Pipe Assemblies and Fittings Fabrication PDF

Pipe Assemblies and Fittings Fabrication of Tube Assemblies Fabrication of tube assemblies consists of tube cutting, deburring, bending and tube joint preparation. The procedures found in this topic are for instructional purposes and cover MS and AN fittings only. Permaswage, Dynatube...

Pipe Assemblies and Fittings Fabrication of Tube Assemblies Fabrication of tube assemblies consists of tube cutting, deburring, bending and tube joint preparation. The procedures found in this topic are for instructional purposes and cover MS and AN fittings only. Permaswage, Dynatube, Rynglok and other connector systems that require specialised tooling are not covered. Expansion and contraction of straight runs of tubing cause excessive pressure on the assembly. Provide enough bend in the tubing to accommodate changes in length caused by environmental and operating conditions. Note: When fabricating tube assemblies, always refer to the manufacturer’s specifications for both material type and fabrication procedures. Calculating Flat Pattern Layout for Tube Bending As with bracket development, the tradesperson must be able to accurately calculate setbacks, bend allowance and flats for manufacturing tube assemblies. The illustration below shows some of the components required for the tube-bending process. Bend radius calculated from centre of tube 2023-11-16 B1-07d Maintenance Practices Page 53 of 335 CASA Part Part 66 - Training Materials Only  Calculating the Setback To calculate the setback required in the manufacture of tubing from a drawing, use the following formula: For 90° bends: F or 90° bends ⟹ SB = (R + 0.5 D) For other angles: F or other angles ⟹ SB = K (R + 0.5 D) R is the bend radius, D is the tube diameter and K is obtained using the K setback chart. K Chart 2023-11-16 B1-07d Maintenance Practices Page 54 of 335 CASA Part Part 66 - Training Materials Only  Calculating the Bend Allowance To calculate bend allowances, use the Bend Allowance Chart, if available. Otherwise, use the bend allowance formula shown below: angle of bend 2πR 360° Calculating Flats To calculate a flat, subtract the setback for each bend from the overall dimension. This leaves the flat dimension. Calculating Overall Length When calculating length, divide the bent object into flats and bend allowances, then number them progressively as shown below. Calculate each length independently, as in 1–2, 2–3, 3–4, etc., then lay out the calculations as follows: Flat 1–2 = X.XXX BA 2–3 = X.XXX Flat 3–4 = X.XXX BA 4–5 = X.XXX Flat 5–6 = X.XXX Development Length = Total (i.e. 1–2 + 2–3 + 3–4 + 4–5 + 5–6) The cutting size equals the development length. Stick diagram of tubing development 2023-11-16 B1-07d Maintenance Practices Page 55 of 335 CASA Part Part 66 - Training Materials Only  Tube Bending The objective in tube bending is to obtain a smooth bend without flattening the tube. Acceptable and unacceptable bends are shown in the illustration. Bending is usually done by using a mechanical or hand-operated tube bender. In an emergency, soft, non-heat-treated aluminium tubing smaller than 1/4 in. in diameter may be bent by hand to form the desired radius. Acceptable and unacceptable tubing bends The minimum bend radius is 2.5 to 3 times the OD. Thin-walled tubing installed in aircraft fluid systems must not be bent with a radius smaller than that, as shown. Tube bending is determined by the radius measurements. Note: The bend radius is measured to the centreline of the tubing. 2023-11-16 B1-07d Maintenance Practices Page 56 of 335 CASA Part Part 66 - Training Materials Only  Minimum bend radius for tubing bends Minimum bend radius for tubing bends table 2023-11-16 B1-07d Maintenance Practices Page 57 of 335 CASA Part Part 66 - Training Materials Only  Hand Tube Bender The hand-operated tube bender, shown below, consists of a handle, radius block, clip and slide bar. The handle and slide bar are used as levers to provide the mechanical advantage necessary to bend tubing. The radius block is marked in degrees of bend ranging from 0 to 180. The slide bar has a mark that aligns with the zero mark on the radius block. The tube is inserted in the tube bender, and after lining up the marks, the slide bar is moved around until the mark on it reaches the desired degree of bend on the radius block. Bending tubing with hand-operated tube bender 2023-11-16 B1-07d Maintenance Practices Page 58 of 335 CASA Part Part 66 - Training Materials Only  Mechanically-Operated Tube Bender The tube bender shown below is a heavy-duty bench model. It is designed for use with larger diameter, aircraft grade, high-strength, stainless-steel tubing as well as all