H2Tech - Q2 2021 - 43

CHEMICAL AND FERTILIZER PRODUCTION

Metallurgical damage mechanisms affecting
equipment in the ammonia industry
S. BERG, D. J. BENAC and D. SHAFFER, Baker Engineering and Risk Consultants, San Antonio, Texas

Considerable investment has been allotted to the research and development of
renewable and alternative forms of energy
in the private sector, in academia and by
governments around the world. The impetus for the recent interest in these energy forms is to provide an alternative to
fossil fuels by deploying new technology
that enables these alternative and renewable forms of energy to address climate
change. Examples of these types of technology include battery energy storage systems; electrochemical fuel cells; and even
new and novel types of batteries, including
graphene and lithium metal batteries.1,2
These technologies are at different stages
of development and vary from commercially available to theoretical research.
Technology utilizing hydrogen fuel has
been successfully implemented as an alternative energy source globally.3 H2 fuel cells
have been available in commercial form in
vehicles and in power generation applications for decades. New electrochemical fuel cells utilizing ammonia fuel are a
promising new technology alternative to
direct H2 and hydrocarbon fuel cells. Recent interest in ammonia anode fuel cells
has sparked investment in this technology
as a potential replacement for petroleumpowered vehicles and power generation.4
Ammonia also provides promise, as it may
provide a source of H2 fuel for H2 technology. However, accommodating increased
usage of ammonia anode and even H2 fuel
cells using ammonia as the H2 source requires significant increases in ammonia
production capacity globally.
Creating large-scale infrastructure for
ammonia and H2 fuels requires an objective assessment of the associated operational and lifecycle risks. It is important
to recognize that consideration of all potential hazards and threats throughout
the supply chain is a multidisciplinary

undertaking to ensure successful deployment and safe operation of the supply
chain. On the production side of the supply chain, ammonia process equipment is
susceptible to hazards and threats in the
form of materials degradation and metallurgical damage mechanisms from the
process fluids handled by ammonia production and handling equipment.
This article highlights three common
metallurgical damage mechanisms that
can result in potentially dangerous equipment failures and costly downtime in
ammonia process equipment if not properly managed. Additionally, this article discusses methods to identify and diagnose
these damage mechanisms, susceptible
materials, inspection methods for identifying damage, and mitigation options and
important points of consideration for operating and maintaining such equipment.
The goal is to connect various parts of the
ammonia production process and process
variables with how they may influence the
damage mechanisms of the production
equipment discussed in this article.
Description of the ammonia process.
It is important to discuss the steps and
units in the ammonia production process.
For the synthesis of ammonia, a carbon/
H2 source, water and nitrogen are fed into
the front end of the plant to provide a feed
stream of fresh syngas: H2 and nitrogen in
an approximate ratio of 3:1.
Normally, the feed stream to ammonia
synthesis (the back end) is free of CO and

CO2, and may contain small amounts of
water and inerts such as methane and argon. In a cryogenic purifier process, the
final front-end steps remove impurities
that make the methanation and molecular
sieve/NH3 washing steps unnecessary.
FIG. 1 shows the units in the ammonia
process, with the top row indicating the
front-end units and the bottom row showing the back-end units.
Ammonia equipment materials of
construction. Most equipment in the

ammonia production process are essentially pressure vessels and piping leading
to storage tanks with pressure boundaries
constructed of metallic materials. All materials of construction used in the ammonia industry are susceptible to degradation
and various types of damage mechanisms.
While it may be possible to select materials of construction that are completely resistant to attack by the process fluids, such
an approach is often impractical.
Carbon and low-alloy steels are the
most commonly used materials of construction for process equipment in the
ammonia industry. These materials offer
a suitable combination of strength and
ductility, and are capable of safely operating in the temperature ranges often seen
in the ammonia industry. However, carbon and low-alloy steels are susceptible to
corrosion damage mechanisms.
Stainless steel alloys and nickel-based
alloys, depending on the types selected,
provide resistance to corrosion attack in

Gas
conditioning

Convention
section

Reforming

Secondary and
heat recovery

Syngas
compression

Molsieves
NH3 wash

Synloop

Refrigeration

Shifts

Puriﬁgation

Methanation

FIG. 1. Typical ammonia production process flow diagram.
H2Tech | Q2 2021

43
H2Tech - Q2 2021

Table of Contents for the Digital Edition of H2Tech - Q2 2021
