01

ARTICLE KD-6DESIGN REQUIREMENTS FOR OPENINGS,CLOSURES, HEADS, BOLTING, AND SEALS

KD-600 SCOPE

The requirements in this Article apply to heads,closures, bolting, and seals. These requirements areadditional to the general requirements given in ArticlesKD-2, KD-3, and KD-4.

KD-601 Openings

The Designer shall consider the influence of crossbores and other openings on the static strength integrityof the vessel. Additional guidance is provided in Non-mandatory Appendix H.

KD-610 THREADED CONNECTIONS

(a) Straight threaded connections are permitted asprovided for in this Article.1 Tapered pipe threads arenot permitted.

(b) Where tapped holes are provided in pressureboundaries, the effect of such holes (e.g., stress riser,material loss) shall be considered in the vessel design.

(c) Thread load distribution shall be considered indesign cyclic analysis per KD-616.

KD-611 Standard Bolt and Nut Pairs

If a standard bolt and nut pair conforming to materialspecifications in Section II, Part D is used and bothmembers are of the same material, the thread shearand bearing capability need not be qualified further.

KD-612 Average Thread Shear Stress

The average shear stress in the threads, calculatedby dividing the design load by the appropriate thread

1 The Designer is cautioned that fine threads may cause assemblyproblems and possible loss of engagement because of thermal expan-sion and dilation due to loading.

67

shear area, shall be limited to 0.25Sy at the designtemperature.

KD-613 Average Thread Bearing Stress

The average bearing stress in the threads due to themaximum design loading shall be limited to 0.75Sy.

KD-614 Limitations on Thread Displacements

Relative radial displacement between mating threadsshall be calculated considering the combination ofapplied loads and thermal effects. No credit shall betaken for thread friction. The results of this analysisshall demonstrate that the threads having relative radialdisplacement less than 10% of the minimum threadoverlap meet the requirements of KD-612 and KD-613. No credit shall be taken for threads whose relativeradial displacement exceeds 10%.

KD-615 Length of Engagement

The length of engagement is to be taken as theminimum which can occur within the drawing toleranceswith no credit for partial threads.

(a) Connections which have imposed loads on threadsin tapped holes shall comply with the requirements ofKD-615(b). The vessel or an integral weld buildupshall have a flat surface machined on the shell toreceive the connection.

(b) Where tapped holes are provided, the threadsshall be full and clean and the engaged length shallnot be less than the larger ofds or

0.75ds 1 Sy of stud material at design temperatureSy of tapped material at design temperature2

in which ds is the root diameter of the stud.

01

COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling ServicesCOPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services

01

KD-616 2001 SECTION VIII — DIVISION 3 KD-621

KD-616 Fatigue and Fracture MechanicsAnalysis

(a) Except as permitted in KD-100(c), a fatigueanalysis in accordance with Article KD-3 or a fracturemechanics analysis in accordance with Article KD-4is required for all threaded connections.

(b) The fatigue evaluation of a threaded joint ismade by the same methods as are applied to any otherstructure that is subjected to cyclic loading.

(c) The stresses developed by the expected serviceshall be analyzed. Unless it can be shown by analysisor test that a lower value is appropriate, the fatiguestrength reduction factor for threads shall not be lessthan 4.0.

(d) ANSI standard nuts of materials permitted bythis Division do not require fatigue analysis. Internalthreads mating with a stud or bolt do not require fatigueanalysis for bolting loads. However, the effects of theinternally threaded penetration on the nominal primary-plus-secondary stresses in the internally threaded mem-ber shall be considered.

KD-617 Special Threads, Sleeve CoupledJoints, and Other Proprietary Joints

Flared, flareless, and compression type joints fortubing are not permitted.

Mechanical joints for which no standards exist andother proprietary joints may be used provided therequirements of KD-617(a), (b), and (c) are met.

(a) Provision is made to prevent separation of thejoints under all service loadings.

(b) A prototype joint shall be subjected to perform-ance tests to determine the safety of the joint undersimulated service loadings per Article KD-12. Whenvibration, fatigue, cyclic conditions, low temperature,thermal expansion, or hydraulic shock is anticipated,the applicable loads shall be incorporated in the tests.

(c) Vent passages shall be provided to prevent pres-sure buildup caused by accidental or incidental develop-ment of any secondary sealing areas exterior to thedesignated sealing surface (e.g., threads).

