By HILTON PREJEANNOV Tuboscope

Inspections for

today’stubular

products

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The drastic change from yesterday’s wells versus today’s wells has pushed the

pipe inspection market to develop highly sophisticated equipment that requires greater accuracy in detecting internal and external flaws along with determining their size, shape and orientation. Since the American Petroleum Institute (API) and International Standards Organization (ISO) joined forces, they have provided a greater worldwide consistency of written specifications and recommended practices used in manufacturing tubular products. Drilling environments with highly technical practices are driving tubular products toward their performance limits, relying signifi cantly on “non-destructive test methods.” These methods reveal true pipe dimensions, such as minimum wall thickness, in addition to validating that no existing defects are present.

Several inspection methods required

The pipe inspection industry has maintained its tradition of requiring inspectors, as a minimum, to be certifi ed to the high standards of American Society for Nondestructive

Testing (ASNT) Level II. These inspectors rely on several test methods such as ultrasonic, electromagnetic, eddy current and magnetic particle in determining fi nal dispositions of pipe strings. A method may be used as a stand-alone test or in unison with other test methods. Inspection systems and process packages play an important role by informing tubular end-users of each tubes actual wall thickness for determining the total length, and it assists engineers with effective string designs. In some cases, inspection data offers an option to reduce a string’s diameter or weight-per-foot on a standard API product, thereby eliminating the need for a more expensive product.

Non-Destructive Testing (NDT)

N o n - d e s t r u c t i v e testing has been practiced by Tuboscope for over seven decades with initial developments in drill pipe tube inspection. In the early days, the primary purpose of testing was to detect large visible defects. The expectation was for a drill pipe not to fail (twist off) during its life. By detecting defects such as large cracks, the pipe could be removed from the drill string and be taken out of service before failure. In response to prolonging service, increasingly sophisticated techniques using ultrasonic, eddy current, electromagnetic, magnetic particle and other forms of interrogating methods emerged.

In 1975, pipe inspection engineers began using the Intel 8080 microprocessor with 256 bytes of memory allowing programs to artifi cially recognize defects. Once this event had taken place, a major change began to sweep through the NDT inspection industry. This epic improvement in technology led to

the ability to detect and classify small fl aws with a “Classifax” unit, but this was viewed as a negative, causing more pipes to be rejected even though a downward trend of “twisted off pipe” was evident. The

discipline of quality pipe inspections emerged, which enabled inspection of drill strings onsite. Other state-of- the-art inspections were developed to amplify the crack size detection resolution. With the advent of all these tools, it became possible for a drill string to last over 100,000 feet drilled before failing. Today, NDT is part of quality assurance maintenance programs that help drill strings drill over half a million feet before failing “cradle to grave.”

Ultrasonic TestingThis NDT method, ultrasonic

testing, is a process for detecting discontinuities in the pipe’s wall thickness and tube body during a volumetric examination using

high- frequency sound waves. The purpose of this testing method is to detect and locate seams, pits, gouges, inclusions, cracks, splits, and the like, by the ultrasonic pulse refl ection method.

Specific techniques of the ultrasonic method include pulse-echo techniques and through transmission, by contact and non-contact, also angle beam with immersion techniques. Artifi cial refl ectors consisting of longitudinal, transverse and oblique reference notches placed on the surfaces of

a reference standard are engaged as the primary means of standardizing the ultrasonic system to a specifi c square area target. The ultrasonic acceptance criteria are specifi ed in API and ISO documents. The intended use for pipe inspection is specifi c to tubular products having an outside diameter approximately 23⁄8˝ and larger, provided that the examination parameters comply with written procedures as intended. This will ensure proper beam angles and beam shapes are used to provide full volume coverage of pipe surface, including those with low ratios of outside diameter-to-wall thickness and to

In the early days, the primary purpose of testing was to detect large visible defects.

Well Servicing November/December 77

The discipline of quality pipe inspections emerged, which enabled inspection of drill strings onsite.

The purpose of this testing is to detect and locate seams, pits, gouges, inclusions, cracks, splits, and the like, by ultrasonic pulse refl ection method.

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avoid spurious signal responses when examining small-diameter, thin-wall tubes. It is extremely important to calculate the helical scan pitch. For a more effi cient and quicker examination, multiple search units and instruments may be used simultaneously to perform automated scanning of the pipe. The personnel performing examinations to API and ISO standards should be qualifi ed in accordance with the nationally recognized NDT personnel qualifi cation standard such as ANSI/ASNT-CP-189, SNT-TC-1A or a similar document.

