Flange Bolt Torque Sequence and
Torque Table – A Complete Bolt
Tightening Procedure
Flange joints require proper tightening to avoid the leak of fluid from the
joint. The bolt tightening sequence or torque sequence is defined in the
torque tightening procedure. Most companies have their Flange bolt
torque tightening procedure used during the plant’s construction and
operation.
Flange joints are torque tight with the help of a torque wrench (Manual or
hydronic wrench). The clamp load produced during tightening is higher
than 75% of the fastener’s proof load. To achieve the benefits of the preloading, the clamping force in the screw must be higher than the joint
separation load.
When the bolt loading requires a torque higher than 678 Nm (500 ft-lbs.) to
be applied, hydraulic bolt torquing is recommended.
Image source- Fluid Power Technology
Maximum Radial Projection of Imperfections that are
Size in
Inch
Size in
mm
1/2
No Deeper Than the Bottom of the
Serrations, mm
Deeper Than the Bottom of the Serrations,
mm
15
3.0
1.5
3/4
20
3.0
1.5
1
25
3.0
1.5
1 1/4
32
3.0
1.5
1 1/2
40
3.0
1.5
2
50
3.0
1.5
2 1/2
65
3.0
1.5
3
80
4.5
1.5
3 1/2
90
6.0
3.0
4
100
6.0
3.0
5
125
6.0
3.0
6
150
6.0
3.0
8
200
8.0
4.5
10
250
8.0
4.5
12
300
8.0
4.5
14
350
8.0
4.5
16
400
10.0
4.5
18
450
12.0
6.0
20
500
12.0
6.0
24
600
12.0
6.0
The torque value is dependent on the friction between the stud bolt
threads and the nut head, this friction can be affected by applying a
lubricant, or any plating (e.g., Cadmium or Zinc) applied to the stud threads.
The bolting standard will define whether the torque value is for a dry or
lubricated stud/bolt thread. If a bolt is torqued rather than the nut, then the
torque value should be increased to compensate for the additional friction
– bolt should only be torqued if they are fitted in clearance holes.
The bolts shall be tightened by torque control, using the Anti-seize
lubricant shall be used such as Molykote or equivalent, before installation.
The specified method of bolt tightening is equally applicable to coated,
galvanized, and ungalvanized bolts.
Flange stud Torque Sequence is extremely important to properly tighten
the flange joint. In this detailed article, I have tried to simplify this Torque
Sequence so that you achieve the desired result without damaging the
flange and studs.
Pre-checks for Bolt Tightening
Flange Condition





Check conditions of flange faces for scratches, dirt, and scale.
Check for corrosion pitting and tool marks.
Inspect the gasket seating surfaces.
Check the areas on the flange where the nuts will sit, it should be flat
and free from pitting and excessive wear.
RTJ Grooves must be kept clean, corrosion-free & undamaged.
The acceptable imperfection of the Pipe flange raised face is given in ASME
16.5 table 3. Refer to the table for Permissible Imperfections in Flange
Facing Finish for Raised Face Flange.
Flange Alignment Checks.
Visually examine the flange alignment to ensure that an acceptable fit has
been obtained. While aligning flanges, make sure that there are no residual
stresses in the joint. Using heat correction for flange alignment is not a
good practice and should be strictly prohibited.


Flange faces should be parallel and aligned.
The flange bolt holes should be in line so that the bolts will pass
freely.
Nut, Stud or Bolt Checks






Visually examine nuts & Stud/bolts before installation to assure they
are free from defects such as corrosion, damaged threads, etc. Nutbolts with damaged threads should not be used.
Check the length of the stud or bolt to avoid short bolting and
excessive threads. Flange bolts shall be furnished with insufficient
length to allow the use of bolt tensioning equipment or spades,
spacers, drip rings, and wafer valves, and the associated extra gaskets.
Visually examine studs and nuts after cleaning to ensure they are free
from burrs. Studs and nuts shall be cleaned using a wire brush to
remove any dirt on the threads. Lubricant (MOLYKOTE) shall be
applied on threads and nuts to flange contact surfaces. Lubricant
shall not be used in the gasket and the gasket seating area.
The bolt and nut material grades should be correctly identified before
they are used.
Bolts and nuts can only be reused if it is known that they have not
been overloaded or exceeded their yield point.
The nut identification marking must always point outwards when
assembling the nut on the bolt.
Gasket Checking


