The article is about the Design of Cathodic Protection for Duplex stainless steel. The design includes many parameters like
Current density.
Coating breakdown factors.
Mass of anode.
Current output and many others.
The article mainly involves the Cathodic Protection design for the Duplex stainless steel pipeline. The Cathodic Protection design is also done for the Carbon steel pipeline(48” diameter with Al anode) and Duplex stainless steel( 24 “ diameter with Zn anode) and is compared and analyzed with the main objective, Duplex stainless steel pipeline (48” diameter with Al anode). Finally, the designs are interpreted, compared, and analyzed.
“an electrochemical protection by decreasing the corrosion potential to a level at which the corrosion rate of the metal is significantly reduced” (ISO 8044).
“a technique to reduce corrosion of a metal surface by making that surface the cathode of an electrochemical cell” (NACE RP0176).
Need for Cathodic Protection
Cathodic protection is one of the important factors in the performance of the pipeline carrying crude or petroleum products. If the pipeline has to be operated until its designed life with the least maintenance activities, Cathodic Protection is the best way to adapt. The pipeline with minimum care can lead to leaks, ruptures, etc, which affects the supply and other contract terms, which results in loss of crude or product, demand, money, time, etc.
The main motto behind Cathodic protection is “prevention is better than cure”. It’s better to design and install perfect cathodic protection rather than opting for complex and unpredictable maintenance schedules.
Fails at higher temperatures, which may result in Hydrogen Induced Stress Corrosion Cracking(HISC).
Need expertise in welding. Otherwise, it may lead to HISC, crevice corrosion, etc.
Design of Cathodic Protection
Basic inputs for cathodic protection-
Pipeline diameter for Duplex with Al anodes, D = 48”.
Length of the pipeline, LP = 71.650km.
Pipeline joint length, Lj = 12m,
Design life, T = 40 years,
Design temperature, t =45 0 c.
Corrosion coating thickness, tc = 5mm.
Mean Coating breakdown factor, fcm= 0.05.
Final Coating breakdown factor, fcf = 0.11.
The gap between half-shells, G = 100mm
Anode spacing, S = 4 joints.
Electrochemical resistivity, for seawater, ξ = 20-ohm cm.
Anode utilization factor, U = 0.8.
Mean current density, i cm or CA = 80 mA/m2
Final current densities, i cm or CF =150 mA/m2
Bracelet type of anode (Fig. 3)
Fig. 3: Bracelet-type Anode
For Duplex stainless steel pipelines, the other parameters considered are:
Al Anode material density, ρ= 2700 kg/m3.
Electrochemical efficiency,ε= 1825 A-hr/kg.
Protective potential, VP = – 500V.
Closed circuit anode potential, VA = -1050 mV.
Design calculations for cathodic protection
Diameter of the anode:
Di=D+2tc=1219+(2*5)=1229mm.
Spacing
SL = S* Lj=48mm.
Number of anodes,
N = LP / SL =1493.
The net mass of each anode
MA= ᴨ/4((D+2tc)2– Di2)-2GtA)LAρ=196.2 kg
Total anode mass
M=NMA= 1493*196.2=292926.6kg.
Mean current output
IMC= εUM/T= 1219.692A
Mean current required, IMR
= CAbAᴨDLF=80* 0.05*ᴨ* 1219*71650= 1097.56A.
Final surface area per anode,
AF=ᴨ[Di+2(1-U)tA-2G]LA
=ᴨ[1229+2(1-0.8)110-2*100]150= = 0.572m2 .
Resistance of each anode,
RA=0.315ξ/√A=0.083ohm.
Final current output
IFC= N[VF – VA]/RA
= 9893.373A.
The final current required,
I FR = CFbFᴨ D LF
= 4527.451A.
The below two parameters will say whether the whole calculation for CP is feasible or not.
Mass requirement = IMC/IMR=692/1097.564= =1.11>1
Final output current = IFC/IFR = 9893.373/4527.451 = 2.19>1.
The calculations are also done for
Carbon steel pipeline with Al anode,48” dia.
Duplex stainless steel pipeline with Al anode,48” dia.
Duplex stainless steel pipeline with Zn anode,24” dia.
Results
From the calculations, it can be inferred that the Duplex stainless steel requires less amount of anodic material.
A graph (Fig. 4) is shown for the Mass of the anode (kg) vs current output(A).
Fig. 4: Mass of the anode (kg) vs current output(A)
It can be inferred that the Duplex with less amount of anodic material can give high current output, in the case of Al anode.
In the case of Zn anode for Duplex stainless steel, more anodic material is needed for maintaining the current output, because the consumption rate of Zn is more.
Consumption Rate (Fig. 5)
Fig. 5: Consumption rate
This graph shows the consumption rate of anodic materials. Zn anode consumption rate is higher than Al. As a result, more amount of material is needed for meeting the current demand when compared to Al.
The aluminum anode is much preferable because of its high capacity compared to other anodic materials. The graph below discusses the
Capacities of anodic materials (Fig. 6):
Fig. 6: Capacities of anodic materials
Resistivity vs Current density
From the graph below (Fig. 7), it can be inferred that the current may decrease along with the increase in resistivity.
Fig. 7: Resistivity vs Current density
Conclusion
The focus is projected on the CP design for DSS and carbon steel with the application of different anodes. The factors like the mass of anode current output etc. are concerned for the performance analysis of CP with different anodes.
It may be interpreted from the article that Duplex stainless steels with Al as anodes are best suitable for offshore applications.
Recommendations
Hg-free Aluminium sacrificial anodes are recommended for the best performance of CP in subsea pipelines.
