Hangers and Supports
© 1996 Bechtel Corp. Piping/Mechanical Handbook 12-1 Section 12 Hangers and Supports GENERAL Pipe supports are designed to restrain piping in relation to an axis. The X-axis by normal convention is north and south, the Y-axis is up-down, and the Z-axis east-west. They may be combined into several categories for pipe supports: Gravity - load of pipe and insulation One Axis - loading along one axis with either positive and/or negative values Two Way - loading in two planes both positive and negative directions Anchor - loads in three planes along with resistance to moments from three axes Rod Hangers The rod hanger is a simple gravity support using a threaded rod between the structure and the piping. This hanger provides an inexpensive method of supporting most pipe sizes. Figure 12-1 shows various types of rod hanger components that are typically used with this type of support. C-CLAMP BEAM CLAMP WELDED ATTACHMENT PIPE CLAMP ADJUSTABLE RING HEAVY DUTY PIPE CLAMP FIGURE 12-1 - ROD HANGER COMPONENTS Section 12 Hangers and Supports 12-2 Piping/Mechanical Handbook 1996:Rev.2 Spring Can Supports A Spring Can support is a rod hanger with a spring inserted. This hanger provides the same relative load carrying capacity in both the cold and hot conditions where thermal growth would be in the vertical axis. Manufacturers generally supply spring cans in six different styles to suit any construction condition or orientation. As shown in Figure 12-2, spring can styles vary by height space, rod type, and access conditions available as follows: Type A are for unrestricted height spaces Type B are suited for limited spaces Type C is also utilized in limited space with a single plate structural attachment Type D places the spring can above the supporting steel with adjustment from the top Type E places two spring cans above the supporting steel in a trapeze arrangement Type F are used for floor mounted supports FIGURE 12-2 - SPRING CAN APPLICATIONS Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-3 Type G are designed to use two rods like a trapeze style support Spring cans are shipped to the job with both the hot and cold load shown and travel stops installed to maintain the cold load setting until the completion of startup activities or turnover to the client. Frame or Box Hangers A Frame or Box hanger is made up from smaller structural steel shapes that are welded together to provide support in one or more axes. They are primarily used as two-way loading restraints. The labor and material cost for this type of support can be higher than the two previous styles. A typical two-way box hanger is shown in Figure 12-3. Anchors Anchors are normally welded directly to the pipe system to provide a three-way direction and three-way rotation restraint and anchorage for the piping system. Sway Struts A Sway Strut is a manufactured support. This hanger will provide support in both positive and negative directions in one plane while allowing lateral movement. A typical sway strut detail is shown in Figure 12-4. FIGURE 12-3 - TWO-WAY RESTRAINT BOX HANGER FIGURE 12-4 - SWAY STRUT ASSEMBLY Section 12 Hangers and Supports 12-4 Piping/Mechanical Handbook 1996:Rev.2 Shock Arrestors Mechanical and Hydraulic Shock Arrestors both provide movement restraint during dynamic loading while allowing the pipe unrestrained motion under normal plant operating conditions. The mechanical snubber acts like a axial clutch that converts linear motion into angular acceleration. The hydraulic snubber operates on fluid velocity. When the motion of the pipe exceeds a set point value, the velocity of the fluid in the snubber is stopped and the assembly becomes a rigid strut. A typical hydraulic shock suppressor detail is shown in Figure 12-5. Both these supports are recommended for piping subjected to shock, sway, or vibration caused by earthquakes, water hammers, or other transient forces. FIGURE 12-5 - HYDRAULIC SHOCK SUPPRESSOR PIPE STRAP SPRING CUSHION HANGER PROTECTION SADDLE SADDLE SUPPORT STANDARD U-BOLT RISER CLAMP FIGURE 12-6 - HANGER COMPONENTS Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-5 Hanger Components A variety of hanger components are available to support piping systems. Each component is designed for a specific function and examples are shown in Figure 12-6. Pipe Guides and Rollers Pipe guides and rollers provide gravity support while still allowing piping system thermal expansion and contraction. Typical guide and roller details are shown in Figure 12-7. Socket Clamp Assemblies Socket clamps support and