packing & installation technque-petronas

8/10/2019 Packing & Installation Technque-Petronas

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Packing seals a moving part. If shaft is perfectly round with fine finish and running dead true, job iseasier. But shafts usually run out at least a few thousandths of an inch ( 1 thousandths of an inch =0.0025400 mm), With grooves or shoulders on the shaft you have a really tough job of preventingleakages, regardless of how good the packing may be for leaking problems.

Fig.1

The degree of sealing packing to accomplish

When you try to seal by tightening packing to varying degrees with a wrench, you go against good mechanics . Reason: machine designer tries to reduce friction but packing acts as brakes on runningshaft.

Many do not know that packing in, say, a centrifugal or reciprocating pump must throttle or encourage a slight leakage - not stop it altogether That is because packing acts like a bearing andmust be lubricated like one. Lubrication comes from the slight leakage of fluid from inside themachine, or, in emergencies, from saturant or oil in the packing. Where these are not practical,

packing must be lubricated some other way. Remember, if packing is dry it runs hot, hardens andscores the shaft like any other bearing that fails.

The same applies to block valves, harden or dead packing would cause the valve to leak into theatmosphere no matter how hard we tighten the packing gland. When tightening a valve packing youneed to only move one notch of the packing glands nut clockwise.

PACKING CLASSIFICATIONS

Packings fall into three broad classes. First, there is the so-called jam type, which includes any

packing that is jammed into a stuffing box and adjusted from time to time by tightening nuts on agland. These packings are braided, twisted, woven or laminated of rubber, leather, fiber, etc. As wewill see, other constructions and materials can also be used.

Fig.2

PETRONAS PENAPISAN (T) SDN. BHDKERTEH REFINERY

MYG/2001 Page 2 of 16


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Next come automatic types - so named because usually they need no gland adjustment. The fluidsealed supplies the needed pressure by forcing packing against wearing face. These packings or oil-seals can be further divided into lip and squeeze types. Better known among lip types are thecup, flange, U, etc. Best known of the squeeze types is the O-ring. Here, interference or tightness is

built into the ring; it is thus squeezed into the groove. Fluid pressure holds it against wearing surface.This type of seal is also used on special type maintenance free block valves.

Third are the floating types. These include segmental rings of carbon, metal, PTFE, plastic, etc., heldaround shaft or against cylinder by springs. Reciprocating Piston rings with built-in tension also fallinto this group. Now that we have a general idea of packing classes, let ussee how jam types seal works.

HOW PACKING SEALS

Volume taken in the stuffing box by jam-type packing is key to understanding how this commonlyused packing works. Manufacturers say packing are normally wasted, rods and shafts scored and

packing needlessly burned up just because a few mechanics working with it do not understand this basic principle.

Sketch A - Figure 2 shows a stuffing box filled with five rings of new packing. In this example, braided packing is saturated with lubricant, coated throughout with graphite and takes up about 9cubic inches ( 147.4 cubic centimeter ) of space in the stuffing box. Here the gland nuts are onlyhand tight because the new packing was just installed.

Sketch B - Figure 2 shows the same packing completely compressed until it shrunk to only 5.4cubic inches ( 88.4 cu.cm ). Volume of lubricant is lost because all saturant has been melted,squeezed or washed out. Because packing cannot be compressed further, it has reached the end of its useful life. You must renew it or it will burn up and score the shaft, causing more damage than thecost of the most expensive packing. Let us read on and learn why packing has saturant, whathappens when this volume of saturant is reduced.

Fig.3

HOW AND WHY PACKING FAILS

Sketch A shows new packing, i.e. before gland has been tightened. As machine runs, some

saturant in packing is washed or squeezed out. As saturen is lost, packing shrinks away from shaft because its volume has been reduced. Here operator usually tightenes gland, stopping all fluid flow.




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With no leakage, there is no lubrication from fluid flow. So rod heats up and temperature of packinggoes up. That is when lubricant placed inside packing material by manuracturer, goes to work. -Sketch B,

High temperature starts to melt oil out of packing which lubricates shaft for just such an emergency.Because more oil has oozed out of packing space taken by it is again reduced. That starts flow of liquid from casing into the stuffing box, which again lubricates rod and packing this also helps tocarry away heat - Sketch C.