Duplex stainless steels are best recommended for subsea pipelines because they are having good mechanical strength, high pitting corrosion, and HISC-resistant properties at normal temperatures.
Highly skilled welding to avoid flaws in the weld. The flaws may result in HISC at the welded portion of the pipeline.
Galvalum-III is the best-recommended anode certified by the DNV RP 401. It can even protect the hot oil pipelines which normal anodes may not do. These anodes are not susceptible to inter angular corrosion and can be used in place of Zn anodes.
Few more Pipeline related useful Resources for You..
Hopefully, all of you have gone through my post on Methods for checking flange leakage. In that article, I mentioned the theoretical background (analysis criteria, the basic theory behind flange leakage checking, analysis methodology, etc.) for checking flange leakage. So click here to refer to the article once again before you proceed with this article. In this current write-up, I will explain the step-by-step method for performing flange leakage analysis methodology following the Pressure Equivalent Method using Caesar II. Click here to learn the ASME Section VIII method.
Fig. 1: Typical flange in Caesar II model
Caesar II methodology for Pressure Equivalent method
Model the complete stress system from the stress isometric. It’s preferable to model each flange separately for analysis. For valve assembly, model the flanges and valves separately. Once the modeling is complete select the flanges that need to be analyzed as per the pressure equivalent method. In Fig. 1, nodes 20-30 and nodes 30-40 denote the flange assembly. Node 30 is the interface point of both flanges where flange leakage checking is required.
Inputs for Flange Analysis
Now refer to Fig. 2 provided below. Click on the Flange checks button (Checkbox) which will activate the flange input module of the Caesar II Input Screen. Now select the Flange Node(From/To/Both) and Calculation Type as shown in Fig. 2. From/To to be selected such that node 30 as mentioned above is selected in the model. For example, as node 30 is the interface point, “To” need to be selected in element 20-30 and “From” to be selected for element 30-40. Both are normally selected for flanged valves keeping the valve active. As we are performing the Pressure Equivalent method, Peq needs to be selected.
Next, Select Flange Class/Grade through the ‘Read from File’ button and refer to ASME B 16.5/ ASME B 16.47 material tables. Select flange pressure class and material grade along with governing ASBE B 16.5 code with year.
Required data will automatically be filled in. By default, the value of G will be taken as the mean gasket diameter. Users can cross-check and update the value of G as per ASME B 16.20 & ASME Sec. VIII Div. 1, Appendix 2, Table 2-5-2. based on the following equation:
b0 = 1/4, G = Mean diameter of the gasket contact face
b0 > 1/4, G = Outside diameter of gasket contact face less 2b, b=basic gasket width from code. check the above-mentioned code table for more details.
Fig. 2: Caesar II Spreadsheet typical input
Flange Leakage Checking Setting and Output Result
Now go to the load case editor of Caesar II and select the temperature at which flange leakage checking is to be performed as shown in Fig. 3. Normally, flange leakage is performed at the maximum design temperature. So, select that temperature. Now run the analysis to check the results. In case the calculated flange stress exceeds the allowable results will be shown in red color. The report will show the % ratio of the calculated equivalent pressure with respect to allowable. Check Fig. 4 for output results.
Fig. 3: Load Case Options module in Caesar II
Fig. 4: Caesar II flange leakage pressure equivalent output
Meaning of Pipe Schedule | Pipe Schedule Chart | Pipe Schedule 40 & 80 Dimensions
The Pipe Schedule describes the pipe wall thickness. With an increase in pipe schedule number pipe thickness increases. The main function of the pipes is to carry fluid (liquid, gas, fluidized solids, slurry, mixed-phase products, etc.) under pressure (internal, external, or both), therefore to sustain the fluid pressure the pipe has to be strong enough to perform its intended duty without failure. Obviously, for pipes containing pressurized fluids the wall thickness, and by implication the pipe’s strength, is the most important parameter. The wall thickness of the Pipe is expressed by “Schedules or Schedule numbers“, referred to as Pipe Schedules or Piping Schedules.
What is a Pipe Schedule?
The pipe Schedule or Pipe Schedule number of a Pipe is a dimensionless number that is related to Pipe Wall Thickness. The piping Schedule Number for a specific pipe size is a pipe thickness designator for that pipe size.
How to Calculate a Pipe Schedule?
Schedule Numbers for pipe size/wall thickness combinations are calculated (approximated) to get a uniform relationship equal to 1000 times the P/S (P=Design Pressure and S=Allowable Stress) expression contained in the modified Barlow formula for pipe wall thickness. The pipe schedule is abbreviated as SCH. So,
SCH=1000*(P/S)
Characteristics of Pipe Schedule
For a given pipe size and schedule the thickness of the pipe is fixed and defined in the applicable ASME standard (ASME B36.10M/ ASME B36.19M). Even though Pipe thickness can also be specified in mm or inches to the value corresponding to that specified in the ASME standard, The Schedule Numbers are strictly used as a convenient designation system while ordering piping items.
For any given pipe size and varying schedule numbers or thicknesses, its Outside Diameter (OD) remains constant and its Internal Diameter (ID) varies. With an increase in thickness, the strength increases but its ID decreases. OD is kept constant to help the support hardware design so that the same support hardware can be used for the same pipe size (varying thicknesses).
Pipe Schedule numbers can be the same for different pipe sizes but that does not mean the pipe thickness is the same. It may be the same or vary with respect to pipe sizes. For example, a 6-inch Schedule 40 pipe has 7.11 mm thickness, while an 8-inch Schedule 40 pipe has 8.18 mm thickness means thickness is increasing even though both Schedule 40.