other metal tubing. It is designed to be fastened to a bench or tripod, and the base is formed to provide a secure grip in a vice. The simple hand bender above uses the handle and slide bar as levers to provide the mechanical advantage necessary to bend the tubing, while the mechanically operated tube bender employs a hand crank and gears. The forming die in the hand bender is keyed to the drive gear and secured by a screw. The forming die on the mechanical tube bender is calibrated in degrees similar to the radius block of the hand-type bender. A length of replacement tubing may be bent to a specified number of degrees, or it may be bent to duplicate the bend in the damaged tube or pattern. The latter is accomplished by laying the pattern on top of the tube being bent and slowly bending the new tube as required. Mechanically-operated tube bender 2023-11-16 B1-07d Maintenance Practices Page 59 of 335 CASA Part Part 66 - Training Materials Only  Tube Cutting When cutting a new piece of tubing, always cut it approximately 10% longer than the tube being replaced. This provides a margin of safety for minor variations in bending. After determining the correct length, cut the tubing with either a fine-tooth hacksaw or a roller type tube cutter. A tube cutter is most often used on soft metal tubing such as copper, aluminium or aluminium alloy. However, it is not suitable for stainless steel tubing because it tends to work harden the tube. To use a tube cutter, begin by marking the tube with a felt-tip pen or scriber. Next, place the tubing in the cutting tool and align the cutting wheel with the cutting mark. Once these are aligned, gently tighten the cutting wheel onto the tube using the thumbscrew. When the cutting wheel is snug, rotate the cutter around the tube and gradually increase pressure on the cutting wheel every one to two revolutions. Be careful not to apply too much pressure at one time, as it could deform the tube or cause excessive burring. Mechanically-operated tube cutter When cutting tubing, it is important to produce a square end, free of burrs. Once the tube is cut, carefully remove any burrs from inside and outside the tube, using a de-burring tool as shown. This tool can remove both the inside and outside burrs by just turning the tool end for end. When performing the deburring operation, use extreme care not to reduce or fracture the wall thickness of the tubing. Very slight damage of this type can lead to fractured flares or defective flares which will not seal properly. If the tube is to be flared, the cut end should be polished with a fine abrasive paper or pad to remove any sharp edges that could cause the tubing to crack. 2023-11-16 B1-07d Maintenance Practices Page 60 of 335 CASA Part Part 66 - Training Materials Only  Mechanically-operated tube cutter - removing sharp edges Tube Flaring Tube Joint Preparation The two major tube joints are the flared fitting and the flareless fitting. Preparation for these tube joints differs. Flared Fitting The two types of flared tubing joints are the single-flared joint and the double-flared joint. Use the tube flaring tool to prepare tube ends for flaring. Check tube ends for roundness, square cut and cleanliness, and be certain there are no draw marks or scratches. Tube flaring tool (single-flare) 2023-11-16 B1-07d Maintenance Practices Page 61 of 335 CASA Part Part 66 - Training Materials Only  Tube flaring tool Draw marks can spread and split the tube when it is flared: Use a de-burring tool to remove burrs from the inside and outside of the tubing. Remove all filings, chips and grit from the inside of the tube and clean it. Slip the fitting nut and sleeve onto the tube. Place the tube into the proper size hole in the grip die. Centre the plunger over the end of the tube, tighten the handle to secure the tube in the grip die and hold the yoke in place. Turn the handle to form the flare. Do not over tighten as this can damage the flare. Loosen the handle and remove the tube from the grip die. Check to make sure that no cracks are evident and that the flared end of the tube is no larger than the largest diameter of the sleeve being used. Tube flare (single-flare) table 2023-11-16 B1-07d Maintenance Practices Page 62 of 335 CASA Part Part 66 - Training Materials Only  Double flare Double Flare are used with small diameter soft aluminium alloys, to reinforce the flare. Double flares are formed with a special tool (Image below). As with a single flare check the ends for roundness, square cut and cleanliness, and be certain there are no draw marks or scratches. Double Flare Manufacture 2023-11-16 B1-07d Maintenance Practices Page 63 of 335 CASA Part Part 66 - Training Materials