Tubing inspection and handling
Inspection of tubing when received and following use are important to ensure that defects or wear do not prevent the tubing from performing as designed. Proper handling, both in transit and on site, are critical to avoiding damage to the tubing. This article provides an overview of inspection and handling considerations for tubing.
API tubing is inspected at the mill in accordance with API Spec. 5CT. Physical properties are checked and each length hydrostatically tested, normally to only 3,000 psi in the plain end (unthreaded) condition. The following are also checked:
Part of this inspection is to drift all lengths.
Despite all the American Petroleum Institute (API) specifications and testing, some tubing defects are still found after delivery; thus, some operators do further inspection of new tubing on critical wells.
Used tubing frequently requires inspection. See API RP 5C1. 
There are several types of tubing inspection methods that may be beneficial. The common methods of inspecting the tubing currently in use in field operation are:
- Magnetic particle
Typical defects are outside and inside pits and longitudinal cuts, transverse laps, and mechanical wear and erosion. API recommends that wall thickness measurements be made with pipe wall micrometers, sonic pulse-echo instruments, or gamma ray devices so that the operator can demonstrate the wall thickness within a 2% accuracy. In addition to the body, the tubing upset and threads often require inspection, typically by magnetic powder and use of thread gauges. The following guidelines are suggested for inspection normally at the well location:
- Visual. The outside of each tubing joint should be inspected visually for mill defects such as seams, slugs, pits, cuts, gouges, dents, or cracks. Each connection should be checked for defective threads and seals. Wall thickness measurements should be considered on critical wells. Internal inspection of tubing requires the use of an optical device and an experienced operator. The operating crews, a manufacturer’s representative, the user’s personnel, or a service contractor typically does such visual inspections.
- Calipers. Tubing calipers, both multifingered feeler and electronic types, normally are run while the tubing is installed in the well. Where significant wall loss is observed, the tubing can be pulled and the damaged joints replaced.
- Hydrostatic. A commonly used inspection method is to test hydrostatically the tubing body and joint internally with water. Test pressures are usually based on 80% of internal yield. Hydrostatic tests of the body are performed on the pipe rack on location and the joints checked while running; however, both can be tested while running. A more stringent test of the joints is obtained by the use of nitrogen with a helium tracer rather than water.
- Electromagnetic. To find pits, transverse and/or longitudinal defects in the pipe body, electromagnetic search coils, which find magnetic flux leakage, are typically used. This technique works for a uniform body and will typically not find defects in the upset and/or threaded area of the tube. The inspection equipment must be in good working order and an experienced and qualified operator is required. Eddy-Current, another electromagnetic inspection method, is used for grade verification.
- Magnetic particle. The magnetic particle inspection methods, both wet and dry, induce either a longitudinal or transverse magnetic field in the tubing and magnetic iron particles dusted on the tubing align at defects. This method is normally used to check the outside surface of upset and end area region for cracks. This method requires a qualified operator, excellent operating environmental conditions, and good operating procedures to be reliable.
- Ultrasonic. Ultrasonic (high frequency sound) is used to find flaws and imperfections in the pipe body wall. The tool is usually stationary and the pipe is rotated and fed mechanically to examine the entire tubing body. The ultrasonic testing equipment must be in good working condition and an experienced and qualified operator is mandatory.
- Hardness testing. The hardness of tubing is often checked when it is to be used in sour service to ensure the tubing meets API Spec. 5CT or to sort mixed grades of tubing.
Inspecting used tubing
Used tubing should be classified according to loss of nominal wall thickness. API RP 5C1 specifies color-coding to indicate thickness. The color coding should consist of a paint band of the appropriate color approximately 2 in. wide around the body of the pipe approximately 1 ft from the box end. There is no standard method for calculating performance properties of used tubing. Tubing reconditioning should be done only in accordance with API specifications.
Proper handling of tubing
Tubing can be damaged during shipment, at the wellsite, and during running and pulling. API RP 5C1 Secs. 2 and 3 should be followed closely. For transportation, slightly different procedures are needed to prevent damage depending on whether shipped by water, rail, or truck. Care must be taken in unloading and storage. Thread protectors must be installed properly and rough handling avoided. Tubing should be stacked on racks following proper procedures, and tubing in storage should be inspected periodically and protected from corrosion. In general, the high-strength materials are more susceptible to handling damage.