Pipe Schedule Governing Standards
In the oil and gas and related downstream industries the most common standards are
ASME B36.10 Welded and Seamless Wrought Steel Pipe, and
ASME B36.19 Stainless Steel Pipe
What is the Nominal Pipe Size (NPS)?
The size of all pipes is identified by the nominal pipe size. The manufacture of pipe NPS 1⁄8 (DN 6) to NPS 12 (DN 300), inclusive, is based on a standardized outside diameter (OD). This OD was originally selected so that a pipe with a standard OD and a wall thickness that was typical of the period would have an inside diameter (ID) approximately equal to the nominal size. Although there is no such relation between the existing standard thickness, OD, and nominal size — these nominal sizes and standard ODs continue in use as ‘‘standard.’’
The manufacture of pipe NPS 14 (DN 350) and larger proceeds on the basis of an OD corresponding to the nominal size. So the OD in mm of a pipe NPS 14 or higher can easily be calculated by simply multiplying the NPS (here 14) by 25.4. But for lower sizes, the OD calculation is not so easy.
Pipe Schedule (SCH) vs Pipe Size
For all pipe sizes, the outside diameter remains constant.Therefore any variation in pipe schedule i.e. wall thickness affects only the inside diameter. As the pipe schedule number increases, the wall thickness increases, and the actual bore is reduced.
Standard (STD) is identical to SCH 40 up to NPS 10. All larger sizes of Standard (STD Schedule) have 9.53 mm wall thicknesses.
Extra-Strong (XS) is identical to SCH 80 up to NPS 8. All larger sizes of Extra-Strong have 12.70 mm wall thicknesses.
The double Extra Strong (XXS) wall is thicker than SCH 160 from NPS 1/8 to NPS 6, and SCH 160 is thicker than the XXS wall for NPS 8 and larger.
With an increase in pipe thickness internal diameter of the pipe reduces as the pipe’s outer diameter remains constant.
Pipe of sizes and wall thicknesses other than those of Standard, Extra-Strong, and Double Extra-Strong, and Schedule Number were adopted from API Specification 5L.
Pipe Schedule / Pipe Wall Thickness Calculation
The calculation of wall thickness varies depending on the usage of the code. All codes (B31.3, B31.1, IBR, B31.4, B31.8, nuclear code, etc.) provide equations for calculating the minimum wall thickness based on the pressure that the pipe has to withstand. The major parameters involved in thickness calculation are Design pressure, Pipe OD, and Allowable Stress at design temperature. After the calculation of minimum wall thickness, corrosion, and mechanical allowances need to be added to that. After that, the actual pipe thickness is selected (immediate higher size thickness of the calculated value) from ASME code tables depending on pipe material (CS or SS).
You may be interested in the following two articles:
A pipe size chart or pipe schedule chart is a tabular representation of pipe NPS and their thicknesses with respect to various schedule numbers. The wall thickness associated with a particular schedule depends on the pipe size. Dimensions (OD, ID, Thickness, and Schedule Number) and Weights of CS and SS pipes are given in the ASME standards mentioned above. The tables in the respective codes are dimensionally complete for all sizes and wall thicknesses within its scope, but some of the larger, heavier wall sections are beyond the capability of seamless mill production and must be obtained from forged and bored billets or other sources.
Stainless steel pipe is more often available in standard weight sizes (noted by the “S” designation, for example, “NPS SCH 10S”). However stainless steel pipe can also be available in other schedules.
Abbreviations used:
STD – Standard,
XS – Extra Strong,
XXS – Double Extra Strong,
A Pipe Schedule chart or pipe size chart is provided in the following table with respect to nominal pipe size and pipe thicknesses.
NPS
OD (in)