restrain bell and spigot piping connections and are typically used in fire protection systems. Typical socket clamp assembly details are shown in Figure 12-8. ROLLER CHAIR PIPE GUIDE PIPE SLIDE FIGURE 12-7 - PIPE GUIDES AND ROLLERS PIPE ANCHOR 1/4 BEND SPIGOT END ANCHOR 1/8 BEND ANCHORS FIGURE 12-8 - SOCKET CLAMP ASSEMBLIES Section 12 Hangers and Supports 12-6 Piping/Mechanical Handbook 1996:Rev.2 PIPE SUPPORT MATERIAL Structural steel is the most common material used for pipe supports. This section will define some of the common codes and standards associated with structural steel and review some common materials, shapes, and connections. Structural Steel Codes and Standards The following codes and standard associations cover the majority of requirements for both structural steel and pipe supports. American Institute of Steel Construction AISC is a nonprofit trade association representing and serving the fabricated structural steel industry of the United States. The AISC publishes the Manual of Steel Construction, the Specification for the Design, Fabrication and Erection of Structural Steel for Buildings, the Code of Standard Practice for Steel Buildings and Bridges. American Iron and Steel Institute AISI Specification for the Design of Cold Formed Steel Structural Members. This specification covers the design of structural members which are cold formed to shape from carbon and low alloy steel sheet or strip used for load carrying purposes in buildings. There is a similar specification for cold formed stainless steel structural members. Steel Structures Painting Council SSPC produces a two volume manual. Volume I covers good painting practice and Volume 2 covers painting systems and specifications. Common Material Grades The AISC Specification for the Design, Fabrication and Erection of Structural Steel for Buildings states that structural steel must conform to any one of a number of ASTM grades of steel. The carbon range for most of the structural steels is 0.15-0.29 percent (mild carbon steel), with manganese up to 1.60 percent. ASTM A36 (structural steel) is a weldable mild carbon steel and has a guaranteed minimum yield of 36 ksi for all shapes and for plates up to 8 inches in thickness. This grade of steel is considered to be the workhorse steel and is the most common steel in use today. ASTM A529 (structural steel with a 42 ksi minimum yield point) is a higher strength carbon steel available in plates and bars up to 1/2 inches in thickness or diameter and shapes. Where 0.02 percent copper is specified, A529 has an atmospheric corrosion resistance equal to twice that of structural carbon steel without copper. This steel is used in the relatively light structural members of standard steel buildings. ASTM A242 (high strength, low alloy structural steel) is a very broad specification stipulating minimum mechanical properties and limits the maximum carbon and manganese for weldability. The specification is limited to material up to 4 inch plate. Generally, these steels have enhanced Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-7 atmospheric corrosion resistance of at least two times that of carbon steels with copper, or four times carbon steel without copper. When self weathering (unpainted) steels are specified, A242 is normally specified with the added requirement that the steel have from four to six times the corrosion resistance of carbon steel. Self weathering is the term used to describe a steel that has chemical properties allowing it to form a very dense and tight oxide (rust), which in effect seals the base metal from further oxidation and therefore affords a means (other than a coating) of protecting the steel from further corrosion. For this to occur, the steel must be exposed to the elements (alternately dry and wet). The tight oxide, or patina as it is called, gives a deep-brown appearance and is frequently used in structures for aesthetic reasons, as well as from the low maintenance point of view. ASTM A441 (high strength, low alloy structural manganese vanadium steel) is a weldable steel with reasonable moderate carbon and manganese content with an added alloy to increase strength. A441 is suitable for welding, riveting, or bolting. The atmospheric corrosion resistance of this steel is about twice that of carbon steel. This specification is limited to material up to 8 inches in plate and bar thicknesses. For thicknesses over 4 inches, the yield point is 40 ksi. ASTM A572 (high strength, low alloy columbium-vanadium steels of structural quality) covers six grades or strength