Machinery Components Maintenance And Repair Episode 1 Part 8 pdf

Text continued from page 157All 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, able quality, and approved materials

(Text continued from page 157)

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, able quality, and approved materials of construction as well as metallurgy

accept-It is 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 withASME B16.5 specifications Special attention should be given to seatingsurface finish and flatness

Only torque wrenches that have been calibrated should be used Theproper bolt tightening pattern must be followed (see Figure 4.6 for properbolting pattern) with the desired ultimate torque value arrived at in aminimum of three equal increments All bolts in the flange should then bechecked 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 theASME ring gasket dimensions No provisions have been made in thesetables 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 aseal The most common cause of leaky gasketed joints is improper instal-lation procedures

Process Machinery Piping 165

Figure 4-6 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, do not tighten any bolts morethan 30 percent of the recommended bolt stress Doing so will causecocking of the flange and the gasket will be crushed

• Upon reaching the recommended torque requirements, do a wise bolt-to-bolt torque check to make certain that the bolts havebeen stressed evenly

clock-• Due to creep and stress relaxation, it is 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 thosefor which the flange was rated, higher bolt pressures must be applied inorder 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 stressvalues required to seat the gasket during hydrostatic tests at higher thanflange-rated pressures may cause the standard bolts to be stressed beyondtheir yield points

Upon completion of hydrostatic testing, relieve all bolt stress by 50percent of the allowable stress

Begin replacing the high-strength alloy bolts (suggested for test tions) one by one with the standard bolts while maintaining stress on thegasket

condi-After replacing all the bolts, follow the tightening procedure mended in the bolting sequence diagrams (Figure 4-6)

recom-Pre-Stressing Bolts for Thermal Expansion

Bolts should be pre-stressed to compensate for thermal expansion aswell as for relaxation, creep, hydrostatic end pressure, and residual gasketloads

166 Machinery Component Maintenance and Repair

A difference in the coefficient of thermal expansion between the rials of the flange and the bolts may change loads In cases of seriousthermal expansion, it may be necessary to apply a minimum of stress tothe bolts and allow the pipe expansion to complete the compression of thegasket.

mate-A gasket with a centering guide ring should be compressed to the guidering A gasket without a centering guide ring must be installed with pre-cautions taken to prevent thermal expansion from crushing the gasketbeyond its elastic limit

Calculating Load Requirements

The load requirements can be calculated from two formulas that definethe minimum load required to effect a seal on a particular gasket The twoformulas are

Wml and Wm2 When these formulas have been calculated, the largerload 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 Figure 4-7

(M = 3 for spiral woud gaskets)

Y = Seating stress “Y” defined in Figure 4-7

(Y = 10,000 psi for spiral wound gaskets)

N = Basic width of a gasket per chart in Figure 4-8

(For raised face flanges see diagram 1a)

B0 = Basic seating width of a gasket per chart, Figure 4-8

(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 gasketface, the OD is equal to the outer diameter of the raised face

168 Machinery Component Maintenance and Repair

Figure 4-7 Gasket factors “M” and “Y.”

Process Machinery Piping 169

Figure 4-8 Effective gasket sealing width.

Given the ID and OD, find the value of N Then define B0 in terms

on the gasket If not, higher bolt stresses or changes in the gasket designare required for an effective seal

NOTE: Flange design code suggestions for low-pressure applicationscalling 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 ditions provide a suitable seating surface For internal pressure to becontained, flange rotation and sufficient residual loads must also be con-sidered in the flange design

con-General Installation and Inspection Procedure

This segment covers recommended procedures relating to the tion and inspection of a joint prior to the actual bolt-up Obviously, hightemperature piping joints in hydrogen-containing streams are less forgiv-ing than those in more moderate service Critical flanges are defined

prepara-as joints in services in excess of 500°F and in sizes above six in in

Wm1 = [p(P)(G 2 )/4] + [2(B 1 )( p)(G)(M)(P)]

Wm2 = p(B 1 )(G)(Y)

170 Machinery Component Maintenance and Repair

Table 4-5 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)

Nominal Number Diameter Stress

Diameter of at Root Area at Root 30,000 psi 45,000 psi 60,000 psi

of Bolt Threads of Thread of Thread Torque Compression Torque Compression Torque Compression (inches) (per inch) (inches) (sq inch) (ft lbs) (lbs) (ft lbs) (lbs) (ft lbs) (lbs)

Table 4-5—cont’d Torque to Stress Bolts

For Machine Bolts and Cold Rolled Steel Stud Bolts (Load in pounds on stud bolts when torque load is applied)

Nominal Number Diameter Stress

Diameter of at Root Area at Root 7,500 psi 15,000 psi 30,000 psi

of Bolt Threads of Thread of Thread Torque Compression Torque Compression Torque Compression (inches) (per inch) (inches) (sq inch) (ft lbs) (lbs) (ft lbs) (lbs) (ft lbs) (lbs)

(Text continued from page 170)

• Indentify critical flanges and maintain records A suitable recordform is attached in Figure 4-9 A suggested identification procedure

is to use the line identification number and proceed in the flow tion with joints #1, #2, etc

direc-Prior to Gasket Insertion

• Check condition of flange faces for scratches, dirt, scale, and trusions Wire brush clean as necessary Deep scratches or dents willrequire refacing with a flange facing machine

pro-• Check that flange facing gasket dimension, gasket material and type,and bolting are per specification Reject nonspecification situations.Improper gasket size is a common error