Do not use sealing compound, grease, or other paste or adhesive on
gasket or flange faces.
While gasket insertion, it shall not be forced into the gasket seat
between the mating flange faces. Once the gasket is seated, the
mating flanges are brought together carefully without shaking the






gasket off the seat, installing all studs, and running up all nuts hand
tight.
Visually examine gaskets before installation to assure they are free
from defects.
Color coding shall be maintained as per the rate and type of gasket
provided by the manufacturer.
Clean gasket seating face using a wire brush.
Make sure the material is as specified; look for any possible defects or
damage in the gasket, such as folds or creases.
All Soft material gaskets should be replaced with new ones whenever
an opened joint is to be closed again.
The spiral wound gasket shall be used only once.
Flange Bolt Torque Sequence
Once all pre-checks are completed. You can go ahead with tightening the
stud in the pre-defined torque sequence mentioned here. Torque bolts and
nuts in a “CRISS-CROSS” sequence using a minimum of three torquing
passes and the maximum bolt stress as defined.



PASS 1 Torque Sequence: Torque to a maximum of 30% of the final
torque value in accordance with the torque sequence. Check that
gasket is getting compressed uniformly.
PASS 2 Torque Sequence: Torque to a maximum of 60% of the final
torque value.
PASS 3 Torque Sequence: Torque to the final torque value (100%).
After the three basic torque passes are completed, repeat torquing the nuts
at least once using the final torque in a “CRISS-CROSS” manner until no
further rotation of the nut is observed.
For easy handling, bolt numbering shall be done clockwise around the
flange with the following sequence.
The table below shows the torque sequence for flanges with 4 to 32 bolts.
Number of Bolt / Stud
Bolt Tightening Sequence to Follow
4 bolt Flange
1,3,2,4
8 bolt Flange
1,5,3,7,2,6,4,8
12 bolt Flange
1,7,4,10,2,8,5,11,3,9,6,12
16 bolt Flange
1,9,5,13,3,11,7,15,2,10,6,14,4,12,8,16
20 bolt Flange
1,11,6,16,3,13,8,18,5,15,10,20,2,12,7,17,4,14,9,19
24 bolt Flange
1,13,7,19,4,16,10,22,2,14,8,20,5,17,11,23,6,18,12,24,3,15,9,21
28 bolt Flange
1,15,8,22,4,18,11,25,6,20,13,27,2,16,9,23,5,19,12,26,3,17,10,24,7,21,14,28
32 bolt Flange
1,17,9,25,5,21,13,29,3,19,11,27,7,23,15,31,2,18,10,26,6,22,14,30,8,24,16,32,4,20,12,28
Torque Table for Class 150 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grade F52
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Graphite Tanged Gasket
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
25,000
22
30
3/4
20
4
½”
UNC
30,000
26
36
1
35
4
½”
UNC
33,000
29
39
1½
40
4
½”
UNC
50,000
44
60
2
50
4
5/8”
UNC
50,000
86
117
3
80
4
5/8”
UNC
50,000
86
117
4
100
8
5/8”
UNC
40,000
69
93
6
150
8
¾”
UNC
45,000
137
185
8
200
8
¾”
UNC
45,000
137
185
10
250
12
7/8”
UNC
40,000
194
263
12
300
12
7/8”
UNC
40,000
194
263
14
350
12
1”
UN8
41,000
296
401
16
400
16
1”
UN8
40,000
289
392
18
450
16
1 1/8”
UN8
40,000
421
571
20
500
20
1 1/8”
UN8
40,000
421
571
24
600
20
1 ¼”
UN8
40,000
588
797
Torque Table for Class 300 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grade F52
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Spiral Wound and Ring Joint
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
40,000
35
47
3/4
20
4
½”
UNC
40,000
69
93
1
35
4
½”
UNC
40,000
69
93
1½
40
4
½”
UNC
31,000
94
128
2
50
4
5/8”
UNC
37,000
64
87
3
