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AMAZON multi-meters discounts AMAZON oscilloscope discounts Fundamentals of Piping Design Criteria It’s certainly not within the scope of this text to deal extensively with piping design and installation criteria; however, there are certain fundamentals which can have an impact on machinery reliability. These must be appreciated by the machinery engineer if he is to retain a good overview of the integrated machinery system. Some key installation procedures and verification criteria are, therefore, included for the machinery engineer's benefit. The design of a piping system consists of the design of pipe, flanges, bolting, gaskets, valves, fittings, and other pressure components such as expansion joints. It also includes pipe supporting elements but does not include the actual support structures such as building steel work, stanchions or foundations, etc. Piping Design Procedure These steps need to be completed in the design of any piping system: • Selection of pipe materials • Calculation of minimum pipe wall thickness for design temperatures and pressures (generally per ANSI B31.3) • Establishment of acceptable layout between terminal points for the pipe • Establishment of acceptable support configuration for the system • Flexibility stress analysis for the system to satisfy the design criteria stipulated by ANSI B31.3 This flexibility analysis is intended to verify that piping stresses, local component stresses and forces/moments generated at the terminal points are within the acceptable limits throughout all anticipated phases of normal and abnormal operation of the plant during its life. Design Considerations A piping system constitutes an irregular space frame into which strain and attendant stress may be introduced by initial fabrication and erection, and also may exist due to various circumstances during operation. Example: three pumps taking suction from and/or discharging into a common header, as shown in FIG. 1. One or two of the three pumps removed for shop repair. Each piping system must be designed with due consideration to these circumstances for the most severe conditions of coincident loading. The following summarizes possible imposed loads that typically need to be considered in a piping design: FIG. 1. Flexibility analysis must consider: • All pumps operating simultaneously • Effect of any pump used as non-running standby spare, or blocked off for maintenance. Design Pressure Loads The pressure at the most severe condition of coincident internal or external pressure and temperature expected during normal operation. Weight Loads • Dead weight loads including pipe components, insulation, etc. • Live weight loads imposed by service or test fluid, snow and ice, etc. Dynamic Loads • Design wind loads exerted on exposed piping systems • Earthquake loads must be considered for piping systems where earthquake probability is significant • Impact or surge loads typically due to water hammer, letdown, or discharge of fluids • Excessive vibration arising from pressure pulsations, resonance caused by machinery excitations or wind loads Thermal Expansion/Contraction Effects • Thermal and friction loads due to restraints preventing free thermal expansion • Loading due to severe temperature gradients or difference in expansion characteristics Effects of Support, Anchor, and Terminal Movements • Thermal expansion of equipment • Settlement of equipment foundations and/or piping supports The When, Who, What, and How of Removing Spring Hanger Stops Associated with Machinery Initial Tasks Prior to Machinery Commissioning • Align machinery without pipe attached • Adjust pipe for proper fit-up and make connection • Observe alignment of machinery with pipe being attached. If excessive movement is noted, the pipe is to be disconnected and modified until misalignment is brought within the limits permitted. • If the pipe is greater than 8 in. NPS, one may need to add sandbags or similar weights to the pipe at the hanger adjacent to machinery to simulate the operating condition of the pipe. • Pull stops on all system hangers • Check to determine that no hanger travel indicator moves out of the "1/3 total travel" cold setting zone. If travel is excessive, refer immediately to the design contractor for modifications of support. • Adjust the hanger to return travel marker to the "C" position • Record alignment of machinery • Reinstall piping system hanger stops Final Check, Immediately Prior to Machinery Operation • Disconnect or dismantle piping as necessary • Flush and/or steam blow • Re-pipe and realign • Weight the hanger adjacent to the machinery • Pull system pins, check "C" settings and fine tune hangers. If travel is excessive (out of the 1/3 total "C" zone) contact the designated piping engineer for resolution. Flange Jointing Practices These steps can be written up in checklist format allowing field personnel to use piping-related guidelines in an efficient manner, as shown in the appendices at the end of this section. The importance