WSRC-TR-94-0343

Seismic Evaluation of Piping Systems Using Screening Criteria (U)

by G. A. Antaki Westinghouse Savannah River Company Savannah River Site Aiken, South Carolina 29808

A document prepared for PROCEEDINGS-CURRENT ISSUES RELATED TO NUCLEAR POWER PLANT STRUCTURES at Orlando from 12/14/94 -12/16/94.

DOE Contract No. DE-AC09-89SR18035 This paper was prepared in connection with work done under the above contract number with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or recipient acknowledges the U. S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper, along with the right to reproduce and to authorize others to reproduce all or part of the copyrighted paper.

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Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Seismic Evaluation of Piping Systems Using Screening Criteria George Antaki*

Prepared for trial application by a task group composed of Messrs. Robert D. Campbell, Donald F. Landers, John C. Minichiello, Gerald C. Slagis, and George A. Antaki.

A. Objective ther evaluations, or be considered a potential This document may be used by a qualified source of seismically induced failure. Oudier review team to identify potential sources of evaluations, which do not necessarily require seismically induced failure in a piping system. the qualification of a complete piping system by stress analysis, may be based on one or Failure refers to the inability of a piping sys• more of the following: simple calculations of tem to perform its expected function following pipe spans, search of the test or experience an earthquake, as defined in Table 1. data, vendor data, industry practice, etc.

The screens may be used alone or with the B. Cautions Seismic Qualification Utility Group - Generic 1. The screening criteria are not equivalent to Implementation Procedure (SQUG-GIP), compliance with the seismic design depending on the piping system's required requirements of ASME B31.1, B31.3, function, listed in Table 1. ASME Boiler and Pressure Vessel Code Section JH, NFPA-13, AWWA or AISC. An Features of a piping system which do not meet existing piping system may comply with the screening criteria are called outliers. the screening criteria but not with the design codes' seismic requirements, and Outliers must either be resolved through fur• vice-versa. Table 1. Procedures Applicable to Required Piping System Functions , FmCTJONS;,; DeUvers'<-' Equipment; > . lieak; lS:^

Maintain No No Yes Yes Piping Screens and Integrity of Pres• SQUG-GIP for Equip• sure ment Anchorage Boundary

Position No No No Yes Subset of Piping Retention Screens (not yet developed)

•Manager, Systems Structural Analysis, WSRC, Aiken, SC 29808

94X04989.FMK WSRC-TR-94-0343 - 1 2. Application of the screening criteria must The authors have relied on the considerable reflect the consensus of a seismic evalua• body of piping test and earthquake data and tion team of two or more engineers, each analytical practice to screen and identify engineer having the following qualifica• the following key attributes which may tions: lead to seismically induced failures of pip• ing systems: a. a minimum of five years experience in seismic design and qualification of pip• a. Material condition: Poor construction ing systems and support structures details and material degradation are at the source of many seismic failures b. required training in this procedure observed in piping systems. Construc• c. capability to apply sound engineering tion quality and material condition are judgement thoroughly covered in the screens. 3. Qualified users of the screening criteria b. Anchor motion: Excessive anchor must complete a training course and suc• motion propagated through equipment cessfully pass an examination in the fol• and headers has resulted in seismic fail• lowing topics: ures of piping systems. The screens pro• a. content and intent of the screening crite• vide for protection against excessive ria anchor motion. b. piping and pipe support design require• c. Brittle features: Brittle materials and ments of ASMEB31.1, ASMEB31.3, certain fittings and joints are screened NFPA-13, AWWA, and AISC out to avoid non-ductile piping systems. c. piping standards ANSI B16 and pipe d. Interactions: Experience data shows hanger standard MSS-SP-69 several failures traceable to seismic interactions on the piping systems, such d. piping materials and degradation mech• as failure of overhead structures or sup• anisms porting walls. Screens are provided to e. support anchorage rules of die SQUG- assess the potential for credible and sig• GIP nificant interactions.

f. earthquake and seismic test experience C. Applicability data for piping systems This procedure, with the following restrictions, 4. The screening criteria reflect the authors' applies to above ground metallic piping sys• consensual opinion of the most likely tems constructed of materials listed in ANSI potential seismic failure modes of piping B31.1, B31.3, AWWA or NFPA: systems, based on past tests, earthquake data and analytical experience. They are 1. Cast iron materials are excluded. Non fer• not keyed to particular stress criteria or rous alloys with a specified ultimate tensile performance goals. strength (UTS) of less than 30 ksi are excluded. Welded aluminum materials are excluded.