levels for shapes, plates, sheet piling, and bars. Grades 42 and 50 are intended for bolted or welded construction of all structures, while grades 60 and 65 are intended for bolted construction of bridges and for welded or bolted construction of other applications. Available grades vary for groupings of shapes and thicknesses of plates. When 0.20 percent minimum copper is specified, the A572 steels provide atmospheric corrosion resistance similar to A242 and A441 steels. ASTM A588 (high strength, low alloy structural steel with 50 ksi minimum yield point to 4 inches thick) was specifically created to maintain a higher yield point level for heavier shapes and thicker plates. The specification covers shapes, plates, and bars for welded and bolted construction. It is intended primarily for use in welded bridges and buildings where savings in weight and added durability are important. The atmospheric corrosion resistance is about four times that of carbon steel without copper. The material makes available all shapes at a 50 ksi yield stress level. Plate yield points vary from 42 ksi to 50 ksi, depending upon the thickness of the material (the 50 ksi yield applies to material up to 4 inches in thickness). Similar to A242, this grade of steel is also used for self-weathering applications. A588 also has enhanced toughness characteristics (resistance to sudden fracture in the presence of notches, dynamic loads, and reduced temperatures). ASTM A514 (high yield strength quenched and tempered alloy steel plate, suitable for welding) is a heat treated steel in plates in thicknesses up to 6 inches and is primarily intended for use in welded bridges and other structures. ASTM A53 (welded and seamless pipe) grade B covers hot formed seamless and welded black and hot dipped galvanized round steel pipe in nominal sizes 1/8 inch to 26 inches inclusive with varying wall thicknesses. Grade B furnishes a guaranteed minimum yield of 35 ksi, although 36 ksi is used in the AISC Manual design tables. Type E (electric resistance welded) and type S (seamless) are both provided. Both are suitable for welding. ASTM A500 (cold formed welded and seamless carbon steel structural tubing in rounds and shapes) covers steel round, square, rectangular, or special shaped structural tubing for welded or bolted construction. The tubing is provided in welded sizes with a maximum periphery of 64 Section 12 Hangers and Supports 12-8 Piping/Mechanical Handbook 1996:Rev.2 inches and a maximum wall thickness of 0.500 inches, and in seamless with a maximum periphery of 32 inches and a maximum wall thickness of 0.500 inches. It is produced in three grades, A, B, and C, and, depending on whether it is round or shaped (square, rectangular, or special) tubing, the yield point varies from 33 ksi to 50 ksi. Under the specification, the maximum sizes would be about 20 inches diameter round, 16 by 16 inches square, or 20 by 12 inches rectangular (although these maximum sizes may not be produced). ASTM A501 (hot formed welded and seamless carbon steel structural tubing) covers square, round, rectangular, or special shaped structural tubing for welded or bolted construction. Square and rectangular (common sizes 3 inches by 2 inches to 10 inches by 6 inches) tubing is furnished in sizes 1 inch to 10 inches across the flat sides with wall thicknesses 0.095 inches to 1.000 inch, depending on size, and round tubing is furnished in nominal diameters 1/2 inch to 24 inches with nominal (average) wall thicknesses 0.109 to 1.000 inch, depending upon size. ASTM A618 (hot formed welded and seamless high strength, low alloy structural tubing) covers three grades of square, rectangular, round, and special shaped tubing for welded and bolted applications in buildings and bridges. For enhanced corrosion resistance, grades I and III are specified. ASTM A570, grades 45 and 50 (hot rolled carbon steel sheets and strip, structural quality). ASTM A606 (steel sheet and strip, hot rolled and cold rolled, high strength, low alloy, with improved corrosion resistance). ASTM A607 (steel sheet and strip, hot rolled and cold rolled, high strength, low alloy, columbium and/or vanadium). Steel Product Classification In response to a recognized need to improve and standardize the designation for structural steel shapes, the Committee of Structural Steel Producers of AISI developed standard nomenclature for structural steel shapes. These designations enable all mills to use the same identification in ordering, billing, and specifying. These designations for various types of shapes are