ID (in)
Schedules (SCH)
Pipe Wall Thick-ness (inches)
Steel Pipe Weight (lb/ft)
OD (mm)
ID (mm)
Pipe Wall Thickness (inches)
Steel Pipe Weight (kg/m)
1/8″
0.41
0.31
10, 10S
0.05
0.19
10.29
7.80
1.24
0.28
0.27
40, STD, 40S
0.07
0.24
10.29
6.83
1.73
0.36
0.22
80, XS, 80S
0.10
0.31
10.29
5.46
2.41
0.47
1/4″
0.54
0.41
10, 10S
0.07
0.33
13.72
10.41
1.65
0.49
0.36
40, STD, 40S
0.09
0.42
13.72
9.25
2.24
0.63
0.30
80, XS, 80S
0.12
0.54
13.72
7.67
3.02
0.80
3/8″
0.68
0.55
10, 10S
0.07
0.42
17.15
13.84
1.65
0.63
0.49
40, STD, 40S
0.09
0.57
17.15
12.52
2.31
0.84
0.42
80, XS, 80S
0.13
0.74
17.15
10.74
3.20
1.10
1/2″
0.84
0.67
10, 10S
0.08
0.67
21.34
17.12
2.11
1.00
0.62
40, STD, 40S
0.11
0.85
21.34
15.80
2.77
1.27
0.55
80, XS, 80S
0.15
1.09
21.34
13.87
3.73
1.62
0.47
160.00
0.19
1.30
21.34
11.84
4.75
1.94
0.25
XXS
0.29
1.71
21.34
6.40
7.47
2.55
3/4″
1.05
0.88
10, 10S
0.08
0.86
26.67
22.45
2.11
1.28
0.82
40, STD, 40S
0.11
1.13
26.67
20.93
2.87
1.68
0.74
80, XS, 80S
0.15
1.47
26.67
18.85
3.91
2.19
0.61
160.00
0.22
1.94
26.67
15.60
5.54
2.88
0.43
XXS
0.31
2.44
26.67
11.02
7.82
3.63
1″
1.32
1.10
10, 10S
0.11
1.40
33.40
27.86
2.77
2.09
1.05
40, STD, 40S
0.13
1.68
33.40
26.65
3.38
2.50
0.96
80, XS, 80S
0.18
2.17
33.40
24.31
4.55
3.23
0.82
160.00
0.25
2.84
33.40
20.70
6.35
4.23
0.60
XXS
0.36
3.66
33.40
15.22
9.09
5.45
1 1/4″
1.66
1.44
10, 10S
0.11
1.81
42.16
36.63
2.77
2.69
1.38
40, STD, 40S
0.14
2.27
42.16
35.05
3.56
3.38
1.28
80, XS, 80S
0.19
3.00
42.16
32.46
4.85
4.46
1.16
160.00
0.25
3.77
42.16
29.46
6.35
5.60
0.90
XXS
0.38
5.21
42.16
22.76
9.70
7.76
1 1/2″
1.90
1.68
10, 10S
0.11
2.09
48.26
42.72
2.77
3.10
1.61
40, STD, 40S
0.15
2.72
48.26
40.89
3.68
4.04
1.50
80, XS, 80S
0.20
3.63
48.26
38.10
5.08
5.40
1.34
160.00
0.28
4.86
48.26
33.96
7.14
7.23
1.10
XXS
0.40
6.41
48.26
27.94
10.16
9.54
2″
2.38
2.16
10, 10S
0.11
2.64
60.33
54.79
2.77
3.93
2.07
40, STD, 40S
0.15
3.85
60.33
52.50
3.91
5.73
1.94
80, XS, 80S
0.22
5.02
60.33
49.25
5.54
7.47
1.69
160.00
0.34
7.46
60.33
42.90
8.74
11.10
1.50
XXS
0.44
9.03
60.33
38.18
11.07
13.44
2 1/2″
2.88
2.64
10, 10S
0.12
3.53
73.03
66.93
3.05
5.25
2.47
40, STD, 40S
0.20
5.79
73.03
62.71
5.16
8.62
2.32
80, XS, 80S
0.28
7.65
73.03
59.00
7.01
11.39
2.13
160.00
0.38
10.01
73.03
53.98
9.53
14.90
1.77
XXS
0.55
13.70
73.03
44.98
14.02
20.39
3″
3.50
3.26
10, 10S
0.12
4.33
88.90
82.80
3.05
6.45
3.07
40, STD, 40S
0.22
7.58
88.90
77.93
5.49
11.27
2.90
80, XS, 80S
0.30
10.25
88.90
73.66
7.62
15.25
2.62
160.00
0.44
14.32
88.90
66.65
11.13
21.31
2.30
XXS
0.60
18.58
88.90
58.42
15.24
27.65
3 1/2″
4.00
3.76
10, 10S
0.12
4.94
101.60
95.50
3.05
7.35
3.55
40, STD, 40S
0.23
9.11
101.60
90.12
5.74
13.56
3.36
80, XS, 80S
0.32
12.51
101.60
85.45
8.08
18.62
2.73
XXS
0.64
22.85
101.60
69.29
16.15
34.00
4″
4.50
4.26
10, 10S
0.12
5.61
114.30
108.20
3.05
8.35
4.03
40, STD, 40S
0.24
10.79
114.30
102.26
6.02
16.06
3.83
80, XS, 80S
0.34
14.98
114.30
97.18
8.56
22.29
3.62
120.00
0.44
19.00
114.30
92.05
11.13
28.28
3.44
160.00
0.53
22.51
114.30
87.33
13.49
33.50
3.15
XXS
0.67
27.54
114.30
80.06
17.12
40.98
4 1/2″
5.00
4.51
STD, 40S
0.25
12.54
127.00
114.45
6.27
18.66
4.29
XS, 80S
0.36
17.61
127.00
108.97
9.02
26.21
5″
5.56
5.30
10, 10S
0.13
7.77
141.30
134.49
3.40
11.56
5.05
40, STD, 40S
0.26
14.62
141.30
128.19
6.55
21.76
4.81
80, XS, 80S
0.38
20.78
141.30
122.25
9.53
30.92
4.56
120.00
0.50
27.04
141.30
115.90
12.70
40.24
4.31
160.00
0.63
32.96
141.30
109.55
15.88
49.05
4.06
XXS
0.75
38.55
141.30
103.20
19.05
57.37
6″
6.63
6.36
10, 10S
0.13
9.29
168.28
161.47
3.40
13.83
6.07
40, STD, 40S
0.28
18.97
168.28
154.05
7.11
28.23
5.76
80, XS, 80S
0.43
28.57
168.28
146.33
10.97
42.52
5.50
120.00
0.56
35.39
168.28
139.73
14.27
52.67
5.19
160.00
0.72
43.35
168.28
131.80
18.26
64.51
4.90
XXS
0.86
53.16
168.28
124.38
21.95
79.11
8″
8.63
8.33
10, 10S
0.15
13.40
219.08
211.56
3.76
19.94
8.13
20.00
0.25
22.36
219.08
206.38
6.35
33.28