But hers is where trouble can start, if operator tightens gland enough to stop leakage again, liquidflow is lost. Again high temperature melts more packing lubricant, reducing volume and starting flowfrom casing automatically as before. This can go on until no saturant is left in packing, until

packings volume cannot be further reduced, When gland is next tightened to stop leakage, packing burns up and rod scores, - SketchD,

This simple principle, once understood, will get the service from packing that is built into it. Everyman given the authority to tighten a packing gland, regardless of how unimportant the job may seem,must understand this or he will score rods, waste packing and cause untolddamage in outage and maintenance bills,

HOW TO TIGHTEN PACKING

Here is something every mechanic must bear in mind, There is only one way to tighten a packinggland. If joint leaks too much, tighten each hexagon nut of the packing gland by only one flat. This isone sixth of a turn. Then wait for about ten minutes. Reason: It may take that long for packing toadjust itself and reduce excessive leakage. After ten minutes, packing has distributed itself in boxand you can further tighten the nuts by another flat if leakage is still too much.

Fig.4




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RING NEXT TO GLAND WORKS HARDEST

It is natural to ask which ring in a stuffing box does the most work. In typical jam-type packings,most sealing is done by the ring next to the gland. In all metallic sets, to be described later, pressuredrop across the set is more uniform, but ring next to the casing or at the bottom breaks down mostof the fluid pressure.

Reason: The mechanical pressure is higher at gland because friction on outside of packing againststuffing box is much greater than friction along the rod. This would be true even if bore of the stuffing

box had same fine finish as rod. If friction along bore were not greater, packing would not anchor tothe wall of the stuffing box and would revolve along with with the shaft. Then it follows that the morerings the gland tries to force against the bottom of the box, the greater the pressure on the first ring it

presses against.

Installing New Packing: If a set of several rings of the same density is not seated ring by ring, butall seating is done by the gland at the same time, rings nearest gland will be highly overloaded. Then,

because of pressure decay, rings in the bottom of the box may do no sealing whatever.

Where a combination set of soft and hard packing is used, softer rings in the set normally do mostsealing. That is why dense rings must be seated correctly in the box to keep fluid pressure and gland

pressure from being exerted against softer rings - which would extrude through the joint opening.

Test Results: Indicate that, on both centrifugal and reciprocating pumps, about 70% of wear is onfirst two packing rings nearest gland. (See Figure 4), Question, then, is why not have two rings onlyor at most three, since they do most sealing ?. Reason is that each additionel ring does throttle somefluid pressure. And on most machines there must be enough rings so if one fails another does thesealing and the machine need not be shut down, That is one of the biggest advanages of packingcompared with mechanical seals.

How many rings? Curve shows eight packing rings,. Only about five of these are needed,according to pressure curve, as bottom three do little sealing, Advantage of using fewer rings is Lessrod wear. and stuffing-box design is simpler as it takes less material. If all packing rings did the sameamount of work, then it is quite logical to assume that five rings would wear rod five times as much

as one ring. But wear is not the only problem. With high temperatures and high pressures, corrosivechemicals or abrasive particles in the fluid, more rings may be the only solution for some services. Insuch cases, the bottom ring contacting the casing fluid may take most of the beating from thesesevere service conditions.




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Fig.5

BOX AND PACKING DESIGN

Packing material, shape and size, box design and clearances all affect sealing. Ideal packing would be one with low coefficient of friction, absence of abrasive effect upon rod, and ability to preventleakage. Since jam-type packings are used in stuffing boxes, let us see what effect box design has onsealing efficiency.

Standard Stuffing Box: For jam-type packing in larger machines has neck bushing, lantern ring andsleeve around shaft, top sketch, Figure 5. Sleeve and neck bushing can be replaced when worn.Grooves in sleeve or rotary shaft are hard on packing because packing must adjust itself to groovesevery time it is tightened. Neck bushing often wears at bottom as shaft bearings wear. Keepingclearance all around shaft and the neck bushing even and at a minimum makeslife easier for the packing.

Lantern ring is for forcing lubrication into packing set from outside source. Or, in some applications,

it is for forcing clean fluid against abrasive fluid to save packing and shaft.

Beveled ends in stuffing box are often a question. Theory is that bevel tends to force packing againstshaft where sealing is needed, giving better sealing with less gland adjustment. This may help some

packings, but it also tends to extrude the end rings of soft packings, scoring rod and wearing packing quickly. Many packing makers are against bevels in boxes, say square ends are best.

For so-called plastic (loose-fill) and metallic packing, use only square ends. Special conical rings doneed bevelled ends to conform to cone-shaped rings, but packing is designed for pinching effect

between rod and housing.




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Clearance at neck bushing and gland is important. Less space gives packing less chance to extrude,reduces friction against rod. Clearences often depend on machines service and the fluid the packingmust seal.

Shoulders on reciprocating rods are hard on packing, especially if neck bushing has excessiveclearance. Rod then wedges into packing, tends to force packing out through clearance at end of each stroke. Shoulders on valve stems and rods are common cause of duplex pump short stroking.All this means that before we can expect packing to do a job, condition of stuffing box, rod andclearances around the rod are very important.

