For the last ten years, composite patch repair has become a norm in nearly every industry globally. Whether it be boats or pipelines, people have turned toward the types of composite repairs for their cost of effectiveness, ease of installation, and, most importantly, reliability.
As of June 2020, according to AP 653, section 9.4, this form of repair is allowed for tank shells. In the past, concerns have been raised about the specific stresses and demands of tank shells such as hoop stress, and the necessity to provide a viable walking bridge on top. But now with more than ten years of history and engineering, there is much more confidence in the capacity of composite repair leaks and corrosion of these specific issues.
Let’s take a look at some specific concerns for tank shell repair using composite patches.
The primary advantage of a composite patch repair is the ability to easily fit any shape hole as well as the stability brought by directional reinforcement through adhesion rather than riveting or welding. This allows for the use of less material in a repair, while still providing a reliable patch.
When it comes to repairing large tank structures using composite patches, there are two general types of repairs: flat surfaces, such as roofs, or curved, like the tank shell. Each of these repairs has its own specific needs and concerns which, with the advent of composite patch repair, have been made much easier and more cost-efficient.
First, we’ll consider a flat surface repair. The major concern for flat surface repairs, with regard to composite patches, is the necessity to maintain structural integrity underweight and provide a suitable and reliable walking bridge. Simply, you don’t want someone falling through the roof. This can be guaranteed using specific design approaches. Once cured, a composite patch system will act as a “flat-plate beam” dispersing loads evenly throughout the composite and attached surface, thus allowing a safe and reliable walking surface.
The next concern for tank repair via composite patches is for the side, or shell of the tank. The main concern here is leaking due to puncture or hoop stress. Both can be quickly and effectively solved by the use of a composite patch. Leaking can be easily and quickly fixed by the use of a patch without the risk of additional damage or the leak breaking again. A patch also requires minimal time to install. This will allow you to get back to using your shell quickly and with confidence.
Hoop shell stress is slightly more complicated than puncturing but can be fixed just as reliably. When dealing with hoop stress, the issue becomes one of containing a point of the entire cylindrical structure rather than one singular spot. Recent studies have provided reliable data for this fix as well, demonstrating that punctures by hoop stress can be effectively fixed using composite patches of composite full encirclement sleeves.
The addition of composite patch repair in the field of tank shells is truly exciting and will save the industry both time and money while still providing a reliable fix to damages. Though the composite patch will be an effective addition to containing the valuable materials within our tank shells, it will be difficult to contain the excitement.