8.07
30.00
0.28
24.70
219.08
205.00
7.04
36.76
7.98
40, STD, 40S
0.32
28.55
219.08
202.72
8.18
42.49
7.81
60.00
0.41
35.64
219.08
198.45
10.31
53.04
7.63
80, XS, 80S
0.50
43.39
219.08
193.68
12.70
64.57
7.44
100.00
0.59
50.95
219.08
188.95
15.09
75.82
7.19
120.00
0.72
61.71
219.08
182.60
18.26
91.83
7.00
140.00
0.81
67.76
219.08
177.83
20.62
100.84
6.81
160.00
0.91
74.79
219.08
173.05
23.01
111.30
6.88
XXS
0.88
72.42
219.08
174.63
22.23
107.77
10″
10.75
10.42
10, 10S
0.17
18.65
273.05
264.67
4.19
27.75
10.25
20.00
0.25
28.04
273.05
260.35
6.35
41.73
10.14
30.00
0.31
34.24
273.05
257.45
7.80
50.95
10.02
40, STD, 40S
0.37
40.48
273.05
254.51
9.27
60.24
9.75
60, XS, 80S
0.50
54.74
273.05
247.65
12.70
81.46
9.56
80.00
0.59
64.43
273.05
242.93
15.09
95.88
9.31
100.00
0.72
77.03
273.05
236.58
18.26
114.63
9.06
120.00
0.84
82.29
273.05
230.23
21.44
122.46
8.75
140, XXS
1.00
104.10
273.05
222.25
25.40
154.92
8.50
160.00
1.13
115.60
273.05
215.90
28.58
172.03
12″
12.75
12.39
10, 10S
0.18
24.16
323.85
314.71
4.57
35.95
12.25
20.00
0.25
33.38
323.85
311.15
6.35
49.67
12.09
30.00
0.33
43.77
323.85
307.09
8.38
65.14
12.00
STD, 40S
0.38
49.56
323.85
304.80
9.53
73.75
11.94
40.00
0.41
53.52
323.85
303.23
10.31
79.65
11.75
XS, 80S
0.50
65.42
323.85
298.45
12.70
97.36
11.63
60.00
0.56
73.15
323.85
295.30
14.27
108.86
11.38
80.00
0.69
88.63
323.85
288.95
17.48
131.90
11.06
100.00
0.84
107.90
323.85
281.03
21.44
160.57
10.75
120, XXS
1.00
125.50
323.85
273.05
25.40
186.76
10.50
140.00
1.13
136.70
323.85
266.70
28.58
203.43
10.13
160.00
1.31
150.30
323.85
257.20
33.32
223.67
14″
14.00
13.62
10S
0.19
27.73
355.60
346.05
4.78
41.27
13.50
10.00
0.25
36.71
355.60
342.90
6.35
54.63
13.38
20.00
0.31
45.61
355.60
339.73
7.92
67.88
13.25
30, STD, 40S
0.38
54.57
355.60
336.55
9.53
81.21
13.12
40.00
0.44
63.44
355.60
333.35
11.13
94.41
13.00
XS, 80S
0.50
72.09
355.60
330.20
12.70
107.28
12.81
60.00
0.59
85.05
355.60
325.48
15.09
126.57
12.50
80.00
0.75
106.10
355.60
317.50
19.05
157.89
12.12
100.00
0.94
130.90
355.60
307.95
23.83
194.80
11.81
120.00
1.09
150.80
355.60
300.08
27.69
224.42
11.50
140.00
1.25
170.20
355.60
292.10
31.75
253.29
11.19
160.00
1.41
189.10
355.60
284.18
35.71
281.41
16″
16.00
15.62
10S
0.19
31.75
406.40
396.85
4.78
47.25
15.50
10.00
0.25
42.05
406.40
393.70
6.35
62.58
15.38
20.00
0.31
52.27
406.40
390.53
7.92
77.79
15.25
30, STD, 40S
0.38
62.58
406.40
387.35
9.53
93.13
15.00
40, XS, 80S
0.50
82.77
406.40
381.00
12.70
123.18
14.69
60.00
0.66
107.50
406.40
373.08
16.66
159.98
14.31
80.00
0.84
136.60
406.40
363.58
21.44
203.28
13.94
100.00
1.03
164.80
406.40
354.03
26.19
245.25
13.56
120.00
1.22
192.40
406.40
344.53
30.99
286.32
13.12
140.00
1.44
223.60
406.40
333.35
36.53
332.75
12.81
160.00
1.59
245.30
406.40
325.48
40.49
365.05
18″
18.00
17.62
10S
0.19
35.76
457.20
447.65
4.78
53.22
17.50
10.00
0.25
47.99
457.20
444.50
6.35
71.42
17.38
20.00
0.31
58.94
457.20
441.33
7.92
87.71
17.25
STD, 40S
0.38
70.59
457.20
438.15
9.53
105.05
17.12
30.00
0.44
82.15
457.20
434.95
11.13
122.25
17.00
XS, 80S
0.50
93.45
457.20
431.80
12.70
139.07
16.88
40.00
0.56
104.70
457.20
428.65
14.27
155.81
16.50
60.00
0.75
138.20
457.20
419.10
19.05
205.66
16.13
80.00
0.94
170.90
457.20
409.60
23.83
254.33
15.69
100.00
1.16
208.00
457.20
398.48
29.36
309.54
15.25
120.00
1.38
244.10
457.20
387.35
35.05
363.26
14.88
140.00
1.56
274.20
457.20
377.85
39.67
408.05
14.44
160.00
1.78
308.50
457.20
366.73
45.24
459.10
20″
20.00
19.56
10S
0.22
48.05
508.00
496.93
5.54
71.51
19.50
10.00
0.25
52.73
508.00
495.30
6.35
78.47
19.25
20, STD, 40S
0.38
78.60
508.00
488.95
9.53
116.97
19.00
30, XS, 80S
0.50
104.10
508.00
482.60
12.70
154.92
18.81
40.00
0.59
123.10
508.00
477.82
15.09
183.19
18.38
60.00
0.81
155.40
508.00
466.75
20.62
231.26
17.94
80.00
1.03
208.90
508.00
455.63
26.19
310.88
17.44
100.00
1.28
256.10
508.00
442.93
32.54
381.12
17.00
120.00
1.50
