Polatrak ROV II - Tip Contact Probe Operation Manual

Transcription

1 This PDF document contains Live Web Links Click them for more information from the web Polatrak ROV II - Tip Contact Probe Operation Manual A Cathodic Protection Probe with dual Ag/AgCl reference cells for unparalleled accuracy. It can be diver held or mounted to an ROV friendly T-Handle (shown here). pg 1 of 15

2 Table of Contents 1 Dive-Spread Installation 3 2 ROV Instalaltion 3 3 Cautionary Notes 4 4 Calibration General Topside Calibrations (Bucket Cal.) Subsea Calibrations 5 5 Operation Wet Check Offshore Probe Maintenance Recording CP Potentials 7 6 Drawings and Calibration Forms ROV II Probe General Assembly ROV II Probe Detailed Assembly CP Survey Wiring w/ POLASCAN 12 panel (optional) 6.4 CP Surevy Wiring w/ Voltmeter Calibration Form (cell to cell) Calibration Form (vs Zn coupon) Calibration Form (vs. Master Ag/AgCl) 16 pg 2 of 15

3 Section 1 Installation for a Dive-Spread When used in conjunction with diving operations, it is recommended that a cable is assembled with a SEACON RMG-3MP connector at the subsea end. The most suitable cable in our experience is the 4 conductor armored spiral comms cable that is used by most divers for diver communications. This has two twisted pairs and is very rugged. A connection whip with this connector os provided with the probe and should be soft spliced onto the end of the comms cable. Ensure that the connection is taped back to the armored wire to provide strain relief on the connection. (If required, Deepwater Corrosion can provide a complete assembly on a 500 foot long umbilical cable.) The appropriate length of wire should be married into the dive hose leaving 4-6 feet of slack at the diver end and at least 50 feet at the topside end. Always install the dummy plug on the connector when the probe is not attached. The topside end of the wire will be run to the dive control area along with the platform ground cable and any ground from pipeline risers. The connections can be made either to a pair of digital multi-meters or to Polatrak Monitoring Panel available from Deepwater Corrosion Services. (Wiring hook-ups are shown in section 6 for the POLASCAN panel.) Section 2 ROV Installation The probe is best installed in or on a manipulator but may be attached directly to the ROV frame if there is no manipulator available (this is best when only proximity readings are required). The recessed grooves in the probe body may be used to accommodate stainless steel hose clamps for attachment, it is recommended that a safely line is provided as well as some neoprene rubber pads between the probe and the mounting surfaces, this will provide a better attachment and some degree of compliance. The connector on the back of the probe is a SEACON RMG-3FS and is wired as shown in Fig. 1 below. PIN 1 CONTACT TIP PIN 2 ELECTRODE #1 (R1) Fig. 1 PIN 3 ELECTRODE #2 (R2) pg 3 of 15

4 A male connector on a 6 0 whip is provided to facilitate splicing into the ROV junction box. It is recommended that the two electrode wires are routed in a shielded twisted pair in the ROV umbilical, the tip wire can be connected to a coaxial cable or any other cable that is straight through to the control van with no breaks. Topside the system can be wired directly into a video annotator (insure that it has an input impedance of at least 10 Meg Ohm / Volt), or onto either a pair of multi-meters or a Deepwater monitoring panel. See attached wiring schematics for hookup options. Section 3 Cautionary Notes Polatrak sintered silver chloride reference electrode elements are designed to withstand normal oilfield operations, but they are consumables that have a given operational life, the life of these electrodes can be extended to several seasons if the following care is taken. Never allow the electrode elements to be directly shorted to ground or any other metallic object when immersed in seawater. Never run the electrode subsea with the underwater connector un-mated. Never read the CP probe with an analog voltmeter, ensure that high input impedance digital equipment is used. Never handle the bare reference electrode element (small gray pellet) with bare or greasy hands. Do not use any type of solvent or detergent on the probe, rinse only in fresh water when not in use. Never immerse the electrode in anything but fresh water or sea-water. Never allow an underwater connector to be immersed unless it is mated or has a sealing dummy plug inserted. Never read the electrode on a multi-meter scale other than DC Volts. When not in use, store the probe in the container provided filled with seawater or tap water. Probe can be stored dry between jobs but should be rinsed in freshwater thoroughly before storage. Do not attempt to field repair any wires on the probe or inside the probe and never attempt to modify the probe tip in any way. pg 4 of 15