WSRC-TR-94-0343-2 94X04989.FMK 2. Pipe and pipe support materials must be 2. Pipe and pipe support member materials ductile at all service temperatures. must be ductile at all service temperatures, 3. Diameter-to-thickness ratio (D/t) of pipe is having total elongation at rupture greater 50 or less. than 10%. Table 2 shows such properties for common piping materials at room tem• 4. Operating temperature is below 300°R perature. When judging material ductility, 5. The average 5% damped free field ground the review team must consider the effect of material degradation on these properties, spectral acceleration (Sa) over any factor of two wide frequency band such as 3 to 6 Hz particularly the potential for reduced elon• or 5 to 10 Hz shall not exceed 0.8g. gation caused by lowered ductility. 6. Threaded joints are excluded where opera- Cast iron or brittle elements in a ductile bility or integrity of pressure boundary are piping system are outliers, but they may be required. accepted if proven to be located in low seismic stress areas, and not susceptible to Commentary impact 1. While the focus of seismic experience has been mostly on welded steel piping, there At liquid gas temperature, soldered is no evidence that piping constructed of joints—unlike brazed joints—tend to metals other than gray cast iron has per• become brittle and must be considered out• formed poorly in past earthquakes. liers. 3. The seismic testing and earthquake experi• Except for aluminum, all grades of non fer• ence data is mostly from standard or thick rous piping allowed by the code have UTS wall pipe. The screening criteria apply of 30 ksi or better. Welded aluminum is directly to piping systems with a D/t ratio excluded since many grades of aluminum of 50 or less. alloy have low specified ultimate and yield strengths, and tend to have low fatigue 4. Below 300°F, thermal expansion loads are strength and limited ductility in the heat negligible for the purpose of seismic evalu• affected zone. ation. 5. Limiting the screening criteria to the speci• The screens may be used for copper piping. fied free field horizontal spectral accelera• The UTS of weldable grades of copper and tion is a precaution introduced to remain bronze piping exceeds 30 ksi. Copper tub• within the scope of earthquake experience ing and piping can also be brazed, and a data for equipment. properly brazed joint is stronger than the pipe. At ambient temperatures, soldered 6. The seismic experience contains a number joints may be considered as strong as the of instances where earthquakes have pipe if standard fittings are used, and if the resulted in leakage of threaded joints. It is joints are visually inspected to verify sound unclear whether these failures were due soldering, as required in the construction solely to the type of joint or whether they quality screen. were the result of other attributes which are covered in the screens, such as excessive

94X04989.FMK WSRC-TR-94-0343-3 Table 2. Properties of Common B31.3 Piping, Tubing, Fitting, and Support Members Materials at Room Tem• perature

ELONGATION ^ULTD^ATE'^' ?j IN2"DIA.ROUND, DESCRIPTION ALLOWABLE rstferfGTTfe* II^TORL^L^ k^/^lsPEGLi-^ ;%;*

fS;

Carbon Steel Pipe A53, . 20.0 35.0 60.0 22-23 GR.B

Carbon Steel 1A105, FR. 23.3 36.0 ' 70.0 18-30 (Forged Fitt.) CL-70

Carbon Steel A106, 20.0 35.0 60.0 16-30 (Seamless Pipe) GR.B

Pipe Fitting A234 20.0 35.0 60.0 14-30 GR.WPB

Carbon Steel Bolt A307, GR. B 13.7 36.0 60.0 - 100.0 18

Stainless Steel Pipe A312, GR. 16.7 25.0 70.0 25-35 TP-304L

Copper Tube B75 12.0 30.0 30.0-37.0 25 Temp. H5

Red Brass Pipe B43 08.0 12.0 40.0 35 Temp. 061

anchor motion or material degradation at The method and calculations to resolve outliers the threaded joint. Pending more detailed shall be documented. studies, threaded joints will be considered outliers where operability or integrity of The purpose of each screening criterion is pressure boundary is required. included in this procedure and explained in the required training course. D. Documentation The review team shall complete a Piping Seis• For each piping system, a complete documen• mic Evaluation Work Sheet (P-SEWS) for tation package will be assembled consisting of each piping system. the P-SEWS with attached notes and calcula• tions, sketches, and photographs. The technical basis for judging each screening criterion shall be described on attached sheets Documentation should be sufficient for inde• and cross referenced in the corresponding pendent review by an experienced piping engi• notes column of the P-SEWS. neer trained in the application of this procedure. Written calculations shall be sufficiently detailed to clarify the purpose of the calcula• tion and the conclusion. All assumptions shall be noted.

WSRC-TR-94-0343-4 94X04989.FMK E. Required Input Piping System Locations and Reference Draw• ings Piping System ID Record the appropriate piping identification Record the piping system location, such as numbers, such as line numbers, chronological building, flooro r room number. numbers, calculation numbers, equipment list item numbers, etc. If the piping system spans different buildings or floors, note all locations. System Description and Fluid Boundaries Piping system descriptions such as system, A list of reference drawing numbers and revi• subsystem, or line number must clearly com• sions used in the evaluation, such as flow dia• municate the scope of the seismic review grams, piping arrangement diagrams, (boundary points) on a flow diagram sketch. isometrics, equipment drawings, etc. is All branch lines shall be identified, and seis• required. A separate sheet may be used if mic/non-seismic fluid boundaries shall be needed. noted. Piping Materials And Sizes (Ref.) Piping System Function and Contents List all pipe materials, sizes (nominal pipe size The contents and function of the piping system and schedule or thickness) and the references during and after the earthquake must be used to determine this information (such as described and categorized as operability, integ• specifications or drawings). rity of pressure boundary or position retention (refer to Table 1). For operability, identify Piping And Contents Linear Weight active equipment Linear weight (lb/ft) of piping and contents must be recorded for each size of pipe. Noted Piping Layout and Structural Boundaries contents (liquid, gas, air, steam, etc.) must be Isometric sketches, based on visual inspection, the same as expected during a postulated earth• must be sufficient for piping engineers to visu• quake. alize system response and calculate approxi• mate span equivalent lengths. Insulation Type And Linear Weight For each change in size and insulation type, Structural boundaries, along with support note the linear weight (lb/ft) of insulation and types and locations shall be noted. If adjacent the references used to determine this informa• walls or structures are relied on for seismic tion (such as specifications or drawings). restraint, these features shall also be noted. In• line equipment and concentrated masses shall Pipe, Contents And Insulation Linear Weight be noted where they contribute to significant weight. This is the sum of the two lines above: pipe and contents linear weight plus insulation lin• ear weight