of getting flanged joints right the first time cannot be overemphasized if trouble-free performance during startup is desired. In order to obtain an adequate joint the first time we must assure ourselves that the contractor, subcontractor, and the working crews appreciate the importance of quality workmanship needed during each stage of the flange joint building process. This includes materials handling and storage operations, piping prefabrication, erection, and bolting-up procedures. Time spent in covering preventive measures, supervision and crew guidance, and/or training (if needed), and assuring adequate quality control will pay dividends. Primary Causes of Flange Leakage Several common causes of flange leakage are hereby outlined to create an awareness of the effects of poor inspection procedure or materials: Uneven Bolt Stress. Flanges bolted up unevenly cause some bolts to be nearly loose while others are so heavily loaded that they locally crush the gasket. This causes leaks, particularly in high-temperature service where the heavily-loaded bolts tend to relax with subsequent loosening of the joint. Improper Flange Alignment. Unevenly bolted joints, improper alignment, and especially lack of parallelism between flange faces can cause uneven gasket compression, local crushing, and subsequent leakage. Proper centerline alignment of flanges is also important to assure even compression of the gasket. See FIG. 2 for general guidance. Improper Centering of Gasket. A gasket which is installed so that its centerline does not coincide with the flange centerline will be unevenly compressed, thereby increasing the possibility of subsequent leakage. Spiral-wound and double-jacketed high-temperature gaskets are provided with a centering ring or gasket extension to the ID of the bolt circle to facilitate centering of the gasket. Even so, the gasket should be centered with respect to the bolt circle. Certain asbestos replacement gaskets should be cut so that the OD extends to the ID of the bolt circle. FIG. 2. Dimensional variations permitted for piping and flanges are independent of pipe size. Dirty or Damaged Flange Faces. These are obvious causes for leakage since damage or dirt (including scale) can create a leakage path along the flange face. Damage includes scratches, protrusions (e.g., weld spatter) and distortion (warpage) of the flange. Excessive Forces in the Piping System at Flange Locations. This can occur because of improper piping flexibility design, or by excessive application of force to attain flange alignment. Improper location of temporary or permanent restraints or supports will also cause high flange bending moments and forces. The Importance of Proper Gasket Selection The following discussion covers some of the more important factors relating to gasket size and type. Flanges are designed to accommodate specific sizes and types of gaskets ( FIG. 3). When the gasket does not meet the requirements necessary to ensure good seating, or is crushed by the bolt load, leakage will result. Heat exchanges girth flanges are more closely tailored to one specific gasket than are piping flanges per ANSI B16.5. Therefore, somewhat greater latitude is possible with the latter. Gasket Width The width of a gasket is considered in the design of a flange. For a given bolt load, a narrow gasket will experience a greater unit load than a wide gasket. It is, therefore, important to determine that the proper width gasket has been used. • For piping gaskets made of an asbestos-replacing material consult ANSI B16.5 • For double-jacketed, corrugated gaskets consult API 601 • For spiral-wound gaskets consult API 601 • For heat exchanger girth flanges, consult the exchanger drawings A common reason for gasket leakage is the use of gaskets which are too wide because of the erroneous impression that the full flange face must be covered. This is not true. The above standards should always be followed. Gasket Thickness Gasket thickness determines its compressibility and the load required to seat it. The thicker the gasket, the lower the load necessary for seating. FIG. 3. Principal flange configurations. FIG. 4. Forces acting on a gasket. All piping flanges are designed to take 1/16 in. thick asbestos-replacement gaskets. The 1/16 in. thickness assures sufficient compressibility to accommodate slight facing irregularities while having a sufficiently high seating load to prevent blowout. One-sixteenth in. thick gaskets should always be used with ANSI B16.5 flanges unless a specific design check has been made to verify another thickness. Spiral-wound and double-jacketed gasket thickness should comply with API 601. Flange Types and Flange Bolt-Up Factors Affecting Gasket Performance A gasket is any deformable material that, when clamped between essentially stationary faces, prevents the passage of media across the gasketed connection ( FIG. 4). Compressing the gasket material causes the material to flow into the imperfections of the sealing areas and effect a seal. This bond prevents the escape of the contained media. In order to maintain this seal, sufficient load must be applied to the connection to oppose the hydrostatic end force created by the internal pressure of the system. Gasket performance depends on a number of factors, including: 1. Gasket metal and filler material: The materials must withstand the effects of: a. Temperature: Temperature can adversely affect mechanical and chemical properties of the gasket, as well as physical characteristics such as oxidation and resilience. b. Pressure: The media or internal piping pressure can blow out the gasket across the flange face. c. Media: The gasket materials must be resistant to corrosive attack from the media. 