Machinery Component Maintenance and Repair Part 5 pdf

A gasket which is installed so that its centerline does not coincide with the flange centerline will be unevenlycompressed, thereby increasing the possibility of subsequent leakage.Spira

Design Pressure Loads

The pressure at the most severe condition of coincident internal orexternal 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 thermalexpansion

• Loading due to severe temperature gradients or difference in sion characteristics

expan-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 tosimulate the operating condition of the pipe

• Pull stops on all system hangers

• Check to determine that no hanger travel indicator moves out of the

“1/3total travel” cold setting zone If travel is excessive, refer diately to the design contractor for modifications of support

imme-• 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

• Repipe 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 designatedpiping engineer for resolution

Flange Jointing Practices

These steps can be written up in checklist format allowing field sonnel to use piping-related guidelines in an efficient manner, as shown

per-in the appendices at the end of this chapter

The importance of getting flanged joints right the first time cannot beoveremphasized if trouble-free performance during startup is desired Inorder to obtain an adequate joint the first time we must assure ourselvesthat the contractor, subcontractor, and the working crews appreciate theimportance of quality workmanship needed during each stage of the flangejoint building process This includes materials handling and storage oper-ations, piping prefabrication, erection, and bolting-up procedures Timespent in covering preventive measures, supervision and crew guidance,and/or training (if needed), and assuring adequate quality control will paydividends

Process Machinery Piping 151

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 benearly loose while others are so heavily loaded that they locally crush thegasket This causes leaks, particularly in high-temperature service wherethe heavily-loaded bolts tend to relax with subsequent loosening of thejoint

Improper Flange Alignment. Unevenly bolted joints, improper alignment,and especially lack of parallelism between flange faces can cause unevengasket compression, local crushing, and subsequent leakage Proper cen-terline alignment of flanges is also important to assure even compression

of the gasket See Figure 4-2 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 unevenlycompressed, thereby increasing the possibility of subsequent leakage.Spiral-wound and double-jacketed high-temperature gaskets are providedwith a centering ring or gasket extension to the ID of the bolt circle tofacilitate centering of the gasket Even so, the gasket should be centeredwith respect to the bolt circle Certain asbestos replacement gaskets should

be cut so that the OD extends to the ID of the bolt circle

Dirty or Damaged Flange Faces. These are obvious causes for leakagesince damage or dirt (including scale) can create a leakage path along the

Figure 4-2 Dimensional variations permitted for piping and flanges are independent of

pipe size.

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 occurbecause of improper piping flexibility design, or by excessive application

of force to attain flange alignment Improper location of temporary or manent restraints or supports will also cause high flange bending momentsand forces

per-The Importance of Proper Gasket Selection

The following discussion covers some of the more important factorsrelating to gasket size and type Flanges are designed to accommodatespecific sizes and types of gaskets (Figure 4-3) When the gasket does notmeet the requirements necessary to ensure good seating, or is crushed bythe bolt load, leakage will result Heat exchanges girth flanges are moreclosely tailored to one specific gasket than are piping flanges per ANSIB16.5 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 givenbolt load, a narrow gasket will experience a greater unit load than a widegasket It is, therefore, important to determine that the proper width gaskethas been used

• For piping gaskets made of an asbestos-replacing material consultANSI 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 aretoo wide because of the erroneous impression that the full flange face must be covered This is not true The above standards should always befollowed

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

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Figure 4-3 Principal flange configurations.

All piping flanges are designed to take 1/16in thick replacement gaskets The 1/16in thickness assures sufficient compressibil-ity to accommodate slight facing irregularities while having a sufficientlyhigh seating load to prevent blowout One-sixteenth in thick gasketsshould always be used with ANSI B16.5 flanges unless a specific designcheck has been made to verify another thickness.

asbestos-Spiral-wound and double-jacketed gasket thickness should comply withAPI 601

Flange Types and Flange Bolt-Up*

Factors Affecting Gasket Performance

A gasket is any deformable material that, when clamped between tially stationary faces, prevents the passage of media across the gasketedconnection (Figure 4-4)

essen-Process Machinery Piping 155

* Major portions contributed by Garlock Sealing Technologies, Palmyra, New York 14522.

