Gys van Zyl

Metal Dusting of Process Gas Heater Convection Tubes

Abstract An investigation was conducted into a failure of convection section tubes in a process gas heater in a steel-making company. Thorough study using various characterisation techniques showed that the failure of the tubes, which were made of low-alloyed steel ASTM A335 P22, was attributed to metal dusting. The attack was accelerated because of the use of incompatible tube material for the intended operating conditions. Moreover, thermal fatigue cracks were discovered on the tube surfaces. Such cracks might have been caused by the high number of plant start-ups and shutdowns. Failure contributing factors and recommendations to avoid similar failure are discussed in this article.

Failure Analysis of Turboexpander

AbstractThis article describes an investigation into a failure of a turboexpander wheel driving a compressor. Some of the wheel blades were completely cracked and detached, while others had cracks of varying lengths running parallel to the root of the blade. Detailed failure investigation using different characterization techniques such as visual examination, chemical analysis, fractography, metallography, SEM/EDX, hardness testing, modal impact testing, and FEA showed that the cracks and fractures in the turboexpander wheel were caused by fatigue which progressed from multiple origins on concave blade side surfaces, near the hub. The fatigue performance of the turboexpander wheel was degraded significantly by the presence of the anodized layer on the wheel surface. Corrective measures to avoid similar failures are suggested and discussed.

Investigation of a Chronic Leaking Problem of a Heat Exchanger Girth Flange

A shell-and-tube heat exchanger experiences frequent leaks from the gasket between the shell girth flange and tube sheet. The leaks manifest during start-up of the equipment and have traditionally been arrested by assembly retorque. An investigation was launched to understand the cause of recurring leaks and propose measures to eliminate the problem. A standard design review using the ASME BPVC [1] rules for bolted flanges found no concern with the design of the flanges. More detailed numerical simulation studies were performed that considered thermal conditions in addition to mechanical loads (pressure and bolt loads). The heat exchanger operation involves phase changes in the media on both the shell and tube sides (boiling/condensing) — as a result, the flanges experience rather severe thermal gradients during regular operation. These thermal gradients cause distortion of the tube sheet and girth flange and result in relaxation of the gasket compression in specific areas. This paper will provide a detailed discussion about the numerical simulation studies that were performed on the girth flange joint, as well as the modifications that were proposed to alleviate the problem.Copyright

Cracking Investigation of Vaporizer Tubes

This article describes the results of an investigation into failures of washing phenol vaporizer tubes. Thorough analyses including visual examination, chemical testing, fractography, metallography, heat treatment, and hardness testing have shown that the vaporizer tube failure is attributed to intergranular corrosion. The failure contributing factors are identified and elucidated.