presented in the AISC Manual of Steel Construction. Sheet piling sections begin with the letter P for piling, with the succeeding letter or letters defining the configuration followed by a two digit number, which indicates the weight of the section in pounds per foot. H-piles are designated by HP followed by the section depth, and the weight of the section in pounds per foot. Steel plate is designated by all dimensions in inches, fractions of an inch, or decimals of an inch. As an alternative, thickness may be specified in pounds per square foot. The semifinished product of the mill goes through rolling mills to produce structural steel shapes, plates, bars, pipes, tubes, or sheet. The W-Shape Section is the most commonly used shape; it has two horizontal elements, called flanges, and a vertical member, referred to as a web. This shape was previously called a wide flange shape, and was designated by the symbol WF. Essentially, W shapes have the inner and outer edges of the top and bottom flange parallel. The same inside to inside of flange dimension is maintained (with a slight variation by groups) for a given depth category of shape. The Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-9 designation W 24 x 76 means a W shape, nominally 24 inches deep (outside to outside of flange) and weighing 76 pounds per lineal foot of span. The S-Shape Section is a rolled shape that also has two parallel flanges and a web. However, the inner surfaces of the flange have a slope of approximately 162/3 % (2 inches in 12 inches). These shapes were previously called American Standard beams. The designation S 24 x 100 means an S shape 24 inches deep (outside to outside of flange) and weighing 100 pounds per lineal foot of span. Some of the S24 and S20 groupings have depths in excess of 24 inches and 20 inches, respectively. The American Standard Channel Section is a cross section that was formerly designated by a turned symbol depending on whether the section's web was vertical or horizontal. However, the symbol C is now used regardless of the orientation of the web. The inner surface of both flanges of the C shape have a slope of approximately 16 2/3 percent (2 inches in 12 inches). The designation C12 x 20.7 indicates an American Standard Channel with a depth (outside to outside of flange) of 12 inches and a weight of 20.7 pounds per lineal foot. To indicate the position of the channel (web horizontal or vertical), the engineer may indicate the appropriate position by the old symbol in addition to the usual designation. The letter HP indicates bearing pile shapes having two parallel flanges with parallel flange surfaces and a web element. The web and flange thicknesses and the width of flange and depth of section are nominally equal in the HP shape. A HP 14 x 73 designates an HP shape nominally 14 inches in depth (outside to outside of flange) and 73 pounds per lineal foot. The letter M refers to shapes that cannot be classified as W, HP, or S shapes. Similarly, MC designates channels that cannot be classified as American Standard Channels. These shapes are not as readily available as W, S, HP, or C shapes. Angle Shapes have two legs of rectangular cross section that are normal to one another. The inner and outer surface of each leg is parallel. Equal leg or unequal leg angles are available. The thickness of each leg is the same. The symbol L is used to designate an angle shape. L 6 x 4 x 5/8 designates an unequal leg angle whose large leg is 6 inches long and 5/8 inches thick and whose short leg is 4 inches long and 5/8 inches thick. Structural Tees (WT or ST Sections) are obtained by splitting the webs of various beams. They may be split from a W shape (WT) or from the S shape (ST). These shapes have a single horizontal flange and a web or stem. WT 12 x 38 designates a structural tee cut from a W shape whose depth (tip of stem to outside flange surface) is nominally 12 inches and weighs 38 pounds per lineal foot. Bars are generally classified as 6 inch or less in width and 0.203 inch and over in thickness. These sections can be rectangular (flat), circular, or square. An example is Bar 2 1/2 x 1/2 indicates a flat bar 2 1/2 inches wide and 1/2 inch thick. Widths are normally specified in 1/4 inch increments and thicknesses are normally specified in 1/8 inch increments. Plates are rectangular in shape, generally over 6 inches in width and 0.230 inches and over in thickness or over 48 inches in width and 0.180 inch and over in thickness. Sheared plates are rolled between horizontal rolls and trimmed (sheared or