94X04989.FMK WSRC-TR-94-0343-5 Concurrent Pressure And Temperature F. Construction Quality Specify the pressure and temperature condi• Piping, components and supports shall be undam• tions expected concurrent with the postulated aged and of good construction. earthquake. The pressure values will be used in Commentary the component rating screen (refer to Con• struction Quality). The temperature must be An assessment shall be conducted of the below 300°F for the screens to apply (refer to design, welding, and fabrication quality, as Applicability Section). well as all visible damage to the piping and the supports, prior to applying the screening crite• Input Response Spectra ria. The input response spectra are used in several The piping system must have been fabricated screens and may be necessary for the resolu• and examined (weld inspections) in accor• tion of outliers. dance with ASME B31, AWWA or NFPA. The review team shall document the appropri• Pressure ratings for branch connections and fit• ate ground and/or floor response spectra, appli• tings shall be checked for adequacy. cable references, and status (final or preliminary). Standard pipe fittings manufactured to specifi• cations must have the same pressure rating as The ground response spectra (at 5% damping) their corresponding size and schedule of shall be used for piping supported from grade. straight pipe. Unreinforced branch connec• tions, or pipe fittings or couplings unlisted in The floor response spectra (at 5% damping) the applicable standards, or which lack stated shall be used for piping supported above pressure ratings, could have significantly grade. lower pressure ratings and seismic capability than their complementary straight pipes, in If the piping terminal ends are at large flexible which case they are outliers. equipment, seismic anchor motion of the equipment nozzles shall be considered. The piping and supports shall be visually inspected for adequate quality of design, fabri• If the piping spans between buildings, the rela• cation, installation and maintenance. Instances tive anchor motions shall be established and of poor quality shall be noted. documented. Signs of poor construction quality or subse• Applicability quent damage include: Limits and conditions as given in the Applica• bility section must be met, to ensure that the 1. excessive distortion of piping or supports material, size (D/t), temperature (300°F) and 2. brazed or soldered joints, apparently of average ground acceleration (0.8g) of evalu• good quality, but without a thin layer of ated piping is appropriate for this screening brazing or solder visible where the tube procedure. extends beyond the fitting socket 3. uneven, undersized or damaged welds

WSRC-TR-94-0343 - 6 94X04989.FMK 4. unusual or temporary repairs G. Internal Degradation 5. evidence of interference having caused sig• Piping and components shall be free of significant nificant bearing, scratch marks or distor• internal degradation. tion to the pipe metal or to components Commentary 6. a pipe dislodged from its support so that the weight of the pipe is distributed Significant degradation refers to that which unevenly on the hangers or saddles may affect the pressure integrity of the piping system. The potential for internal degradation 7. the deformation of a thin vessel wall in the must be investigated and documented from vicinity of a pipe attachment two aspects. 8. pipe supports forced out of plumb by 1. the piping system performance records, expansion or contraction of the piping and 9. the shifting of a base plate, breaking of a 2. a metallurgical assessment foundation, or shearing of foundation bolts of mechanical equipment to which piping It is unnecessary to perform new nondestruc• is attached tive surface or volumetric examinations of the 10. missing nuts or bolts piping system for this screen. The review of performance records and metallurgical assess• 11. signs of leakage (discoloration, dripping, ments are to be based on existing data. If either wet surface) of these data sources suggest potential internal 12. cracks in connecting flanges or the cases of degradation, the system must be classified as pumps or turbines to which piping is an outlier. attached If the condition of the piping system is judged 13. deterioration of protective coatings, fire- adequate, but some degradation is expected to proofing or other periodic maintenance occur in the future, the system must be sub• conditions jected to periodic in service inspection or eval• 14. general physical damage uated for the affects of the expected 15. movement or deterioration of concrete degradation. footings Performance Record 16. failure or loosening of foundation bolts The system cognizant engineer must identify 17. insecure attachment of brackets and beams and assess past maintenance, repairs and to the support replacements performed on the piping system, 18. restricted operation of pipe rollers or slide or on similar systems, to judge if they indicate plates potential metallurgical or mechanical degrada• 19. insecure attachment or improper adjust• tion mechanisms. ment of pipe hangers The system cognizant engineer must identify 20. broken or defective pipe supports any history of abnormal events or loadings, 21. oversized bolt holes such as flowinduce d vibration, water hammer, misalignment, binding, and excessive tempera• ture cycling, to judge if they may have caused