2. Joint design: The force holding the two flanges together must be sufficient to prevent flange separation caused by hydrostatic end force resulting from the pressure in the entire system. 3. Proper bolt load: If the bolt load is insufficient to deform the gasket, or is so excessive that it crushes the gasket, a leak will occur. 4. Surface finish: If the surface finish is not suitable for the gasket, a seal won’t be effected. Spiral Wound Gaskets Manufactured in Accordance with American Society of Mechanical Engineers (ASME) B16.20 Spiral wound gaskets made with an alternating combination of formed metal wire and soft filler materials form a very effective seal when compressed between two flanges. A "V"-shaped crown centered in the metal strip acts as a spring, giving gaskets greater resiliency under varying conditions. Filler and wire material can be changed to accommodate different chemical compatibility requirements. Fire safety can be assured by choosing flexible graphite as the filler material. If the load available to compress a gasket is limited, gasket construction and dimensions can be altered to provide an effective seal. A spiral wound gasket may include a centering ring, an inner ring, or both. The outer centering ring centers the gasket within the flange and acts as a compression limiter, while the inner ring provides additional radial strength. The inner ring also reduces flange erosion and protects the sealing element. Resiliency and strength make spiral wound gaskets an ideal choice under a variety of conditions and applications. Widely used throughout refineries and chemical processing plants, spiral wound gaskets are also effective for power generation, aerospace, and a variety of valve and specialty applications. The spiral wound gasket industry is currently adapting to a change in the specification covering spiral wound gaskets. Previously API 601, the new specification is ASME B16.20. These specifications are very similar, and experienced gasket producers follow manufacturing procedures in accordance with the guidelines set forth in the ASME B16.20 specifications. (See FIG. 5 for markings.) Torque Tables Tables 1 through 4-4 are representative of tables that were developed to be used with Garlock spiral wound gaskets. They are to be used only as a general guide. Also they should not be considered to contain absolute values due to the large number of uncontrollable variables involved with bolted joints. If there is doubt as to the proper torque value to use, we suggest that the maximum value be used. FIG. 5. Gasket identification markings required by ASME B16.20. Table 1 Torque Tables for Spiral Wound Gaskets, ASME B16.5 Table 2 Torque Tables for Spiral Wound Gaskets, ASME B16.5 Tables are based on the use of bolts with a yield strength of 100,000 psi. WARNING: Properties/applications shown throughout this brochure are typical. Your specific application should not be undertaken without independent study and evaluation for suitability. For specific application recommendations consult Garlock. Failure to select the proper sealing products could result in property damage and/or serious personal injury. Performance data published in this brochure has been developed from field testing, customer field reports and/or in-house testing. While the utmost care has been used in compiling this brochure, we assume no responsibility for errors. Specifications subject to change without notice. This edition cancels all previous issues. Subject to change without notice. Table 3 Torque Tables for Spiral Wound Gaskets, ASME B16.5 Table 4 Torque Tables for Spiral Wound Gaskets, ASME B16.5 All bolt torque values are based on the use of new nuts (ASTM A194, GR 2H) and new bolts (ASTM A193, GR 87) of proper design, accept able quality, and approved materials of construction as well as metallurgy. It’s also required that two hardened steel washers be used under the head of each nut and that a non-metallic-based lubricant (i.e., oil and graphite) be used on the nuts, bolts, and washers. The flanges are assumed to be in good condition and in compliance with ASME B16.5 specifications. Special attention should be given to seating surface finish and flatness. Only torque wrenches that have been calibrated should be used. The proper bolt tightening pattern must be followed (see FIG. 6 for proper bolting pattern) with the