296.40
508.00
431.80
38.10
441.09
16.50
140.00
1.75
341.10
508.00
419.10
44.45
507.61
16.06
160.00
1.97
379.20
508.00
408.03
50.01
564.31
24″
24.00
23.50
10, 10S
0.25
63.41
609.60
596.90
6.35
94.36
23.25
20, STD, 40S
0.38
96.42
609.60
590.55
9.53
143.49
23.00
XS, 80S
0.50
125.50
609.60
584.20
12.70
186.76
22.88
30.00
0.56
140.70
609.60
581.05
14.27
209.38
22.63
40.00
0.69
171.30
609.60
574.70
17.48
254.92
22.06
60.00
0.97
238.40
609.60
560.43
24.61
354.78
21.56
80.00
1.22
296.80
609.60
547.73
30.96
441.69
20.94
100.00
1.53
357.40
609.60
531.83
38.89
531.87
20.38
120.00
1.81
429.40
609.60
517.55
46.02
639.02
19.88
140.00
2.06
483.10
609.60
504.85
52.37
718.93
19.31
160.00
2.34
542.10
609.60
490.58
59.54
806.73
30″
30.00
29.38
10, 10S
0.31
98.93
762.00
746.15
7.92
147.22
29.25
STD, 40S
0.38
118.65
762.00
742.95
9.53
176.57
29.00
20, XS, 80S
0.50
157.53
762.00
736.60
12.70
234.43
28.75
30.00
0.63
196.06
762.00
730.25
15.88
291.77
36″
36.00
35.38
10.00
0.31
118.92
914.40
898.55
7.92
176.97
35.25
STD, 40S
0.38
142.68
914.40
895.35
9.53
212.33
35.00
XS, 80S
0.50
189.57
914.40
889.00
12.70
282.11
34.75
30.00
0.63
235.13
914.40
882.65
15.88
349.91
48″
48.00
47.25
STD, 40S
0.38
190.74
1219.20
1200.20
9.53
283.85
47.00
XS, 80S
0.50
253.65
1219.20
1193.80
12.70
377.47
Table 1: Pipe Schedule Chart
Pipe Schedule 40 Dimensions
Pipe Schedule 40 is a basic pipe thickness designator. It only denotes that for a given material, Sch 40 Pipes can withstand certain pressures. Schedule 40 for a pipe is identical to Schedule STD for pipe sizes up to NPS 10.
The following table will provide an example of Schedule 40 Steel Pipe Dimensions.
Pipe Schedule 80 has more thicknesses as compared to SCH 40 pipes. So, automatically Sch 80 Steel Pipes are stronger. The following table provides the dimensions for Pipe Schedule 80 Steel Pipes.
Nominal size, NPS
Outside diameter, in
Wall thickness, in
Weight, lb/ft
Outside diameter, mm
Wall thickness, mm
Weight, kg/m
1/8
0.405
0.095
0.31
10.3
2.41
0.47
1/4
0.54
0.119
0.54
13.7
3.02
0.8
1/2
0.84
0.147
1.09
21.3
3.73
1.62
3/4
1.05
0.154
1.47
26.7
3.91
2.2
1
1.315
0.179
2.17
33.4
4.55
3.24
1 1/4
1.66
0.191
3
42.2
4.85
4.47
1 1/2
1.9
0.2
3.63
48.3
5.08
5.41
2
2.375
0.218
5.02
60.3
5.54
7.48
2 1/2
2.875
0.276
7.66
73
7.01
11.41
3
3.5
0.3
10.25
88.9
7.62
15.27
3 1/2
4
0.318
12.5
101.6
8.08
18.63
4
4.5
0.337
14.98
114.3
8.56
22.32
5
5.563
0.375
20.78
141.3
9.53
30.97
6
6.625
0.432
28.57
168.3
10.97
42.56
8
8.625
0.5
43.39
219.1
12.7
64.64
10
10.75
0.594
64.43
273
15.09
96.01
12
12.75
0.688
88.63
323.8
17.48
132.08
14
14
0.75
106.13
355.6
19.05
158.1
16
16
0.844
136.61
406.4
21.44
203.53
18
18
0.938
170.92
457
23.83
254.55
20
20
1.031
208.87
508
26.19
311.17
24
24
1.125
296.58
610
30.96
442.08
Table 3: Schedule 80 Pipe Dimensions
Details about CAESAR II Error: “Material is Outside the Temperature Range”.
While working with Caesar II software, many of you must have received a message stating that the material is outside the temperature range (Refer to Fig. 1) even though you know/believe that you are operating your piping system within allowed temperature limits in CAESAR II.
Fig. 1: Figure showing typical CAESAR II Error: “Material is Outside the Temperature Range”.
You are sure that you have entered temperatures that are allowed for the material, but still, the error is showing. The main reason could be found easily if you check the ambient temperature used for stress analysis of that material. Normally most of the piping codes publish material expansion coefficient data from 70 degrees F onwards that is why it is the CAESAR II default ambient temperature value. So if you have used ambient temperature less than 70 degrees F (21.12 degrees C) you may find the above-mentioned error while running the Caesar file because it could be a case of missing expansion coefficient data in the material database.