94X04989.FMK WSRC-TR-94-0343-7 system degradation due to fatigue or localized 11. ferrous and nonferrous piping subject to yielding. stress corrosion cracking 12. alkali lines subject to caustic embrittlement Evidence of pipe leakage, pipe repair, support and resultant cracking failures, or abnormal vibration may indicate significant cyclic loading, which shall be 13. areas near flanges or welded attachments resolved. that act as cooling fins, causing local corro• sion because of temperature differences Metallurgical Assessment 14. locations where impingement or changes The metallurgical assessment of the piping in fluid velocity can cause local accelerated systems must be performed with the help of corrosion or erosion materials engineering. When considering 15. points of accidental contact or insulation materials, fluids and operating conditions, the breakdown that causes contact of dissimi• materials engineer must judge the potential for lar metals reduced performance capability resulting from 16. an area where steam or electric tracing material degradation, erosion or corrosion. contacts piping handling material such as caustic soda, where concentrated heat can Guidance: Susceptible Areas cause corrosion or embrittlement The following areas are most susceptible to 17. an area immediately downstream of a corrosion, erosion, and other forms of material chemical injection point, where localized degradation. corrosion might occur in the reaction zone 1. points at which condensation or boiling of 18. heat-affected zones (around and in welds) acids or water is likely to occur in non-post weld heat-treated carbon steel piping in amine service 2. points at which acid carryover from pro• cess operations is likely to occur 19. dissimilar metal welds 3. points at which naphthenic or other organic The potential for general corrosion or erosion acids may be present in the process stream that could result in pipe wall thinning shall be 4. points at which high-sulfur streams at assessed. If wall thinning potential exists in the moderate-to-high temperatures exist material or environment, sample measure• 5. points at which high- and low-temperature ments shall be taken. If the predicted thinning hydrogen attack may occur exceeds 20% of the pipe wall for the planned life of the piping system, the system is an out• 6. dead ends subject to turbulence, or where lier. liquid-to-vapor interface or condensation occur If stress corrosion cracking is likely, examina• 7. valve bodies and trim, fittings, ring tions shall be performed. grooves and rings, and flange facings 8. welded areas subject to preferential attack The hazard of embrittlement (due to hydrogen, hydrogen cracking, irradiation, thermal aging, 9. catalyst, flue-gas, and slurry piping etc.) for the planned life of the piping system 10. steam systems where condensation occurs shall be assessed. If it is possible for pipe duc-

WSRC-TR-94-0343 - 8 94X04989.FMK tility (total elongation at rupture) to be reduced 4. Copper and Copper Alloys by 10% or more, the system is an outlier. a. possible dezincification of brass alloys Guidance: Material Compatibility b. susceptibility to stress-corrosion crack• The following possible material conditions ing of copper-based alloys exposed to must be evaluated, along with other service fluids such as ammonia or ammonium specific conditions: compounds

1. Carbon Steel, and Low and Intermediate c. possible unstable acetylene formation Alloy Steels when exposed to acetylene a. possible embrittlement when handling H. External Corrosion alkaline or strong caustic fluids Piping, components and supports shall be free of sig• b. possible hydrogen damage to piping nificant external corrosion. material when exposed (under certain Commentary temperature-pressure conditions) to hydrogen or aqueous acid solution Significant corrosion refers to metal thickness loss of more than 20%. A surface discoloration c. possible stress corrosion cracking or thin layer of rust does not harm structural when exposed to wet hydrogen sulfide, integrity. Rust forms a surface coating which and the further possibility of deteriora• protects the inner metal from further corrosion. tion (sulfidation) in the presence of A loss in thickness can be measured by com• hydrogen sulfide at elevated tempera• paring the pipe diameter at the corroded area tures with the original pipe diameter. The depth of d. the need to limit maximum hardness of pits can be determined with a depth gauge. metals in applications subject to stress Stainless steel, copper, nickel, and their alloys corrosion are typically used in B31.3, and resist atmo• 2. High Alloy (Stainless) Steels spheric corrosion. They may be accepted with• out further review. Iron and carbon (low alloy) a. possible stress corrosion cracking of steels, however, may be subject to attack, par• austenitic stainless steels exposed to ticularly in areas where moisture can accumu• media such as chlorides and other late. If piping is insulated and made of iron or halides either internally or externally as carbon/low alloy steel, insulation should be a result of improper selection or appli• removed at 3 accessible and susceptible points cation of thermal insulation and the pipes inspected for corrosion. 3. Nickel and Nickel Base Alloys Significant corrosion (uniform loss of more a. possible stress corrosion cracking of than 20% of metal thickness) can impair the nickel-copper alloy (70Ni-20Cu) in ability of the supports or piping to carry loads. hydrofluoric acid vapor if the alloy is For supports, areas to consider include highly stressed or contains residual threaded sections and pipe-clamp or pipe-sad• stress from forming or welding dle interfaces. Local metal loss exceeding 20%

