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Ultrasonic Wall Thickness Measuring of Oil Country Tubular Goods

The inspection market for tubular products used in critical oil field applications requires highly sophisticated equipment with great accuracy providing wall thickness measurements for the full tube body of casing, tubing and drill pipe. NDT techniques play an important role of measuring actual wall thicknesses and detecting flaw indications that may reduce remaining wall per pipe. Software has been designed to gather each data point and create a detailed map unique to each pipe showing its minimum and maximum wall thicknesses. By knowing actual pipe dimensions the engineer now has the ability to design a more effective casing string using API RP 5C3 (ISO 10400) recommended formulas. On the economic front an API 5CT tubular product when correctly inspected can eliminate the need for higher cost exotic products and also may allow for the reduction of a string’s diameter or weight while maintaining safety factors. INTRODUCTION For this paper we will focus on casing and will leave tubing and drill pipe for another occasion. To retrieve oil and gas from down deep in the earth petroleum engineers have developed a safe manner by using multiple layers of protective steel called casing. Under the strictest regulations from both state and federal agencies the wellbore must be secured in place with layers of concrete. Casing is very large diameter pipe in 40 ft lengths using threaded and coupled connections to make long strings which hang down in the wellbore. Conductor casing is at the very top of wellbore to protect ground from caving in and providing strength for wellhead equipment including BOP (blow out preventer) safeguarding drilling activities. Typical casing diameters are 24 in. to 60 ft deep, then 20 in. diameter runs through conductor pipe and goes 500 ft deep for additional protection through the fresh-water aquifer. Surface casing 13 3/8 in. diameter runs inside conductor pipe cemented in place up to 1000 ft with intermitted casing 9 5/8 in. diameter continuing vertical part of well down to 8000 ft deep. Production casing 5 ½ in. diameter is used to make the bend into horizontal direction connecting targeted pay zones of oil and gas. Some wells still produce “open hole” but most wells are being completed with “horizontal direction” extended reach techniques using “hydraulic fracturing” to stimulate product flow in what’s called shale plays. NDT plays an extremely important role in reducing risk with these very expensive projects. Most casing receives NDT at pipe manufacturer’s facility as part of their quality program. As casing integrity requirements increase for deeper higher pressure wells “post mill” NDT inspections are performed in addition to manufacturer’s inspections to verify material meets specification. Figure

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