The Solution:
So what can you do in such situations? Well, you have two choices:
Increase the ambient temperature to 70 F, which may not be accepted and thus not allowed because due to harsh environmental conditions, you may have selected a lower ambient temperature.
Add the missing expansion coefficient to the material database. This could be the right approach.
Changing the Ambient Temperature:
If you plan to change the ambient temperature, open the piping input spreadsheet and select Environment->Special Execution Parameters. Refer to Fig. 2.
Fig. 2: Figure showing the procedure to change the ambient temperature
Changing the Expansion Coefficient:
To update or add the expansion coefficient for the specific material you have to follow the following steps:
From the CAESAR II main menu, select Utilities-> Tools->Materials (Refer to Fig. 3-1)
It will open the material database editor. Then in the Material Database Editor, select Material->Edit (Refer to Fig. 3-2)
Next, in the search box type in the material number and click Search or press Enter on the keyboard (Refer to Fig. 3-3).
Double-click on the Material Name that corresponds to the piping code you are using (Refer to Fig. 3-3).
Fig. 3: Figure showing the editing procedure for a typical material in Caesar II database value
On double-clicking, the material name a window similar to Fig 4 will open and the screen will be available for editing. The highlighted cell shows that the expansion coefficient does not exist below 70 F. In this case, you have to extrapolate the value for the mentioned temperature and add it here. Take precautions to edit the cell because the piping codes may have restrictions on the minimum metal temperature that you are allowing for the given material.
Fig. 4: Caesar II material database editor.
Now simply type in your calculated extrapolated value and then select Material->Save.
Now change the Applicable Piping Code (Fig. 4) to the right of the material Name to ALL CODES, and select Material->save again.
At this point, you are ready to use this material in your CAESAR II input file. Remember that these changes do not affect the CAESAR II material database as the changes are stored in a user-defined database. However, user-defined materials are used by default in place of the CAESAR II material entries when new files are created.
When you next open your input file you will be prompted that the material properties have changed as shown in Fig. 5.
Fig. 5: Prompt showing that material properties have changed.
You should select the No-Update option (Fig. 5) to read in the new material properties and begin using your material in your input file. Now the error checker will not show the earlier material error and the problem will be solved.
What Will You Do if Carbon Steel Pipe is Installed in Place of LTCS: CS vs LTCS
Low Temperature Carbon Steel Pipes, often referred to as LTCS pipes, are a type of steel pipe specifically designed to operate in environments with extremely low temperatures. These pipes are widely used in industries such as oil and gas, petrochemical, and chemical industries where they must withstand temperatures below -29°C and beyond. The LTCS grade A333-6 is most frequently used for flare lines to withstand a temperature of -46°C.
Low-Temperature Carbon Steel (LTCS) is used in piping systems when there is a possibility of process fluid temperature falling below -29 degrees centigrade during operation. In a typical refinery, ASTM A106 Gr B material is used for carbon steel, and ASTM A333 Gr 6 is used for LTCS in normal operation. There is no major difference between these two materials in the composition. Also, no non-destructive testing is available which can ensure these two materials. So if by mistake CS and LTCS mix up with one another and someone installs CS in place of LTCS without knowing the major operational impact what’s the solution?
Reason for Mix-up:
In construction sites sometimes material mix-up may occur. Someone may be wondering how Carbon steel (CS) and Low-Temperature Carbon Steel (LTCS) material could mix up. The main reason is that no physical identification is possible and There are various possibilities that can arise at a construction site:
Common surface preparation & painting yard for all materials.
On pipe fittings, identification marks are written by a low-stress punch which was not visible after painting.
Common store/contractor/fabrication area on the construction site.
Ignorance of all concerned about the criticality & impact of a mix-up with normal carbon steel.
So what would you do in such a situation?
Process piping code ASME B31.3 provides guidelines in such situations. There is a provision in ASME B31.3 codes that is based on the stress ratio, the minimum allowable temperature of carbon steel materials can be further lowered without any impact testing.
So what’s this stress ratio?
The stress ratio can be defined as the maximum of the
a) Nominal pressure stress divided by allowable stress at design minimum temperature.
b) For piping components with pressure ratings, the operating pressure is divided by the rated pressure at the design minimum temperature.
c) Combined longitudinal stress, without stress intensification factor, due to pressure, deadweight, and displacement strain divided by allowable stress at the design minimum temperature. (Coincident Conditions)
Note that the Stress Ratio requires computed stresses at minimum temperature and coincident pressures and No stress intensification factor to be used for stress calculations.
Fig. 1: Reduction in Minimum Design Metal Temperature without Impact Testing
So, calculate the stress ratio as per the above guidelines.
Now the code provides a graph (reproduced above in Fig. 1) from where you can calculate the amount of temperature reduction with respect to the stress ratio. From the figure for a temperature reduction of -17 degrees centigrade (to make it -29-17=-46 degree centigrade) the required stress ratio is 0.65. So if the calculated stress ratio is within 0.65 then do not be worried. In case the stress ratio exceeds 0.65 provide additional support to reduce the stress ratio within that limit.
In this way, you can reduce the probable huge impact of material changing (thereby cost) after the erection of piping is already over.