94X04989.FMK WSRC-TR-94-0343-9 of the wall thickness may be acceptable, but Cracks in fireproofing concrete, particularly at each occurrence must be evaluated. the top where the concrete ends, also allow moisture to penetrate and hidden corrosion to Atmospheric Corrosion occur. Protective organic coatings may be use• ful, especially in seacoast areas where chlo• When metals such as iron or steel are exposed rides can come from the air rather than from to the atmosphere, they will corrode due to the the insulation. Inhibited insulation, or insula• presence of water or oxygen. Below 60% tion free of water-soluble chlorides, should be humidity, corrosion of iron and steel is negligi• used with austenitic (300 series) stainless ble. To prevent atmospheric corrosion, it is steels to prevent stress corrosion cracking. necessary to protect the surface of the metal from water by means of a protective barrier or coating. Defects in protective coatings and the water• proof coating of insulation will permit mois• The normal rate of atmospheric corrosion of ture to contact the piping. When defects are unpainted steel in rural atmospheres is low, found in the waterproof coating of insulation, ranging from 0.001 to 0.007 inches per year. enough insulation should be removed to allow However in some atmospheres, a steel corro• the extent and severity of corrosion to be sion rate of 0.05 inches per year is possible. determined. Sections of insulation should be The rate of corrosion accelerates at any break removed from small connections, such as bleed lines and gauge connections, since these in a protective coating because the exposed locations are particularly vulnerable to atmo• metal at the break becomes anodic to the spheric attack due to the difficulty of sealing remaining metal surface. At such breaks, deep the insulation. pits will form.

Equipment which is located next to boiler or Corrosion of Piping at Contact Points furnace stacks and exposed to corrosive gases Piping installed directly on the ground suffers such as sulfur dioxide and sulfur trioxide is severe corrosion on the underside from damp• subject to accelerated corrosion. These gases, ness. If grass or weeds are allowed to grow dissolved in water condensate from flue gas, beneath and around piping, the underside of rain, or mist, form dilute acids which act as the pipe will remain damp for long periods and electrolytes. In addition, chlorides, hydrogen will corrode. Lines laid directly on supports, sulfide, cinders, fly ash, and chemical dusts or hung by clamps, often show crevice corro• present in industrial atmospheres may act in a sion at the contact points. similar manner. Lines that sweat are susceptible to corrosion at Corrosion Under Insulation and Fireproofing support contact points, such as under clamps Materials on suspended lines. Piping mounted on rollers Inadequate weatherproofing on piping allows or welded support shoes is subject to moisture moisture to penetrate to the underlying steel, accumulation and corrosion. Loss of vapor- where hidden corrosion takes place. Such hid• sealing mastic from the piping insulation can den corrosion is often severe in refrigeration result in local corrosion. Pipe walls inside systems. The skirts of all vessels, regardless of open-ended trunnion supports are subject to operating temperatures, are subject to severe corrosion. These points should be investi• corrosion under insulation or fireproofing. gated.

WSRC-TR-94-0343 - 10 94X04989.FMK Corrosion of Structures The equivalent span length Lei in a given direc• tion i is defined as L = (W + W )/w. Structures that provide crevices where water ei pi ci may enter and remain for long periods are sub• ject to severe corrosion. Examples are struc• Wpj = weight of pipe length in span between tural members placed back to back, and consecutive supports in direction i, platforms installed close to the tops of towers including insulation and contents or drams. Structures located near furnace stacks and cooling towers are particularly sus• W^ = weight of in line components in span ceptible to this type of attack. w = weight per unit length of pipe size and Leakage contents in span

The walkdown team must check for the possi• Vertical loading can be resisted by engineered bility of leaking fluids, suggested by local dis- deadweight supports, or structures that are not colorations or wet surfaces on the pipe or floor. considered deadweight supports, such as pene• trations through walls, certain types of box Bolted joints such as valve packings or flanges beam horizontal restraints, and floor slabs. may leak. This is especially true for water lines following prolonged periods of sub-freezing weather. Performance records of frozen water Table 3. Vertical Equivalent Span for Screening pipes show incidents of leakage due to frozen ;N6^jnM4PipeSize; " yliiquid'Seryice' ' : ;" '-- gaskets. : : l 10 13

Leaks from bolted joints allow fluid to either 2 15 19 collect on the pipe or drip onto other systems. 3 18 22 In areas where leaks are encountered, the walk- down team should ensure either that the bolts 4 21 25 and fluid are compatible or that the bolting has 6 25 31 not been subjected to process fluid attack from 8 28 36 gasket leakage. 12 34 45 I. Vertical Span 16 40 52 Piping shall be well supported vertically. 24 48 63

Commentary The following vertical support configurations A piping system may be considered well sup• shall be considered outliers in seismic screen• ported for deadweight if the equivalent vertical ing evaluations (see Figure 1, based on MSS- span length, for liquid or gas service, is as SP-69)1. shown in Table 3, which lists maximum acceptable vertical support spacing for this 1. friction type connection to structures screen. The spans in this table correspond to 150% of the ASME B31.1 suggested pipe sup• 2. shallow pipe saddle support or pipe rolls port spacing.

94X04989.FMK WSRC-TR-94-0343-11 3. bottom support if not positively attached to may be provided either by an engineered lateral the pipe and floor, and if the lateral move• support, or by other means, such as illustrated ment of the pipe could possibly tip the sup• in Figure 2. port Interferences 4. pipe resting on a support, free to slide later• ally so as to fall off the support Lateral interferences will limit motion in pip• ing routed along a wall or structural member. 5. A clamp on a vertical riser without positive Although this restraint occurs in one direction attachment to the pipe, such as lugs above only, it significantly restricts the response of the clamp. the system to a reversing load.

