Mastering Flange Tightening Torque Determination: A Comprehensive Guide

Exploring the Fundamentals of Tightening Torque: Theory and Applications

This article will guide you through the process of calculating the minimum torque required for fastening screws that connect flat gaskets and flanges.

References:

• American Society of Mechanical Engineers (ASME)
• American National Standard Institute (ANSI)
• American Society for Testing and Materials (ASTM)

Approach to Determining Tightening Torque

Initial Preload Requirements for Orifice Gaskets in High-Pressure Systems

When dealing with orifice gaskets within high-pressure systems, it’s crucial to understand that internal pressure, thermal concentration, and dead load moments are the primary factors leading to joint losses.

The application of torque necessitates the use of impact wrenches, torque wrenches, or torque wrenches. The specific torque to be applied is influenced by the following factors:

1. Nut and bolt classification
2. Nut burr
3. Lubrication
4. Presence of dust, chips, or debris on bolts and nuts
5. Existence of notches
6. Condition of the flange surface intended for rotation

Applying appropriate lubrication can significantly enhance efficiency, potentially improving performance by up to 50% compared to assemblies without lubrication. For standard applications, a heavy graphite or oil mixture is generally sufficient.

Fricton Coefficients for Nuts and Bolts

Materials	Lubricants	Friction µ ± 20%
Steel	Graphite, petroleum or oil	0.07
Steel	Molybdenum disulfide grease	0.11
Steel	Machine oil	0.15
Cadmium Plated Steel	Does not require	0.12
Zinc plated steel	Does not require	0.17
Steel bronce	Does not require	0.15
Corrosion resistant alloy or nickel or silver based	Does not require	0.14
Titanium steel	Graphite in petroleum	0.08
Titanium	Molybdenum disulfide grease	0.10

Significance of Preload in Mechanical Assemblies

The Importance of Adequate Preload in Flanged End Holes

Maintaining an optimal preload within flanged end holes is essential to ensure that the assembly remains in contact and under pressure. Inadequate preload levels could lead to pressurized liquid leakage, compromised sealing integrity during cyclic loading, and a diminished lifespan of the seal. The diagram below illustrates the correlation between seal lifespan and preload.

Consider an axially loaded flanged joint where bolts were not subjected to preload, depicted by the line OAB. In this scenario, the stress experienced by the bolt matches that exerted on the joint. When joint stress varies between Pa and Pb, the bolt load variation is denoted by the segment on the vertical axis, represented as Pba and PBb. However, introducing preload alters this dynamic. The bolt load variation becomes milder than that of the joint (as depicted by line PB1A, possessing a gentler slope than OAB). This occurs because a portion of the load is absorbed through gasket compression due to preload. Consequently, the axial load on the bolts fluctuates between PBa’ and PBb’ when joint force modification occurs between Pa and Pb. These conditions lead to a significant reduction in cyclic load variation for the bolts, ultimately extending the joint’s operational lifespan.

Optimizing Preload in Flanged Assemblies for Enhanced Performance

Achieving an Effective Seal through Precision Assembly of Flange Components

Attaining a reliable seal within a flange connection hinges on the precise mounting of all components. The primary culprit behind leaks often traces back to inadequate assembly practices. Prior to initiating the assembly process, meticulous consideration must be given to angular and centering tolerances pertinent to the pair of flanges constituting the assembly.

Employing excessive force during assembly can prove detrimental to the joint, accelerating its wear and tear and elevating the risk of operational losses.

Step-by-Step Assembly Procedure

1. Begin by positioning the gasket onto the surface of the designated flange to be sealed.
2. Align the second flange in a way that it comes into contact with the gasket.
3. Thoroughly clean and appropriately lubricate the studs. A recommended mixture could be a blend of oil and graphite.
4. Insert the lubricated studs into their respective holes.
5. Initially tighten the nuts by hand.
6. Adhere to the adjustment sequence outlined in the accompanying figures.
7. Exercise caution not to exceed 30% of the specified torque values for the studs. Over-tightening could result in improper joint seating.
8. Once the torque level suggested in the provided table is attained, perform a subsequent tightening pass in hourly intervals to ensure consistency.
9. Due to stress relaxation and creep effects, pre-tightening the studs becomes imperative to maintain accurate torque values during system operation.

