TPi November 2017

Recent advances in ultrasonic inspection of seamless tube and pipe Improved accuracy of detection of oblique flaws and increased manufacturing productivity By Frank Kahmann, GE Oil & Gas, Digital Solutions

for gathering lines to connect several wells. (Offshore, line pipe can be called riser pipe and it needs to have good axial strength and fatigue resistance.) All manufactured pipe undergoes rigorous inspection, and non-destructive testing is used to assess any defects in terms of size, sharpness, orientation and location, in order to determine whether those defects will compromise integrity during a pipe’s operational life. Inspection techniques Various non-destructive testing techniques are used for the inspection of pipe and tube. These include eddy current technology and magnetic particle inspection to detect near- surface or surface-breaking cracks, radiography, which is often used for in-depth weld inspection, and hydrostatic testing. However, ultrasonic inspection is the technology most widely used for the inspection of pipes and tubes in pipe mills. Seamless tubes are tested ultrasonically for various flaw types in the pipe wall, over the entire circumference and length. Because of the manufacturing process, longitudinal flaws, which are parallel to the length axis of the pipe, are the most common in seamless tube and pipe, but historically, inspection has also covered transverse flaws, which are at right angles to the longitudinal axis, wall thickness measurement, eccentricity, ovality and testing for lamination type flaws. High specification, hot finished seamless tubes for the oil sector are also tested, with differing degrees of success, for oblique flaws. The acceptance criteria embodied in a wide range of inspection standards, such as BS EN 13445, relating to ultrasonics, specify identification of planar indications based on the height, length and amplitude. Conventional ultrasonic seamless pipe inspection Ultrasonic (UT) pipe inspection is usually carried out in-line. A UT inspection machine generally consists of four parts: a mechanical system to rotate or convey the tube to be tested

Although quality control is an essential stage of pipe manufacture, it does not add any tangible or financial value to the end product. However, it must be carried out to meet international quality standards. It is also vital to the marketing of the end product to assure end users of the integrity in service of the pipe or tube. In addition, rigorous quality control procedures can help to increase productivity by providing early warning of material flaws, which can be intrinsic to the material or induced during the manufacturing process. To date, inspection procedures have been unable to identify specific flaws, such as oblique flaws, with absolute certainty, but with the introduction of a new inspection technique from GE, it is now possible for pipe mills to carry out 360° gapless inspection of seamless tube and pipe. Introduction Seamless tube and pipe finds wide application throughout the industrial and process sectors. In its smaller diameters, it is used for bicycle frames, pressure vessels, steel scaffolding and automobile transmission shafts, on account of its structural strength. In its larger diameters, it is widely used throughout the oil and gas sector, as it offers significant advantage over longitudinally welded pipe in certain situations. Typical applications for seamless pipe in the oil and gas sector include drill strings – thick-walled pipe with good torsional strength used for drilling; well casings, to line wells after drilling, needing good axial strength and high burst pressure; and line pipe, which is attached to the well head and is used P ipe mills, whether they produce seamless or welded pipe, are constantly trying to marry the needs of high quality product to meet customer requirements with improved productivity to ensure continued or enhanced profitability. Unfortunately, these two commercial aims can sometimes be conflicting. One area where this conflict of interest is especially acute is quality control and, specifically, non-destructive testing.

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TUBE PRODUCTS INTERNATIONAL November 2017

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