Box Beam A box beam, while not designed to provide horizontal restraint, will do so once the pipe moves through the gap and contacts the beam. Friction Connection Shallow Pipe Roll When evaluating the effectiveness of a box beam's horizontal restraint potential, the gap on

"r- ---, both sides of the pipe must be considered. Note -1 — I"' » * , i that, should the pipe impact the vertical mem• bers of the beam, significant energy is dissi• pated and the frequency response of the system is modified.

Pipe Saddle Support Bottom Support

Figure 1. Potentially Unstable Support Configura• tions

J. Lateral Span Piping shall be sufficiently restrained in the lateral direction.

Commentary A piping system may be considered suffi• ciently restrained in the lateral direction if the equivalent lateral span length for liquid or gas service does not exceed three times the spans in Table 3, which corresponds to approxi•

mately four times the ASME 31.1 suggested 94X02775.12JUL vertical pipe support spacing. Lateral restraint Figure 2. Potential lateral restraints

WSRC-TR-94-0343 - 12 94X04989.FMK U-Bolts K. Anchor Motion U-bolts provide significant horizontal restraint, Piping must have sufficient flexibility to accommo• even when the side load design capacity of the date the seismic motions of structures, equipment U-bolt is exceeded. Should the U-bolt yield and headers to which it is attached. under seismic stress, it will bend, resisting hor• Commentary izontal motion by tension. One of the most common causes of piping fail• Saddles ure in strong motion earthquakes is seismic anchor motion (SAM) resulting from: There are generally two types of pipe saddle supports; a simple saddle on which the pipe 1. large displacement of unanchored tanks or merely rests, and that which includes a yoke equipment (strap or U-bolt) to restrain the pipe in the sad• 2. failure of the tank or equipment anchorage dle. A shallow simple saddle provides practi• cally no horizontal restraint, and could permit large differential motions of structures to the pipe to escape from its support during a which the piping is attached seismic event A deep saddle support will 4. large motions of header piping induced into restrain the pipe in the lateral direction. smaller branch piping Floor and Wall Penetrations SAM caused by these sources imposes large strains in rigid sections of the piping system as Piping often passes through openings in floors, illustrated in Figures 3, 4, and 5. Most of the grating or walls. Since these openings are not common piping failures are in small diameter designed as supports, gaps between the pipe pipes with non-welded connections to tanks, and the structure exist. When made in floorso r pumps, and larger header pipes. walls, the openings are usually secured by a sleeve; in gratings, a sleeve or a ring is used. In order to screen out SAM as a potential fail• These penetrations provide significant lateral ure mode for piping, the following conditions restraint during dynamic seismic events and, must be verified; otherwise the effect of anchor like the box beam, prevent displacement, dissi• motion must be calculated. pate energy and modify system frequency. 1. Tanks and equipment to which the piping Rod Hangers attaches must be properly anchored to pre• The lateral support capacity of rod hangers is vent sliding, rocking or overturning. measurable as a function of the swing angle of Equipment anchorage shall be evaluated the rod when subjected to a given lateral load. using the SQUG-GIP. While this lateral support capacity is not pro• 2. Tanks and equipment to which the piping vided by design, it can be important in prac• attaches, and the supports for the tanks and tice. The length of the rod is significant equipment should be relatively stiff to min• because for shorter rods, the swing angle and imize SAM. resistance to horizontal displacement is greater. An effective lateral spring rate formula Note: When vibration isolators are present, for short rod hangers is W/1, where W is the vibration isolators on equipment are a source tributary weight on the rod and 1 is the length of SAM, and must be evaluated as provided in of the rod. the SQUG-GIP. If there are no seismic stops

94X04989.FMK WSRC-TR-94-0343 - 13

"^"^??"s;-* v -:- built into the isolators, the equipment will likely require the addition of seismic restraints to limit motion. If seismic stops are installed with the vibration isolators, the attached piping must be assessed for the maximum motion that can be realized before impacting the stops.

3. Piping rigidly attached to two different buildings, or substructures within a build• ing, must be sufficiently flexible to accom• modate the differential motion of the attachment points. Usually, structural dis• placements are relatively small, and the motion can be easily accommodated by pipe bending. Particular attention should be focused on piping that has its axial motion restrained at support points in two Figure 3. Example of seismic hazard to component different structures. conduits 4. Header motion imposed on small branch lines must be assessed, or the header must be restrained near the branch. The elastically calculated unintensified stress amplitude due to SAM (M/Z) may be limited to twice the material yield stress for screening purposes. When considering lateral movement of header pipes and restraint of branch pipes, it is necessary to define a lateral restraint, as dis• cussed in Section J, Lateral Span.

Figure 4. Example ot seismic hazard to a branch line. The vulnerable joints are indicated.

WSRC-TR-94-0343 - 14 94X04989.FMK MxnmetM.