General Consideration

1. Solids

Solids in the process stream, viscous materials, and corrosive usually alter the approach taken in theapplication of packing. Generally, where, a flushing medium. can be tolerated as an additive to the

process stream, satisfactory packing life can be expected. Where this is not possible, packing lifehas not been as good. The use of additional teflon throat (PTFE) bushings, harder shaft sleeves, theuse of grease injected at the lantern ring, or relieving the stuffing box to a low pressure source haskept packing life within tolerable limits, The type of packing used in abrasive service must resistwear and prevent solids from becoming imbedded in the packing surface. Three basic arrangementshave proven successful. They are:

a) high solids - alternate rings of aluminium and lead foil b) medium solids - alternating rings of lead foil and asbestosc) low solids - alternate rings of lead foil and plastic.

2. Cause of Packing Failure

Packing on rotary shafts, if considered for a controlled leakage opertion, depends on the bearingsurface of the packing and sleeve, A number of factors influence leakage besides packing

composition. The primary consideration is the shaft and shaft sleeve.

A. Shaft and Shaft Sleeve

Any eccentricity of the shaft or shaft sleeve in relation to the base of the stuffing box will usuallyresult in leakage, it is important to be sure of the placement of the bearing housing, lack of play in the

bearings, trueness of the shaft sleeve, and a good polished surface on the shaft sleeve, These itemscan normally be checked with a machinists dial indicator without removing the pump from service.




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B. Installations

Correct installation of a proper packing should result in a minimum of leakage. Correct installation presumes that each ring of packing is cut to fit exactly and is compressed in position. In this way, a portion of the pressure breakdown occurs at each ring and not just at the last ring. To complete theinstallation, a running in period should be provided to allow for proper setting of the packing.

C. Pump Internals

Wear on internal parts of the pumps, specifically the wear rings and throat bushing, can cause packing problems by allowing greater pressure to enter the stuffing box. Checking these itemsrequires disassembly of the pump and should not be overlooked in chronic leakage cases.

D. Cooling Water

Like all materials, packing is subject to destruction by heat. The source of heat can be the producttemperature or friction caused by the lack of lubrication to the packing. Cooling water is sometime used when the product temperature is above 350 oF (176 oC ), the vapor pressure isabove 14 p.s.i.a ( 1.033 kg/cm 2) and/or the suction pressure is above 150 p.s.i.g ( 10 kg/cm 2).

E. Pump Operation

Pump operation can also affect packing life. Operation back on the pump curve; that is, near shutoff,usually is the case where most packing problems are magnified. High pressures and heat aregenerated resulting in excessive packing wear. Where this type of operation can occur frequently,

bypass lines from the pump discharge and stuffing box are used to increase flow and reduce pressure at the packing.

TIPS ON MECHANICAL PACKING

Hydraulic packing on moving piston should be of endless rings, if possible.

Remember, over-tightening is the greatest cause of packing failure.

If ram are grooved or worn, recondition as no packing stands up under these disadvantages. Onhigh pressure jobs, make clearance as close as possible to avoid extrusion.

If bushing on large female adapter is worn, renew bushing. during emergency repair, use specialfemale adapter ring.

Packing are usually the weakest link in any machine. Wrong packing - or right packing improperly

installed - can be very costly.




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Always remove all turns of old packing from a stuffing box. If female adapter for lip-type packingkeeps failing, make adapter of soft metal as it takes all packing load.

Clean stuffing box thoroughly with abrasive cloth after removing old packing. Also, clean theshoulder and ram.

PACKING STUFFING BOX OP PUMP

1. Loosen and remove bolts and gland.

2. Remove all old packing. Aim packing hooks at bore of the box to keep from scoring shaft. Clean box thoroughly and flush out with compressed air if necessery to insure that all pieces of old packingare completely removed

3 On reciprocating pumps check for bent rods, grooves or shoulders.if neck bushing clearance in bottom of box is great. use a stiffer bottom ring or replace the neck bushing.

Fig.6On centrifugal pumps turn shaft and check for run-out with dial indicator, (figure 6) If greater than.003( 0.076 mm ) proceed to check bearing and shaft. Check sleeve for grooves and shoulders, if worn in excess it may be necessery to replace.

4. Check for the proper size of packing by subtracting the shaft diameter from the stuffing boxdiameter and dividing it by 2 (Figure 7). Packing size is too critical for guesswork. Check depth of stuffing box for number of rings of packing. Subtract the width of lantern ring if used

Fig.7




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5. Wind packing, needed for fillig stuffing box snugly around rod (for the same size shaft held in vise)and cut through each turn while coiled, as shown (See Figure 8). If packing is slightly too large,never flatten with a hammer, Place each turn on a clean newspaper and then roll out with pipe asyou would with a rolling pin (Figure 8)

Fig.8

6. Cutting off rings while packing is wrapped around shaft will give you rings with parallel ends. Thisis very important if packing is to do the required job..