KD-620 BOLTING

The number and cross-sectional area of bolts requiredto resist primary loads shall be determined. The yieldstrength values to be used are the values given inSection II, Part D for bolting materials.

68

(a) The average primary stress intensityS shall bebased on the thread root diameter and shall not exceedthe following limit:

S p1

1.8Sy

(b) For bolts with a reduced shank, which has adiameter less than 0.9 times the thread root diameter,the above equation shall be replaced by:

S p1

1.5Sy

provided the actual shank diameter is used.(c) Primary-plus-secondary membrane stress intensity

in bolts shall not exceed 0.75Sy. Primary-plus-secondarymembrane plus bending stress intensity in bolts shallnot exceedSy due to the combination of both the designloads and preloads. Stress intensification due to thethreads shall not be considered in the above analysis.

KD-621 Threading and Machining of Studs

Studs shall be threaded full length, or shall bemachined down to the root diameter of the thread inthe unthreaded portion. The threaded portions shallhave a length of at least 11⁄2 times the nominal diameter,unless analysis (see KD-612 through KD-616) using themost unfavorable combination of tolerances at assemblydemonstrates adequate thread engagement is achievedwith a shorter thread length.

Studs greater than eight times the nominal diameterin length may have an unthreaded portion which hasthe nominal diameter of the stud, provided the followingrequirements are met.

(a) The stud shall be machined down to the rootdiameter of the thread for a minimum distance of 0.5diameters adjacent to the threaded portion.

(b) A suitable transition shall be provided betweenthe root diameter portion and the full diameter portion.

(c) Threads shall be of a “V” type, having a minimumthread root radius no smaller than 0.08 times the pitch.

(d) Fillet radii at the end of the shank shall be suchthat the ratio of fillet radius to shank diameter is notless than 0.060.

01

COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling ServicesCOPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services

KD-630 PART KD — DESIGN REQUIREMENTS KD-651

KD-630 LOAD-CARRYING SHELL WITHSINGLE THREADED ENDCLOSURES

Because of the many variables involved, and in ordernot to restrict innovative designs, detailed rules arekept to a minimum. The effects of the total load tobe resisted, the number of threads, the thread form,the relative stiffness of mating parts, and friction shallbe considered in both the static and fatigue analysesof the closure. Stresses can be minimized by providinggenerous undercuts ahead of the first threads and provid-ing flexibility in mating parts to promote equalizationof the thread loads.

KD-631 Stresses in Vessel at Threads

The Designer shall identify the area of the threadedclosure where the maximum stress intensity occurs.This is generally the area at the root of the most highlyloaded thread, which is usually the first or secondthread. Calculation of this stress intensity requires con-sideration of the actual thread load, stress concentrationfactor due to thread form (in particular, the thread rootradius), thread bending stress, and the membrane andbending stresses in the vessel at the thread.

KD-631.1 Longitudinal Bending Stresses.Unlessit can be shown by analysis or test that a lower valueis appropriate, the primary longitudinal bending stressin the vessel at the first thread shall be considered tobe 3.0 times the primary longitudinal membrane stress.

KD-631.2 Circumferential Stresses.The circumfer-ential stresses are significantly affected by the distanceto the pressure seal. Unless shown by analysis or testthat a lower value is appropriate, the circumferentialstresses in the vessel at the first thread shall be consid-ered to be those in the cylinder derived with theequations in Article KD-2. In addition, circumferentialstresses due to resultant radial loading of the threadsshall be included.

KD-631.3 Thread Load Distribution. In general,the threads do not carry the end load uniformly. TheDesigner shall determine thread load distribution. SeeE-200.

KD-631.4 Fracture Mechanics Analysis.Fracturemechanics analysis shall be made in accordance withArticle KD-4. This analysis shall include as a minimumthe combined effects of bending of the thread, and theshell membrane and bending stresses.

KD-631.5 Progressive Distortion.Screwed-on capsand screwed-in plugs are examples of nonintegral con-

69

nections which are subject to failure by bell mouthingor other types of progressive deformation. Such jointsmay be subject to ratcheting, causing the mating mem-bers to progressively disengage. See KD-210(e)(9).

KD-631.6 Interrupted Threads. Closures utilizinginterrupted threads may be analyzed as closures withcontinuous threads provided that a multiplier is appliedto the resultant stresses. The multiplier is the ratio ofthe continuous thread circumferential length to that ofthe interrupted thread. The contact length used whencalculating the stress distribution for an interruptedthread may be less than the thread length because ofthe profiling of the thread ends.

