Hydrocarbon Processing - December 2020 - 47

Plant Design, Engineering and Construction
to manufacture Division 2 vessels. The requirements on materials, fabrication, inspection, testing and marking are the same
for both classes, with minimal changes. Therefore, Class 1 vessels can be treated as vessels that are built to Division 2 quality,
and these vessels can be economical vs. Division 1.
Division 2 rules result in lesser wall thickness vs. Division
1 due to the different theories of failures that they are based
on. With the introduction of Mandatory Appendix 46 in Division 1 (or due to the presence of Code Case 2695), it has now
become on par with Division 2 in terms of design rules. Therefore, with everything else becoming the same, the distinguish-

250

250

200

200

150

150

UTSmin/2.4
UTS/3.0
UTS/3.5
Y/1.5

50

12
10
8

100

6

Division 1
Division 2 Cl.1
Division 2 Cl.2
Thickness reduction

50

4

0
0

75

150

225
Temperature, °C

300

375

0

450

75

150

225
Temperature, °C

300

375

Thickness reduction, %

100

0

16
14

Stress, MPa

Stress, MPa

requiring detailed fatigue analysis (cycles > 1,000).
* Class 1 vessels still require a vessel manufacturer
to develop a manufacturer's design report, but it is
exempted from endorsement by a certifying engineer
unless a detailed fatigue analysis is required by the UDS
and/or design-by-analysis methods are employed.
It is now simpler for fabrication shops that are already authorized to manufacture Division 1 vessels to obtain authorization to manufacture Class 1 vessels without a need to undergo
full assessments amounting to Division 2. This reduces the dependency on only a few fabrication shops that are authorized

2
0
450

FIG. 2. Plot for SA-387 Gr.11 Cl.2 (1.25 Cr-0.5 Mo): (A) y(T), UTS(T) and UTSmin with design margins; (B) allowable stresses and percent reduction
in wall thickness between Division 1 and Division 2 Class 1.

250

250
200
Stress, MPa

150
100
UTSmin/2.4
UTS/3.0
UTS/3.5
Y/1.5

50

75

10

150

8
100

6

Division 1
Division 2 Cl.1
Division 2 Cl.2
Thickness reduction

50

4

0

0
0

12

150

225
Temperature, °C

300

375

0

450

75

150

225
Temperature, °C

300

375

Thickness reduction, %

14

200
Stress, MPa

16

2
0
450

FIG. 3. Plot for SA-387 Gr.22 Cl.2 (2.25 Cr-1 Mo): (A) y(T), UTS(T) and UTSmin with design margins; (B) allowable stresses and percent reduction
in wall thickness between Division 1 and Division 2 Class 1.

16

300

250

250

200

200

14

Stress, MPa

Stress, MPa

12
150
100

8
6

Division 1
Division 2 Cl.1
Division 2 Cl.2
Thickness reduction

100

UTSmin/2.4
UTS/3.0
UTS/3.5
Y/1.5

50

10

150

50

4

0

0
0

75

150

225
Temperature, °C

300

375

450

0

75

150

225
Temperature, °C

300

375

Thickness reduction, %

300

2
0
450

FIG. 4. Plot for SA-542 Ty.D Cl.4a (Cr-Mo-V): (A) y(T), UTS(T) and UTSmin with design margins; (B) allowable stresses and percent reduction
in wall thickness between Division 1 and Division 2 Class 1.
Hydrocarbon Processing | DECEMBER 2020

47
Hydrocarbon Processing - December 2020

Table of Contents for the Digital Edition of Hydrocarbon Processing - December 2020