Only  Flareless Fitting The heavy-walled tubing used in some high-pressure systems is difficult to flare. For these applications, the flareless fitting is designed to produce leak-free attachments without flares. Pre- setting is necessary to form the seal between the sleeve and the tube without damaging the connector. It should always be accomplished with a pre-setting tool, such as the one shown below. These tools are machined from tool steel and hardened so that they may be used with a minimum of distortion and wear. Special procedures are used in the pre-setting operation. Select the correct size pre-setting tool or a flareless fitting body. Clamp the pre-setting tool or flareless fitting body in a vice. Slide a nut and then a sleeve onto the tube, and make sure the pilot and cutting edge of the sleeve points towards the end of the tube. Lubricate the fitting, insert the ram and tap lightly with a hammer or mallet until the upset flare punch contacts the die blocks and the die blocks are set against the stop plate on the bottom. Place the tube end firmly against the bottom of the pre-setting tool seat as shown while slowly screwing the nut onto the tool threads with a wrench until the tube cannot be rotated with thumb and fingers. At this point, the cutting edge of the sleeve is gripping the tube and preventing tube rotation; the fitting is ready for the final tightening force needed to set the sleeve on the tube. Tighten the nut to the number of turns specified in the maintenance manual. Pre-set sleeve After pre-setting, unscrew the nut from the pre-setting tool or flareless fitting body; check the sleeve and tube. 2023-11-16 B1-07d Maintenance Practices Page 64 of 335 CASA Part Part 66 - Training Materials Only  Flareless fitting The sleeve cutting lip should be embedded into the tube's outside diameter between 0.003 and 0.008 in., depending on the size and tubing material. A lip of tube material will be raised under the sleeve pilot. The sleeve should be bowed slightly. It may rotate on the tube and have no lengthwise movement. The sealing surface of the sleeve, which contacts the 24° angle of the fitting body seat, should be smooth, be free from scores, and show no lengthwise or circular cracks. The minimum internal tube diameter should not be less than the value shown in the table below. Minimum inside diameter of tubing 2023-11-16 B1-07d Maintenance Practices Page 65 of 335 CASA Part Part 66 - Training Materials Only  Beading Tubing may be beaded with a hand beading tool, with machine beading rolls or with grip dies. The method depends on the diameter and wall thickness of the tube and the material from which it was made. Hand beading tool The hand beading tool is used with tubing of 1⁄4- to 1-in. outside diameter. The bead is formed by using the beader frame with the proper rollers attached. The inside and outside of the tube are lubricated with light oil to reduce the friction between the rollers during beading. The sizes, marked in 16ths of an inch on the rollers, are for the outside diameter of the tubing that can be beaded with the rollers. Separate rollers are required for the inside of each tubing size, and care must be taken to use the correct parts when beading. The hand beading tool works somewhat like the tube cutter in that the roller is screwed down intermittently while the beading tool is rotated around the tubing. In addition, a small vice (tube holder) is furnished with the kit. For larger tube diameters machines are available. When installing a hose between beaded tubes, it is important that they do not have an excessive offset or angle to each other. 2023-11-16 B1-07d Maintenance Practices Page 66 of 335 CASA Part Part 66 - Training Materials Only  Hose clamp mounting Minimum Gap 'G" shall be 1/2 inch or tube OD/4 whichever is greater Maximum Gap "G" is not limited except on suction lines, where Maximum "G" shall be 1.5 inches or one tube diameter, whichever is greater. 2023-11-16 B1-07d Maintenance Practices Page 67 of 335 CASA Part Part 66 - Training Materials Only  Rigid Tube Installation Pre-installation Before installing a rigid tube, carefully inspect it for nicks, scratches and dents. Ensure the mating surfaces are clean to ensure a good seal, and ensure that the fittings and unions are serviceable. Other considerations during tube installation: Never apply sealing compound or anti-seize to a fitting’s sealing surfaces. Ensure line assembly is properly aligned prior to installing. Never use a wrench to start a nut onto a fitting – the nut must run down by hand only. A tubing installation under tension is undesirable, so never pull an assembly into alignment by tightening the nut. Always install