gas cut) on all edges. Universal plates (UM) are rolled between horizontal and vertical rolls and trimmed (shear or gas cut) on the ends only. Types of Connectors Section 12 Hangers and Supports 12-10 Piping/Mechanical Handbook 1996:Rev.2 There are two basic types of structural steel connecting methods: Bolting Welding Sometimes bolting and welding are combined on a single connection. Welding is as economical as any mechanical means of connecting. AWS D1.1 is the nationally accepted specification that covers all the facets of welding in the United States. It is referred to in the AISC Specification, as well as in most other specifications and codes. The two basic types of structural steel bolts include, the "common" or machine bolt (ASTM A307) and the high strength bolts (ASTM A325 and A490). ASTM A193 bolts may also be specified for some pipe hangers. The chemical and physical properties of bolting materials are found in the applicable ASTM Specification. The AISC Manual includes a reprint of Specification for Structural Joints Using ASTM A325 or A490 Bolts. These specifications cover the hardware requirements, allowable working stresses, installation procedures and methods, as well as inspection procedures. Table 12-1 shows typical tensile strengths for common bolting materials: Common bolts are also referred to as A307, machine, unfinished, or rough bolts. These bolts should meet ASTM A307, Specification for Low Carbon Steel Externally and Internally Threaded Standard Fasteners. This type of bolt is significantly cheaper than high strength bolts. They generally have heads and nuts with no marking on the head surface. The bolts are available in 1/4 to 4 inch diameter. Threads are unified coarse thread series (UNC Series), class 2A (see ANSI B1.1, Unified Screw Threads). Common bolts are easily tightened by using spud wrenches. The tension induced by turning is usually low, and it is usually considered that no clamping force is developed. The most common mechanical fastener is the high strength A325 bolt with heavy hexagonal nuts and having heavy hexagonal heads. These bolts have shorter thread lengths than other bolts. A325 bolts come in three types. Type 1 is produced from a medium carbon steel (available sizes are from 1/2 inch to 1 1/2 inch in diameter). TABLE 12- 1 - STRUCTURAL BOLTING STRENGTHS BOLT TYPE MIN YIELD STRENGTH MIN TENSILE STRENGTH A307 60 ksi A325 (to 1" dia.) 92 ksi 120 ksi (1 1/8" - 1 1/2") 81 ksi 105 ksi A490 125 ksi 150 ksi B7 105 ksi Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-11 Type 2 is produced from low-carbon martensite steel and is limited to 1/2 inch to 1 inch diameter sizes. This type should not be hot dipped galvanized. Type 3 is produced from steels with self weathering characteristics comparable to ASTM A588 and A242 steels and are available in sizes from 1/2 inch to 1 1/2 inch in diameter. Identifying marks on the heads of each of the three types of A325 bolts distinguish them. At the option of the manufacturer, Type 1 bolts are identified by the mark "A325" and the manufacturer's symbol and by three radial lines 120 apart. Type 2 bolts are identified by three radial lines 60 apart. Type 3 bolts are identified by the mark "A325" underlined and, at the option of the manufacturer, any other additional marks to identify the bolt as a self weathering type. The A490 bolt is stronger than the A325 bolt and is produced from an alloy steel. A490 bolts are marked by "A490" and the manufacturer's symbol. The heavy hexagonal nuts for A325 bolts are similarly marked for identification on at least one face. These marks are the manufacturer's symbol and the number "2" or "2H," by three equally spaced circumferential lines or by the mark "D" or "DH." The nuts for A325 type 3 bolts are marked on one face by three circumferential marks and the number "3" in addition to any other marks desired by the manufacturer. A490 nuts are marked by "2H" and the manufacturer's mark or by "DH." Washers for A325 type 3 bolts bear the mark "3" near the outer edge of one face and any other marks desired by the manufacturer. All high strength bolts (HSBs) are heat treated by quenching and tempering. High strength bolts installed in bearing connections not subject to direct tension are only required to be brought to a snug tight condition and do not require any specific pretensioning. A snug tight condition is defined as sufficient tightening to bring the two faying surfaces of the bearing connection into contact without the evidence of a gap. HSBs that are used in slip limited connections