On-Stream Repair MethodsThe justification for using reformer tube crimping, hot-tapping, and line-stopping is straightforward. These serviceselimate the need for unscheduled shutdown and all the costsassociated with it.

G.W. HarrisonTeam, Inc.Alvin, Tex.

The need for on-stream services in the refinery and petro-chemical plants has never been more critical than it is today.With energy, labor, and equipment costs skyrocketing andfederal regulations on the increase, it becomes imperative toinsure safe, continuous, and economical plant operations.

In recent years, many new techniques have been develop-ed which permit repair and/or modifications to be made safe-ly on operating equipment. These include methods to 1) re-pack valves and pumps, 2) eliminate flange joint leaks,piping and fitting leaks, vessel leaks, compressor and turbinecase joint leaks etc., and 3) hot-tap and line-stop processesoperating at elevated temperatures, to around 1000 F.(538°C) and pressures to 6,000 Ib/in2 gauge (41.4 MPa).Line stops for hours, days, weeks or even months, in severechemical services are now possible.

First, this article will outline the services available andtheir special applications, then look at determining feasibilityof these services, and finally, will discuss the justification fortheir use.

Prior to the recent birth of the on-stream leak repair indus-try, it was quite common to see steam and water leaksthroughout a plant. In some cases, these leaks have existedfor 5, 10, 15 or 20 years, and some even longer. Most plantswould go through a periodic leak elimination campaign inwhich a good part of the leaks would be repaired, usually bywelding and/or banding. These, of course, necessitatedreplacing the valve and companion flange at some futureshutdown. Valve packing leaks were also found difficult tohandle due to bad back seats, corroded gland bolts, and dam-aged valve stems. As a result of the many difficulties encoun-tered, some leaks were not repaired, that is, until theybecame a safety hazard, noise level problem, or just leakedtoo much steam or water. As for the process leaks, they nor-mally required a shutdown.

Figure 1 illustrates a typical valve packing leak. Leaks ofthis magnitude are easily eliminated by an on-streamdrill-and-tap method. This means drilling into the packinggland area and injecting a packing material that will remainpliable, even at elevated temperatures. Pliable packing per-mits continued operation of the valve, including motor-

operated valves. Also, it will not score the valve stem andpermits future repacking, should the need arise. When thevalve is properly repaired by this method, the packing glandwill be completely filled and the gland follower fully extend-ed, so that the packing can be adjusted from time to time.

In cases where the valve is in corrosive services or the gér-erai condition of the valve is questionable, a hot-tap blockshould be used to permit full thread engagement of the injec-tion valve. When a valve is severly deteriorated, or for somereason the drill-and-tap method would not be desirable, anauxiliary packing gland can be installed to fit above the pack-ing gland follower. The auxiliary packing gland has alsobeen installed on centrifugal pumps and agitators, eliminat-ing the need for shutdown. When it is necessary to drill intovalves containing hazardous or dangerous materials, or thoseunder high pressures, the final drill-through should beaccomplished through a packing gland arrangement to con-tain the materials.

Figure 1. A typical valve packing leak.

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Figure 2. Heat exchanger with a severe joint leak. Figure 4. Heat exchanger with the leakage con-tained.

Drill-and-tap meets standardWhen the drill-and-tap method is properly used, the in-

tegrity of the piping system can be maintaned and the ANSIB31.3 standards requirements will be met. The section of thestandards involved is 314.2.1 (b) (4): "Couplings havingstraight threads shall not be used for other than Category Dfluids. ' ' Category D fluid service is defined as, "a fluid ser-vice in which all the following apply: 1) the fluid handled isnonflammable and nontoxic, 2) the design gauge pressuredoes not exceed 150 Ib/in2 ( 1.0 MPa), and 3) the design tem-perature is between -20 F (-29'C) and 360 F (182 C)."

Repacking of centrifugal pumps, agitators, mixers and de-fiberators by a method similar to the drill-and-tap has beenextremely successful. In some cases, service life has been ex-tended tenfold over the use of conventional braided pack-ings. This method has also been effective on reciprocatingpumps, hydraulic rams, and expansion joints. Again, the useof the auxiliary packing gland should be considered, particu-larly when the shaft run-out is excessive and shaft sleeve isdeteriorated. As a note of interest, the stern tubes on ocean-going steamships have also been repacked by this method,and delayed the dry-docking of the ships for over a year.