desired ultimate torque value arrived at in a minimum of three equal increments. All bolts in the flange should then be checked in consecutive order in a counterclockwise direction. The contact dimensions listed are taken from the inside diameter (ID) and outside diameter (OD) of the windings, which are different from the ASME ring gasket dimensions. No provisions have been made in these tables to account for vibration effects on the bolts. These tables are based on ambient conditions, without compensation for elevated temperatures. If conditions different from these exist, we suggest that further analysis be performed to determine the appropriate torque values. Gasket Installation In a flanged connection, all components must be correct to achieve a seal. The most common cause of leaky gasketed joints is improper installation procedures. FIG. 6. Installation sequence for 4-, 8-, and 16-bolt flanges. Bolting Procedures • Place the gasket on the flange surface to be sealed • Bring the opposing flange into contact with the gasket • Clean the bolts and lubricate them with a quality lubricant, such as an oil and graphite mixture • Place the bolts into the bolt holes • Finger-tighten the nuts • Follow the bolting sequence in the diagrams above • During the initial tightening sequence, don’t tighten any bolts more than 30 percent of the recommended bolt stress. Doing so will cause cocking of the flange and the gasket will be crushed • Upon reaching the recommended torque requirements, do a clock wise bolt-to-bolt torque check to make certain that the bolts have been stressed evenly • Due to creep and stress relaxation, it’s essential to pre-stress the bolts to ensure adequate stress load during operation Hydrostatic Testing Precautions If hydrostatic tests are to be performed at pressures higher than those for which the flange was rated, higher bolt pressures must be applied in order to get a satisfactory seal under the test conditions. Use high-strength alloy bolts (ASTM B193 grade B7 is suggested) during the tests. They may be removed upon completion. Higher stress values required to seat the gasket during hydrostatic tests at higher than flange-rated pressures may cause the standard bolts to be stressed beyond their yield points. Upon completion of hydrostatic testing, relieve all bolt stress by 50 percent of the allowable stress. Begin replacing the high-strength alloy bolts (suggested for test conditions) one by one with the standard bolts while maintaining stress on the gasket. After replacing all the bolts, follow the tightening procedure recommended in the bolting sequence diagrams ( FIG. 6). Pre-Stressing Bolts for Thermal Expansion Bolts should be pre-stressed to compensate for thermal expansion as well as for relaxation, creep, hydrostatic end pressure, and residual gasket loads. A difference in the coefficient of thermal expansion between the materials of the flange and the bolts may change loads. In cases of serious thermal expansion, it may be necessary to apply a minimum of stress to the bolts and allow the pipe expansion to complete the compression of the gasket. A gasket with a centering guide ring should be compressed to the guide ring. A gasket without a centering guide ring must be installed with pre cautions taken to prevent thermal expansion from crushing the gasket beyond its elastic limit. Calculating Load Requirements The load requirements can be calculated from two formulas that define the minimum load required to effect a seal on a particular gasket. The two formulas are Wml and Wm2. When these formulas have been calculated, the larger load of the two is the load necessary to effect a seal. Let: p= 3.14 p = Maximum internal pressure M = Gasket factor "M" defined in FIG. 7 (M = 3 for spiral wound gaskets) Y = Seating stress "Y" defined in FIG. 7 (Y = 10,000 psi for spiral wound gaskets) N = Basic width of a gasket per chart in FIG. 8 (For raised face flanges see diagram 1a) B0 = Basic seating width of a gasket per chart, FIG. 8 (For raised face flanges, B0 = N/2) B1 = Effective seating width of a gasket; must be determined. ID = Inside diameter of gasket OD = Outside diameter of gasket For gaskets where the raised face is smaller than the OD of the gasket face, the OD is equal to the outer diameter of the raised face. Find: ID = __________ OD = __________ FIG. 7. Gasket factors "M" and "Y." FIG. 8. Effective gasket sealing width. Given the ID and OD, find the value of N. Then define B0 in terms of N (see FIG. 8): N = __________ B0 = __________ Determine if B0 is greater or less than 1/4=, then find B1: If B0 £ 1/4=, then B1 = B0; If B0 > 1/4=, then B1 = (÷B0)/2; B1 = __________ Using B1, determine G: G = OD - [(B1)(2)] Now, insert these values in the final equations to determine minimum required load: Wm1 = [p(P)(G2)/4] + [2(B1)(p)(G)(M)(P)] Wm2 =p(B1)(G)(Y) When Wm1 and Wm2 have been calculated, the larger of the two numbers is the minimum load required to seat a gasket. In most cases the available bolt load in a connection is greater than the minimum load on