Designers are conservative for a reason. The equations used for design purposes are largely based on empirical data. Factors of safety are used to account for the "unknown" or "unforeseen" conditions such as bolt holes that are torch cut to accommodate hole misalignment, columns that aren't as plumb as they should be and welds that are not as large as they should be or undercut along the edges of the weld.
It is less expensive and safer to be conservative than to reduce the safety factor in most instances. The exception to the use of a large safety factor is in the aerospace industry where the cost of in-depth research and design is less expensive (than heavier aircraft) over the life time of the aircraft. However, to ensure the design requirements are fully implemented each component is subjected to rigorous inspection and quality control not seen in other industrial sectors.
There is a well established history of problems resulting from diffusible hydrogen in welds and other fabricated components such as cracking towers used in the petrochemical industry that offer hydrogen rich carbon rich environments. Cracking and blistering in the petrochemical industry as a result of hydrogen diffusing into the lattice of the high strength low alloy steel is a well established phenomenon. There are steps that can be taken to mitigate those problems and they are enforced when the cost of failure cannot be tolerated.
Steel structures utilizing high strength low alloy steels are seeing expanded use because they lower overall cost by reducing the weight of the steel required, reduces the size and cost of the foundation as well as the cost of erection. The use of the higher strength steels allows the use of lighter members and in some cases the engineer uses fewer members so there is less redundancy, meaning if one member fails, there is no alternate load path to the foundation. The bottom line is that when a nonredundent member fails, the entire structure fails.
High strength low alloy steels are not as tolerant as the steels traditionally used in steel structures. The alloy content makes them more susceptible to delayed cold cracking than low carbon steel such as ASTM A36 or A53. Additional precautions are required to minimize the potential of developing a hard brittle heat affected zone and to minimize the potential for introducing diffusible hydrogen into the weld puddle where it can diffuse into the HAZ while it is austenized. To limit the diffusible hydrogen available in the weld or HAZ we use low hydrogen electrodes or select a welding process that is recognized as a low hydrogen welding process because they use bare electrode or an electrode flux that is protected from the environment, i.e., FCAW. Be aware that all FCAW electrodes are not created equal and if hydrogen is a concern, the welding engineer must be selective of which electrode classification is specified.
The bottom line is that we as welding professionals must be aware of what we can and what we cannot do to ensure the structures we fabricate and erect are safe for the intended service conditions and they do not pose a danger to the people using them or to the general public.
The professional will not gamble with other people’s lives or well being by taking short cuts. “We’ve always done it that way” is not an acceptable reason for ignoring code requirements or the engineer’s instructions.
Times are changing. The materials we use to construct structures with are changing. Some of those materials are less fault tolerant and we have to understand how they behave and how they respond to welding and forming operations. What we did and how we did it does not mean we can continue to follow “old school methodology”. We have an opportunity to learn from the mistakes made in the past and we can learn from the failures that have occurred. It is our job, as professionals, be it as a welder, inspector, detailer, or engineer, to do our best to maintain our level of understanding of current requirements. As a welder, the task includes following the written instructions provided by our employers. If sufficient instructions are not provide, ask for the information that is needed.
I have nothing but distain for the welder or inspector that doesn’t take pride in their work or refuses to follow the instructions provided by the employer or the design professional. We expect the designers and the engineers to do their job in a conscientious manner. They have a right to expect the inspector and welder to do their part to follow the rules, regulations, codes, and work instructions as well.
The public expects the engineer, designer, inspector, and the welder to know how to do their jobs correctly. They pay for our services and they have a right to have the work done in a proper manner.
Best regards – Al
John
Hi John!