Differences between LTCS and CS
The major differences between LTCS and CS materials are listed in Table 1 below:
Carbon Steel
Low Temperature Carbon Steel (LTCS)
CS usually has a higher carbon content (typically >0.2%)
LTCS, in general, have a lower carbon content (typically <0.2%)
Carbon steel in general operated for normal temperature service (above freezing point)
LTCS is specifically designed for low-temperature service (below freezing point, down to -46°C or lower)
CS Pipes may have reduced impact toughness at low temperatures, leading to brittle behavior
LTCS Pipes have enhanced impact toughness to resist brittle fracture at low temperatures
The microstructure of CS Metallic Pipes are usually ferritic, pearlitic, or other structures based on the carbon content
The microstructure of LTCS pipes is generally ferritic or pearlitic microstructure
CS pipe materials may not require specialized low-temperature heat treatment
LTCS pipe material requires specific heat treatment to optimize low-temperature performance
START-PROF has Smart Operation Mode Editor instead of Load Case Editor.
When you add new load F or support movement D in CAESAR II , you must add it into load case editor manually, thinking thoroughly well what load cases should be created to properly consider it. If you will not add this load F or movement D into Load Case Editor, CAESAR II will not consider loads in the analysis.
In START-PROF you just add the load F or support movement D. Nothing more. It will be added automatically in that load cases where it should be added.
CAESAR II users who use the START-PROF for a first time always ask us the same question: “Where is the Load Case Editor in START-PROF?” or “How to create load cases in START-PROF?”. But START-PROF doesn’t have Load Case Editor. You don’t need to create load cases. At all.
The situation is similar to moving from Car Manual Transmission to the modern Car Automatic Transmission. People who drive only cars with manual transmission ask a lot of unnecessary questions: How does automatic transmission works? How to shift the gear manually? How can I be sure that automatic transmission will shift the gear correctly? Young drivers just sit in the car and enjoy driving without any questions about transmission, because it is working perfect.
It is hard to imagine how to work without Load Case Editor for people who used it for a many years. They ask a lot of questions: How do automatic load cases work? How to change the load cases manually? How can I be sure that automatic load cases work correctly, where to see it? But young engineers just draw piping in START-PROF and enjoy the quick analysis results.
Load Case Editor is just technology from the past. Our idea is that engineers should think about piping design (driving a car), but not about load cases (how does automatic transmission works).
You have to create the following load cases manually:
L1: W+P for sustained stresses (SUS) L2: W+P+T for support loads (OPE) L3: W+P+T+F for support loads with force F (OPE+OCC) L4: L2-L1 (Algebraic) for expansion stresses (EXP) L5: L3-L2 (Algebraic) Internal forces difference between operational mode with force F (L3) and operational mode without force F (L2). This way we get the pure internal forces from force F, but considering nonlinear behavior of structure (gaps, one-way restraints etc.) L6: L1+L5 (Scalar) occasional stress is equal to the sum of stresses from sustained loads (L1) and stresses from pure internal forces (L5)
To understand how to create these load cases and what results should be analyzed from each load case, what is the difference between “Algebraic” and “Scalar” sum, engineer must spend a lot of time reading the literature, attend training courses, ask other people at forums etc. Only piping stress engineers with 5-10 year experience can create the correct load cases for each special situation without any errors.
Example of possible incorrect load cases:
L1: W+P (SUS) L2: W+P+T (OPE) L3: W+P+T+F (OPE+OCC) L4: T (EXP) MISTAKE: nonlinear piping behavior will not be considered properly L5: W+P+F (OCC) MISTAKE: nonlinear piping behavior will not be consideredproperly
There can be a lot of other human mistakes while creating load cases. The reason can be lack of knowledge or just misprint. Or you can just forget to consider some special features.
In START-PROF you can’t do a mistake with load cases. It’s like a car with automatic transmission, car developers already adjusted it to get the best results. You just create additional force-based loading (1.1) for the main operation mode (1). Number of submodes is almost unlimited. For example you can specify 100 submodes to model waterhammer loads using static method at different moments of time.
And add the thrust force.
START-PROF has a standard load cases inside. You can’t see it in software as you can’t see the mechanism of the car automatic transmission while driving. For above example the force F will be applied in L11. See the table for ASME B31.3 code below. This table is just example. Each piping code has own template load cases inside START-PROF which accumulated our piping stress engineering experience for last 50 years to get best and accurate results.
Load Cases L11 will be used to show displacements, loads, expansion joint deformations in the tables for user.
Load Cases L13 will be used to show occasional stresses
User can’t see the stresses from the L11 load case and can’t see the displacements from L13 load case. Because it doesn’t make sense.
Example 2
This diagram shows 39 loads cases from real project in CAESAR II, created manually. And shows operation modes in START-PROF that do the same job, but better, easier and faster (job analysis time in START-PROF is 2 times faster).
Operation modes are very easy to understand:
#1: OPE1 – operation mode with temperature 65 deg. Friction is switched off. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads. Hangers are selected in this mode. Also installation (cold) state calculated for this mode
#2: OPE2 – operation mode with temperature -100 deg. Friction is switched off. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads.
#3: OPE3 – operation mode with temperature -47 deg. Friction is switched off. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads.
#4: OPE1 – operation mode with temperature 65 deg. Friction is turned on. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads.
#5: OPE2 – operation mode with temperature -100 deg. Friction is turned on. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads.
#6: OPE3 – operation mode with temperature -47 deg. Friction is turned on. Occasional wind loads added (4 directions +X, -X, +Y, -Y). Two additional load cases added: snow and ice loads.
#7: Operation mode with no fluid weight, operation temperature 0 deg. Friction is turned on.
#8 Test mode. Test temperature and pressure used. Friction is turned on
Stress range is calculated between 1H-1C, 1H-2H, 2H-1C, where 1 and 2 is operation mode number (#1 and #2), H – hot state, C – cold (installation) state