80
4
5/8”
UNC
42,000
127
173
4
100
8
5/8”
UNC
45,000
137
185
6
150
8
¾”
UNC
45,000
137
185
8
200
8
¾”
UNC
45,000
218
296
10
250
12
7/8”
UNC
45,000
325
441
12
300
12
7/8”
UNC
43,000
453
614
14
350
12
1”
UN8
45,000
474
643
16
400
16
1”
UN8
31,000
456
618
18
450
16
1 1/8”
UN8
34,000
500
678
20
500
20
1 1/8”
UN8
40,000
588
797
24
600
20
1 ¼”
UN8
31,000
809
1097
Torque Table for Class 600 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grades F52 and F60
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Spiral Wound and Ring Joint
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
40,000
35
48
3/4
20
4
½”
UNC
40,000
69
94
1
35
4
½”
UNC
40,000
69
94
1½
40
4
½”
UNC
45,000
137
185
2
50
4
5/8”
UNC
50,000
86
117
3
80
4
5/8”
UNC
45,000
137
185
4
100
8
5/8”
UNC
45,000
218
296
6
150
8
¾”
UNC
45,000
325
441
8
200
8
¾”
UNC
50,000
526
714
10
250
12
7/8”
UNC
45,000
662
897
12
300
12
7/8”
UNC
45,000
662
897
14
350
12
1”
UN8
45,000
894
1213
16
400
16
1”
UN8
45,000
1175
1593
18
450
16
1 1/8”
UN8
45,000
1507
2044
20
500
20
1 1/8”
UN8
45,000
1507
2044
24
600
20
1 ¼”
UN8
45,000
2354
3191
Torque Table for Class 900 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grades F52, F60 and F65
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Spiral Wound and Ring Joint
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
40,000
121
165
3/4
20
4
½”
UNC
40,000
121
165
1
35
4
½”
UNC
40,000
194
263
1½
40
4
½”
UNC
45,000
325
441
2
50
4
5/8”
UNC
40,000
194
263
3
80
4
5/8”
UNC
50,000
243
329
4
100
8
5/8”
UNC
45,000
474
642
6
150
8
¾”
UNC
50,000
526
714
8
200
8
¾”
UNC
45,000
894
1213
10
250
12
7/8”
UNC
50,000
994
1347
12
300
12
7/8”
UNC
50,000
994
1347
14
350
12
1”
UN8
50,000
1306
1770
16
400
16
1”
UN8
50,000
1675
2271
18
450
16
1 1/8”
UN8
50,000
2615
3545
20
500
20
1 1/8”
UN8
50,000
3195
4332
24
600
20
1 ¼”
UN8
45,000
5713
7746
Torque Table for Class 1500 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grades F52, F60 and F65
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Spiral Wound and Ring Joint
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
40,000
121
165
3/4
20
4
½”
UNC
45,000
137
185
1
35
4
½”
UNC
45,000
218
296
1½
40
4
½”
UNC
50,000
361
489
2
50
4
5/8”
UNC
50,000
243
329
3
80
4
5/8”
UNC
50,000
526
714
4
100
8
5/8”
UNC
50,000
735
997
6
150
8
¾”
UNC
50,000
994
1347
8
200
8
¾”
UNC
50,000
1675
2271
10
250
12
7/8”
UNC
50,000
2615
3545
12
300
12
7/8”
UNC
50,000
3193
4329
14
350
12
1”
UN8
45,000
4133
5603
16
400
16
1”
UN8
45,000
5713
7746
18
450
16
1 1/8”
UN8
45,000
7652
10375
20
500
20
1 1/8”
UN8
45,000
9986
13539
24
600
20
1 ¼”
UN8
45,000
15983
21670
Torque Table for Class 2500 Flange
Flange Materials : ASTM A105, ASTM A182 grades F50 and F51, ASTM A350 grades LF2 and LF3, ASTM A694
grades F52, F60 and F65
Bolting Materials : ASTM A193 grades B7 and B7M, ASTM A320 grades L7, L7M and L43.
Gasket Type : Spiral Wound and Ring Joint
Bolt Lubricant Molykote 1000 (µ = 0.11)
Size in Inch
Size in mm
No. of Bolt
Bolt Dia.
Thread Type
Bolt Stress
lb/in2
Torque
lbf.ft.
Torque
Nm
1/2
15
4
½”
UNC
45,000
137
185
3/4
20
4
½”
UNC
50,000
152
206
1
35
4
½”
UNC
50,000
243
329
1½
40
4
½”
UNC
55,000
579
785
2
50
4
5/8”
UNC
55,000
397
538
3
80
4
5/8”
UNC
55,000
809
1097
4
100
8
5/8”
UNC
55,000
1436
1947
6
150
8
¾”
UNC
50,000
3195
4332
8
200
8
¾”
UNC
50,000
3195
4332
10
250
12
7/8”
UNC
50,000
6348
8606
12
300
12
7/8”
UNC
50,000
8502
11527
Disclaimer – Please check with Professional Engineer before using it