5 Section 4 Calibration 4.1 General It is imperative to follow calibration procedures precisely and to change electrodes if a probe shows to be out of calibration. Improperly reported CP readings could cause serious problems to the facility operator and may have to be repeated. The most common cause of problems, particularly on diver surveys, is damage to the cable insulation, this causes an offset in the reading which would usually be interpreted as inadequate protection levels, for this reason both topside and subsea calibrations should be performed before, during, and after every dive. Note: Oil company calibration specifications must be met, but we strongly advise also using the attached procedures. 4.2 Topside Calibrations (Bucket Calibration) If probes have been stored for a significant period, and have been allowed to dry out, it may take 1-2 hours of immersion time before the electrodes stabilize. The attached sheet shows the procedure; ensure that either native seawater or artificial seawater (3% by weight salt) is used. Procedures (forms are included for Cell to Cell, Master Silver/Silver Chloride, and zinc coupon checks). The zinc calibration coupon is provided as standard, but the master silver/silver chloride procedure is recommended). NEVER USE A METALLIC CONTAINER WHEN PERFORMING CALIBRATIONS OR FOR STORAGE. 4.3 Subsea Calibrations The subsea calibration procedures should be followed and the results logged at least once per dive Cell To Cell Calibrations This procedure checks one cell in the probe against the other, and should be performed with all the cable immersed as it will quickly detect any cable damage. If dual readouts are used as shown in the wiring diagrams, the cell to cell reading is displayed continuously, this is the recommended procedure. The cells should read within +/- 5 mv DC. If the value drifts outside this range then one of the following has happened: pg 5 of 15

6 1. Lead wire is damaged exposing copper to seawater. 2. A connector is not properly made or is leaking. 3. One cell has failed. If in the middle of a dive it is possible to complete the dive, however the defective cell should be isolated and the good cell used to finish the dive. The bad cell will normally be the one, which displays the most positive potential. So read a potential on the structure with both elements, the most negative cell should be used to complete the dive, and the offset noted. When recovering the umbilical cable from such a dive, monitor the cell-to-cell value, if the problem is lead wire damage, the value will revert to within +/- 5mV as soon as the damaged area clears the water, in this way the damage can be quickly located and repaired Ground Check This procedure verifies that the platform ground wire and the probe tip will yield the same reading at any point on the main structure. This is particularly important when the probe is being used in proximity mode. The POLASCAN READOUT has a facility to switch between tip and platform ground. To verify the ground, stab the steel structure under survey with the probe and record the value switching grounds from tip to platform, the reading should be identical, if it varies by more than +/ 3 mvdc, check the platform ground connection. Section 5 Operation Most oil companies will have their own survey procedures that should be followed. The following guidelines are given as guidance only. Connect the system as shown on the attached wiring schematics. 5.1 Wet Check When interfaced to an ROV, it important to perform a wet check before every dive. Signal errors caused by umbilical power cable interference could introduce reading errors. With the probe wire to the ROV, immerse the system to at least (-) 30 feet, and with the vehicle still in it s TMS bring up one electrical system at a time and note the potential of the tip (it will vary some depending on immersion time). If there is a problem, the potential will change rapidly or will spike when the circuit is powered. Repeat for all electrical and hydraulic systems. If a problem is detected it should be fixed, usually it s a poor ground connection or a faulty leaking underwater connector that cause the problem. If the system at fault can be switched off without hindering operation, this is an acceptable option. pg 6 of 15

7 5.2 Offshore Probe Maintenance Changing Electrodes - Spare plug-in electrode elements can be provided with the ROV II probe, these elements will also work in the CP Gun. If the elements or one element needs to be changed, follow this procedure: 1. Take the probe into a clean inside working area, with a clean grease free work surface. 2. Locate the assembly drawing at the back of this manual. 3. Remove the head assembly carefully by removing two screws on back of probe, pull out gently until two electrode connectors are visible. 4. Using an ohm meter measure between the connector pin and the electrode element to verify which is which. (Do not handle electrode elements). 5. Unplug the bad electrode(s) from connector(s), and discard. 6. Apply a small smear of silicone grease into the open female connector and insert the new electrode. (Avoid using excess grease, and any grease contact with electrode element.) 7. Check the integrity of the tip wire connector, re-make as necessary. 8. Carefully re-insert the electrodes into the probe body and replace the head assembly. 5.3 Recording CP Potentials If wired correctly the CP potentials should have a negative polarity. Accurate readings will be steady and not drifting so long as the probe is not moving. If readings are erratic this is a sign of a connection problem, and the cause should be isolated and fixed. To obtain accurate readings the probe apertures should be within 2 of the structure surface. The further away the probe is held from the structure area under investigation, the less accurate will be the reading. On offshore structures protected with zinc or aluminum anodes the following potential ranges should be observed. (-) (-) Volts On Jacket Members / Pipelines (-) (-) Volts On Anodes Readings outside of these ranges should be double-checked. It is possible to see potentials less negative than (-) Volts, but this would mean an unprotected structure with large numbers of consumed anodes or a high ratio of low potential anodes. pg 7 of 15

8 Section 6 Drawings and Calibration Forms The following drawings and forms are attached for reference: 1. Polatrak ROV II Dive Probe GA Page Polatrak ROV II Dive Probe Assembly Page CP Survey Wiring with Optional POLASCAN Monitoring Panel Page CP Survey Wiring Schematic with Twin Voltmeter Setup Page Calibration Form Cell to Cell Page Calibration Form vs. Zinc Coupon Page 14 \ 7. Calibration Form vs. Master Ag/AgCl Electrode Page 15 pg 8 of 15

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