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API RP 932-B Document Information:
Title
Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems
American Petroleum Institute
Publication Date:
Jul 1, 2004
Scope:
This recommended practice provides guidance to engineering and plant
personnel on equipment and
piping design, material selection, fabrication, operation, and
inspection practices to manage
corrosion and fouling in the wet sections of hydroprocessing reactor
effluent systems. The reactor
effluent system includes all equipment and piping between the
exchanger upstream of the wash water
injection point and the cold, low-pressure separator (CLPS). The
majority of these systems have an
air cooler, however, some systems utilize only shell and tube heat
exchangers. Reactor effluent
systems are prone to fouling and corrosion by ammonium bisulfide
(NH4HS) and ammonium chloride
(NH4Cl) salts.
An understanding of all variables impacting corrosion and fouling in
these systems is necessary to
improve the reliability, safety, and environmental impact associated
with them. Past attempts to
define generic optimum equipment design and acceptable operating
variables to minimize fouling and
corrosion have had limited success due to the interdependence of the
variables. Corrosion can occur
at high rates and be extremely localized, making it difficult to
inspect for deterioration and to
accurately predict remaining life of equipment and piping. Within the
refining industry, continuing
equipment replacements, unplanned outages, and catastrophic incidents
illustrate the current need
to better understand the corrosion characteristics and provide
guidance on all factors that can
impact fouling and corrosion.
This recommended practice is applicable to process streams in which
NH4Cl and NH4HS salts can form
and deposit in equipment and piping or dissolve in water to form
aqueous solutions of these salts.
Included in this practice are:
a. details of deterioration mechanisms,
b. methods to assess and monitor the corrosivity of systems,
c. details on materials selection, design and fabrication of equipment
for new and revamped
processes,
d. considerations in equipment repairs, and
e. details of an inspection plan.
Table 1 lists key issues to REAC system performance and section
reference for more detail.
Materials and corrosion specialists should be consulted for additional
unit-specific interpretation
and application of this document. This is especially important since
new proprietary research is
underway which challenges several previously held beliefs about NH4HS
corrosion in the reactor
effluent system. Each facility needs to establish its own safe
operating envelope to assure
satisfactory service. This recommended practice helps to identify key
variables necessary for
monitoring and establishing the operating envelope.
Other equipment downstream of the REAC can also deteriorate from these
ammonium salts. These
include the recycle gas, sour gas and the H2S stripper and product
fractionator overhead systems.
Although these are beyond the scope of this document, plant personnel
should be alert to these
other locations where ammonium salt fouling and corrosion can occur.
A joint industry sponsored research program in progress is developing
new data on NH4HS corrosion
relevant to these systems. This parametric study is defining
additional key variables that affect
the corrosivity and is showing that past guidelines are inadequate.
The new data are not yet
available in the published literature; hence, they are not included in
this recommended practice.
However, since companies contributing to this practice are
participating in the study, the data
were used to "remove" past guidelines that could be misleading.
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