Hydrocarbon Processing - July 2021 - 35

Special Focus Plant Design, Engineering and Construction
A. CHAUDHARI and M. KULKARNI,
BASF Chemicals India Pvt. Ltd., Mumbai, India
Evaluation of high-strength steel SA-517-Gr-F
for large pressure vessels
Conventionally, carbon steel material has been widely used
around the globe for the fabrication of static equipment-such
as tall towers, vessels, heat exchangers, etc.-for less-corrosive
service. This material is generally procured in a normalized or
quenched and tempered condition to gain benefits towards an
exemption from impact test requirements and to obtain a refined
grain structure.
In this work, the effect of using a high-strength, low-alloy
material SA-517-Gr-F has been studied as an alternative to
the conventionally used carbon steel SA-516-Gr-60/70, specifically
for large towers in a seismic prone zone and extreme
weather conditions. The composition of SA-517-Gr-F is ¾
nickel (Ni)-½ chromium (Cr)-½ molybdenum (Mo-V). The
alloying elements are present in very low percentages and this
material has a very high mechanical strength. Therefore, it is
termed as high-strength, low-alloy steel. The composition of
SS 304L is 18 Cr-8 Ni. The alloying elements are present in
higher percentages, which improves their corrosion resistance
property against SA-517-Gr-F.
In this work, literature on the use of SA-517-Gr-F has been
checked in terms of machinability and fabrication, along with
commercial factors. Also, fabrication challenges and limitations
have been identified by consulting renowned pressure
vessel fabricators.
SA-517-Gr-F is a high-strength alloy material that can be
explored as an alternative to normal carbon steel (SA-516Gr-60/70)
owing to its very high ultimate tensile strength and,
therefore, its higher allowable stresses. TABLE 1 presents further
details. These allowable stresses remain constant for a wide
range of temperatures. The difference in thicknesses between
SA-517-Gr-F and SA-516-Gr-70 are in the range of 50%-80%,
based on design temperature. Recently, the application of SA517-Gr-F
seems to be limited in the industry. The constraints
that limit the use of this material have been studied technically
as well as commercially.
In this work, the use of SA-517-Gr-F has been holistically explored,
and conclusions and key observations have been detailed.
Discussion. The selection of appropriate material of construction
(MOC) for the design and fabrication of any pressure vessel
is crucial. These are regulated by many factors, including:
* Type of service
* Fluid in contact
* Corrosivity of the fluid
* External environmental factors
* Availability of the material
* Economics (cost of the equipment)
* Overall weight
* Machinability and weldability of material.
The most widely used MOC in the design and fabrication of
static equipment is carbon steel-SA-516-Gr-70 (ASME SEC
II Part D).1
However, in specific cases, SA-517-Gr-F (ASME
SEC II Part D)-an alternative for SA-516-Gr-70-should
be evaluated for reduction in thicknesses and optimization in
overall weight. This leads to an overall reduction in associated
costs like logistics, transportation, installation (erection) and
required civil structure or foundation.
SA-517-Gr-F is evaluated for static equipment with a base
MOC of carbon steel and:
* Large static equipment (specifically, large inside diameter)
° Spheres
° Large process columns
° Reactors
* High-pressure equipment
* High-temperature service
* Very high external loads, wind or seismic.
INLFUENCING FACTORS
Type of service. It is imperative to match the most optimal
MOC with the type of the service handled by the equipment.
TABLE 1. Comparison of SA-516-70 and SA-517-Gr-F
SA-516-Gr-70
Carbon steel
Parameters
Type
SA-517-Gr-F
Low-alloy,
high-strength
Uns
Size limitation
P no.
PWHT requirement
K02700
No limitation
1
Mandatory over
38 mm
Minimum tensile strength 485 MPa
Minimum yield strength
260 MPa
¾Ni-½Cr-½Mo-V
K11576
Available up to
65 mm only
11 b
Mandatory over
15 mm
795 MPa
690 MPa
Hydrocarbon Processing | JULY 2021 35
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