the gasket. If not, higher bolt stresses or changes in the gasket design are required for an effective seal. NOTE: Flange design code suggestions for low-pressure applications calling for minimum seating stress (Y value) are sometimes inadequate to seat the gasket because the bolting and flange rigidity are insufficient to effect a proper seal. Care should be taken to ensure that flange conditions provide a suitable seating surface. For internal pressure to be contained, flange rotation and sufficient residual loads must also be considered in the flange design. General Installation and Inspection Procedure This segment covers recommended procedures relating to the preparation and inspection of a joint prior to the actual bolt-up. Obviously, high temperature piping joints in hydrogen-containing streams are less forgiving than those in more moderate service. Critical flanges are defined as joints in services in excess of 500°F and in sizes above six in. in diameter. • Indentify critical flanges and maintain records. A suitable record form is attached in FIG. 9. A suggested identification procedure is to use the line identification number and proceed in the flow direction with joints #1, #2, etc. Prior to Gasket Insertion • Check condition of flange faces for scratches, dirt, scale, and protrusions. Wire brush clean as necessary. Deep scratches or dents will require re-facing with a flange facing machine. • Check that flange facing gasket dimension, gasket material and type, and bolting are per specification. Reject non-specification situations. Improper gasket size is a common error. • Check gasket condition. Only new gaskets should be used. Damaged gaskets (including loose spiral windings) should be rejected. The ID windings on spiral-wound gaskets should have at least three evenly spaced spot welds or approximately one spot weld every six in. of circumference (see API 601). • Use a straightedge and check facing flatness. Reject warped flanges. • Check alignment of mating flanges. Avoid use of force to achieve alignment. Verify that: 1. The two flange faces are parallel to each other within 1/32 in. at the extremity of the raised face 2. Flange centerlines coincide within 1/8 in. Joints not meeting these criteria should be rejected. === FIG. 9. Typical flanged joint record form. ==== Table 5 Torque to Stress Bolts The torque required to produce a certain stress in bolting is dependent on several conditions, including: • Diameter and number of threads on bolt • Condition of nut bearing surfaces • Lubrication of bolt threads and nut bearing surfaces. The tables below reflect the results of many tests to determine the relation between torque and bolt stress. Values are based on steel bolts that have been well-lubricated with a heavy graphite and oil mixture. A nonlubricated bolt has an efficiency of about 50 percent of a well-lubricated bolt. Also, different lubricants produce results that vary from 50 to 100 percent of the tabulated stress figures. For Alloy Steel Stud Bolts (Load in pounds on stud bolts when torque load is applied) === Controlled Torque Bolt-Up of Flanged Connections Experience shows that controlled torque bolt-up is warranted for certain flanged connections. These would typically include: • All flanges (all ratings and sizes) with a design temperature >900°F • All flanges (all ratings) 12 in. diameter and larger with a design temperature >650°F • All 6 in. diameter and larger 1,500 pound class flanges with a design temperature >650°F • All 8 in. diameter and larger 900 pound class flanges with a design temperature >650°F • All flanges not accessible from a maintenance platform and >50 ft above grade Table 6 Flange and Bolt Dimensions for Standard Flanges In addition, it’s generally appropriate to apply the above criteria to: flanged connections on equipment and other components such as: • Valve bonnets, where the valve is positioned to include the above referenced design temperature/size/flange rating category • Flanged equipment closures where they qualify for inclusion in the above categories • All flanged connections which will eventually be covered with low temperature insulation within the above reference criteria Adherence to the following procedure is recommended for controlled torquing of line flanges, bonnet joints, etc., when specified. Preparation • Thoroughly clean the flange faces and check for scars. Defects exceeding the permissible limits given in Table 7 should be repaired. • Check studs and nuts for proper size, conformance with piping material specifications, cleanliness, and absence of burrs • Gaskets should be checked for size and conformance to specifications. Metal gaskets should have grease, rust, and burrs completely removed. • Check flange alignment. Out-of-alignment of parallelism should be limited to the tolerance given in FIG. 2. • Number the studs and nuts to aid in identification and to facilitate applying crisscross bolt-up procedure • Coat stud and nut thread, and nut and flange bearing surfaces with a liberal amount of bolt thread