservoir minyak, pengeboran lurus/vertical tidak mungkin dilakukan. Karena bila pengeboran menembus kubah garam (salt dome) akan mengakibatkan masalah yang serius terutama akan terjadinya blow out sehingga perlu dilakukan pengeboran berarah atau horizontal (Directional and Horizontal Drilling) yangakan mengarah langsung ke reservoir minyak. Gambar dibawah memperlihatkan reservoir yang berada di bawah kubah garam (salt dome).
   
   
   
4.  Side Tracking atau Straightening
   Kadangkala dalam melakukan operasi pengeboran lurus/vertikal terjadi pembelokan yang sangat parah sehingga menjauh dari target, sehingga perlu untuk meluruskan kembali lubang sumur tersebut.
   Untuk itu dilakukan side tracking dengan melakukan pengeburan berarah. Atau pada kejadian dimana fish yang tidak dapat diangkat dan terkubur dilubang bor, pengeboran harus menghindari fish tersebut agar peralatan pengeboran tidak rusak maka dilakukan side tracking.
5. Relief Well DrillingPada kejadian sumur yang blow out, salah satu cara untuk menanggulanginya adalah dengan mengebor atau membuat relief well. Relief well merupakan sumur yang dibuat di dekat sumur yang blow out dengan tujuan untuk mengalirkan fluida yang mengakibatkan blow out sehingga dapat dikendalikan. Biasanya relief well dilakukan dengan pengeboran berarah atau horizontal (Directional and Horizontal Drilling).
   
   
   

Pemboran berarah dapat dikerjakan dengan peralatan membor konvensional, dimana pipa bor diputar dari permukaan untuk memutar mata bor di bawah. Kelemahannya, sudut yang dapat dibentuk sangat terbatas. Pemboran berarah sekarang lebih umum dilakukan dengan memakai motor berpenggerak lumpur (mud motor) yang akan memutar mata bor dan dipasang di ujung pipa pemboran. Seluruh pipa pemboran dari permukaan tidak perlu diputar, pipa pemboran lebih dapat “dilengkungkan” sehingga lubang sumur dapat lebih fleksibel untuk diarahkan.

Mud motor

Ilustrasi proses horizontal directional drilling dapat dilihat pada video berikut ini.

Referensi :

Dasar-Dasar Teknik Pengeboran (2013), Kementrian Pendidikan dan Kebudayaan Republik Indonesia

Pipeline Elbow

Elbows are categorized based on various design features as below:

• Long Radius (LR) Elbows – radius is 1.5 times the pipe diameter
• Short Radius (SR) Elbows – radius is 1.0 times the pipe diameter
• 90 Degree Elbow – where change in direction required is 90°
• 45 Degree Elbow – where change in direction required is 45°

90 degree Elbow Pipe

A 90 degree elbow is also called a “90 bend” or “90 ell”. It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe. It used to change the direction in piping and is also sometimes called a “quarter bend”. A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead. It can also attach to rubber with stainless steel clamps. It is available in many materials like silicone, rubber compounds, galvanized steel, etc. The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains. These elbows can be made from tough nylon material or NPT thread.

45 Degree Elbow Pipe

A 45 degree elbow is also called a “45 bend” or “45 ell”. It is commonly used in water supply facilities, food industrial pipeline networks, chemical industrial pipeline networks, electronic industrial pipeline networks, air conditioning facility pipeline, agriculture and garden production transporting system, pipeline network for solar energy facility, etc.

Most elbows are available in short radius or long radius variants. The short radius elbows have a center-to-end distance equal to the Nominal Pipe Size (NPS) in inches, while the long radius is 1.5 times the NPS in inches. Short elbows are widely available, and are typically used in pressurized systems.

Elbow Pipe having a lot of usage. One of the elbow usage in a pipe line is for determining the rate of flowing the pipe

INTRODUCTION THE USE OF AN ELBOW IN A PIPE LINE FOR DETERMINING THE RATE OF FLOWING THE PIPE

1. Object and Scope of Investigation.-The tests herein reporter were made for the purpose of obtaining information concerning the feasibility of using an elbow in a pipe line as a means of determiningthe flow of a fluid through the pipe, by measuring the difference between the pressures of the fluid on the inside and outside curves of theelbow, respectively, as indicated in Fig. 1. Some of the desirable characteristics of an elbow used as a flow meter are low initial cost, smallcost of upkeep, and no additional resistance to flow due to the elbowbeing converted into a meter.

There are very few published data’-9* available concerning elbowsused as flow meters, especially data concerning the ordinary commercial type of elbow.

The tests reported in this bulletin were made on threaded andflanged elbows of long and short radii, ranging in diameter from oneinch to twenty-four inches. Sixteen different elbows were tested innearly forty different positions and locations in various pipe lines. Allthe elbows tested were 90-deg. bends; typical elbows are shown inFig. 2. Water was the only fluid used in the tests of the elbow metersherein reported.

