Proper design and fabrication, heat treatment and inspection practices play a vital role in achieving good quality and performance of low alloy steel piping. These materials have narrower fabrication windows as the alloy content goes up and non-adherence to correct execution practices may lead to leakage by delayed hydrogen cracking, stress corrosion cracking or fatigue resulting in unplanned shutdowns and costly repairs.
This paper describes details about strengths and weaknesses of support design and fabrication practices for such attachment welds. The paper discusses various precautions to be taken during the design and fabrication stages for low alloy steel supports attachment welds. It will discuss heat treatment cycles viz. preheat, interpass, dehydrogenation treatment (post heating) and post weld heat treatment (PWHT). The control of consumables, welding environment conditions, and the weld heating cycle is essential to prevent hydrogen assisted cold cracking in high hardness microstructures in weld and HAZ, and for achieving successful relief of residual welding stresses.

The integrity of new pipeline projects is critical to Saudi Aramco to avoid any short or long-term impact on the supply of energy. During construction activities, pipeline internal welding inspection is carried out in compliance with international and Saudi Aramco requirements. The visual inspection of internally cladded girth welded pipes requires extra care to avoid any improper field fabrication errors during welding, especially at the root pass area. Such errors can limit the inspection capability and compromise the integrity of pipeline network with possible degradation of corrosion resistance at/near the weld rot, resulting in premature failures. Currently, projects utilize conventional tools such as borescope which is time consuming with limited inspection capabilities (up to 150 meters inside the pipe) and system maneuverability at inspection locations.
The Saudi Aramco Inspection Department enhanced their active inspection technology program and collaborated with a local technology developer. They trialed a wireless crawler robot, which is a high resolution remotely operated robot capable of inspecting internal girth welds with 5000 meters travel capability inside the pipes. The robot can inspect internal girth welds in the field, and inside pipelines with internal diameters of 6 inches and above, and wirelessly transmits the visual inspection results to the outside control room for a timely assessment and critical decision making. The internal visual inspection with wireless crawler robot will help in improving the project progress, reducing repair costs, by identifying defective welds before coating application.

Process equipment which employs a corrosion resistant alloy (CRA) layer cladded to steel is common in refineries, petrochemical plants and other plants processing highly corrosive media. There are two regularly employed methods for welding attachments and internals to clad process vessels. One is to remove the CRA cladding for welding the attachment to the steel base metal assuming dissimilar welds and restoring CRA by weld overlay. The other eliminates the step of removing the cladding, simplifying the attachment process by direct welding of the internals onto the clad layer. With the lack of data to prove the integrity of direct welding attachment onto the clad layer, designers frequently demand the cladding be removed or allow only a conservatively low stress limit for what can be attached directly to the clad surface. It is well understood that eliminating the step of removing clad increases the simplicity, improves the lead-time, and reduces the cost of making these attachments for trays or other internals, but there are concerns about clad disbonding risks. With the aim to provide data around the integrity of direct welding attachments for better risk assessments, a technical study was undertaken. In this study, it will be shown that the bond between clad material and the base steel is robust enough to withstand the heaviest attachments and harshest conditions. The theory behind the technical study will be presented along with the results of this study