compound === Table 7 Flange Face Damage/Acceptance Criteria Type Gasket Type Used Damage Critical Defect Permissible Limits === Equipment For studs larger than 1 1/2 in. in diameter, use "Select-A-Torq" hydraulic wrench (Model 5000 A) supplied by N-S-W Corp. of Houston, Texas, the "Hydra-Tork" wrench system (Model HT-6) supplied by Torque System, Inc., the "Hytorc" ( FIG. 10), tensioners by Hydratight-Sweeney ( FIG. 11), or one of many available Furmanite "Plarad" devices ( FIG. 12). Torque wrenches can be used on small flanges, with stud diameters less than 1 1/2 in. The torque wrenches should be calibrated at least once per week. FIG. 10. "Hytorc" stud tensioner. Hot Bolting and Leakage Control Hot bolting during startup and during process runs has been found to be an important factor in minimizing flange leakage. During heat-up and because of temperature changes, the bolts and gaskets deform permanently. This causes a loss of bolt stress after the temperature changes have smoothed out. Hot bolting helps correct this. FIG. 11. Tensioners by Hydrotight-Sweeney. Hot Bolting Procedure The objective of hot bolting is to restore the original bolt stress which has dropped due to yielding and/or creep of the flange joint components. If possible, this should be done with a bolt tensioning device. Hot bolting should start at the point of leakage and proceed in a crisscross pattern as described previously. Seized bolts sometimes present a problem when hot bolting. In such cases, it’s necessary to use a wrench on both nuts. Using Bolt Tensioners There exists considerable experience with the use of various bolt tensioners for hot bolting. These procedures typically involve first running a die over the stud projections to facilitate subsequent installation of the tensioner heads. Mechanics are instructed to leave the heads in place for the minimum time necessary so as to prevent leakage of hydraulic fluid at the seals. Past procedures called for immersion of heads in water between applications; however, this is no longer necessary. FIG. 12. Furmanite "Plarad" hydraulic tensioning devices in action. Using Hammer and Wrench or Torque Wrench If leaks occur, it may be necessary to employ a 7 lb or heavier hammer to stop the leak. Tightening should first be done where the leakage has originated and the crisscross pattern should be used from there. Joints with spiral-wound gaskets can be tightened only to the limit of the steel centering ring thickness. Further tightening is fruitless if a spiral-wound gasket has already been tightened to this point. If Hot Bolting Does Not Stop Leak If leakage cannot be stopped by tightening, the line must be isolated and the joint broken to determine the cause: • Examine flange facings for damage, distortion (warping), or foreign matter • Check flange alignment, cut and realign piping if necessary • Check gasket for proper material, dimensions, and type. Use a new gasket for reassembly of the joint. • Check gasket deformation to determine if it was centered. This is best done by noting the position of the gasket before it’s withdrawn and examining it immediately after withdrawal. • Reassemble the joint • If leakage persists, piping support and flexibility must be examined. It may be necessary to revise the support system or install spring hangers to lower bending moments. • If leakage occurs during rainstorms, it will be necessary to install sheet metal rain shields, which may cover the top 180° of the flange, to prevent such leakage. These should be located about four inches away from the flange surface and should have sufficient width to cover the bolts plus two inches on each side. • If leakage occurs during sudden changes in process temperatures, examine the process sequence to determine if steps can be taken to minimize rapid heat-up or cooling of lines. It may only be necessary to open a valve more slowly. Recommendations for the Installation, Fabrication, Testing, and Cleaning of Air, Gas or Steam Piping The importance of starting any compressor with clean piping, particularly on the intake to any cylinder, cannot be over-emphasized. This is particularly important with multi-stage high-pressure compressors where special metallic packing is required and parts are much more expensive than in a low-pressure compressor. Any dirt, rust, welding beads or scale carried into the compressor will cause scored packing rings, piston rods, cylinder bores, and pitted, Leaky valves. It’s important that the piping be fabricated with sufficient flange joints so that it can be dismantled easily for cleaning and testing. It’s far better to clean and test piping in sections before actual erection than after it’s in place. If it’s necessary to conduct the final test when the piping is in position, care should be taken to provide vents at the high spots so that air or gas won’t be trapped in the piping. Make provision for complete drainage after the test is completed. These connections should be planned in advance. When piping is cleaned in sections before erection, it’s possible