In the construction of pipelines/ pipework for the transporting of petroleum, gas, chemical, or other fluids/slurries, it is critical to perform nondestructive testing (NDT) of the welds. Why? Comprehensive visual weld inspection in conjunction with other NDT inspection methods, such as radiographic testing (RT) and ultrasonic testing (UT), mitigates the risk of a containment breach as the result of a weld/weldment failure.
Personal injury or death, property damage, and/or an environmental disaster could result from a containment breach. Catastrophic weld/weldment failure and service life deterioration are affected by the type and extent of weld defects present. A weld or heat-affected zone (HAZ) crack and/or weld defects or discontinuities that could potentially lead to a crack or fracture are the most severe. Therefore, the performance of in-process visual testing (VT) weld inspection to identify weld defects as well as faulty welding and fabrication practices as they occur in production is crucial. Adverse welding and fabrication practices not recognized during production pose a hidden threat to public safety and to the service life and operational characteristics of the weldment. The sooner a weld defect and/or faulty welding and fabrication practices are identified, liability risks and rework costs decrease, and weld/weldment integrity increases. Although multiple NDT methods exist for the inspection of pipe welds, this article focuses on visual weld inspection.
The Need for Qualified Welding Inspector
Qualified personnel are required to perform pipeline and pipework weld inspection. Fortunately, several avenues are available for a person to become qualified as a welding inspector. There are the SNT-TC-1A Visual Testing technician, AWS Senior Certified Welding Inspector (SCWI) and Certified Welding Inspector (CWI) programs, the API 1169 Pipeline Inspector and API 570 Piping Inspector Programs, and the TWI CSWIP 3.1 and 3.2 Welding Inspector programs.
Inspection of Pipe Welds
Fundamentally, as a visual welding inspector, you are inspecting for compliance. For example, in the construction of a multimegawatt power generation facility, there are several miles of pipework being fabricated. The alloys used for the pipework could include Chrome-Moly A335, P-Grades P5, P9, P11, P22, P91; austenitic stainless steel pipe, Grades 304L, 316L, 317L; and carbon steel pipe such as A106 and A333.
Production welds originate from the qualification of project Procedure Qualification Records (PQRs) and Welding Procedure Specifications (WPSs). On a power generation project, welding inspectors are assigned the responsibility to visually inspect pipework welds to do the following:
1) Determine if the weld meets visual acceptance criteria in accordance with the respective project weld code(s) such as ASME B31.1, Power Piping, and ASME B31.3, Process Piping.
2) Verify that production welds and weldments are in accordance with pipe spool and structural drawings.
3) Verify that weld variables being used in production are in accordance with qualified WPSs. The variables could include weld joint cleaning; amps; volts; travel speed; heat input; multipass weld bead sequence; weld filler metal; preheat, interpass, and postweld temperatures; and joint geometry.
As with ensuring compliance, the monitoring of welding and fabrication practices and weld quality are vital elements of job-site responsibilities. Not only are visual welding inspectors engaged in the monitoring of pipe welding and fabrication practices, their additional responsibilities entail developing weld maps and maintaining weld traceability documentation, witnessing/supporting welder qualifications, resolving weld rework/repair activities, and working with NDT inspection crews.
Pipeline Inspection
Visual welding inspectors on pipeline projects are also inspecting for compliance to visual weld code acceptance criteria and are verifying that qualified WPS weld variables are being used during welding. Inspectors working on a new pipeline construction project will support weld crews as they advance down the line from weld joint to weld joint. During welding, the root pass, hot pass, fill passes, and cover/cap passes are inspected. Upon weld completion, welding inspectors work with radiographic testing crews as they test designated welds.
The primary codes used for oilfield pipeline construction are API 1104, Welding of Pipelines and Related Facilities; ASME B31.4, Pipeline Transportation Systems for Liquids and Slurries; and ASME B31.8, Gas Transmission and Distribution Piping Systems. Carbon steel alloys as specified within API 5L, Specification for Line Pipe, including Grades X42, X46, X52, X56, X60, and X65 through X120, comprise most pipeline materials.
