Hydrocarbon Processing - May 2022 - 57

Process Optimization
posed loading ability. The worked example here will demonstrate
this approach.
Worked example. A pressure vessel with an outer diameter
of 2,000 mm is equipped with torispherical heads (type korbbogen,
according to DIN 2801311
). The wall thicknesses are
net 10 mm. A flush nozzle with a nominal diameter of 12 in.
(NB 300) is fitted to the cylindrical shell. The nozzle neck of
this nozzle has a nominal thickness of 17.48 mm (corresponds
to schedule 80) and is provided with a Class 150 welding neck
flange (according to ASME B16.5). The bottom is equipped
with a flush 20-in. nozzle (NB 500), of which the nominal neck
thickness is 15.09 mm (Schedule 40) and is located in the middle
of the curved part of the head. This nozzle is also equipped
with a Class 150 welding neck flange.
The shell and head are made of ASTM A515 Grade 60 material,
while the nozzle necks are made of ASTM A106 Grade B
seamless pipe material. Both nozzle flanges are made of ASTM
A105 forged material. The nozzle flange connections are provided
with a spiral wound gasket according to ASME B16.2012
.
The pressure vessel has a design pressure of 10 bar and a design
temperature of 200°C. The rated pressure of the Class 150
flange is 13.8 bar at 200°C. No corrosion allowance applies.The
design code for this pressure vessel is EN 13445. The design
stress is 126 MPa (two thirds the yield strength at 200°C).
* Step 1: The design calculation is performed by
the vessel design engineer according EN 13445-3
considering only internal pressure (TABLE 5).
* Step 2: The maximum allowable individual loads
of Nozzle N1 located on the spherical part of the
head and Nozzle N2 located on the cylindrical shell
are determined. The calculation schedule is shown
in TABLE 6.
* Step 3: A summary of individual allowable flanged
nozzle loads is shown in TABLE 7.
* Step 4: Successively, the vessel design engineer must
provide the piping stress analyst with the calculated
allowable individual allowable loads. This implies that
the vessel design engineer must make the summary of
Step 3 available to the piping stress analyst.
* Step 5: The pipe stress engineer performs the
pipe stress analysis using software approved by the
inspecting body and client. Determining the piping
reactions is part of the pipe stress analysis.
* Step 6: The pipe stress engineer successively makes
a summary of the loads acting on the process nozzle
(piping reactions). For the relevant nozzles N1 and N2,
the loads in TABLE 8 have been derived from the formal
pipe stress analysis.
* Step 7: Perform load interaction checks for nozzles
N1 and N2.
° Nozzle N1: At nozzle-head intersection:
utilization factor = 0.9392 < 1 r OK!
At flange facing: utilization factor = 0.3218 < 1 r OK !
° Nozzle N2: At nozzle- shell intersection:
utilization factor = 0.9739 < 1 r OK!
At flange facing: utilization factor = 0.2623. < 1r OK!
Conclusion: All piping reactions remain within
acceptable limits.
TABLE 7. Summary individual allowable flanged nozzle loads
Nozzle-head intersection
F (N)
Nozzle
N1
Nozzle
N2
F (N)
94,256
M (Nm)
11,970
Nozzle-cylindrical shell intersection
Ml (Nm) Mc
7,597
23,459
(Nm)
2,463
TABLE 8. Summary of piping reactions
Nozzle mark
N1
N2
F (N)
11,750
1,950
M (Nm)
9,750
-
F (N)
92,661
F (N)
38,144
Flange facing
M (Nm)
49,995
Flange facing
M (Nm)
16,813
Ml
(Nm)
-
3,375
Mc
(Nm)
-
1,100
Takeaway. The protocol developed is ideal for processing in a
spreadsheet. The worked example proves its applicability and is
a guideline for the user. In addition, it lends itself well to implementation
in an engineering specification. The advantage lies
in the simplicity of the protocol and it provides a safe approach
to the assessment of nozzle loads. Time is also saved when using
the protocol and additional costs for strengthening the nozzles
can be avoided. The protocol has an excellent track record over
many years in the hydrocarbon processing industry (HPI).
ACKNOWLEDGEMENTS
The author would like to express sincere thanks to Keith Kachelhofer from
MacAljon Fabrication/MacAljon Engineering (USA) and Daniel Hofer from BASF
(Germany) for reviewing the manuscript.
LITERATURE CITED
1 EN 13445 Standard, " Unfired pressure vessels: Part 3-Design, " EU, Iss. 5, 2018.
2
3
4
5
PD 5500 " Specification for unfired fusion welded pressure vessels, " British
Standard, 2018 (UK).
American Society of Mechanical Engineers (ASME) BPVC, " Rules for construction
of pressure vessels, " Section VIII, Div. 1, 2017.
Welding Research Council (WRC) Bulletin 107, " Local stresses in spherical and
cylindrical shells due to external loadings, " January 1965.
Welding Research Council (WRC) Bulletin 537, " Precision equations and
enhanced diagrams for local stresses in spherical and cylindrical shells due to
external loadings for implementation of WRC Bulletin 107. "
6
7
8
9
10
Welding Research Council (WRC) Bulletin 297, " Local stresses in cylindrical
shells due to external loadings on nozzles, " supplement to WRC Bulletin 107.
EN 13445 Standard, " Unfired pressure vessels: Part 3-Design, " Addendum A8,
2019.
Stikvoort, W., " Review of buffer approach to compensate unknown nozzle loads, "
American Journal of Engineering Research (AJER), Vol. 9, Iss. 3., 2020.
Stikvoort, W., " Load capacity limits of flanged pressure vessel nozzles, " Chemical
and Petroluem Engineering, January 2018.
Dekker, C. J. and H. J. Bos, " Nozzles-on external loads and internal pressure, "
International Journal of Pressure Vessels and Piping, June 1997.
11 DIN 28013 " Ellipsoidal dished ends, " König + Co., 1993.
12
American Society of Mechanical Engineers (ASME) B16.20, " Metallic gaskets for
pipe flanges, " 2017.
WALTHER STIKVOORT is a renowned authority in the field of
mechanical and structural integrity of static pressure
equipment. He has more than 50 yr of experience designing
pressure vessels and piping and has developed numerous
technical standards and practices to improve asset integrity of
reputable operating companies. Mr. Stikvoort is the author of
numerous peer-reviewed international journal articles spanning
the field of mechanical and structural integrity. He is active as a helpdesk
consultant static pressure equipment for P3 Engineering in Delft, the Netherlands.
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