2. Acknowledgments.-The investigation reported in this bulletin was carried out in the Hydraulics Laboratory of the University ofIllinois as part of the work of the Engineering Experiment Station,of which DEAN M. L. ENGER is the director, and of the Department ofTheoretical and Applied Mechanics, of which PROF. F. B. SEELY isthe head.The tests on the 24-in. elbows were made by MR. E. C. CHAMBERLIN, JR., a senior student at the University of Illinois, in satisfyingthe requirement for a thesis for the degree of Bachelor of Science.

Reference :

Lanford, Wallace M. 1936. The Use Of An Elbow In A Pipe Line Fordetermining The Rate Of Flowin The Pipe. University Of Illinois Bulletin.

Pipeline Inspection

Pipeline inspection is part of pipeline integrity management for keeping the pipeline in good condition. The rules governing inspection are the pipeline safety regulation. In most cases, the pipeline is inspected regularly. 

The pipeline safety regulations require that the operator ensure that a pipeline is maintained in an efficient state, in efficient working order, and in good repair. In fact, the pipeline operator has a vested interest in the pipeline being operated effectively and safely to satisfy the appropriate authority and save the failure cost in environment, loss of production, and repair. The pipeline inspection includes external inspection and internal inspection. The subsea pipeline external inspection looks at the pipeline's external condition, such as concrete weight coating. trench and concrete mattress losses, marine growth, anode wastage, and corrosion, free span and global buckling condition, and damages due to external load through visual observation. The subsea pipeline internal inspection is normally carried out though nondestructive testing techniques and technologies by intelligent pigs, such as magnetic-flux leakage technology in axial and circumferential conditions, ultrasound technologies, eddy-current technologies, and other technologies. 

The table below summarize the common type of survey and inspection methods for subsea pipelines. 

The abbreviationsin the table are defined as

• RAT : Rope access technicians; rope access is a means of working at height or depths in location that would be difficult or dangerous to reach by other means
• GI : General imaging, inspection using side scan sonar
• GVI : General visual imaging, using cameras
• NDT : Nondestructive testing
• FMD : Flooded member detection
• CP : Cathodic protection
• ROTV : Remotely operated towed vehicle
• WROV : Work-class remotely operated vehicle

In DNV RP F116, there are some other inspection method that can used to maintain subsea pipeline

• CVI : Close visual inspection
  A high standard of cleaning is required for this type of inspection, all hard and soft marine growth should be removed. The purpose of the inspection is to establish a detailed inspection of an area of specific interest. Requires either a diver or workclass ROV.
• HPS : Hig hprecison survey
  A high accuracy positional survey to determine the absolute position and relative year to year lateral movement of the pipeline on the seabed. This is achieved using a workclass pipeline ROV (as used for GVI), in conjunction with high accuracy calibrated positional equipment (e.g. high performance corrected DGPS, transponders (USBL/ LBL systems), ROV mounted survey quality gyro and motion sensor, high frequency doppler velocity log etc.). Inspection rate can be expected to be slower and will require more calibration time than standard GVI.
• ILI : In-line inspection
  Intelligent pigging of the pipeline. Utilizing various non-destructive testing (NDT) methods to measure continuous end to end pipeline wall thickness loss or pipeline anomalies/defects.
• Monitoring
  Following up of corrosion probes, impressed current system, process parameters, fluid composition and any onshore monitoring of load/stresses.

Source :
Yong Bai, Qiang Bai (2014), Subsea Pipeline Integrity and Risk Management, Elsevier
Det Norske Veritas Recommended Practice (DNV RP F116) : Integrity Management of Submarine Pipeline System

Pig Launcher, Pig Receiver & Intelligent Pig

PIG LAUNCHERS AND RECEIVERS

In simplest terms the PIG launchers and PIG receivers are the sections of the pipeline which allow the PIG to enter and exit the pipeline. They are generally funnel, Y-shaped sections of the pipe which can be pressurized or depressurized and then safely opened to insert or remove PIGs. Most pigging systems use bidirectional launchers and receivers that can work in either direction. This is important to allow the PIG to be retrieved by the launcher if there is a blockage in the pipeline which prevents it from reaching the receiver.

PIG launchers and receivers come with safety valves and locking system to prevent accidents. They are also optimized to be suitable to the pressure and temperature requirements of the pipeline. Launchers and receivers may be horizontal or vertical depending on the needs of the pipeline.

Some launchers are designed to hold multiple PIGs at once and configured to launch them according to preset conditions. This is very useful because it allows much of the work to be done remotely. Additionally it prevents the launcher from having to be depressurized and repressurized again each time a single PIG is needed. It is the pressure from the flow of product that moves the PIGs through the pipeline. Thus one of the main roles of launchers and receivers is to safely interface between the low-pressure outside world and the high-pressure pipeline.