For pipelines in operation, visual welding inspectors are involved with in-service weld repairs in accordance with API 1104, Section B. In-service weld repairs mean that welding transpires while the pipeline is in operation. In-service weld repairs are complex, involving variables such as fluid and pipe temperature, pressure, flow rates, and pipe wall thickness.
In addition, visual welding inspectors are involved with hot-tapping applications. As with in-service weld repairs, hot tapping is performed while the pipeline is in operation. It is not uncommon for welding inspectors to be involved in non-welding activities such as the inspection of a pipeline for corrosion or hydrostatic testing of pipeline sections.
In-Service Pipeline Welding
Due to the seriousness of pipeline in-service weld repairs and hot tapping welding applications, a visual welding inspector will be given responsibility for witnessing and documenting the weld variables (e.g., volts, amps) employed for each individual weld bead during welding (i.e., root pass, hot pass, fill passes, and cap/cover passes). This is done to ensure the contractor’s compliance with the qualified WPS. The inspector will also perform visual inspection of each individual weld bead during welding and of the completed weld. Upon final completion of the weld repair and/or hot tapped welds, the welding inspector may witnesses radiographic testing of complete-joint-penetration welds and magnetic particle testing of fillet welds. The inspector also documents test results.
In-service pipeline weld repairs are performed in accordance with API 1104 Section B. Additionally, API RP 2201, Procedure for Welding or Hot-Tapping on Equipment in Service, is an authoritative document referenced for in-service welding and hot-tapping applications.
The Weld Root
The pivotal weld in all pipeline and pipework welding is the root weld. The root surface contour and amount of root weld reinforcement are crucial. To facilitate successful welding of the root weld, proper weld joint fit up is required. When an open root weld joint is used, welders and weld inspectors employ flashlights to peer through the root opening to inspect the weld. Root weld underfill/concavity, incomplete penetration, excessive mismatch, internal undercut, or excessive root weld reinforcement will result in a failure to pass radiography. Also, if the root surface contour is such that the weld toes are not fused with the base metal, an incomplete fusion weld defect will result. For piping applications, an inspection mirror and a high quality flashlight are essential tools for a welding inspector.
Practicing Your Craft
Keep in mind that visual welding inspectors need a variety of tools and should be aware of what’s happening all around the welding environment. While their primary job is to inspect welds, they’ll also be called upon to perform a variety of other tasks.
For instance, it is pertinent for visual welding inspectors to be cognizant of the welding environment and the alloy being welded. For example, they should be aware of the potential for hydrogen induced cracking in the welding of alloy steels and carbon steel line pipe. When reviewing project WPSs, possessing a basic understanding of low-hydrogen practices and being able to ask relevant questions could ultimately prevent the occurrence of weld metal/HAZ cracking. It is pertinent as well that welding inspectors understand applicable weld codes, be adept in pipe drawing interpretation, be familiar with weld symbols, and be able to recognize various types of pipe and pipe fittings.
Tools commonly carried on a job site include a professional and objective attitude; various types of gauges to measure weld reinforcement, fillet weld sizes, mismatch, undercut, pit depth, root openings, porosity, and bevel angles; as well as a flashlight, mirrors, camera, stopwatch, 6-in. scale, loupes with 5× and 10× magnification, 25-ft tape measure, welding helmet, calculator, a calibrated volt/amp meter, and a contact pyrometer.
When on a job site, in addition to visually inspecting welds, visual welding inspectors are often called upon by welders, pipefitters, site engineers, and so on to provide weld process and fabrication troubleshooting and to participate in root cause analysis inquiries.
Summary
In the fabrication of pipelines/ pipework, comprehensive visual weld inspection in conjunction with other NDT methods, such as RT and UT, mitigate the risk of a containment breach as the result of a weld or weldment failure. The performance of diligent in-process visual weld inspection facilitates identification of weld defects as well as faulty welding and fabrication practices as they occur in production. The sooner a weld defect and/or faulty welding and fabrication practices are identified, liability risks and rework costs decrease, and weld/weldment integrity increases.