Ultrasonic testing (UT) has been practiced for many decades and continues through the present day. Computers have provided technicians with smaller and more rugged instruments with greater capabilities. Thickness gauging

is an example application where instruments have been refi ned to make data collection easier and better. Some instruments have the capability to capture waveforms as well as thickness readings. The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection. Also, some instruments are capable of modifying the measurement based on the surface condition of the material. For example, the

signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface, resulting in more accurate and repeatable fi eld measurements. Many ultrasonic fl aw detectors have a trigonometric function that allows for fast and accurate location determination of fl aws when performing shear wave inspections. Cathode ray tubes (CRT), for the most part, have been replaced with LED or LCD screens. In most cases these screens are extremely easy to view in a

wide range of ambient lighting. Along with computers ,

motion control and robotics have contributed to the advancement of ultrasonic inspections. Early on, the advantage of a stationary platform was recognized and used in industry. Computers can be programmed to inspect large, complex shaped components with one or multiple transducers collecting information. Automated systems typically consisted of an immersion tank, scanning system and recording system for a printout of the scan. The immersion tank can be replaced with bubbler systems, which allows the sound to be transmitted through a water column. Scanning

of components is considerably faster than contact hand scanning; the coupling is much more consistent. The scan information is collected

by a computer for evaluation, transmitted to a customer and archived.

Magnetic Particle TestingThis non-destructive method,

magnetic particle inspection (MPI), is based on establishing a magnetic fi eld with high fl ux density in a ferromagnetic material. The fl ux lines leap out when a defect passes through the magnetic fi eld. Since the fl ux lines cannot cross, this leaping action forces some of

the fl ux lines out of the material which is called fl ux leakage. Flux leakage in a pipe may be caused by defective areas such as a reduction in material (cross-sectional area) or a sharp dimensional change like a defect’s edge. If the fl ux leakage is strong enough, fluorescent and non-fluorescent magnetic particles will accumulate making the defect visible. The amount of fl ux leakage at the defective area depends primarily on the following factors: flux density, material size, defect’s orientation, depth and length.

Two techniques, dry and wet magnetic particle testing, provide two levels of sensitivity for detecting cracks and other surface discontinuities. The wet particle testing is the more sensitive with smaller iron fi lling in a mobilizing

fl uid. Magnetic particle testing may be applied to raw material such as billets, blooms, castings, forgings as well as fi nished materials like casing, tubing, drill pipe, line pipe, risers, etc., regardless of heat treatment.

A ferromagnetic material (API pipe) can be circumferentially magnetized by passing an electric current through a central conductor placed through the inside of the pipe and longitudinally magnetized by placing the pipe inside a magnetic coil.

When a discontinuity is oriented parallel to the magnetic field lines, it will be undetectable. Therefore, since discontinuities may occur in any orientation, it may be necessary to magnetize the pipe in different directions and longitudinal to perform an adequate examination. The magnetic fi eld

Along with computers, motion control and robotics have contributed to the advance-ment of ultrasonic inspections.

78 Well Servicing November/December

Remember, what you don’t know about your pipe could cost you.Remember, what you don’t know

When a discontinuity is oriented parallel to the magnetic fi eld lines, it will be detectable.

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must be of sufficient strength to indicate those discontinuities which are unacceptable. Magnetic powder accumulations show the distortion of the magnetic field as the defects are outlined on the surface. All indications must be examined, classified, compared with the acceptance standards and a decision made by the certified inspector regarding the disposition of the pipe.

The Electromagnetic method uses the flux leakage principle of magnetism in a pipe with specially engineered electronic sensors to detect defects. This is a highly automated process producing very accurate results at high speeds.

Next generation inspectionFit for service assessment is

a multi-disciplinary engineering analysis of pipe to determine if it is fit for the intended service and for the duration of a specified period. The next generation of inspections is being driven to add cross sectional area dimensions, ovality measurements and wall mapping with analytical programs directly related to exact material types.

Know your tubular productsIt is very important to realize

that the inspection of each pipe in a tubular string is the way to find the weak link. When examining the reasons to inspect or not to inspect, or to partially inspect, a practical and economic view of true cost is strongly suggested. Connection failures bring about the risk of having to shut down drilling activity for many hours. Remember, what you don’t know about your pipe could cost you.

About tHE CoMPANY: National Oilwell Varco is a worldwide leader in the design, manufacture and sale of comprehensive systems and components used in oil and gas drilling and production, drill stem products, tubular inspection, internal tubular coatings, integrated systems, downhole tools and drill bits. NOV’s Tuboscope division provides corrosion control products and inspection services. The inspection services provided cover the reclamation of drill pipe, casing, tubing and sucker rods at company-owned locations or customer-owned facilities. For information, visit www.nov.com.

Well Servicing November/December 79

Based on API RP-67(Recommended Practices for Oil eld Explosive Safety)

Oilfi eld Explosives Safety Seminar

OwenOil Tools, LP

Presented by

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