to do a thorough job of eliminating all acid. This is difficult to do with piping erected and in position, because carry-over of acid into the cylinders is almost certain to occur when the machine is started. This can cause extensive damage. The use of chill-rings for butt welds in piping is recommended. This prevents welding beads from getting into the pipe to carry through, not only on the original starting, but later on during operation. After hydrostatic tests have been made and the pipe sections have been cleaned as thoroughly as possible on the inside, the piping should be pickled by this procedure: 1. Pickle for 14 hours with hydrochloric acid. Circulate the acid continuously by means of a small pump. Use a five to 12 percent solution of hydrochloric acid, depending upon the condition of the pipe. 2. Neutralize the caustic. 3. Blow hot air through for several hours. 4. Fill with mineral seal oil and drain. 5. Blow out with hot air. 6. Pipe is now ready to use. If the pipe section is not to be assembled immediately, seal the ends tightly until ready for use. Then, before installation, pull through a swab saturated with carbon tetrachloride. Even though this procedure has been carefully followed; on reciprocating compressor piping, a temporary filter (such as Type PT American Filter, Type PS Air-Maze, or equal) should be installed in the suction line to the suction bottle to remove particles 230 microns (0.009 in. diameter) or larger. Provision must be made in the piping to check the pressure drop across the filter and to remove the filter cell for cleaning. Filter cell should be removed and left out only when the inlet line is free of welding beads, pipe scale, and other extraneous matter. On large piping (where a man can work inside), the pickling procedure can be omitted if the piping is cleaned mechanically with a wire brush, vacuumed and then thoroughly inspected for cleanliness. Time and trouble taken in the beginning to ensure that the piping is clean will shorten the break-in period, and may save a number of expensive shutdowns. Pickling Procedure for Reciprocating Compressor Suction Piping: Method I General Recommendations 1. The job should be executed by experienced people. 2. Operators must wear adequate safety equipment (gloves and glasses). 3. Accomplish entire pickling operation in as short a time as possible. Preliminary Work 1. Install an acid-resistant pump connected to a circulating tank. 2. Provide 1 1/2 in. (or greater) acid resistant hoses for the connections (prepare suitable assembly sketch). 3. For ensuring the filling of the system, flow must go upward and vents must be installed. 4. Provide method for heating the solutions (e.g., a steam coil). Pretreatment Pretreatment is required only when traces of grease are present. 1. Fill the system with water at 90°C (194°F). 2. Add 2 percent sodium hydroxide and 0.5 percent sodium metasilicate (or sodium orthosilicate if cheaper). If these compounds are not available and only a small amount of grease is present 2 percent of NaOH and 3 percent of Na2CO3 may be used. 3. Circulate for 20-30 minutes at 90°C (194°F). 4. Dump the solution and wash with water until pH = 7. Acid Treatment 1. Fill the system with water at 50°C (122°F). 2. Add 4 percent of Polinon 6A and circulate to ensure its complete distribution. 3. Add hydrochloric acid to reach the concentration of 7 percent. 4. Circulate intermittently for about 45 minutes or more until the pickling has been accomplished. Notes: 1. In order to avoid corrosion: (a) Keep the flow rate lower than 1m/sec. (b) Take samples of the solution and check for the Fe+++ content: if [Fe+++] > 0.4 percent dump solution. 2. In order to determine when the system has been adequately pickled, put a piece of oxidized steel in the circulation tank and inspect it frequently. Neutralization 1. Add sodium hydroxide for neutralizing the acid, and water to avoid a temperature rise. 2. Circulate for 15-30 minutes. 3. Dump the solution and wash with water until pH = 7. Note: The concentration must be calculated on the overall volume of the solution. Passivation 1. Fill the system with water at 40°C (104°F). 2. Add 0.5 percent of citric acid and circulate to ensure complete mixing. 3. Check the pH of the solution: if pH < 3.5, slowly add ammonia to raise pH to 3.5. 4. Circulate for 15-20 minutes. 5. Slowly add ammonia to raise pH to 6 in 10 minutes. 6. Add 0.5 percent sodium nitrite (or ammonium persulfate). 7. Circulate for 10 minutes. 8. Add ammonia to raise pH to 9. 9. Circulate for 45 minutes. 10. Stop the pump and hold the solution in the system for at least three hours. 11. Dump the solution. Cleaning of Large Compressor Piping: Method II Cleaning of the piping may be done by commercial companies with mobile cleaning equipment or by the following recommended cleaning procedure. After hydrostatic tests have been made and the pipe sections have been cleaned as thoroughly as possible on the inside, the piping should be pickled by the following (or equivalent) procedure: 1. Remove all grease, dirt, oil, or paint by immersing in a hot, caustic bath. The bath may be a solution of eight ounces of sodium hydroxide to one gallon of water with the solution temperature 180°-200°F. The time of immersion is at least thirty minutes, depending on the condition of the material. 