fittings to the specified torque as over-tightening may damage the sealing surface or cut off the flare. All fluid lines should be routed through the aircraft to achieve the shortest practical length. All fluid lines should follow structural members of the aircraft. Scratch limitations Scratches in tubes for fluid systems with working pressures of 500 psi or greater shall not exceed 5% of the tube’s nominal wall thickness. Working pressures less than 500 psi shall not exceed 10% of the tube’s nominal thickness. Dent limitations A dent less than 20% of the tube diameter is permitted if it is not in the heel of a bend. Tube Flatness The tube flatness for fluid systems with working pressures of 1000 psi or greater must not exceed 5%, and working pressures less than 1000 psi must not exceed 10% of the tube OD. Tube flatness 2023-11-16 B1-07d Maintenance Practices Page 68 of 335 CASA Part Part 66 - Training Materials Only  Wrinkle or Kink Limitations Any wrinkles or kinks in tubes for fluid systems with working pressures of 500 psi or greater must not exceed 1% of the tube OD, and working pressures less than 500 psi must not exceed 2% of the tube OD. Wrinkle or kink limitations Typical Repairs Occasionally, it may be necessary to repair or replace damaged aircraft fluid lines. Very often the repair can be made simply by replacing the tubing. However, if replacements are not available, the needed parts may have to be fabricated. Replacement tubing should be of the same size and material as the original tubing. All tubing is pressure-tested prior to initial installation and is designed to withstand several times the normal operating pressure to which it will be subjected. If a tube bursts or cracks, it is generally the result of excessive vibration, improper installation or damage caused by collision with an object. All tubing failures should be carefully studied and the cause of the failure determined. Typical repairs 2023-11-16 B1-07d Maintenance Practices Page 69 of 335 CASA Part Part 66 - Training Materials Only  Clamps Unless otherwise specified, where tubing is supported to structure or other rigid members, a minimum clearance of 1/16 in. or, where related motion of adjoining components exists, a minimum clearance of 1/4 in. is to be maintained. The table shows the maximum allowable distance between supports. Flexible grommets or hose should be used at points where the tubing passes through bulkheads. You should check clamps to make sure they are the correct type and size, that the position of the hose is correct within the clamp, and that the cushion material is positioned correctly. Maximum distance and supports for tubing table 2023-11-16 B1-07d Maintenance Practices Page 70 of 335 CASA Part Part 66 - Training Materials Only  Tube securing to airframe Cushioned P clamp 2023-11-16 B1-07d Maintenance Practices Page 71 of 335 CASA Part Part 66 - Training Materials Only  Installation Be sure that the tube assembly is properly aligned before tightening the fittings. Do not pull the tubes into place with torque on the nut. Rigid tubing expands and contracts under pressure and is subject to vibration and therefore should have at least one bend to remove stress (see the illustration). The pipe should be located so that it can be supported by clamps, removing these stresses from the fittings. Some operators may require the application of a witness mark across the union after installation as an indicator for loose nuts, as shown. Rigid tube installation 2023-11-16 B1-07d Maintenance Practices Page 72 of 335 CASA Part Part 66 - Training Materials Only  Hose Assemblies and Fittings Fabricating Hose Assemblies Fabricating hose assemblies from bulk hose and reusable end-fittings requires some basic skills and a few hand tools. The skills required are the ability to follow step-by-step instructions and to use the required hand tools. Equipment and tools The basic hand tools required to fabricate hose assemblies up to 3000 psi operating pressure are a bench vice, a hose cut-off machine, a fine-tooth hacksaw, open-end wrench sets, a sharp knife, slip- joint pliers, an oil can for lubricating oil, a marking pencil, a small paintbrush, masking or plastic electrical tape, a steel ruler, a thickness gauge (leaf type) and a protractor. Mandrels are special hand tools (shown below) that are not required but are recommended for fabricating hose assemblies. Mandrel kit During hose assembly fabrication, mandrels protect sealing surfaces, support inner tubes and guide fitting nipples into hoses. Using a mandrel also reduces the possibility of damaging the hose while installing the nipple. If the nipple is misaligned, it will skive a shaving from the inside of