Page 1 of 7 NONMANDATORY APPENDIX Q ARTICLE Q-1000 DESIGN RULES FOR CLAMP CONNECTIONS Q-1100 INTRODUCTION Q-1110 SCOPE (a) The rules in Nonmandatory Appendix Q apply specifically to the design of clamp connections for pressure vessels and vessel parts and may be used in conjunction with the applicable requirements in Subsections NC, ND, and NE. These rules are not to be used for the determination of the thickness of supported or unsupported tubesheets integral with a hub nor for the thickness of covers. These rules provide only for hydrostatic end loads and gasket seating and do not consider external loads or thermal effects. (b) The design of a clamp connection involves the selection of the gasket, bolting, hub, and clamp geometry (see Figure Q-1130-1). Bolting shall be selected to satisfy the requirements of Q-1140. Connection dimensions shall be such that the stresses in the clamp and hub, calculated in accordance with this Appendix, do not exceed the allowable stresses specified in Q-1180. All calculations shall be made on dimensions in the corroded condition. Calculations for both assembly and operating conditions are required. (c) It is recommended that either a pressure energized or a low seating load gasket, or both, be used to compensate for possible nonuniformity in the gasket seating force distribution. Hub faces shall be designed so as to have metal to metal contact outside the gasket seal diameter. This may be provided by recessing the hub faces or by use of a metal spacer (see Figure Q-1130-1). The contact area shall be of sufficient cross sectional area to prevent yielding of either the hub face or spacer under both operating and assembly axial loads. (d) It is recognized that there are clamp designs which utilize no wedging action during assembly since clamping surfaces are parallel to the hub faces. These designs should satisfy the bolting and corresponding clamp and hub requirements of a clamp connection design with a total included clamping angle of 10 deg. This will provide some safety against loads imposed by angular deflections of the connection faces during operation and also provide some compensation against mechanical and thermal ratcheting. (e) The rules of this Appendix should not be construed to prohibit the use of other types of clamp connections provided that they are designed in accordance with good engineering practice and the method of design is acceptable to the Inspector. These rules shall apply only to new construction. (f) Clamps designed to the rules of this Section shall be provided with a bolt retainer. The retainer shall be designed to hold the clamps together independently in case of failure of the primary bolting. An appropriate external yoke or multiple bolting is considered satisfactory for this requirement. Clamp hub friction shall not be considered as a retainer method. Q-1120 MATERIALS (a) Materials used in the construction of clamp connections shall comply with the requirements given in Article NC-2000, Article ND-2000, or Article NE 2000, as applicable. (b) Hubs and clamps shall not be machined from plate. Q-1130 NOTATION The symbols defined below are used in the equations for the design of clamp type connections (see also Figures Q-1130-1 and Q-1130-2). A outside diameter of hub A 1 partial clamp area (C w 2C t )(C t ) A 2 partial clamp area 1.571C t 2 A 3 partial clamp area (C w C g )l c A b totalcross sectional area of bolts per clamp lug using the root diameter of the thread or least diameter of unthreaded portion, whichever is less. Cross sectional area of bolt retainer shall not be included in calculation of this area. A c total effective clamp cross sectional area A 1 + A 2 + A 3 A m total required cross sectional area of bolts per clamp lug taken as the greater of A m 1, A m 2,or A m 3 ð15þ 385
Page 2 of 7 A m 1 totalcross sectional area of bolts per clamp lug at root of thread or section of least diameter under stress, required for the operating conditions W m 1 /2S b A m 2 totalcross sectional area of bolts per clamp lug at root of thread or section of least diameter under stress, required for gasket seating W m 2 /2S a A m 3 totalcross sectional area of bolts per clamp lug at root of thread or section of least diameter under stress, required for assembly conditions W m 3 /2S a B inside diameter of hub b effective gasket or joint contact surface seating width (see Table XI-3221.1-2) B c radial distance from connection centerline to effective center of bolts b o basicgasketorjoint contact surface seating width (see Table XI-3221.1-2) C diameter of effective clamp hub reaction load (A + C i )/2 C g effective clamp gap taken at clamp hub contact center (C) C i inside diameter of clamp C t effective clamp thickness C w effective clamp width e b radial distance from effective center of the bolts to the centroid of the clamp body B c (C i /2) l c X f hub stress correction factor from Figure XI-3240-6. (This is the ratio of the stress in the small end of the hub to the stress in the large end.) (For values below limit of the Figure, use f 1.0.) G diameter at location of gasket load reaction. Except as noted in Figure Q-1130-1, G is defined as follows (see Table XI-3221.1-2): (a) when b 0 1 / 4 in. (6 mm), G meandiameter