KD-632 Special Closures and Materials

Threaded closures for which no standards exist maybe used, provided the requirements of KD-632(a), (b),and (c) are met.

(a) The design shall prevent separation of the closureparts under all service conditions stated in the User’sDesign Specification.

(b) The closure is analyzed in accordance with therules of Articles KD-2, KD-3, and KD-4, or a prototypehas been evaluated in accordance with the rules ofArticle KD-12.

(c) For parts for which it is impossible or impracticalto measure the yield strength after final processing, themaximum allowable tensile stress at design pressureshall be one-third the ultimate strength at design temper-ature, so long as the final processing does not adverselyaffect the ultimate strength.

KD-640 FLAT INTEGRAL HEADS

Except as provided in KD-240, flat heads shall meetthe design criteria in KD-230.

For guidance on the design of integral heads (blindheads), see E-100.

KD-650 QUICK-ACTUATING CLOSURES

KD-651 General Design Requirements

Quick-actuating closures shall be so designed andinstalled that it can be determined by visual externalobservation that the holding elements are in goodcondition and that their locking elements, when theclosure is in the closed position, are in full engagement.Alternatively, other means may be provided to ensurefull engagement.

COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling ServicesCOPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services

KD-652 2001 SECTION VIII — DIVISION 3 KD-662.2

KD-652 Specific Design Requirements

Quick-actuating closures that are held in position bypositive locking devices and that are fully released bypartial rotation or limited movement of the closureitself or the locking mechanism, and any automatedclosure, shall be designed to meet the following condi-tions.

(a) The closure and its holding elements are fullyengaged in their intended operating position before thevessel can be pressurized.

(b) Pressure tending to open the closure shall bereleased before the locking mechanism is disengaged.

(c) A coefficient of friction less than or equal to0.02 shall be used in the design analysis.

KD-652.1 Permissible Design Deviations for Manu-ally Operated Closures.Quick-actuating closures thatare held in position by a locking device or mechanismthat requires manual operation and are so designed thatthere shall be leakage of the contents of the vesselprior to disengagement of the locking elements andrelease of closure need not satisfy KD-652(a), (b), and(c). However, such closures shall be equipped with anaudible or visible warning device that shall serve towarn the operator if pressure is applied to the vesselbefore the closure and its holding elements are fullyengaged in their intended position and, further, willserve to warn the operator if an attempt is made tooperate the locking mechanism or device before thepressure within the vessel is released.

KD-652.2 Yokes.Yokes or frames shall comply withall requirements of this Division.

KD-653 Required Pressure Indicating Devices

All vessels having quick-actuating closures shall beprovided with a pressure indicating device visible fromthe operating station.

70

KD-660 REQUIREMENTS FOR CLOSURESAND SEALS

The requirement of a leak-tight seal is of primaryimportance in closures for high pressure vessels. Thisis because even small leaks produce a damaging (cut-ting) effect through the sealing surfaces, which mayprogress rapidly to increasingly hazardous conditions.

KD-661 Requirements for Closures

(a) The seal closure shall have the capability tocontain pressure with the same assurance against failureas the vessel for which it will be used.

(b) Adequate venting shall be provided in the closuredesign in the event of seal failure.

(c) The effects of dilation, distortion, or both on theclosure components under all expected conditions ofpressure and temperature shall not result in an increasein the seal clearances greater than the values requiredto retain the sealing element.

(d) A complete stress analysis shall be made of allcomponents that contribute to the strength and sealingcapability of the closure.

(e) For applications involving cyclic loads, the re-quirements of Articles KD-3 or KD-4, as applicable,shall be met for all parts except the sealing element.

KD-662 Requirements for Sealing Elements

The material selected shall be compatible with allnormally expected process and environmental condi-tions, such as pressure, temperature, corrosion, solubil-ity, chemical reaction, etc., as specified in the User’sDesign Specification.

KD-662.1 Contained Sealing Elements.The materi-als of construction for sealing elements are generallynot covered in Part KM. The User’s Design Specificationshall either specify the required material or furnishenough information to enable the Designer to make anappropriate selection.

KD-662.2 Unsupported Metallic Sealing Elements.Sealing elements which themselves provide the strengthrequired to contain the pressure (i.e., cone joint, lappedjoint, etc.) shall satisfy the requirements of this Division.

COPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling ServicesCOPYRIGHT American Society of Mechanical EngineersLicensed by Information Handling Services