Calculating Tightening Torque for Flat Joints: A Comprehensive Guide

To Calculate Required Torque: Initiating with Essential Surface Pressure for Effective Joint Sealing

The torque will be given by the following expression

Variables Involved in Torque Determination and Joint Sealing	Factors Influencing Stud Torque Calculation for Flanges with Flat Gaskets
Key Variables: Ecal: Calculated Surface Pressure (Bar) Emin: Minimum Surface Pressure (Bar) R: Radial Pressure (R = m * Pd) y: Set Pressure (Bar) H: Flange Separation Force (H = Ai * Pd) A: Gasket Contact Area Pd: Design Pressure (Bar) Ai: Internal Duct Area	Key Variables: Ejun: Joint Surface Pressure (Bar) A: Joint Contact Area d: Effective Stud Diameter N: Number of Studs
By understanding and manipulating these variables, the torque necessary for proper joint sealing can be effectively determined.	When determining the torque to be applied to the studs within flanges outfitted with flat gaskets, the higher of the two values – the minimum torque and the calculated torque – should be employed for optimal results.

Precision Calculation of Tightening Torque for Screws: A Comprehensive Approach

Initial Step: Calculating Torque for Flange Bolt Tightening to Ensure Proper Joint Sealing

Our first task involves determining the torque required for tightening the flange bolts. This torque aims to achieve a specific surface pressure on the joint, thereby guaranteeing a precise and effective seal. This calculation aligns with the designated design pressure values corresponding to different pipe classes. The corresponding values are as follows:

Minimum and Calculated Torque Specifications for ANSI S-150# Flanges

DN	Db	Dr	N	di	de	e	Pa	m	Pd	Ai	Ecal.	Tcal	Tmin
pulg.	mm.	mm.	c/u.	mm.	mm.	mm.	Bar	–	Bar	cm2	Bar	Nm.	Nm.
1/2	12.7	10.17	4	22.0	34.9	1.60	400	4.00	19.50	3.80	490.86	14	12
3/4	12.7	10.17	4	27.8	42.9	1.60	400	4.40	19.50	6.07	492.12	21	17
1	12.7	10.17	4	34.5	50.8	1.60	400	4.40	19.50	9.35	494.69	27	22
1 1/2	12.7	10.17	4	49.6	73.0	1.60	400	4.40	19.50	19.32	494.72	57	46
2	15.9	12.88	4	61.9	92.1	1.60	400	4.40	19.50	30.09	494.07	116	94
2 1/2	15.9	12.88	4	74.6	104.8	1.60	400	4.40	19.50	43.71	498.03	136	110
3	15.9	12.88	4	90.7	127.0	1.60	400	4.40	19.50	64.61	498.30	199	160
4	15.9	12.88	8	116.1	157.2	1.60	400	4.40	19.50	105.87	501.40	142	114
6	19.1	15.75	8	170.7	215.9	1.60	400	4.40	19.50	228.85	510.52	276	216
8	19.1	15.75	8	221.5	269.9	1.60	400	4.40	19.50	385.33	518.23	381	294
10	22.2	18.55	12	270.3	323.8	1.60	400	4.40	19.50	573.83	522.82	404	309
12	22.2	18.55	12	327.0	381.0	1.60	400	4.40	19.50	839.82	532.54	494	371
14	25.4	21.27	12	350.3	412.7	1.60	400	4.40	19.50	963.77	528.26	700	530

