OPERATION & MAINTENANCE SPECIFICATIONS MANUAL 09 09

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1 S SCOPE This section is intended for the guidance of NDE personnel qualified in accordance with the requirements of M&NP Training and Qualification of Personnel. The inspection processes and procedures described in this document may be used for line pipe, piping components and pressure vessel plates. Ultrasonic Thickness testing may also be used to evaluate the thickness of the parent material after grinding etc. This procedure is not intended to be exhaustive in the treatment of ultrasonic technique as it is provided for general guidance only. A complete and thorough reference for ultrasonic systems, equipment used, and techniques is ASME B&PV Section V Nondestructive Examination, and the methods referenced in this guideline document shall comply with that overriding Standard. SAFETY Prior to excavation for inspection, verification shall be made that the pipeline has been established at a safe working pressure in accordance with the requirements of M&NP Section 12, Reference 17 - Safe Working Pressure. Defect excavation shall then be completed in accordance with the requirements of M&NP Section 11, Reference 13 - Defect Excavation and Assessment. EQUIPMENT Transducers and Instrument The Instrument and Transducer are shown schematically in Figure 1. Figure 1 Transducer and Instrument The instrument used for signal processing and display shall be capable of displaying wall thickness information by means of any of the following formats: Cathode Ray Tube (CRT), or Digital display Page 1 of 12

2 At least once per year, the instrument s performance characteristics shall be checked in accordance with the requirements of ASTM Practice E Standard Practice for Evaluating Performance Characteristics of Ultrasonic Pulse- Echo Examination Instruments and Systems Without the Use of Electronic Measurement Instruments. The frequency range for transducer selection shall be straight beam 1 to 10 MHz, single or dual and of an appropriate size for the defect profile being examined. Calibration shall be performed in accordance with the requirements of the Use of Ultrasonic Testing Equipment in Measuring Thickness section of this reference. Couplant A couplant, usually a liquid or a gel, is required between the face of the search unit and the examination surface to permit the transmission of ultrasonic waves from the search unit into the material under examination. Typical couplants include glycerin, water, cellulose gel, oil, water-soluble oils and grease or soft rubber. Corrosion inhibitors or wetting agents or both may be used. Couplants must be selected that are not detrimental to the product or the process. The couplant used in calibration should be used for the examination. The couplant manufacturer s guidelines and datasheet shall be reference to ensure that the applicability range is suitable for the couplant s intended application. At elevated temperatures (above 125 F), heat-resistant coupling materials such as silicone oils or greases should be used. Further, intermittent contact of the search unit with the surface or auxiliary cooling of the search unit may be necessary to avoid temperature changes that affect the ultrasonic wave transmission properties of the wedge material or the characteristics of the transducer. At higher temperatures, certain couplants based on inorganic salts or thermoplastic organic materials, hightemperature wedge materials, and transducers that are not damaged by high temperatures, may be required. Couplants shall be completely removed after completion of the examination. SURFACE PREPARATION The finished contact surfaces of the material being tested shall be free from weld spatter, dirt, rust, loose scale, loose paint or any other roughness that would interfere with free movement of the search unit or impair the transmission of ultrasonic energy. If necessary, smoothing or flattening of the contact surfaces may be required. When surface contouring or flattening is done by abrasive means, the precautions detailed in M&NP Section 03, Reference 06 - Assessment and Removal of Gouges, Grooves, Cracks, Arc Burns and Other Surface Metallurgical Anomalies by Grinding shall be followed. The use of soft rubber couplant shall be investigated as referenced in Clause 3.2, and used in lieu of surface contouring or flattening wherever possible. The outside and inside surfaces should be parallel or concentric. USE OF ULTRASONIC TESTING EQUIPMENT IN MEASURING THICKNESS Orientation and Progression of Measurements Page 2 of 12

3 The thickness determination shall be conducted in such a manner that will permit the recorded measurements to be accurately correlated to the applicable area of interest on the material being examined. Datum points will be as follows: For horizontal pipe or component: From the portion of the material that is closest to the top, and proceeding clockwise in the direction of product stream flow, For vertical or near vertical pipe or component: From the portion of the material that is closest to the north, and proceeding clockwise when looking down. All measurements will be related to these datum points and when required an orientation drawing will be produced. The start point measurement will be made from the nearest upstream weld. Grid patterns will follow the above format. Calibration Calibration shall be performed immediately prior to each use using a calibration block that is within 25% of the thickness of the material being measured. The material from which the standardized calibration blocks are made shall be acoustically similar to the material being tested. Temperatures should be similar between the calibration block and the material being tested. For the purposes of calibration, it is often necessary to know the acoustic velocity of the material that is being tested. The acoustic velocities of various materials are provided in Table 1. Table 1 Mean Sound Velocity For Various Materials Imperial Units in/μs Metric Units m/s Aluminum Cast Iron Copper Steel Calibration and Operation shall be specific to each type of equipment. Calibration procedures for Krautkramer DM- 2LCD, DM-1B, and DME models are provided in the respective sections below. Krautkramer Model DM-2LCD NOTE: This model is available in two versions, one providing readouts in inches and the other providing readouts in millimeters. The metric version is identified as Model DM-2LCDM. The Krautkramer model DM-2LCD is illustrated in Figure 2. Page 3 of 12