The exact procedure for operating a PIG launcher or PIG receiver will vary somewhat depending on the particular pigging system being used. However, for the most part it will include the following steps:

Launcher:

• Pipeline operator should make sure that the isolation valve and kicker valve are closed.
• If the system is a liquid system then the drain valve and vent valve should then be opened to allow air to displace the liquid; if the system is a gas system then the vent should be opened so that the launcher reaches atmospheric pressure.
• After the PIG launcher is completely drained to 0 psi, with the vent and drain valves still open, the trap door should then be opened.
• The PIG should then be loaded with its nose in contact with the reducer.
• Closure seals and other sealing surfaces should be cleaned and lubricated as needed and then the trap door should be closed and secured.
• The drain valve is then closed and the trap is slowly filled by gradually opening the kicker valve.
• Once filling is complete the vent valve is closed so that the pressure will equalize across the isolation valve.
• The isolation valve is then opened and the PIG is ready for launching.
• Next the main valve is gradually closed, increasing the flow through the kicker and behind the PIG until finally the PIG leaves trap altogether and enters the pipeline itself.
• After the PIG leaves the launcher the mainline valve is fully opened and the isolation valve and kicker valve are closed.

Pig launcher

Receiver:

• The receiver should be pressurized.
• The bypass valve should be fully opened.
• The isolation valve should be fully opened and the mainline valve partially closed.
• Once the PIG arrives the isolation and bypass valves should be closed.
• The drain valve and vent valve are then opened.
• Once the trap is fully depressurized to 0 psi the trap can be opened and the PIG removed.
• The closure seal and other sealing surfaces should be cleaned and lubricated as needed and the trap door should then be re-shut and secured.
• The receiver should then be repressurized and returned to its original condition.
• These processes may differ somewhat on different systems and of course if the launcher will be launching multiple PIGs then they should all be loaded at the loading stage.

Pig receiver

INTELLIGENT PIGS

Intelligent pig

The accuracy of location and measurement of anomalies by the intelligent pigs has continued to improve. Initially, the electronics and power systems were so large that intelligent pigs could be used only in lines 30 in. and greater in size. The continued sophistication and miniaturization of the electronic systems used in the intelligent pigs has allowed the development of smaller pigs that can be used in small-diameter pipelines. Newly enacted DOT pipeline-integrity regulations and rules acknowledge the effectiveness of the intelligent pigs and incorporate their use in the pipeline-integrity testing process.

Reference :

http://en.wikipedia.org/wiki/Pigging
http://setxind.com/midstream/what-are-pig-launchers-and-receivers/

Pipeline Corrosion Resistance Alloy Material

Corrosion Resistance Alloy Pipe merupakan pilihan utama untuk pipa penyalur cairan yang sangat korosif. Hal ini disebabkan oleh karena lapisan internal yang terbuat dari material-material yang tahan korosi. 

Potongan corrosion resistant alloy pipe

Material tersebut terbagi menjadi beberapa jenis, yaitu :

• Stainless Steel

Merupakan material tahan karat. Biasanya material pembentuknya menggunakan steel dengan kode bahan 316L, 625 (Inconel), 825, 904L, dll

• Chrome Based Alloy

Merupakan material tahan karat yang menggunakan senyawa krome sebagai bahan tambahan dalam pembuatan alloy. Biasanya Chrome Based Alloy menggunakan kode13 Cr, Duplex, Super Duplex.

• Nickel Based Alloy

Nikel merupakan material tahan karat lainya. Material ini cocok digunakan untuk transport fluida hydrocarbon dengan temperature rendah. Seperti LNG ( Liquified Natural Gas ) yang memiliki suhu – 160oC. contoh material berbasi nickel adalah 36 Ni (Invar)

• Titanium

Titanium merupakan material tahan karat dengan banyak kelebihan, selain anti karat, bahan ini juga ringan ( 56% berat steel ), selain itu memiliki tensile strength yang tinggi ( hingga 200 ksi ). Kekurangan material ini ada pada ongkons pembuatanya yang mahal ( 10x ongkos pembuatan steel).

• Alumunium

Alumunium merupakan logam yang termasuk kedalam jenis Corrosion Resistan Alloy material. Material ini termasuk material yang ringan beratnya hanya 1/3 dari berat steel. Namum memiliki tensile strength yang relative rendah kurang lebih hanya 90 ksi. 

Berikut adalah table yang menunjukan kandungan senyawa crome dalam material pipa berdasarakan jumlah asam yang terkandung dalam fluida.

Referensi :

Keuter, Johannes, 2014, IN-LINE INSPECTION OF PIPES USING CORROSION RESISTANT ALLOYS (CRA), Pigging Products & Services Association