Minimum and Calculated Torque Specifications for ANSI S-300# Flanges

DN	Db	Dr	N	di	de	e	Pa	m	Pd	Ai	Ecal.	Tcal	Tmin
pulg.	mm.	mm.	c/u.	mm.	mm.	mm.	Bar	–	Bar	cm2	Bar	Nm.	Nm.
1/2	12.7	10.17	4	22.0	34.9	1.60	400	4.00	49.90	3.80	632.50	19	12
3/4	15.9	12.88	4	27.0	42.9	1.60	400	4.40	49.90	5.73	632.33	36	22
1	15.9	12.88	4	34.5	51.0	1.60	400	4.40	49.90	9.35	641.70	46	29
1 1/2	19.1	15.75	4	49.6	73.0	1.60	400	4.40	49.90	19.32	642.39	114	71
2	15.9	12.88	8	61.9	92.1	1.60	400	4.40	49.90	30.09	640.71	75	47
2 1/2	19.1	15.75	8	74.6	104.8	1.60	400	4.40	49.90	43.71	650.86	109	67
3	19.1	15.75	8	90.7	127.0	1.60	400	4.40	49.90	64.61	651.55	159	98
4	19.1	15.75	8	116.1	157.2	1.60	400	4.40	49.90	105.87	659.48	229	139
6	19.1	15.75	12	170.7	215.9	1.60	400	4.40	49.90	228.85	682.81	246	144
8	22.2	18.55	12	221.5	269.9	1.60	400	4.40	49.90	385.33	702.54	406	231
10	25.4	21.27	16	270.3	323.8	1.60	400	4.40	49.90	573.83	714.30	474	266
12	28.6	24.45	16	327.0	381.0	1.60	400	4.40	49.90	839.82	739.16	678	367
14	28.6	24.45	20	350.3	412.7	1.60	400	4.40	49.90	963.77	728.21	666	366
16	31.8	27.62	20	410.3	469.9	1.60	400	4.40	49.90	1322.19	759.73	865	455
18	31.8	27.62	24	461.8	533.4	1.60	400	4.40	49.90	1674.94	748.94	965	515

Minimum and Calculated Torque Specifications for ANSI S-600# Flanges

DN	Db	Dr	N	di	de	e	Pa	m	Pd	Ai	Ecal.	Tcal	Tmin
pulg.	mm.	mm.	c/u.	mm.	mm.	mm.	Bar	–	Bar	cm2	Bar	Nm.	Nm.
1/2	12.7	10.17	4	22.0	34.9	1.60	400	4.00	96.50	3.80	849.63	25	12
3/4	15.9	12.88	4	27.0	42.9	1.60	400	4.40	96.50	5.73	849.30	48	22
1	15.9	12.88	4	34.5	50.8	1.60	400	4.40	96.50	9.35	868.61	61	28
1 1/2	19.1	15.75	4	49.6	73.0	1.60	400	4.40	96.50	19.32	868.75	154	71
2	15.9	12.88	8	61.8	92.1	1.60	400	4.40	96.50	30.00	865.04	102	47
2 1/2	19.1	15.75	8	74.6	104.8	1.60	400	4.40	96.50	43.71	885.12	148	67
3	19.1	15.75	8	90.7	127.0	1.60	400	4.40	96.50	64.61	886.46	217	98
4	22.2	18.55	8	116.1	157.2	1.60	400	4.40	96.50	105.87	901.80	369	164
6	25.4	21.27	12	143.7	215.9	1.60	400	4.40	96.50	162.18	862.75	624	289
8	28.6	24.45	12	170.7	269.9	1.60	400	4.40	96.50	228.85	850.33	1190	560
10	31.8	27.62	16	221.5	323.8	1.60	400	4.40	96.50	385.33	870.87	1318	605
12	31.8	27.62	16	276.0	381.0	1.60	400	4.40	96.50	599.15	892.88	1334	598
14	34.9	30.80	20	327.0	412.7	1.60	400	4.40	96.50	839.82	948.77	1455	613
16	38.1	33.97	20	410.4	469.9	1.60	400	4.40	96.50	1322.83	1096.31	1532	559
18	41.3	37.15	20	461.8	533.4	1.60	400	4.40	96.50	1674.94	1074.81	2235	832
20	41.3	37.15	24	513.2	584.2	1.60	400	4.40	96.50	2068.54	1112.20	2107	758
24	47.6	43.49	24	615.9	692.1	1.60	400	4.40	96.50	2979.28	1153.27	3272	1135
30	50.8	46.67	28	730.3	857.0	1.60	400	4.40	96.50	4188.38	1041.81	5488	2107