Dr. Ali Khatami, PE, is SCS Engineers’ National Expert for Landfill Design. Over his 40-year career, he has developed countless innovative engineering solutions to improve landfill design and function. He likes to share his wealth of knowledge and expertise with clients and colleagues and has prepared a series of videos to explore various landfill design components in depth. In the first blog of this series, we shared Dr. Khatami’s videos on modern landfill design. This second blog introduces his videos covering pipe pressure testing and applications for the two types of double-cased pipe centralizers. These modern landfill approaches provide efficiencies and economic benefits to landfill operations and effective solutions to challenging issues. Connect with Dr. Khatami on LinkedIn.
This video covers pressure testing of double-cased pipe leachate force mains, condensate force mains, and gas well liquids force mains. These pipes, installed in segments, are welded together to maintain the system’s integrity, which is paramount to prevent leaks. Pressure testing is conducted on each pipe before and after installation to ensure the welds are intact and the pipes are not leaking. Although not always required, double-cased piping is a method to encase a main carrier pipe inside a larger pipe and create leak detection and prevention. In this video, Dr. Khatami discusses the process and his recommendations for properly pressure testing landfill piping systems to avoid problems during and after installation. [Run time 17:49]
Dr. Khatami explores the impact of the ambient temperature when testing HDPE pipes with incompressible fluids (such as water) [note: if using air for the pressure testing, the information in this presentation would not apply]. Pressure testing is conducted on each pipe before and after installation to ensure that the pipe welds are intact and the pipes are not leaking. The design engineer’s typical specifications for this type of testing address initial pressure, test duration, and the allowable pressure drop; however, they do not usually consider the impact of ambient temperature.
Dr. Khatami discusses how the pressure inside a pipe changes as pipes expand or contract based on the ambient temperature. He also provides methods to distinguish pressure changes attributable to a leak versus temperature differences. This can be an important distinction when determining a pipe pressure pass/fail. If ambient temperature causes pressure changes, the landfill operator may avoid the time and money to make pipe repairs. [Run time 19:43]
Centralizers are used in double-cased pipes to keep the inner pipe centered within the outer pipe for proper alignment during fusing. They are at locations where a double-cased pipe is butt welded to another double-cased pipe. In this video, Dr. Khatami describes the two types of centralizers, perforated and non-perforated, and discusses their various applications. Perforated centralizers allow for flow within the casing pipe (outside the main pipe) and with flow detection systems for leak monitoring. Non-perforated centralizers prevent flow within the casing pipe and isolate the casing pipe to prevent leakage into other locations. Examples include in the double-cased leachate force main at the outer boundaries of a disposal cell, or to surround detection systems to locate leaks more easily. [Run time 16:40]
