Session: 03-02-01: Integrity and Performance of Welded Joints

Submission Number: 157504

Fit for Purpose and Inspection of Subsea Equipment Dissimilar Welds 

This paper presents a technical solution for a Subsea System Project involving well completion equipment, such as BAPs and MCVs, which faced challenges due to dissimilar welds. Specifically, some components were supplied with structural welded joints of low alloy steel AISI 4130, buttered with Alloy 625 consumable, and post-weld heat treated (PWHT). This created a dissimilar interface that is metallurgically susceptible to Hydrogen Induced Stress Cracking (HISC) in the presence of atomic hydrogen from the cathodic protection system. Catastrophic failures in similar joint features have been documented in subsea equipment pipelines from projects such as Åsgard, Thunderhorse, and others in the North Sea. Following these failures, different design solutions were adopted by suppliers and operators. Although Petrobras’ welding specifications included technical requirements to prevent similar failures, a recent supply contract retained the structural dissimilar interface between low-alloy steel and nickel alloy. Instead of selecting materials less prone to hydrogen embrittlement, the supplier limited the stress levels at this interface to an internally established criterion. This approach was deemed unsafe and insufficient, as it did not eliminate the most susceptible dissimilar interface, thus allowing the possibility of flaw initiation and propagation depending on the presence and size of discontinuities in the welded joint. Given the advanced production schedule, there was insufficient time to qualify new welded joint configurations. Petrobras specialists provided technical advice in metallurgy, welding, fracture mechanics, and inspection to assess the criticality of planar flaws, thereby increasing the reliability of the equipment throughout its operational life. The assessment was based on the Failure Analysis Diagram (FAD) method and API 579 guidelines. Finite Element Analysis (FEA) was conducted to determine stress levels at the dissimilar interfaces of the flow lines between the production and annular connectors, with and without a safety factor of 1.2. A lower bound material toughness figure K_IH, 44 MPa√m, was adopted in the analyses. All dissimilar joints involving low alloy steel components buttered with Alloy 625 and then heat treated were reassessed for their suitability under operating conditions, including exposure to hydrogen from cathodic protection. These joints were reinspected by ultrasonic techniques at their dissimilar interfaces. Some joints required reworking (finishing or access improvement) to allow for reinspection, and one joint needed repair, following a procedure approved by Petrobras. Although a complete validation program for the detectability of the ultrasonic inspection procedures was missing, a conservative approach was taken through sensitivity calibration, analyses, and evaluation criteria methodology, using two ultrasonic techniques (TFM/FMC and Phased Array). This approach, along with other premises adopted for loads and fracture toughness, provided consistency in the analyses. Thus, it can be concluded that the equipment and respective joints, in their final delivery condition, were fit for purpose. It is worth noting that some closure weld configurations cannot be double-sided welded, necessitating the use of nickel alloy consumables to join their members and a low carbon C-Mn buttering solution. However, even today, there is no consensus on which low alloy steel dissimilar interfaces are indeed not susceptible to HISC for such configurations. In summary, despite the challenges and uncertainties associated with dissimilar welds, especially those susceptible to HISC, the adopted technical approach and thorough assessments ensured the operational reliability of the subsea equipment. This work underscores the importance of meticulous evaluation and robust engineering practices in managing dissimilar welds in subsea systems.

Presenting Author: Petronio Zumpano Jr Petrobras

Presenting Author Biography: Academic Education:
Graduated Mechanical Engineer at Federal University of Uberlandia, 1986.
Specialized in Petroleum Equipment Engineering - Petrobras / UFRJ, 1990
Master Degree in Mechanical Engineering at State University of Campinas, 2003. Area: Fracture Mechanics and Physical Metallurgy.

Professional Experience:
Engineer @ Petrobras – Petroleo Brasileiro SA, since March, 1990
Current Position (since Sept 2016) @ Petrobras RD&I Center: Senior advisor in welding and structural integrity (fracture and fatigue). Specialized in welding and integrity of offshore rigid pipeline systems.
From July 1998 to Sept 2016 @ Petrobras Engineering Department – Advisor in welding and structural integrity (fracture and fatigue);
From March 1990 to July 1998 @ Petrobras Exploration & Production Department – Equipment Engineer (inspection);

Duties and activities in last years:
Technical consultancy on welding and integrity area. Developing or supporting technical specifications on welding and integrity area, advising welding and integrity area of the offshore industry (subsea pipeline, risers and subsea equipment of Petrobras Projects).
Supporting and giving advice on WPQT, welders qualification, technical issues in projects governed by DNVGL-ST-F101, ASME SEC IX, API 1104, AWS D1.1, ASME SEC VIII D1 & 2, ISO 13628-15, and others. Advising failure analysis and engineering critical assessment of weldments in carbon-manganese and low alloy steels, austenitic steels, SDSS and nickel alloys. Fomenting, developing, supporting and following up R&D projects on welding and integrity area for O&G industry. Participating in technical groups in welding and integrity area.

Recent R&D Petrobras Sponsored Programs followed:
- Weldability and Integrity of MLP and Triple Point (UFC and UFSC - 2023);
- Effect of Purge Deficiency on Corrosion Resistance of Welded Joints of Duplex Steels and Carbon Steels Clad in Alloy 625 in Media Present in the Oil and Gas Industry (UFRJ - 2022);
- Evaluation of The Influence of Interpass Temperature on Welding Microalloyed, HRLA And Claded Steel With Ni Alloys (UFRJ - 2021).
- Reliability in The Inspection of Triple Point by Ultrasonic in the MLP Fabrication (UFRJ - 2022);
- Optimization of Fracture Toughness Tests for Pipeline ECA Rigid Submarine (UFRGS - 2022);
- Development of nanoparticle addition technology during welding of offshore bimetallic pipelines (UNICAMP - 2021);
- Preferential Welding Corrosion in welded joints (IPT - 2021)

Qualification & Certification
Senior Welding Inspector @ CSWIP, since November, 2001;
Welding Inspector @ AWS, since October, 2004
Level II Welding Inspector (equivalent to SWI)) @ Brazilian FBTS / SNQC-PS (National Scheme for Qualification and Certification of Welding Professionals) since February, 1999
Level III Visual Inspector @ ABENDI / SNQC-END (National Scheme for Qualification and Certification of NDT Professionals) since September, 1999

Publications:
Author of technical papers (welding, fracture, fatigue) in several international congress: ASME IMECE 2003; ASME PVP 2005 and 2008; ASME OMAE 2012, 2015, 2019, 2021; Rio Pipeline 2009, 2011, 2013, 2015, 2017, Rio Oil and Gas 2018. Author of several technical papers in national congress in Brazil (@ CONSOLDA, COTEQ, COBEM, CIBEM, etc)