Welding is a critical function in the construction of oil-and-gas industry infrastructure, and there are numerous insights and fine points about that sector that young welding engineers and inspectors will need to learn in order to advance in their profession.

The following methods are used mainly used to inspect welding project during the execution process and after completion. Except for destructive and Charpy testing, all the methods described here are non-destructive testing (NDT) methods.
• Visual inspection
• Radiography
• Ultrasound testing
• Liquid-penetrant testing
• Destructive testing
• Magnetic particle testing
• Eddy-current testing
• Hardness testing
• Charpy V notch testing.

What follows here is a series of brief details about each of these methods, and their practical applications.
Visual inspection — Visual inspection is the method involving the human eye and some tools. It is the easiest, least expensive and most effective welding inspection method. This technique is used while welding is in progress in a field or a workshop.

A welder certificate, joint preparation, condition of electrode, current used, weather conditions, slag removal, etc., can be checked effectively by visual inspection.

Radiography — Radiography or X-ray methods are also known as non-destructive testing (NDT), and the process is used to examine the internal structure of a weld without destroying the welded component. X-ray films are produced with the help of iridium isotope producing x-rays passing through the weld.

Excessive penetration, lack of fusion, concavity, cracks, etc., are inspected through radiography.

Ultrasound testing — High-frequency sound vibrations are transmitted by ultrasound equipment through a welded joint. The signals that are received in return on a glass screen determine the defect in the welded joint.

The thickness of a welded joint, cracking, lack of penetration, and blow holes can be detected by way of the ultrasound method.

Liquid-penetrant testing — This method detects surface defects in a weld, such as hairline cracks, porosity, etc. In this test, a liquid penetrant is applied on the weld surface. Next, a developer is applied that renders the defects visible.

Destructive testing — In this test the completed weld is cut into pieces, as per the code for face bend, root bend, side bend, and tensile tests, etc. It’s a method that is effective for locating porosity, slag inclusion, undercutting, and like defects in a weld.

Magnetic particle testing — This is a method used to detect surface and slightly subsurface discontinuities in a weld. Electric current is passed through the weld to form a magnetic field. Iron particles are applied in that magnetic field. The iron particles will build up in the defect area, isolating it and helping to determine its cause.

Eddy-current testing — Very small cracks are detected through this method. A circular coil carrying an alternating current is placed near the test specimen. The AC in the coil generates a magnetic field that interacts with the test specimen and generates eddy current. The presence of any flaw will cause a change in the eddy current, and this change can be measured by a receiver coil.

Hardness testing — This test is carried out by striking a specific load on an indicator placed on the weld. The size of the indentation that is so produced can be referred to a table measuring hardness.

Charpy V notch testing — By this method, the toughness of a weld is measured. It is performed by collecting a sample of the weld, cut to a specific size, into which a V-shaped notch is carved. Then, the sample is held in a clamp. A pendulum strikes the notch and swings upward, and the result is a measurement of the weld’s toughness.

M. Younas Malik is a qualified mechanical engineer from the University of Engineering and Technology Lahore and holder of a B.S. in Technical Education from a polytechnic program established by the Oklahoma State University in Rawalpindi, Pakistan. He has been a member of the American Welding Society (AWS) and The American Society of Mechanical Engineers (ASME.) He has 30 years of professional experience in the oil-and-gas industries of UAE, Iran, Pakistan, Oman, and Kuwait, with companies such as Saipem, Snamprogetti, Techint, Bureau Veritas, Palmer & Tritton, OGDC, KNPC, and OMV. Contact him at maliks00@hotmail.com.