Figure 4-4 Forces acting on a gasket.

Compressing the gasket material causes the material to flow into theimperfections of the sealing areas and effect a seal This bond preventsthe escape of the contained media In order to maintain this seal, suffi-cient load must be applied to the connection to oppose the hydrostatic endforce 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 theeffects of:

a Temperature: Temperature can adversely affect mechanical andchemical properties of the gasket, as well as physical character-istics such as oxidation and resilience

b Pressure: The media or internal piping pressure can blow out thegasket across the flange face

c Media: The gasket materials must be resistant to corrosive attackfrom the media

2 Joint design: The force holding the two flanges together must be ficient to prevent flange separation caused by hydrostatic end forceresulting from the pressure in the entire system

suf-3 Proper bolt load: If the bolf 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, aseal will not 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 formedmetal wire and soft filler materials form a very effective seal when compressed between two flanges A “V”-shaped crown centered in themetal strip acts as a spring, giving gaskets greater resiliency under varyingconditions

Filler and wire material can be changed to accommodate differentchemical compatibility requirements Fire safety can be assured by choos-ing flexible graphite as the filler material If the load available to compress

a gasket is limited, gasket construction and dimensions can be altered toprovide an effective seal

A spiral wound gasket may include a centering ring, an inner ring, orboth The outer centering ring centers the gasket within the flange and acts

as a compression limiter, while the inner ring provides additional radialstrength The inner ring also reduces flange erosion and protects thesealing element

Resiliency and strength make spiral wound gaskets an ideal choiceunder a variety of conditions and applications Widely used throughoutrefineries and chemical processing plants, spiral wound gaskets are alsoeffective for power generation, aerospace, and a variety of valve and specialty applications.

The spiral wound gasket industry is currently adapting to a change inthe specification covering spiral wound gaskets Previously API 601, thenew specification is ASME B16.20 These specifications are very similar,and experienced gasket producers follow manufacturing procedures inaccordance with the guidelines set forth in the ASME B16.20 specifica-tions (See Figure 4-5 for markings.)

Torque Tables

Tables 4-1 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 absolutevalues due to the large number of uncontrollable variables involved withbolted joints If there is doubt as to the proper torque value to use, wesuggest that the maximum value be used

(Text continued on page 165) Process Machinery Piping 157

Figure 4-5 Gasket identification markings required by ASME B16.20.

Table 4-1 Torque Tables for Spiral Wound Gaskets, ASME B16.5

Class 150

Max Torque Max Gsk Min Gsk Minimum Max Gsk.

Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Comp Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Recomm Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) Avail (psi) (ft lb)

Max Torque Max Gsk Min Gsk Minimum Max Gsk.

Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Comp Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Recomm Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) Avail (psi) (ft lb)

Table 4-2 Torque Tables for Spiral Wound Gaskets, ASME B16.5

Class 400

Max Torque Max Gsk Min Gsk Minimum Max Gsk.

Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Comp Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Recomm Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) Avail (psi) (ft lb)

Max Torque Max Gsk Min Gsk Minimum Max Gsk.

Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Comp Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Recomm Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) Avail (psi) (ft lb)

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 4-3 Torque Tables for Spiral Wound Gaskets, ASME B16.5

Class 900

Max Torque Max Gsk Min Gsk Minimum Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) (ft lb)

Table 4-4 Torque Tables for Spiral Wound Gaskets, ASME B16.5

Class 2500

Max Torque Max Gsk Min Gsk Minimum Nom Gsk ID Gsk OD Gsk Area No Size of per Bolts @ Comp per Comp Comp Torque Prefer’d Pipe Size Contact Contact Contact of Bolts 60 ksi Bolt Bolt @ Available Recomm per Bolt Torque (inches) (inches) (inches) (Sq in.) Bolts (inches) Stress (ft lb) 60 K (ft lb) (psi) (psi) (ft lb) (ft lb)

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.

(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

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 = 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

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

Process Machinery Piping 169

Figure 4-8 Effective gasket sealing width.