Running and pulling tubing
Numerous factors must be considered when running and pulling tubing. The operating personnel should ensure that good practices are followed. Each length of tubing should be measured and drifted in compliance with American Petroleum Institute (API)/International Standards Organization (ISO) specifications. The tubing should be handled with thread protectors, which are not removed, until the tubing is ready to stab. Adequate thread cleaning is essential for proper connection makeup and pressure-tight strings. (See Ref. 2.) Apply a good thread compound but avoid excessive amounts. Collar-type tubing elevators are adequate for API nonbeveled couplings; however, slip-type elevators are recommended when running tubing with beveled couplings, special clearance couplings, and integral joint tubing. Check spider slips to ensure they will not damage the tubing body.
Use of power tongs is necessary to obtain consistent makeup torque. Properly maintained, installed, and calibrated tongs are essential. Follow the API recommended tubing makeup torque for nonupset, external-upset, and integral-joint tubing. Follow the manufacturer ’ s recommendations for specialty joints. However, the makeup torque may vary depending on the thread coatings and lubricant type; thus, adjustments in makeup torque values are sometimes required. Torque values listed in API RP 5C1 apply to tubing with zinc-plated or phosphate-coated couplings. For tin-plated couplings, use 80% of the listed values as a guide for proper makeup. To establish the correct torque for API tubing threads, make up the first few joints to the recommended values and examine the connection. There should be no excessive heat, approximately two turns beyond the hand-tight position with all threads buried. Back out the connection (noting torque) and check threads for galling. If needed, adjust torque and repeat. Use the established makeup torque for the remainder of the string.
- To obtain maximum leak resistance with the API-tapered thread, the pin end of the connection is made up to slightly beyond the point of yielding. Consequently, API EUE connections may make up slightly more on repeated operations. The problem of makeup is to use torque that is sufficient to provide the needed seal without permanently damaging the connection. Good experience has been reported with the torque-turn method with API EUE tubing. In the torque-turn method, the power tongs are calibrated to record both the number of turns and the torque to make up the API tubing coupling to the point of yielding. In many of the proprietary connections, there must be ample makeup torque so that the metal-to-metal seals are energized. Check with the manufacturer for makeup guidelines.
API-modified thread compound generally has been accepted for a wide range of service conditions over many years. The placement of thread compound at the root of the rounded API threads with the bearing pressure on the thread flanks (the interference fit, power tight makeup) produces the sealing mechanism. The thread compound also provides the lubrication to deter galling. The compound is a mixture of metallic and graphite powders uniformly dispersed in a grease base. API RP 5A3 and ISO 13678 provide the means for evaluating the suitability of thread compounds for use on API round threads in high-pressure service. For specialty connections, consult with the manufacturer on the proper thread compound. Environmentally non-damaging thread compounds meeting API thread-compound performance requirements are available.
Evaluation procedures for connections
Evaluation procedures for casing and tubing connections tests to be performed to determine the galling tendency, sealing performance, and structural integrity of tubular connections, especially for high-pressure application are under study. See ISO/DIS 13679. Table 1 shows example relationships between test classes and service applications. Other relationships may be more appropriate for individual users. Class IV connections are intended for the most severe application, and Class I connections are intended for the least severe application.
- RP 5C1, Care and Use of Casing and Tubing, 18th edition, API, Washington, DC (1999).
- MR0175/ISO 15156, Petroleum and Natural Gas Industries—Materials for Use in H2S Containing Environments in Oil and Gas Production, first edition. 2001. Houston, Texas: NACE.
- API RP 5A3/ISO 13678, Thread Compounds for Casing, Tubing, and Line Pipe, second edition. 2003. Washington, DC: API.
- ISO/ISO 13678, Petroleum and Natural Gas Industries: Evaluation and Testing of Thread Compound Systems for Use With Casing, Tubing and Line Pipe, first edition. 2000. Geneva, Switzerland: ISO.
- ISO/DIS 13679, Petroleum and Natural Gas Industries: Testing Procedures for Casing and Tubing Connections, first edition. 2002. Geneva, Switzerland: ISO.
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