Analiza mikrostrukture zavarenog spoja na cjevovodu za transport vodika od čelika API 5L X70

master's thesis

• Title (english): Analysis of the microstructure in the weld joint on hydrogen pipeline made of API 5L X70
• Author: Ivan Huđ
• Mentor: Ivica Garašić (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2024-12-05, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Cjevovodi za transport nafte, plina te sve češće i vodika suočavaju se s izazovima očuvanja
mehaničkih svojstava zbog povećanih zahtjeva za promjerima, tlakovima i raznolikosti
transportiranih resursa, što je potaknulo upotrebu čelika visoke čvrstoće poput API 5L X70.
Vodik, kao gorivo budućnosti, dodatno ističe potrebu za specifičnim procesima toplinskomehaničke obrade čelika, koji prilagodbom mikrostrukture osiguravaju visoku čvrstoću,
žilavost i otpornost na djelovanje vodika. Budući da puknuća cjevovoda često počinju na
zavarima, detaljna istraživanja mehaničkih svojstava zavarenih spojeva ključna su za sigurnost
i pouzdanost transportnih sustava. Vodikova degradacija značajno utječe na mehanička svojstva
čelika, povećavajući rizik od havarija u cjevovodima, spremnicima i strojevima, a njen
intenzitet ovisi o uvjetima okoline, koncentraciji vodika i svojstvima materijala.
U eksperimentalnom dijelu rada, zavaren spoj izrađen automatiziranim MAG postupkom
podvrgnut je detaljnom ispitivanju kako bi se analizirala njegova struktura i mehanička
svojstva. Provedena su ispitivanja makrostrukture, mikrostrukture i tvrdoće, pri čemu su
posebno obrađeni osnovni materijal, zona utjecaja topline te metal zavara. Analiza
makrostrukture uključivala je pregled geometrije zavarenog spoja, dok su mikrostrukturna
ispitivanja pružila uvid u detalje rasporeda zrna i promjena u mikrostrukturi unutar zavara i
okolnih zona. Mjerenje tvrdoće metodom po Vickersu provedeno je radi kvantifikacije
mehaničke otpornosti različitih dijelova zavarenog spoja, čime su dobiveni ključni podaci za
procjenu kvalitete zavara i njegove otpornosti na vanjske utjecaje, poput djelovanja vodika.

Abstract (english)

Pipelines for the transport of oil, gas, and increasingly – hydrogen, face challenges in
maintaining mechanical properties due to growing demands for larger diameters, higher
pressures, and a wider variety of transported resources. This has driven the adoption of highstrength steels such as API 5L X70. Hydrogen, as the fuel of the future, further underscores the
need for specific thermo-mechanical processing of steel to tailor microstructures that ensure
high strength, toughness, and resistance to hydrogen effects. Since pipeline failures often
originate at welds, detailed investigations into the mechanical properties of welded joints are
essential for the safety and reliability of transport systems.
Hydrogen degradation significantly impacts the mechanical properties of steel, increasing the
risk of failures in pipelines, storage tanks, and machinery. The severity of this phenomenon
depends on environmental conditions, hydrogen concentration, and material properties.
In the experimental part of the study, a welded joint created using an automated MAG process
was subjected to detailed examinations to analyze its structural and mechanical properties. Tests
included macrostructure, microstructure, and hardness evaluations, focusing on the base
material, the heat-affected zone and the weld metal. The macrostructural analysis provided an
overview of the general appearance of the welded joint, while the microstructural tests offered
insights into grain distribution and microstructural changes within the weld and surrounding
areas. Hardness measurements using the Vickers method were conducted to quantify the
mechanical resistance of different parts of the welded joint, yielding critical data for assessing
weld quality and its resistance to external effects, such as hydrogen interaction.

• Keywords: vodik; čelik API 5L X70; vodikove pukotine; automatizirani MAG
• Keywords (english): hydrogen; API 5L X70 steel; hydrogen cracking; automated MAG welding
• Language: croatian
• URN:NBN: urn:nbn:hr:235:308233
• Study programme: Title: Mechanical Engineering; specializations in: Design, Process and Energy Engineering, Production Engineering, Engineering Modelling and Computer Simulation, Marine Engineering, Industrial Engineering and Management, Materials Engineering, Mechanics and Robotics, Autonomous Systems, Mechatronics and Robotics; Course: Production Engineering; Study programme type: university; Study level: graduate; Academic / professional title: sveučilišni/a magistar/magistra inženjer/inženjerka strojarstva (sveučilišni/a magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Embargoed access; Embargo expiration date: 2026-12-05
• Created on: 2024-12-04 17:42:28