4 Figure 2 External Components and Functions Krautkramer Model DM-2LCD Calibration of this model shall be done in accordance with the following procedure. 1. Depress "Power on" button. The LCD display will immediately go on and will display all zeroes. The colon, which indicates a stored reading, will also go on. 2. A low battery charge level is indicated by an LCD decimal point in the readout. If the decimal point blinks, this indicates a low charge level on the batteries. If the readout does not light at all when the "Power on" button is depressed, the batteries are dead. 3. To change the batteries, unlock the battery pack by rotating the battery pack lock counterclockwise, and remove the batteries. The Model DM-2LCD requires five rechargeable NiCad cells (supplied with the unit) Page 4 of 12

5 or five 1.5 V, size AA dry cells (not rechargeable). To replace the batteries, insert the battery pack into the instrument housing and rotate the battery pack lock clockwise until it is firmly tightened. NOTE: If a battery pack has been incorrectly inserted, the "Power on" switch will be blocked so that neither the electronics nor the batteries can be damaged. 4. Plug the large connector end of the transducer cable into the instrument and attach the small connectors to the probe. 5. Set the appropriate acoustic velocity for the material being tested on the velocity controls. When testing steel pipe, plate or fittings, the velocity control should be set to 232 in/sec on the Model DM-2LCD (velocity controls should be set to 590 cm/sec on the Model DM-2LCDM). 6. Couple the probe to the reference block on the front of the instrument. Using the zero control knob, set the digital readout to the thickness marked on the reference block. This will calibrate the instrument. NOTE: When a 0.250" reference block is used, adjust the zero control to keep the readout in the range of 0.245" to 0.250". When welding on a live pipeline, it is always safer to slightly underestimate the pipe wall thickness rather than overestimate. Page 5 of 12

6 Krautkramer DM-1B The Krautkramer model DM-1B is illustrated in Figure 3. Figure 3 External Components and Functions Krautkramer Model DM-1B Calibration of this model shall be done in accordance with the following procedure. 1. Before using, always check the battery charge level. This is accomplished by connecting the probe lead wires to the probe connection on the instrument. Depress the ON/OFF button for one second. Couple the probe to the reference block on the instrument (use couplant grease or light oil on the reference block if necessary). Ensuring that the L.E.D. digital readout is illuminated, check the position of the pointer on the battery level indicator. If the pointer is in the grey field of the meter, the batteries must be recharged before use. If rechargeable type NiCad batteries are in the instrument, they may be recharged by connecting a MLA/DMK-1 or WMLA-2 charger to the battery charger connection. As a rule of thumb, allow 1.5 times as much time for recharging as was used in discharging. NEVER attempt to recharge batteries that are not of the rechargeable type. 2. To calibrate the instrument, set the material calibration selector switch to position #2 and ensure that the sensitivity switch is in the KMR position. If the batteries require changing, loosen the screw at the rear of the Page 6 of 12

7 instrument housing and remove the rear panel. Remove the batteries from the instrument with the aid of the cloth strap. The Model DM-1B requires five rechargeable NiCad cells (supplied with the unit) or five 1.5 V size C dry cells (not rechargeable). When installing the new batteries, be certain to observe the polarity markings contained in the battery compartment. Re-position the rear cover and retighten the retaining screw. 3. Connect the probe to the probe connection on the instrument. Push the on/off switch to the ON position. 4. Couple the probe to the reference block. Adjust the zero control until the L.E.D. digital readout indicates between and This will tend to slightly underestimate the thickness, which provides a margin of safety if welding on live pipelines. Page 7 of 12

8 Krautkramer DME The Krautkramer model DME is illustrated in Figure 4. Figure 4 External Components and Functions Krautkramer Model DME The DME has the ability to measure wall thickness, which range from 0.30 inches to inches or 0.5 mm to 300 mm in metric mode. This range may vary slightly depending on the probe used and the test material. Page 8 of 12