2. Remove pipe from caustic and immediately rinse with cold water. 3. Place pipe in an acid pickling bath. Use a 5 to 12 percent solution of hydrochloric (muriatic) acid, depending upon the condition of the pipe. Rodine inhibitor should be added to the solution to prevent the piping from rusting quickly after removal from the acid bath. The temperature of the bath should be 140°-165°F. The time required in the acid bath to remove scale and rust will vary, depending on the solution strength and condition of piping; however, six hours should be a minimum. The normal time required is about 12 to 14 hours. 4. Remove pipe from acid bath and immediately wash with cold water to remove all traces of acid. 5. Without allowing piping to dry, immerse in a hot neutral solution. A one to two ounce soda ash per gallon of water solution may be used to maintain a pH of 9 or above. The temperature of the solution should be 160°-170°F. Litmus paper may be used to check the wet piping surface to determine that an acidic condition does not exist. If acidic, then repeat neutral solution treatment. 6. Rinse pipe with cold water, drain thoroughly and blow out with hot air until dry. 7. Immediate steps must be taken to prevent rusting, even if piping will be placed in service shortly. Generally, a dip or spray coating of light water displacement mineral oil will suffice; however, if piping is to be placed in outdoor storage for more than several weeks, a hard-coating water displacement type rust preventative should be applied.
8. Unless piping is going to be placed in service immediately, suit able gasketed closures must be placed on the ends of the piping and all openings to prevent entrance of moisture or dirt. Use of steel plate discs and thick gaskets is recommended for all flanges. Before applying closures, the flange surfaces should be coated with grease. 9. Before installation, check that no dirt or foreign matter has entered piping and that rusting has not occurred. If in good condition, then pull through a swab saturated with carbon tetrachloride. 10. For nonlubricated (NL) units where oil coating inside piping is not permissible (due to process contamination), even for the starting period, consideration should be given to one of the following alternatives: (a) Use of nonferrous piping materials, such as aluminum. (b) Application of a plastic composition or other suitable coating after pickling to prevent rusting. (c) After rinsing with water in step six, immerse piping in a hot phosphoric bath. The suggested concentration is three to six ounces of iron phosphate per gallon of water, heated to 160°-170°F, with pH range of 4.2 to 4.8. The immersion time is three to five minutes or longer, depending on density of coating required. Remove and dry thoroughly, blowing out with hot air. CAUTION: Hydrochloric acid in contact with the skin can cause burns. If contacted, acid should be washed off immediately with water. Also, if indoors, adequate ventilation, including a vent hood, should be used. When mixing the solution, always add the acid to the water, never the water to the acid. On large piping (where a man can work inside), the pickling procedure can be omitted if the piping is cleaned mechanically with a wire brush, vacuumed and then thoroughly inspected for cleanliness. Time and trouble taken in the beginning to insure that the piping is clean will shorten the break-in period, and may save a number of expensive shut downs. Temporary Line Filters When first starting, it’s advisable to use a temporary line filter in the intake line near the compressor to catch any dirt, chips, or other foreign material that may have been left in the pipe. But clean the pipe first. Don’t depend on a temporary line filter. If the gas or air being compressed may, at times, contain dust, sand, or other abrasive particles, a gas scrubber or air cleaner must be installed permanently and serviced regularly. Even though the previous cleaning procedure has been carefully followed on the compressor piping, a temporary filter (such as Type PT American Filter or equal) should be installed in the suction line to the suction bottle to remove particles 230 microns (0.009 in.) in diameter or larger. If the compressor is an "NL" (nonlubricated) design, the filter should be designed to remove particles 140 microns (0.0055 in.) in diameter or larger. Provision must be made in the piping to check the pres sure drop across the filter and to remove the filter cell for cleaning. If the pressure drop across the filter exceeds 5 percent of the upstream line pres sure, remove the filter, clean thoroughly and reinstall. The filter cell should be removed and left out only when the inlet line is free of welding beads, pipe scale, and other extraneous matter. |