the hose. A common, and potentially very dangerous, method of removing the skived piece of rubber is to take a piece or rod or tubing and try to poke it loose. During this process, a flap of hose liner can be cut without being noticed. The hose then contains a one-way flapper valve that is waiting to create a failure of fluid flow. 2023-11-16 B1-07d Maintenance Practices Page 73 of 335 CASA Part Part 66 - Training Materials Only  Procedures When failure occurs in a flexible hose equipped with swaged end fittings, the unit is generally replaced without attempting a repair. The correct length of hose, complete with factory-installed end fittings, is ordered from a supplier or drawn from inventory. When failures occur in hose assemblies equipped with reusable style end fittings, fabricating the replacement unit is the task of the technician. Undamaged end fittings on the old length of hose may be removed and reused; otherwise, new fittings must be drawn from inventory along with a sufficient length of hose. The first step is to determine the necessary hose length from the table and diagram. Hose cut-off factor (in inches) Determining hose assembly length 2023-11-16 B1-07d Maintenance Practices Page 74 of 335 CASA Part Part 66 - Training Materials Only  Once the hose length is determined, add 5%–8% to allow for expansion or contraction from pressure application. Wrap the circumference of the hose with masking or plastic electrical tape at the cut-off to prevent braid flare-out if the hose outer cover is wire braid. Hose with a rubber or fabric outer cover does not require wrapping with tape. Measure the hose to the required length and cut off the required length, making sure it is square, using a cut-off machine. Blow the hose clean with filtered shop air after cutting. Remove the tape and the clamp socket in a vice. Hose end fitting installation A Hose end fitting installation B 2023-11-16 B1-07d Maintenance Practices Page 75 of 335 CASA Part Part 66 - Training Materials Only  Hose end fitting installation C Hose end fitting installation D Do not over-tighten a vice on thin-walled lightweight fittings. Screw the hose anti-clockwise into the socket using a twisting, pushing motion until the hose bottoms on the socket shoulder. Back the hose out a quarter turn. Assemble the nipple and nut with a standard matching the inside diameter of the hose. Nipples have three configurations for the hose-to-tube or component surface-sealing portion: flared, flareless and flanged. The socket fits over the outside diameter of the hose and secures one end of the nipple to the hose. The swivel nut or flange secures the other end of the nipple to the mating connection in the fluid system. The table shows typical hose end fittings. For Teflon® hose, some manufacturers have a sleeve in addition to the nipple, socket, and nut or flange. Each manufacturer may have unique characteristics and tolerances that prevent interchangeability between parts. 2023-11-16 B1-07d Maintenance Practices Page 76 of 335 CASA Part Part 66 - Training Materials Only  Do not intermix nipples and sockets from one manufacturer to another. Hose fittings are identified by applicable MIL specification (MS) and manufacturer's name or trademark on fittings and nuts. Flared or flareless fittings and nuts are colour-coded to show materials for hose fittings and sleeves. Pressure Test Stands All flexible hose manufactured in the shop must be hydraulic or pneumatic pressure tested prior to installation in the aircraft. Some aircraft manufacturers may give standard pressures for testing; most refer to FAA specifications. Fabricated hoses must be tested to 1.5 times system pressure. A new purchased hose from a approved vendor can be operationally checked after installation in the aircraft by using system pressure in lieu of pressure testing. Most maintenance facilities have an existing method of testing assembled hoses. Be sure to check the operation of any fabricated hoses and follow all safety procedures. Any hose assembly failing the pressure test can be very dangerous to personnel and property. Pressure test stand 2023-11-16 B1-07d Maintenance Practices Page 77 of 335 CASA Part Part 66 - Training Materials Only  Pre-installation Procedures Check hose or hose assembly installations carefully to make sure identification bands and protective closures are present as required after proof pressure testing. Proper routing and clamping are mandatory. If retaining wires on swivel nuts are backed out, replace the hose assembly. Look for kinks or twists. Observe the lay line, if possible. A kinked hose or hose assembly must be replaced. One that is twisted may be relieved by loosening clamps and swivel