• Check gasket condition Only new gaskets should be used Damagedgaskets (including loose spiral windings) should be rejected The IDwindings on spiral-wound gaskets should have at least three evenlyspaced spot welds or approximately one spot weld every six in ofcircumference (see API 601)

• Use a straightedge and check facing flatness Reject warped flanges

• Check alignment of mating flanges Avoid use of force to achievealignment Verify that:

1 The two flange faces are parallel to each other within 1/32in at theextremity of the raised face

2 Flange centerlines coincide within 1/8in

Joints not meeting these criteria should be rejected

Controlled Torque Bolt-Up of Flanged Connections

Experience shows that controlled torque bolt-up is warranted for certainflanged connections These would typically include:

• All flanges (all ratings and sizes) with a design temperaure >900°F

• All flanges (all ratings) 12 in diameter and larger with a design perature >650°F

tem-• All 6 in diameter and larger 1,500 pound class flanges with a designtemperature >650°F

• All 8 in diameter and larger 900 pound class flanges with a designtemperature >650°F

• All flanges not accessible from a maintenance platform and >50 ftabove grade

Process Machinery Piping 175

Table 4-6 Flange and Bolt Dimensions for Standard Flanges

2500 psi

WARNING: Properties/applications shown throughout this table are typical Your specific

application should not be undertaken without independent study and evaluation for ability For specific application recommendations consult the manufacturer Failure to select the proper sealing products could result in property damage and/or serious personal injury Performance data published in this table have been developed from field testing, customer field reports and/or in-house testing.

suit-While the utmost care has been used in compiling this material, we assume no bility for errors.

In addition, it is generally appropriate to apply the above criteria toflanged 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 theabove categories

• All flanged connections which will eventually be covered with lowtemperature insulation within the above reference criteria

Adherence to the following procedure is recommended for controlledtorquing of line flanges, bonnet joints, ect., when specified

Preparation

• Thoroughly clean the flange faces and check for scars Defectsexceeding the permissible limits given in Table 4-7 should berepaired

178 Machinery Component Maintenance and Repair

Table 4-7 Flange Face Damage/Acceptance Criteria

only

seating surface only

2 Spiral wound in Scratch-like > 1/2 of tongue/ 1 mil maximum

joint

3 Spiral wound in Scratches, Smooth > 1/2 of seated Up to 1/2 of raised face joint depressions & gen’l width (min of serrated finish

metal loss due to 1/4≤ intact depth

• Check studs and nuts for proper size, conformance with piping rial specifications, cleanliness, and absence of burrs

mate-• Gaskets should be checked for size and conformance to tions Metal gaskets should have grease, rust, and burrs completelyremoved

specifica-• Check flange alignment Out-of-alignment of parallelism should belimited to the tolerance given in Figure 4-2

• Number the studs and nuts to aid in identification and to facilitateapplying crisscross bolt-up procedure

• Coat stud and nut thread, and nut and flange bearing surfaces with aliberal amount of bolt thread compound

Process Machinery Piping 179

Figure 4-10 “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 andbecause of temperature changes, the bolts and gaskets deform perma-nently This causes a loss of bolt stress after the temperature changes havesmoothed out Hot bolting helps correct this

180 Machinery Component Maintenance and Repair

Figure 4-11 Tensioners by Hydrotight-Sweeney.

Hot Bolting Procedure

The objective of hot bolting is to restore the original bolt stress whichhas dropped due to yielding and/or creep of the flange joint components

If possible, this should be done with a bolt tensioning device Hot boltingshould start at the point of leakage and proceed in a crisscross pattern asdescribed previously Seized bolts sometimes present a problem when hotbolting In such cases, it is necessary to use a wrench on both nuts

Using Bolt Tensioners

There exists considerable experience with the use of various bolt sioners for hot bolting These procedures typically involve first running adie over the stud projections to facilitate subsequent installation of the ten-sioner heads Mechanics are instructed to leave the heads in place for theminimum time necessary so as to prevent leakage of hydraulic fluid at theseals Past procedures called for immersion of heads in water betweenapplications; however, this is no longer necessary

ten-Process Machinery Piping 181

Figure 4-12 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 hasoriginated and the crisscross pattern should be used from there Joints withspiral-wound gaskets can be tightened only to the limit of the steel cen-tering ring thickness Further tightening is fruitless if a spiral-woundgasket 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 isolatedand the joint broken to determine the cause:

• Examine flange facings for damage, distortion (warping), or foreignmatter

• Check flange alignment, cut and realign piping if necessary

• Check gasket for proper material, dimensions, and type Use a newgasket 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 is 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 springhangers to lower bending moments

• If leakage occurs during rainstorms, it will be necessary to installsheet metal rain shields, which may cover the top 180° of the flange,

to prevent such leakage These should be located about four inchesaway from the flange surface and should have sufficient width tocover 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 tominimize 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, larly on the intake to any cylinder, cannot be over-emphasized This is par-ticularly important with multi-stage high-pressure compressors where

particu-182 Machinery Component Maintenance and Repair

* Refer to appendices at the end of this chapter for typical checklists.