of gasket or joint contact face (b) when b 0 > 1 / 4 in. (6 mm), G outside diameter of gasket contact face less 2b g 0 thickness of hub neck at small end g 1 thickness of hub neck at intersection with hub shoulder g 2 heightofhubshoulder(g 2 shall not be larger than T) radial distance from the hub inside diameter to the hub shoulder ring centroid H total hydrostatic end force 0.785 G 2 P h hub taper length axial distance from the hub face to the hub shoulder ring centroid h 2 average thickness of hub shoulder T (g 2 tan ϕ)/2 H D hydrostatic end force on bore area 0.785 B 2 P h D radial distance from effective clamp hub reaction load to the circle on which H D acts [C (B + g 1 )]/2 H G difference between total effective axial clamping preload and the sum of total hydrostatic end force and total joint contact surface compression [1.571W/tan(ϕ + μ)] (H + H p ) h G radial distance from effective clamp hub reaction load to the circle on which H G acts (for full face contact geometries h G 0) H m total axial gasket seating requirements for makeup (3.14bGy or the axial seating load for selfenergizing gaskets, if significant) h n hub neck length [minimum length of h n is 0.5g 1 or 1 / 4 in. (6 mm), whichever is larger] h o H p total joint contact surface compression load 2b 3.14GmP (for self energized gaskets, use H p 0 or actual retaining load if significant) H T difference between total hydrostatic end force and hydrostatic end force on bore area H H D h T radial distance from effective clamp hub reaction load to the circle on which H T acts [C (B + G)/2]/2 I c effective moment of inertia of clamp relative to axis of entire section I h effective moment of inertia of hub shoulder ring relative to its neutral axis L a distance from W to the point where the clamp lug joins the clamp body l c effective clamp lip length L h clamp lug height l m effective clamp lip moment arm l c (C C i )/2 L w clamp lug width m gasket factor from Table XI-3221.1-1 M D component of moment due to H D H D h D M F offset moment H D (g 1 g o )/2 M G component of moment due to H G H G h G 386
Page 3 of 7 M H reaction moment at hub neck M O total rotational moment on hub (see Q-1150) M P pressure moment 3.14 PBT(T/2 ) M R radial clamp equilibrating moment M T component of moment due to H T H T h T N outside diameter of hub neck P Design Pressure Q reaction shear force at hub neck r clamp body radius (shall be less than or equal to C t ) S 1 hub longitudinal stress on outside at hub neck S 2 maximum Laḿe hoop stress at bore for hub neck section S 3 hub axial shear stress (maximum) across the hub shoulder S 4 hub radial shear stress (maximum) across the hub neck S 5 clamp longitudinal stress at clamp body inner diameter S 6 clamp tangential stress at clamp body outer diameter S 7 shear stress (maximum) across clamp lips S 8 clamp lug bending stress S 9 effective bearing stress between clamp and hub S a allowable bolt stress at atmospheric temperature (see Section II, Part D, Subpart 1, Table 3) S AC allowable design stress for clamp material at (assembly condition) atmospheric temperature (see Section II, Part D, Subpart 1, Tables 1A and 1B) S AH allowable design stress for hub material at (assembly condition) atmospheric temperature (see Section II, Part D, Subpart 1, Tables 1A and 1B) S b allowable bolt stress at Design Temperature (see Section II, Part D, Subpart 1, Table 3) S OC allowable design stress for clamp material at (service condition) Design Temperature (see Section II, Part D, Subpart 1, Tables 1A and 1B) S OH allowable design stress for hub material at (service condition) Design Temperature (see Section II, Part D, Subpart 1, Tables 1A and 1B) T thickness of hub shoulder for design purposes. The hub shoulder ring is the ring with crosssectional dimensions T by (A B)/2. W total design bolt load required for service or assembly, as may apply W e total effective axial clamping preload on one clamp lip and hub shoulder (gasket seating or assembly) 1.571W/tan(ϕ + μ) W m 1 minimum required total bolt load for the service conditions [see Q-1140(b)(1)] W m 2 minimum required total bolt load for gasket seating [see Q-1140(b)(2)] W m 3 minimum required total bolt load for assembly [see Q-1140(b)(3)] X radial distance from inside surface of clamp body to the centroid of the clamp body y gasket or joint contact surface unit seating load (see Table XI-3221.1-1) Z effective clamp hub taper angle, deg (for gasket seating and preload, Z ϕ + μ; for operating, Z ϕ μ) [see Q-1140(b)(4)] α hub neck pipe transition taper, deg (α shall not be greater than 45 deg) μ effective friction angle, deg ϕ clamp hub taper angle, deg (ϕ shall not exceed 35 deg) Q-1140 BOLT LOADS (a) General. During assembly of the clamp connection, the design bolt load W is transferred via the clamp hub taper angle to an axial load (effective clamp preload W e ). In addition, the effect of friction will cause W e to be reduced for a given W. Friction effects can be reduced by lubrication or by jarring the clamps during assembly. An appropriate friction angle shall be established for both assembly and operating conditions. (b) Calculations. In the design of the bolting for a clamp connection, complete calculations shall be made for three