Figures. Pipe break potential for unanchored tanks

L. Mechanical Joints Figure 6. Bell-and-spigot piping joints are brittle. Piping shall not contain mechanical joints which rely solely on friction. M. Flanged Joints Commentary Flanged joints shall withstand the expected seismic Piping joints which rely on friction to hold the moments without leakage. joint together include Victaulic™ couplings, bell and spigot joints (see Figure 6), and Commentary Dresser couplings. These mechanical joints Flanged joints have leaked under severe seis• can partially or fully separate during a seismic mic loads, and sometimes may leak under nor• event, and should be considered outliers. mal service loads. If the flanged joint is a B16.5 flange having high strength bolts, ade• The seismic experience data contains a number quate preload (around 40,000 psi), and a rated of instances where mechanical joints have pressure above the operating pressure, the leaked. While it is not clear whether this leak• flange is acceptable. Other flanged joints with age was due to seismic anchor motion effects lesser capacities should not be located in high (already covered by an earlier screen), these stress areas. One method of assessing moment joints must be classified as outliers pending capacity at flanges is to determine excess pres• further studies. Joint vendors may be contacted sure capability (rating minus operating pres• to obtain allowable loads, and simple span for• sure) and convert that into an equivalent mulas may be used to estimate applied loads to moment. The rated pressure of flanged joints be compared to the vendor allowables. shall be established.

Wedge type SWAGELOK™ joints which rely If there are indications of leakage at the joint in on plastic deformation of pipe are not included past service, the flanged joint is an outlier. in this category and are not considered outli• ers, as they have been tested and have not Lap joint flanges are only acceptable if located shown a pattern of failure under seismic load• in areas of the piping system with estimated ing.

94X04989.FMK WSRC-TR-94-0343 -15

^t&vm unintensified seismic stress less than approxi• rules. Eccentric pipe segments, such as unsup• mately 10,000 psi. ported vents or drains, shall be evaluated using the peak spectral acceleration at 5% damping N. Equipment Nozzle Loads (or a better estimate of the spectral accelera• Equipment shall not be subjected to large seismic tion at the pipe frequency) and an allowable loads from the piping systems. unintensified elastically calculated stress of twice the material yield stress. Commentary To be considered operable, active equipment P. Flexible Joints (such as pumps and valves) has to meet the Flexible joints shall be properly restrained to keep requirements of the SQUG-GIP (refer to Table relative end movements within vendor limits. 1), in addition to the following requirements: Commentary Equipment nozzles, except for valves that are For unsupported flexible joints such as expan• stronger than the pipe, should be protected, by sion joints, bellows, or flexible joints (see Fig• appropriate restraints, from excessive seismic ure 7), the relative displacements need to be loads, particularly where the equipment nozzle limited to prevent tearing or buckling the joint. or joint is of smaller size than the pipe. The piping layout shall be reviewed to verify that large seismic loads are not reacted at the equipment nozzle. One potential problem is a long axial run of pipe not restrained from axial movement except at the equipment nozzle. If there is a possibility of large seismic loads, the unintensified bending stress at the nozzle shall be elastically evaluated and compared to twice the material yield stress.

Piping reaction loads at the nozzles of rotating equipment may affect their function. The seis• mic reaction loads imparted by the piping on the nozzle of the active (rotating) equipment shall be estimated. These loads shall be small (unintensified bending stress less than 6000 psi), or within the estimated capability of the equipment

O. Concentrated and Eccentric Weights Eccentric weights in piping systems shall be evalu• ated. Figure 7. Flexible couplings without pipe restraints cannot handle imposed pipe loads. Commentary Where manufacturer's limits can be exceeded, The adequacy of valves with eccentric opera• the Review Team should ensure the joint has tors shall be evaluated using the SQUG-GIP

94X04989.FMK WSRC-TR-94-0343 - 16 sufficient mobility to absorb the seismic tioned or designed attachments could result in deflections. When such joints are adequately failure of the pressure boundary under large supported on either side this is not usually an loads. A pipe elbow with a small lug or trun• issue. nion subjected to a large compressive seismic load is susceptible to large local stresses. If the configuration is such that excessive seis• mic movements at the expansion joint could Seismic Demand tear or buckle the joint, the expansion joint is The calculation of horizontal and vertical seis• an outlier. Calculation of seismic displace• mic loading on pipe supports is based on the ments and comparison to established allowable tributary weight of adjacent piping spans mul• displacements are required to resolve the out• tiplied by one of the following factors: lier. 1. For piping supported from grade, multiply Q. Support Capacity Review by the peak of the 5% damped ground The structural capacity of pipe supports shall be cal• spectrum. culated by evaluating two or more, but at least 10%, of the bounding vertical and horizontal supports. 2. For piping supported above grade, multi• ply by the peak of the 5% damped floor Commentary response spectrum. The review team shall calculate the seismic Seismic Capacity load and capacity of a minimum of two bound• ing vertical and two bounding lateral supports The review team shall evaluate the seismic judged to have the largest load/capacity ratio. capacity of support members along the seismic At least 10% of the supports on the system load path. The capacity of support members, shall be calculated. The basis for the support welds and joints may be estimated using AISC selection shall be documented. rules, multiplying the AISC allowables by 1.7. Where manufacturer design limits are pro• Examples of bounding supports are: vided for standard pipe support elements (excluding anchor bolts in concrete), the seis• • supports with largest spans or close to heavy compo• mic capacity may be taken as twice the design nents limit for members loaded in tension, bending • supports reacting the load from long axial runs or shear. For compression members, if the • short rods adjacent to longer rods design limit is based on buckling, the seismic capacity shall be the same as the manufacturer • supports with fewest or smallest anchor bolts design limit • gang supports reacting loads fromsevera l pipes • three way supports or anchors Anchorage shall be inspected, and capacity calculated, using the rules and documentation Pipe anchors at the terminal ends of a piping oftheSQUG-GIP. system shall be considered pipe supports and reviewed as such. The review team must take care to limit their calculations to credible failure modes which Welded attachments to the pipe such as lugs or can hinder the function of the piping system. trunnions that react seismic loads shall be Limited yielding is, in most cases, not a credi• judged for adequate strength. Poorly propor• ble failure mode.