Fig.9

7. If you cut packing while stretched out straight, the ends will be at an angle. With gap at angle, packing on either side squeezes into top of gap and ring cannot close. This brings up the questionabout gap for expansion. Most packings need none. Channel-type packing with lead core may needslight gap for expansion. (Figure 10).




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Fig.10

8. Paint or coat packing with graphite and oil compound. This includes foil type (Figure 11).

Fig.11

9. Open ring joint sidewise, especially lead-filled and metallic types. This prevents distorting themolded circumference - or breaking the ring while on the opposite direction..

10. The bottom ring of packing should be inserted in the box and forced with split bushing and packing gland against bottom of the box until it is well seated in place. On centrifugal pumps theshaft should be rotated a few turns by hand. It is essential that this first ring of packing be firmly

seated in the stuffing box so as to fit snugly against the shaft and the cylindrical wall of the stuffing box.




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11. Each sucessive rings should be installed lightly in the same manner using less pressure for eachring, The packing joints should be staggered. (Figure l3).

Fig.12

12. Install pecking so lantern ring lines up with cooling liquid opening, Also, remember that this ringmoves back into the stuffing box as packing is compressed. Leave space for gland to enter asshown,. (Figure14). Tighten gland with wrench - back off finger-tight, Allow the packing to leak untilit seats itself, then allow a slight operating leakage.

Fig.13

Fig.14




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13. As for block valves, to achieve a complete seal, turn gland nuts one-sixth of a turn or one notchat a time every once in a while until acceptable or complete sealing is achieved.

----------------------------------------------------------------------------------------------------SECTION 2

SUBJECT: BLANKING PIPELINES AND EQUIPMENT A. Objective

To teach how to install a blind flange and the technique of installation.

B. Tools and Equipment

Hammer, wrenches, graphite, wire-brush, and scraper.

1. INSTALLING A SLIP BLIND

a. Safety Precautions

(1) Secure work permit.(2) Make sure blank is the required thickness.

(3) Inspect area for hazards.(4) Wear protective equipment.




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2. INSTALLING A BLIND FLANGE (Solid Blank)


(1) Secure work permit.(2) Make sure blank is the required thickness.(3) Inspect area for hazards.(4) Wear protective equipment.(5) Work above and to one side of the line.(6) Use the correct tools and in good. condition.(7) Do not attempt to use your fingers to center gaskets.

B Installing Blind Flange on End of Line or on Equipment

1. Clean face of flange on which blind flange is to be installed.2. Clean face of blind flange.3. Install blind flange and. bottom half of bolts.4. Clean and coat gasket, with mixture of oil and graphite.

5. Wedge open flanges, if necessary.6. Install remaining bolts and tighten using the cross-over method as shown on sheet How toAssemble a Flanged Joint under title, Installation of Flanged Pipe and Fittings.

7. Install gasket making sure it is centered.8. Clean up area as part of good housekeeping.




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SECTION 3

CLEANING STRAINER (Bucket type)

A. Objective

To teach how to clean a bucket type strainer and the technique of installation.

B. Tools and Equipment

Hammer, wrenches, graphite, wire-brush, cotton rags and scraper.


(1) Secure work permit.(2) Make sure strainer has been fully drained.(3) Inspect area for hazards.(4) Wear protective equipment.(5) Work above and to one side of the line.(6) Use the correct tools and in good condition.(7) Do not attempt to use your fingers to center gaskets.(8) Use gloves to avoid fingers from being injured by sharp edges of strainer.

b. Opening Up and Cleaning of Strainer

(1) Loosen bolts in bottom half of flange, but do not remove.(2) Wedge open flange, slacking top bolts if necessary.(3) When certain there is nothing in line, remove all bolts.(4) Pull out strainer from housing(5) Clean strainer using high pressured water and let dry using compressed air.

c.. Installing Strainer and Bolting Up Flange

(1) Carefully push clean strainer into housing and install cover flange.(2) Align bolt holes using drift pins or spud wrench, if necessary.(2) Install bolts in bottom half of flange.(3) Clean both faces of the flange.(4) Clean and install gaskets coated with graphite.(5) Install remaining bolts and, tighten using the cross-over method as shown on sheet How to

Assemble a Flanged Joint under title, Installation of Flanged Pipe and Fittings.(6) Clean up area as part of good housekeeping.



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