and connections subject to direct tension are required to be pretensioned. This pretension, induced by nut rotation, produces a high clamping force, which allows the contact surfaces to carry loads solely by friction. With this pretension, there will be little or no increase in internal bolt tension when a load is applied to the connection. Tightening may be accomplished by direct tensioning, turn of the nut, torque wrenches, or load indicating washers. Torque control bolts are also commonly used for high strength bolts that require pretensioning. These bolts are supplied with a spline that twists off at the predetermined torque required to pretension the bolt. All HSB dimensions conform to ANSI B18.2.1, American National Standard for Square and Hex Bolts and Screws and the heavy hex nut dimensions conform to ANSI B18.2.2. Threads are Unified Coarse Thread Series as specified by ANSI B1.1, American National Standard for Unified Screw Threads and have class 2A tolerances for bolts and class 2B tolerances for nuts. Dimensions of the washers conform to those of the Specification for Structural Joints Using ASTM A325 or A490 Bolts issued by the Research Council on Riveted and Bolted Structural Joints of the Engineering Foundation. Unless otherwise specified, washers are circular. A second basic specification covering HSBs is entitled Structural Joints Using ASTM A325 or A490 Bolts, which is approved by the Research Council on Riveted and Bolted Structural Joints (RCRBSJ) of the Engineering Foundation. This specification is endorsed by both AISC and the Section 12 Hangers and Supports 12-12 Piping/Mechanical Handbook 1996:Rev.2 Industrial Fasteners Institute (IFI). The specification covers the design and assembly of structural joints using high strength bolts. The AISC Specification dealing with HSBs conforms to the RCRBSJ specification. This specification covers: The specification requirements for bolts, nuts, and washers The dimensions of the bolts, nuts, and washers Bolted parts Permissible joint surface coatings (paint is permitted without consideration as to type in bearing joints and certain contact surface coatings are permitted with friction joints) Design stresses for applied tension, shear, and bearing Acceptable installation procedures which include the minimum tension corresponding to the size and grade of fastener Required inspections Oversized and Slotted Holes All standard holes for HSB should be 1/16 inch greater than the nominal bolt diameter. The holes can be punched (provided the thickness of material is no more than 1/8 inch greater than the nominal bolt diameter), sub-punched and reamed or drilled. Oversized holes for HSB are not allowed to be more than: 3/16 inch greater than the nominal bolt diameter for bolts equal to or less than 7/8 inch in diameter 1/4 inch greater than the nominal bolt diameter for 1 inch diameter bolts 5/16 inch greater than the nominal bolt diameter for 1 1/8 inch and greater diameter bolts Oversized holes can be used in any or all plies of slip limited connections. Hardened washers should be used over oversized holes in an outer ply. Short slotted holes are nominally 1/16 inch wider than the nominal bolt diameter, and have a maximum length 1/16 inch greater than the maximum allowable oversize hole size. Short slotted holes may be used in any or all plies of both slip limited and bearing type connections. In bearing connections, the slots should be normal to the direction of loading. In slip limited connections, the slots may be in the direction of loading. Hardened washers must be used over exposed short slotted holes. Long slotted holes are also nominally 1/16 inch wider than the nominal bolt diameter and have a length larger than 2 1/2 times the nominal bolt diameter. In bearing connections, the slots should be normal to the direction of loading. These slots may be used in slip limited connections regardless of direction of loading. A minimum 5/16 inch thick plate structural steel grade washer or continuous bar having standard holes completely covering the slot should be used where long slotted holes are used on an outer ply of the connection. If hardened washers are required, they must be placed over the outer surface of the plate washer or continuous bar. The slots may be used in only one of the connected parts of either bearing or slip limited connections at an individual contact surface. Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-13 Bolting Installation Procedure Both ASTM A325 or A490 bolts may be installed by any of the installation methods mentioned previously. Tightening may be done by turning either the bolt head or the bolt nut and preventing the unturned element from turning. All fasteners in a connection should be tightened to the minimum tension called for in the specification. Turn of the Nut Tightening The turn of the nut tightening method is a strain control procedure, as contrasted with a torque control procedure (as is the case with the torque wrench, torque control bolt or calibrated wrench methods). The effectiveness of the method depends on the uniformity of the starting point from which rotations of the turned element (usually the nut) are measured. This starting point is called the snug tight position. This position is defined as the position at which the faying surfaces of the connection are in full contact and no gap is present. After the snug condition is achieved, further nut rotation results in bolt elongation or deformation, which produces the required clamping force. Required nut rotations are stipulated in the specification. The normal bolt tightening procedure is to bring enough bolts into a snug tight condition so the connection surfaces have good contact. Additional bolts are then placed in the remaining holes and these bolts are also brought to a snug tight condition. All bolts are then tightened by the amount prescribed by the specification. The tightening procedure should systematically progress from the most rigid part of the connection to the free edges. To retain a uniform level of deformation in all the bolts, the required nut rotation is different for different bolt lengths. This method of bolt torquing is the least consistent and requires the highest intensity of inspection to verify proper torquing since the inspection must be done at the time of tightening. Calibrated Wrench Tightening When using calibrated wrenches to tighten a connection, efforts must taken to ensure the torque wrench is properly calibrated. This installation method is one of torque control. The tightening procedure is further checked by verifying during actual installation that the turned element rotation from snug position is not greater than the prescribed amount. The identical recommended sequence of tightening designated for the turn of the nut method is prescribed for this method of installation. It is recommended that the wrench be used to verify previously tightened bolts which may have loosened by the tightening of other bolts in the same connection. This retightening is not considered to be reuse of the bolt. A325 bolts may be reused, but A490 and galvanized A325 bolts may not be reused after pretensioning. Section 12 Hangers and Supports 12-14 Piping/Mechanical Handbook 1996:Rev.2 Direct Tension Tightening Direct tension devices pull the bolt to apply the required pretension to the bolt. An example of a direct tension system is the Huck Bolt tensioning system. Torque Control Bolts Torque control bolts are the easiest bolting system to install, torque, and inspect. Using a light weight electric torque wrench, the bolts are installed and tightened. When the required bolt pretension is achieved, the twist off wrench attachment breaks off ensuring proper tightening. Bolt Inspection The inspection of bolts installed by the turn of nut or calibrated wrench method is usually made at the time of installation to ensure that the proper procedure is used. An additional inspection method is through the use of an inspecting wrench (a torque or power wrench), which can be adjusted in the same manner as described for calibrated wrench tightening. With the direct tension indicator, inspection is also made at the time of installation. CONCRETE ANCHOR BOLTS Concrete anchor bolts are used to fasten hanger base plates and other commodities to concrete walls and floors. Typically, a hole is drilled into the concrete and the anchor is set to manufacturers directions. There are several suppliers of concrete anchor bolts with a variety of styles. Construction site installation specifications or instructions must be followed when installing any type of concrete anchor. Three typical concrete anchor bolting methods include: Concrete Expansion Anchor Adhesive Bonding Maxi-Bolts To install a concrete expansion anchor, a hole is drilled in the concrete that is only slightly larger than the anchor bolt diameter. After the hole is drilled, it should be checked for proper depth, angularity, and cleanliness. The anchor is typically inserted by lightly hammering the anchor into the hole. A protective device should be used on the threads to prevent