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Mechanized GMAW Root Profile Irregularities and Its Effects

Picture for Mechanized GMAW Root Profile Irregularities and Its Effects
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This paper illustrates and discusses a failure that occurred during construction of a carbon steel pipeline, in which the root profile irregularities led to an unacceptable surface condition that affected the application of liquid epoxy coating. This irregularity was identified to be weld root protrusions having sharp edges due to poor implementation of Mechanized GMAW welding process and periodic maintenance of equipment which left a gap between copper backing shoes of the internal clamps. Therefore, the integrity and effectiveness of applying internal coating of carbon steel pipeline was jeopardized, which necessitated all effected weld joints with unacceptable root profile to be rectified.
In order to identify the root cause(s) of these irregularities, the client and contractor performed an in-depth thorough investigation. In addition to the investigation findings, the paper will also highlight the following:
a. The resolution, which involved the cutting out and re-welding of more than 1200 joints.
b. The significant impact of the rectification process on the project’s schedule and cost.
c. Recommendations for future projects.
Furthermore, as all data and findings collected during this investigation were crosschecked against project design and construction requirements, the following identified areas of improvement and preventive measures are recommended:
a. Proper project planning, execution and resource availability.
b. Pre-production qualification of welding/coating application and quality assurance process.
c. Periodic preventive maintenance of the welding equipment.
d. Application of improved techniques/technologies to verify the weld root profile.
Implementing the above should result in enhanced process control, improved root profile and reduced coating application deficiencies that will minimize reworks, reduce rejection, improve
progress, and ultimately provide the desired quality for both weldments and coating at an optimum cost.

Product Number: MPWT19-15392
Author: Alawi Al Saigh, Fahad Al Mahashir,
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This paper presents basic information on fusion welding processes used to weld pressure pipes. More specifically, it looks at the technical improvements of the past 20 years. It details the changes to the GMAW process achieved when Lincoln Electric Company introduced the STT GMAW approach, which revolutionized the industry. It then explains how this new GMAW process allowed welding shops to achieve root pass penetration and fusion that rivaled those achieved with GTAW but with much higher productivity and far less experienced welders. The STT also facilitated the automatization of pressure pipe welding. We will show the impact on quality and productivity for carbon steel. This paper results from reviewing several research articles and from shop experiments performed in a welding shop in Hamriyah Free Zone UAE
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