The T-8-20 Task Group conducted a survey of plant practices and of the performance of materials of constrution in HF Alkylation Units. A Primary goal of the survey was to expand the limited body of the information on alternative ally performance in HF Alkylation units and to better define the susceptibility of steel to hydrogen induced cracking.
Apart from the well-tried cellulosic electrodes, in the range from E6010-E9010, there are
also low hydrogen grades of weld consumables, which are used in vertical downhill
position - commonly called as BVD (Basic Vertical Down) electrodes. In addition, the
seamless flux cored wires, are gaining prominence in the welding industry as a better
solution compared to the conventional cellulosic electrodes.
The development of BVD electrodes started because of the desire to use high-strength
TM pipe steels with relatively high toughness (e.g. X80). Cellulosic electrodes could not
meet the requirements for cold crack resistance and high toughness properties of the
weld metal. To a high degree, economical efficiency is determined by the achievable
deposition rate and the possible welding speeds. In comparison to basic vertical-up
electrodes, significant time advantage of 40-50% can be achieved with the use of BVD
electrodes for the fill and cap layers.
Seamless Flux Cored wires for pipeline applications follow a different manufacturing
approach compared to the conventional folded techniques and are much reliable with
consistent performance in terms of weldability and quality. The seamless FCAW wires,
offers a unique and trustworthy solution in terms of arc stability and low defect rates.
These wires are also suitable to be used under sour service applications having been
tested for Hydrogen Induced Cracking (HIC) and Sulfide Stress Cracking applications.