9 Calibration of this model shall be done in accordance with the following procedure. 1. Attach the probe to the instrument. 2. Press the ON key. The DME will perform a brief display test; all segments of the display will briefly light. After the display test is complete, the DME will display either (0.0 if in metric mode) if the instrument is in thickness mode, or it will display the last velocity value stored if the instrument is in material mode. NOTE: If at this time the low battery indicator light comes on; this indicates that approximately 1 hour of battery life remains. If the readout does not light at all when the ON key is depressed, the batteries are dead. To change the batteries, loosen the battery cover screws on the back of the instrument and remove the battery cover. Insert 3 "AA" alkaline batteries, make sure the batteries are installed with the correct polarity as indicated in the battery compartment; otherwise damage to the instrument may result. 3. Select the units you wish to work with by depressing the INCH/MM key see the keyboard controls in Figure 7. If the symbol IN appears on the bottom right hand corner of the display, it indicates the units being displayed are in inches. If the symbol MM appears in the bottom right hand corner of the display, it indicates the units being displayed are in millimeters. 4. Press the ZERO key. The instrument will display PO. 5. Apply a small amount of couplant (a light oil will do) to the built-in reference block, located next to the ON key. Couple the probe to the reference block and leave in this position for a few seconds. If properly coupled, the coupling indicator will appear in the display. 6. The instrument will display a material velocity. The velocity displayed will be the last velocity value stored in the instrument. For measuring the thickness of steel material, the velocity displayed should be or 5920 if in metric mode. If the correct velocity value appears in the display, proceed to Step 8. Otherwise, proceed to Step If a velocity value different than the one you wish to work with appears in the display, press the CAL key, a row of dashes appears in the display. Now use the numeric keys to enter the desired velocity (see Table 1). Four digits must be entered, for example, 1/4 inch would be entered as The C key may be used to clear the display if an error is made while entering the digits. 8. Press the MAT/THK key to put the instrument in thickness mode. The instrument is now ready to take thickness measurements. 9. Remove any dirt, scale or flacking from the test surface. Spread a thin layer of couplant over the entire area that will be tested. NOTE: A couplant must always be used when testing. The couplant removes any air pockets that may develop between the probe and the surface being tested. Any good commercial couplant, grease or light oil will work as long as it will remain on the surface being tested. Page 9 of 12

10 10. Place the probe gently but firmly on the couplant surface. If the probe is properly coupled the coupling indicator and thickness value will appear on the display. Detecting Pipe Flaws Prior to taking measurements a sufficient amount of couplant shall be applied to the pipe surface. For curved surfaces, such as pipe, the probe shall be placed on the surface in such a way that ensures that the maximum amount of probe surface area is sitting on the pipe. This is best achieved when the cross-talk barrier, which divides the end of the probe in half, is firmly against the pipe in the direction of the pipeline (see Figure 5 below). For highly-curved surfaces (generally, for radii of less than 100 mm), it may be necessary to utilize a speciallyshaped transducer to ensure that sound is transmitted efficiently into the material being examined. Figure 5 Probe Alignment on Curved Surfaces Initially, when the instrument is taking readings, the figures on the readout will vary, until it arrives the most accurate reading. Steady pressure should be maintained on the probe during the test. Various types of defects can be detected using ultrasonic thickness testing equipment. These defects, and the means by which they may be identified are described below. Laminations Laminations are thin separations or flattened impurities in the pipe wall. Laminations are generally aligned parallel to the surface of the pipe wall, as illustrated in Figure 6. Page 10 of 12

11 \ Figure 6 Examination of Laminations Detection of laminations is typically characterized by a sudden apparent reduction in wall thickness. The position of the lamination from the examination surface is indicated by the thickness reading shown on the instrument. Internal Corrosion or Erosion While external corrosion is visible to the naked eye, internal corrosion is not. When the measured wall thickness reduces noticeably and varies throughout a localized area, this is usually indicative of internal corrosion or internal erosion. The types of readings obtained from internal corrosion are similar to what would be expected when examining an area of external corrosion, as is illustrated in Figure 7. Before it can be confirmed that an internal corrosion or internal erosion defect exists at the area of examination, the following items should be checked, as each one can cause variability in readings, similar to what might be expected when examining internal corrosion or internal erosion: a) Insufficient couplant; b) Low batteries; or, c) Electric interference by overhead high tension hydro lines or by cathodic rectifiers in the vicinity. Page 11 of 12

12 TROUBLESHOOTING Figure 7 Examination of Corroded Areas When the apparent thickness of the material varies greatly without significant movement of the probe, this can be a result of: a) Improper placement of the probe on an uneven surface (see Figure 5), or, b) Insufficient couplant. When there is insufficient couplant sound waves cannot reach the pipe material due. Additional problems can result in variability of the apparent thickness being measured, and trouble shooting measures to detect such problems should be undertaken as was discussed in the Detection Pipe Flaws, Internal Corrosion or Erosion reference in this section. DOCUMENTATION The results of the detailed defect assessment, including maximum depth, and length of defect shall be documented and appended to the Defect Site Description Report referenced in M&NP Section 11, Reference 13 - Defect Excavation and Assessment, Page 12 of 12