damage while hammering. After the anchor is set in the hole, the base plate is placed over the anchors and the anchor nuts tightened. The bolt anchors itself in the concrete hole by the expansion of the wedges at the bottom of the anchor bolt when the anchor nut is tightened. Adhesive anchors are installed in a similar manner as expansion anchors. The anchor hole is drilled to a prescribed size, and the hole is filled with a bonding compound or chemical cartridge. The anchor bolt is then inserted into the hole per manufacturer recommendations. The advantage of this type of anchor include: There are fewer mechanical components involved The user can be much surer of obtaining the desired holding capacity when the bolt is set The exact location of the anchor bolt holes is not critical Hangers and Supports Section 12 1996:Rev.2 Piping/Mechanical Handbook 12-15 Maxi-bolts are also installed in a similar manner as expansion anchors except that a second drilling operation is performed that cuts a conical shape at the bottom of the hole. This conical shape accepts the maxi-bolt sleeve wedges that expand when the bolt is tightened and provide the holding force that secures the bolt. This particular anchor is called a "ductile anchor". This means that failure of the anchor system will occur in the anchor bolt itself rather then from anchor withdrawal or pull-out from the concrete as can happen with the previous two systems. Do not mix different styles of concrete anchors on the same baseplate. If possible, it is also recommended that the project only use a single type of concrete anchor to reduce tooling and training. HANGER INSTALLATION GUIDELINES Check that the correct materials and sizes are installed. Check that the installation specification tolerances are satisfied. Check that the location and orientation of the pipe is correct. Check that pre-engineered components are installed per supplier instructions. Install spring cans with the travel stops in the cold load setting Verify that material substitutions are acceptable such as: Larger hanger rod sizes Larger structural shapes Thicker plate materials Locking devices should be installed on all bolted connections, by methods such as: Double nuts Half or jam nuts Staking Locking nuts Welding substitutions are normally allowed by installation specifications. One example would be placing the weld metal on the inside of a wide flange rather than on the outside of the flange. Even though the weld symbol on the hanger drawing pointed to the outside of the flange. LINE BALANCING This process sets the hanger loads at the design cold load setting position for critical systems as specified in the design documents. The process involves using several dynamometers to measure the actual loads at the hangers. A typical set-up is as follows: Verify all rigid supports are carrying a load. Verify that all piping is insulated and at ambient temperature. Water systems should be filled. Verify that the spring cans are at their cold load setting with the travel stops removed. Install the dynamometers at the first three consecutive rigid supports, counting from the terminal end. Section 12 Hangers and Supports 12-16 Piping/Mechanical Handbook 1996:Rev.2 Adjust the tension at each dynamometer until all are carrying the design cold load as indicated on the support drawing. The readings should be within plus or minus five percent of their design load reading, if not, adjust the tension in the adjacent support within the plus or minus 5 percent goal. With all the dynamometers reading their design goal, check and adjust the closest spring can if needed. Recheck the dynamometers on the end and adjust if required. Transfer the load from the first dynamometer to the hanger by adjusting or shim as needed. After the load transfer, check the other supports again and if within range, remove the dynamometer and proceed to the next hanger. Set-up and adjust the next hanger down the line. Repeat for the second and third and continue the process on down the line. When branches exist, do one branch at a time. Branches less than 2 inch are generally excluded from the balancing process. Pump Alignment Pump alignments are easier when the first few piping supports closest to the pump are adjustable. If a rigid hanger is within the first few supports, have the hanger built with larger gaps around the pipe and position the pipe correctly with shims. The shims should only be tack welded to allow for possible future modification during pump alignment.
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