Safe Operation of Aging Hydrogen Generation Plants

Introduction

Hydrogen plants are subject to severe operating conditions that can induce accelerated aging of piping and fixed equipment. Damage mechanisms associated with the aging process include corrosion, creep, high temperature hydrogen attack (HTHA), thermal fatigue, stress relaxation cracking, sigma phase embrittlement, oxidation, and carburization, among others. Factors such as cyclic service, high operating temperatures, unexpected shutdowns, and operational breaches (outside normally expected or design conditions) can induce or enhance the occurrence of the damage mechanisms and accelerate the aging process; therefore, special attention is needed to avoid unexpected catastrophic failures.

RBI methodologies incorporating a damage mechanism review (DMR) can be used to manage the assets in aging plants and reduce the risk of loss of containment by identifying the damage mechanisms that are expected to occur in each piece of fixed equipment and piping, calculating the risk associated with a potential loss of containment, and clearly defining inspection plans based on the RBI assessment results. If inspection results show symptoms of degradation or accelerated aging, fitness for service (FFS) evaluations may be required to ensure the mechanical integrity of the asset.

Since RBI utilizes process conditions essentially as a “snapshot” in time to recommend inspection plans, day-to-day changes in process conditions are not fed back into the risk calculation. A well-designed and implemented integrity operating windows (IOW) program can help bridge the gap by providing real time notification of key process parameters that can accelerate degradation and increase risk.   

This article discusses the use of the RBI methodology supplemented by a well-designed IOW program to assess and manage aging in fixed equipment and piping in hydrogen generation units; a similar methodology can be used to manage aging of other process units.

What is an Aging Plant?

The concept of aging plants is not straightforward since it is not just about the time the asset has been in service. The UK Health and Safety Executive (HSE) published guidelines for managing aging plants that describe aging plants as follows:

• — Aging is the effect whereby a component suffers some form of material deterioration and damage.
• — Aging is not about how old your equipment is; it is about its condition and how that is changing over time.
• — Just because equipment is old does not necessarily mean it is significantly deteriorating and damaged.