nuts, and then straightening the hose by hand. Re-torque the swivel nuts and tighten the clamps. A preformed hose or hose assembly may have a smaller bend radius; do not attempt to straighten it. Lay line Inspect hose for proper type and size, and for aging (signs of deterioration such as cracks, discoloration, hardening, UV / Heat damage). Check the braid for broken wires. Evidence of internal restriction of tube due to collapse, kinking, wire-braid puncture or other damage. Look for flaring or fraying of the braid. Look for blisters, bubbles or bulging. Inspect for corrosion. A hose that has carbon steel wire braid is subject to corrosion, which may be detected as brownish rust colouration penetrating the outer braid. Inspect end fittings for proper type and size, corrosion and cleanliness, nicks, scratches or other damage to the finish that affects corrosion resistance. Look for damage to threaded areas, cone-seat sealing surfaces and flange fittings; warping of the flange; and nicks or scratches on the sealing surface or gasket. 2023-11-16 B1-07d Maintenance Practices Page 78 of 335 CASA Part Part 66 - Training Materials Only  Fraying Rejection Standards Rejection and replacement of hose or hose assemblies after inspections are based on the standards normally specified in the applicable maintenance instruction manual or maintenance requirement cards. Where rejection standards are not specifically outlined or if doubt exists as to the acceptability of a hose or hose assembly, replace it. Installing Hose or Hose Assemblies There are guidelines you should remember about installing hose or hose assemblies. The replacement part must be a duplicate of the one removed in length, outside diameter, material, type, contour and associated markings. Fluid used as a lubricant for fitting installation should be spelled out in the maintenance manual. If it is not, use only the fluid the particular hose will contain. To use anything else is to risk cross contamination. Compatible oil, approved for the purpose, may be used in all other types of fuel, oil and coolant hose installations. When you install or handle hose or hose assemblies, you can sustain injuries to your hands or damage to the hose if it is kinked. Take care to prevent situations where injuries or kinking can occur. A hose that is bent to a smaller radius than specified might cause kinking. Minimum bend radii are contained in either the maintenance manual or approved aircraft documentation. Also, kinking is more likely to occur in a preformed hose assembly, one that has become set-to-shape in its operating position, one that is straightened or handled without a protective restraint, or one that is twisted during handling, removal or installation. 2023-11-16 B1-07d Maintenance Practices Page 79 of 335 CASA Part Part 66 - Training Materials Only  Installation Procedures Remove the protective closures from hydraulic lines, hose or hose assemblies. When possible, install hose or hose assemblies so that identification markings are visible. Install them without twisting, chafing, or over bending. Observe the bend radius. A greater bend radius is preferred where possible. Allow enough slack in the hose line to provide for component movement and possible changes in length when pressure is applied. The hose may change in length from +2% to -4%, depending on hose construction. Length contraction may occur under pressure impulses, and hose routing must take this into account. Finger tighten swivel connector nuts to avoid stripping threaded areas of fittings. Before applying final torque to end fittings, make sure hose assemblies are properly aligned and free of twists and kinks. Complete tightening by using torque values specified in the applicable maintenance manual. Hold the fitting stationary with one wrench and use a torque wrench to tighten the swivel nut. When applying final torque, hold the hose manually to prevent rotation and scoring of the fitting's sealing surface. Lockwire the swivel nut (if applicable). Support the flexible hose or hose assemblies by routing and clamping them securely to avoid abrasion and kinking where flexing occurs. Cushion-type clamps should be used to prevent chafing. Make sure support clamps do not restrict hose travel or subject the hose or hose assembly to tension, torsion, compression or shear stress during flexing cycles. Where flexing is required in an installation, bend the hose in the same plane of movement to avoid twisting. Installation 2023-11-16 B1-07d Maintenance Practices Page 80 of 335 CASA Part Part 66 - Training Materials Only  Installation 2023-11-16 B1-07d Maintenance Practices Page 81 of 335 CASA Part Part 66 - Training Materials Only