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Velocity Ratings of Thermowells

In some cases, well failures are due, not to the effect of pressure, temperature, or corrosion, but to the vibrational effects to which they are subjected. Fluid, flowing by the well, forms a turbulent wake (the Von Karman Trail) with a definite frequency based on well dimensions and fluid velocity. If the natural frequency of the well equals the wake frequency, the well stem will vibrate to destruction and break off in the piping. It is, therefore, important that the well have sufficient design to prevent a frequency equality condition.

In the following tables, a recommended maximum velocity rating can be found for several standard well lengths and materials. To simplify the information, ratings given are based on operating temperatures of 1000° F. for wells made of Carbon Steel (C-1018) and Stainless Steel (304 and 316). Values for brass wells are based on 350° F. Operation limits for Monel wells are based on 900° F service. Slightly higher velocity is possible at lower temperatures. Single values appearing in the velocity tables may be considered safe for water, steam, air or gas. In shorter insertion lengths, consideration is given to the velocity pressure effect of water flowing at higher velocities. The values in parenthesis, therefore, represent safe values for water flow while the unbracketted value may be used for steam, air, gas and similar density fluids.

Maximum Fluid Velocity Feet per Second

Well Type

Material

Insertion Length -“U”

1V & 3V

1G & 3G

and

Carbon Steel

304 & 316 SS

Monel

404

(129)

430

(179)

350

(143)

184

(71.2)

192

(99.3)

168

(79.8)

67.0

(42.7)

69.7

(59.6)

(47.7)

34.0

35.4

31.0

20.6

21.5

18.8

13.7

14.3

12.5

7.4

7.7

6.7

2V & 4V

2G & 4G

and

Carbon Steel

304 & 316 SS

Monel

410

(152)

444

(211)

338

(168)

248

(84.3)

285

(117)

226

(93.3)

91.3

(50.6)

95.2

(70.3)

83.3

(56.0)

45.7

47.6

41.6

27.6

28.8

25.2

18.5

19.3

16.9

10.0

10.4

9.1

Maximum Fluid Velocity Feet per Second

Well Type

Material

Insertion Length -“U”

2 1/2

4 1/2

7 1/2

10 1/2

13 1/2

16 1/2

19 1/2

22 1/2

and

Brass

Carbon Steel

304 & 316 SS

Monel

207

(59.3)

290

(106)

300

(148)

261

(118)

89.1

(39.8)

123

(71.2)

128

(99.3)

112

(79.8)

32.2

(23.9)

44.9

(42.7)

46.4

40.6

16.4

22.8

23.6

20.7

9.9

13.8

14.3

12.4

6.6

9.3

9.6

8.3

4.8

6.7

6.9

6.1

3.6

4.9

5.1

4.5

and

Brass

Carbon Steel

304 & 316 SS

Monel

207

(59.3)

290

(106)

300

(148)

261

(118)

102

(47.6)

143

(84.3)

148

(117)

128

(93.3)

37.0

(28)

51.6

(50.6)

53.5

46.7

18.8

26.2

27.2

23.7

11.4

15.9

16.5

14.4

7.6

10.6

11.0

9.5

5.5

7.6

7.9

6.9

4.1

5.7

5.9

5.1

Maximum Fluid Velocity Feet per Second

Well Type

Material

Insertion Length -“U”

2 1/2

4 1/2

7 1/2

10 1/2

13 1/2

16 1/2

22 1/2

Carbon Steel

304 & 316 SS

290

(106)

300

(148)

123

(71.2)

128

(99.3)

44.9

(42.7)

46.4

22.8

23.6

13.8

14.3

9.3

9.6

4.9

5.1

Carbon Steel

304 & 316 SS

290

(106)

300

(148)

143

(84.3)

148

(117)

51.6

(50.6)

53.5

26.2

27.2

15.9

16.5

10.6

11.0

5.7

5.9

and

Carbon Steel

304 & 316 SS

426

(260)

449

(360)

192

(144)

199

69.5

71.9

35.4

36.6

20.5

21.2

14.3

14.8

7.7

8.0

Maximum Fluid Velocity Feet per Second

Well Type

Material

Insertion Length -“U”

2 1/2

4 1/2

7 1/2

10 1/2

13 1/2

16 1/2

19 1/2

22 1/2

and

Brass

Carbon Steel

304 & 316 SS

Monel

305

(97.5)

386

(175)

440

(243)

354

(195)

93.8

(54.1)

180

(97.2)

197

(135)

155

(108)

33.9

65.3

(58.3)

71.2

56.1

17.1

33.0

36.0

28.4

10.5

20.1

22.0

17.3

7.0

13.4

14.7

11.6

5.0

9.6

10.5

7.5

3.7

7.1

7.8

5.6

and

Brass

Carbon Steel

304 & 316 SS

Monel

354

(161)

448

(289)

490

(403)

410

(322)

108

(89.5)

209

(161)

228

(225)

179

(178)

39.4

75.7

82.5

65.1

19.8

38.4

41.8

33.0

12.2

23.3

25.5

20.1

8.1

15.5

17.1

13.5

5.8

11.1

12.2

8.7

4.3

8.2

9.1

6.5

Maximum Fluid Velocity Feet per Second
Well Type	Material	Insertion Length -“U”
Well Type	Material	2 1/2	4 1/2	7 1/2	10 1/2	13 1/2	16 1/2	19 1/2	22 1/2
2A & 4A and 2B & 4B	Brass Carbon Steel 304 & 316 SS Monel	290 (145) 326 (260) 349 (360) 316 (320)	150 (80) 192 (144) 199 189 (178)	54.1 (48) 69.5 71.9 68.1	27.6 35.4 36.6 34.8	16.7 20.5 21.2 20.8	11.1 14.3 14.8 14.0	8.0 10.3 10.7 10.0	6.0 7.7 8.0 7.5

Maximum Fluid Velocity Feet per Second
Well Type	Material	Insertion Length -“U”
Well Type	Material	2 1/2	4 1/2	7 1/2	10 1/2	13 1/2	16 1/2	19 1/2	22 1/2
4C and 4D	Brass Carbon Steel 304 & 316 SS Monel	321 (150) 410 (270) 483 (350) 396 (300)	129 (83.5) 249 (150) 272 (208) 214 (167)	46.8 90.3 97.3 77.5	23.6 45.6 49.7 39.2	14.5 27.8 30.4 23.8	9.6 18.5 20.3 16.0	6.9 13.2 14.5 10.3	5.1 9.8 10.7 7.7

Maximum Fluid Velocity Feet per Second
Well Type	Material	Insertion Length -“U”
Well Type	Material	2 1/2	4 1/2	7 1/2	10 1/2	13 1/2	16 1/2	19 1/2	22 1/2
2C and 2D	Brass Carbon Steel 304 & 316 SS Monel	319 (148) 358 (264) 390 (355) 347 (315)	141 (82) 234 (146) 248 (203) 209 (165)	51.0 84.5 89.0 75.0	25.0 43.0 45.0 38.0	15.6 26.0 27.5 22.0	10.4 17.4 18.0 15.0	7.0 12.0 13.2 10.0	5.3 9.0 9.9 7.6

Velocity Ratings of Thermowells

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