94X04989.FMK WSRC-TR-94-0343 - 17 An explicit calculation of weld capacities is • unstable or light weight structures not required if the welds are estimated to be • electrical cabinets and panels the same size, and develop the same strength, • sprinkler heads as connecting members. Generally, impact may be of little consequence R. Interaction on Other Structures if it affects the following components: The piping being reviewed shall not be a source of • walls interactions by displacement or swing impact on • large frames or structures adjacent components. • passive components (tank, check valve, etc.) • pipes of approximately the same or larger diameter Commentary A piping system subjected to seismic loads In all cases the review team must use judge• will displace or swing laterally, and may ment in estimating the extent of movement of impact adjacent components (see Figure 8). the pipe under review and the capacity of the impacted equipment. Estimate of Displacement Without detailed analysis, lateral displace• S. Interaction from Other Structures ments or swing deflections of piping spans can The piping being reviewed shall not be a be estimated. target of interactions from overhead falling structures. An approximate formula to estimate pipe dis•

placements (Sd) at spectral acceleration (Sa) Commentary for a pipe frequency f, is: The Review Team shall visually inspect all 2 structures and commodities located above the Sd=1.3S3/(2 7cf) pipe and identify those hazards which are where 1.3 is the mode participation factor for a judged to be credible (may fall on the pipe) simply supported beam. An approximate upper and significant (fall impact may cause pipe bound for a 0.3g Regulatory Guide 1.60 spec• failure as defined in Table 1). The SQUG-GIP trum at low frequency Oess than 0.25 Hz) is guidance for equipment interactions may be about 28" for 5% damping. Actual displace• used for this evaluation. ments of piping systems which meet the screens are rarely larger than 12".

Estimate of Impact Consequences In all cases, the review team will have to care• fully estimate the extent of pipe deflection and the component's capacity to absorb impact.

Generally, impact must be avoided if it affect- sthe following components: • active equipment (motors, fans, pumps, etc.) • instrumentation • tubing Figure 8. Proximity and impact interaction hazard

WSRC-TR-94-0343 - 18 94X04989.FMK T. Bibliography Codes and Standards ASME B31.1, "Power Piping", American Society of Mechanical Engineers, New York, N.Y.

ASME B31.3, "Chemical Plant and Petroleum Refinery Piping", American Society of Mechanical Engineers, New York, N.Y.

NFPA-13, "Installation of Sprinkler Systems", National Fire Protection Association, Quincy, MA.

AWWA-M11, "Steel Pipe—A Guide for Design and Installation", American Water Works Associ• ation, Denver, CO.

MSS-SP-69, "Pipe Hangers and Supports—Selection and Application", Manufacturers' Standard• ization Society of the Valve and Fittings Industry, Inc., Falls Church, VA.

AISC, "Manual of Steel Construction", American Institute of Steel Construction, Chicago, IL.

Test and Earthquake Experience NUREG-1061, "Report of the U.S. Nuclear Regulatory Commission Piping Review Committee", "Strong-Motion Earthquake Seismic Response and Damage to Aboveground Industrial Pip• ing", "Summary and Evaluation of Historical Strong Motion Earthquake Seismic Response and Damage to Aboveground Industrial Piping", Volume 2 Addendum, USNRC, Rockville, MD, April 1985.

EPRI NP-5617, "Recommended Piping Seismic Adequacy Criteria Based on Performance During and After Earthquakes", Volume 1 & 2, Electric Power Research Institute, Palo Alto, CA, February 1987, January 1988.

EPRI NP-6628, "Procedure for Seismic Evaluation and Design of Small Bore Piping (NCIG-14)", Electric Power Research Institute, Palo Alto, CA, April 1990.

G.C. Slagis "Review of Seismic Response Data for Piping", ASME Pressure Vessel Research Council Grant 92-03.

J.D. Stevenson, "Application of Bounding Spectra to Seismic Design of Piping Based on the Per• formance of Above Ground Piping in Power Plant Subjected to Strong Motion Earthquakes", Stevenson and Associates, May 11,1992.

Seismic Qualification Utilities Group (SQUG) "Generic Implementation Procedure (GIP) For Seismic Verification of Nuclear Plant Equipment", Revision 2A, March 1993.

94X04989.FMK WSRC-TR-94-0343 - 19 T. Bibliography (contd)

Stevenson and Associates "Survey of Strong Motion Earthquake Effects on Thermal Power Plants in California with Emphasis on Piping Systems", March 31,1993. DJ. Freeland and T.R. Roche, "Performance of Piping During the January 17, 1994, Northridge Earthquake", EQE Engineering Consultants, March, 1994.

U. Acknowledgement

1 Extracted from MSS-SP-69, 1991, with permission of the publisher, the Manufacturers Stan• dardization Society.

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