Porosity variation along multipass underwater wet welds and its influence on mechanical properties

Characterization of the underwater welding arc bubble through a visual sensing method

Effect of Ni on microstructure and mechanical properties of underwater wet welding joint

Evaluation of stress corrosion cracking and hydrogen embrittlement in an API grade steel

Development of high-strength steels in recent years has required the weld metal to also improve in terms of mechanical properties. However, strengthening the weld metal tends to increase susceptibility to hydrogen-assisted cracking (HAC); therefore, diffusible hydrogen content in the weld metal, attributed to be a major cause of HAC, must be drastically reduced. Flux ingredients containing fluoride ions (F -1 ) such as fluorspar (CaF 2 ) have been reported to reduce diffusible hydrogen content in steel welds. It is believed fluoride reacts with hydrogen in the arc atmosphere to form HF, which is removed from the molten iron because of its low solubility. Preliminary thermodynamic calculations considering the reaction between hydrogen in the arc atmosphere and the fluoride in the slag were performed and predictthat KF, MnF 3 and K 3 AIF 6 are more effective in reducing hydrogen than CaF 2 , which is a common flux ingredient. To verify their predicted effectiveness, experimental FCAW consumables with additions of these fluorides were designed and fabricated at the Colorado School of Mines (CSM). Welds were produced using these electrodes and the amounts of diffusible hydrogen were measured. The experiments proved the effectiveness of fluoride additions as predicted by the thermodynamic calculations. For example, reductions of 39-67%, 21-34% and 22-31% in diffusible hydrogen were achieved with the additions of 7.4 wt-% of KF, 4.8 wt-% of MnF 3 and 5.5 weight percent of K 3 AlF 6 , respectively, in comparison with the experimental results with those of the base electrode (with only CaF 2 ).

Hydrogen control in steel weld metal by means of fluoride additions in welding flux

The Effect of Nickel on the Mechanical Properties of High-Oxygen Underwater Wet Welds

Shielded metal arc wet welding, due to its flexibility and ease of mobilization, is one of the most attractive methods for repair of underwater structures. However, the quality of the weld metals deposited by this process is detrimentally affected by the direct contact of the welding arc with the aqueous environment. Oxygen and hydrogen generated by the decomposition of water in the arc are responsible for the main problems related to this specific process: loss of deoxidizers, oxygen pickup, increase in oxide inclusions content, hydrogen-induced cracking, and porosity. Rutile electrodes are recognized in the literature as being able to deposit welds with adequate mechanical properties but with high hydrogen content. Oxidizing electrodes, on the other hand, are able to deposit welds with lower hydrogen content but higher oxygen content. Welds deposited by rutile electrodes presented approximately 90 ml/100g of diffusible hydrogen while oxidizing electrodes produced welds with diffusible hydrogen contents varying from 40 to 50 ml/100g. It was found that the measured diffusible hydrogen contents of underwater wet welds are more dependent on the type of electrode covering than on the weld metal oxygen content. The residual hydrogen content of underwater welds showed a tendency to increase to a constantmore » level of approximately 5 ml/100g as the oxygen content of the weld increased to the saturation value (0.22 wt.pct.). It seems, therefore, that the diffusible hydrogen content of underwater wet welds is more influenced by the amount of total hydrogen absorbed by the liquid metal before solidification than by the amount of inclusions, acting as hydrogen traps, in the weld metal.« less

Hydrogen content of underwater wet welds deposited by rutile and oxidizing electrodes

The use of oxidizing electrodes for wet welding of offshore structural steels, in spite of their low susceptibility to hydrogen HAZ cracking, is limited, in part by the poor mechanical properties of their weld deposits. Low levels of carbon, manganese and other deoxidizers, together with high oxygen contents seems to be one of the reasons for this low performance. This work investigated the influence of nickel additions on the tensile strength and impact resistance of wet welds deposited at 1.1 m of water depth. It was found that maximum values of toughness and tensile strength occur for nickel contents between 2 and 3 weight percent. Nickel additions also had a strong effect in reducing the grain size of equiaxed ferrite in the reheated region of underwater wet welds thereby improving their mechanical properties. The deterioration of mechanical properties for nickel contents higher than 3 weight percent was attributed to weld metal solidification cracking.

Use of nickel to improve the mechanical properties of high oxygen underwater wet welds

This paper describes the analyses performed in a circumferential rupture that occurred in a pipeline crossing a high slope region in the Southern part of Brazil. The pipeline was made of API 5L-X46 steel, coal tar coated, and has been in operation since 1977. The failure occurred after a period of heavy rains and was clearly associated to land creeping. The fracture occurred in parent metal 2770 mm away from the nearest circumferential welding. This fracture initiated in an approximately 3×70 mm external surface crack. Besides, several secondary parallel cracks were detected at a 6 o’clock position.Copyright © 2002 by ASME

Alexandre M. Pope

Papers

The Effect of Nickel on the Mechanical Properties of High-Oxygen Underwater Wet Welds

Hydrogen content of underwater wet welds deposited by rutile and oxidizing electrodes

Use of nickel to improve the mechanical properties of high oxygen underwater wet welds

Circumferential SCC in Pipeline Due to Land Creeping

Integrity Assessment and On-Site Repair of a Floating Production Platform