separate and independent sets of conditions which are defined as follows. (1) The required bolt load for the service conditions W m 1 shall be sufficient to: (-a) resist the hydrostatic end force H exerted by the maximum allowable working pressure on the area bounded by the diameter of gasket reaction; and (-b) maintain on the gasket or joint contact surface, a compression load H p which experience has shown to be sufficient to ensure a tight joint. The minimum operating bolt load W m 1 shall be determined in accordance with eq. (1). (2) Before a tight joint can be obtained, it is necessary to seat the gasket or joint contact surface properly by applying a minimum initial load (under atmospheric temperature conditions without the presence of internal pressure), which is a function of the gasket material and ð1þ 387
Page 4 of 7 Figure Q-1130-1 Typical Hub and Clamp 1 /4 in. (6 mm) min. radius Hub 1 /4 in. (6 mm) min. radius h α h n φ T g 2 A h α h n φ T g 2 A g o g 1 g o g 1 N B N B (a) (b) W e H G W e h G g 1 g o h D H D C h T H T H p or H m g 1 g o h D H D C h T H G H p or H m H T G G (c) (d) Clamp L a B c Neutral Axis Neutral Axis Clamp Lug L h W/2 C i /2 W/2 C g C W e X r C w e b C i m c C t (e) (f) 388
Page 5 of 7 Figure Q-1130-2 Typical Clamp Lug Configurations 389
Page 6 of 7 the effective gasket area to be seated. The minimum initial bolt load required for gasket seating W m 2 shall be determined in accordance with eq. (2). (3) To ensure proper preloading of the clamp connection against service conditions, an assembly bolt load W m 3 shall be determined in accordance with eq. (3). (4) In eq. (1)(1) credit for friction is allowed based on clamp connection geometry and experience, but shall be limited to a value in which (ϕ μ) is equal to or greater than 5 deg. In eqs. (2)(2) and (3)(3), friction shall be considered and be such that μ is equal to or greater than 5 deg. This will then satisfy the requirements of Q-1110(d). (5) The need for providing sufficient bolt load for either gasket seating in accordance with eq. (2)(2) or assembly in accordance with eq. (3)(3) will prevail on many low pressure designs and with facings and materials that require a high seating load where the service bolt load computed by eq. (1)(1) is insufficient to properly preload the connection. (c) Required Bolt Area. The total cross sectional area of bolting A m required shall be the greater of the values for service conditions A m 1, gasket seating conditions A m 2,or assembly condition A m 3. Bending of the bolting due to nonparallel nut bearing surfaces shall be compensated for by use of a stress correction factor in bolt area calculations or by use of spherically seated nuts and/or washers. (d) Clamp Connection Design Bolt Load W. The bolt load used in the design of the clamp connection shall be the values obtained from eqs. (4) and (5). For service conditions: For assembly conditions: Q-1150 HUB MOMENTS In the calculation of hub stresses, the moment of a load acting on the hub is the product of the load and its moment arm. The moment arm is determined by the relative position of the effective hub clamp reaction diameter with respect to that of the load producing the moment [see Figure Q-1130-1, sketches (c) and (d)]. In addition to the load moments, additional reaction moments with relation to the hub shoulder ring centroid are considered to compensate for hub to pipe transition, radial pressure, and clamp radial equilibrating effects. ð2þ ð3þ ð4þ ð5þ For the service conditions, the rotational hub moment M O is the sum of six individual moments M D, M G, M T, M F, M P,andM R based on the design bolt load of Q-1140(d) eq. (4) with moment arms as given in Figure Q-1130-1. For assembly, the rotational hub moment M O is based on the design bolt load of Q-1140(d) eq. (5) in which case Q-1160 CALCULATION OF HUB STRESSES The stresses in the hub shall be determined for both the service and the assembly conditions. (a) The reaction moment M H and reaction shear Q as defined in Q-1130 shall be calculated at the hub neck for rotational moment M O. (b) Hub stresses are to be calculated from the following equations: Hub longitudinal stress Hub hoop stress Hub axial shear stress Hub radial shear stress ð6þ ð7þ ð8þ ð9þ ð10þ Q-1170 CALCULATION OF CLAMP STRESSES The stresses in the clamp shall be determined for both the service and the assembly conditions. Clamp stresses are to be calculated from the following equations: Clamp longitudinal stress Clamp tangential stress Clamp lip shear stress ð11þ ð12þ 390
Page 7 of 7 Clamp lug bending stress ð13þ ð14þ Table Q-1180-1 Allowable Design Stress for Clamp Connections Stress Category S 1 Allowable Stress 1.5S OH or 1.5S AH In addition, a bearing stress calculation is to be made from eq. (15) for either the clamp or hub. S 2 S 3 S 4 S 5 S OH 0.8S OH or 0.8S AH 0.8S OH or 0.8S AH 1.5S OC or 1.5S AC Q-1180 ALLOWABLE DESIGN STRESS FOR CLAMP CONNECTIONS ð15þ Table Q-1180-1 gives the allowable stresses that are to be used with the equations of Q-1160 and Q-1170. S 6 1.5S OC or 1.5S AC S 7 0.8S OC or 0.8S AC S 8 S OC or S AC S 9 [Note (1)] NOTE: (1) 1.6 times the lower of the allowable stresses for hub material (S OH, S AH )and clamp material (S OC, S AC ). 391