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Figure 3. Heat exchanger with a leak repair clamp inplace.

Figure 2 illustrates a heat exchanger with a severe jointleak. Figure 3 illustrates the same heat exchanger with a leakrepair clamp in the place and in the process of being sealed.The clamp is permitted to vent through the injection portswhile sealant is being injected. As the sealant reaches an in-jection port, the injection is moved to that port, and so com-pletely around the clamp, insuring that the entire void area isfilled and sealant is forced to the point of leakage. Figure 4illustrates the same heat exchanger with the leakage contain-ed.

Figure 5 illustrates a leak repair clamp installed on the tophead joint of an ammonia synthesis converter; the flangediameter is 94.5 in (2.4 m). The converter operates at 3,300Ib/in2 gauge (22.8 MPa) and the temperature is 425 F(218.3 C) at this location. This leak repair clamp was instal-led in February of 1976 and is sill in place.

At times it is necessary to enclose a valve, check valve,motor valve, relief valve, expansion joints, and other equip-ment in order to contain a leak. Leak repair technology is byno means limited to the use of clamps and enclosures. Manyof the flange joint leaks can be eliminated by a method knownas " wire-and cable. ' ' The wire-and-cable method consists ofreplacing some of the flange joint studs and nuts with specialslotted studs and injection nuts. The void area between theflanges is then filled by wrapping successive layers of hightensil wire, compatible with the service. A backup cable isplaced around the periphery of the wrapped wire and tension-ed. Sealant is then injected through the injection nuts and theslotted studs, into the void within the wire wrap and themating flange faces.

In the case of compressor or turbine case joints or similartype joint leaks, the sawtooth isolation method has been veryeffective.

Non-destructive methods

The methods discussed above are non-destructive and canbe readily performed on hydrocarbon, acid or other types ofleaks, as well as on stem and water ruptures.

Another service available is the isolation of reformer tubesin service. Tube isolation is limited to reformers with pig-

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Figure S. Leak repair clamp instalSed on the top headjoint of an ammonia synthesis converter.

tails, and is accomplished by crimping both the inlet and out-let pigtails. The equipment used consists of two compacthydraulic stud tensioners mounted on a single base; one ofthese is required on both the inlet and outlet pigtails. Thecrimping units are both operated by an air-operated portablepump.

Figure 6 illustrates a crew installing the crimping equip-ment on an outlet pigtail after cutting out a section of the re-former casing. Figure 7 illustrates the crimper in position onan outlet pigtail. Figure 8 shows a crimping block on thecrimped outlet pigtail; this block remains on the pigtail. Fig-ure 9 illustrates a crimping block on the crimped inlet pigtal;this block also remains on the pigtail. The need for weldingon either the pigtail or crimping blocks is eliminated by selec-ting the proper blocks for size and schedule of the pigtal. Insome cases, because of internal scale or pigtail wall deterior-ation, it is necessary to crimp a pigtal twice and inject a seal-ant between the crimps.

After crimping, the reformer casing is reinstalled. Somereformers have a flexible piping pigtail between the inletheader and the tube; this type of pigtal does not lend itself tothe crimping operation. Instead, the tube is sealed by drillingand tapping a series of injection and vent ports into the inlet

Figure 6. Crew Installing crimping equipment on anoutlet pigtail.

flange of the tube. A sealant is injected to bridge the catalystand seal off the tube.

Hot-tapping and line-stopping have been used in the pipe-line industry for a number of years, and in the past severaldecades, have moved into refining and petrochemical plants.Much of the equipment used in the pipeline industry hadlimited application in refining and petrochemical industries

Figure 7. The crimper in position.

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Figure 8. A crimping block on the outlet pigtail.

due to pressure, temperature and material in compatibility.Hot-tap equipment has been developed to make hot taps to6,000 lb/in2 gauge (41.4 MPa), temperatures in the 1,000 F(538 JC) range, make tangential and angular taps, and eventap around 90 ~ ( 1.57 Rad) elbows. It is also possible to installpermanent thermowells in operating lines. The hot-tap canalso be used to open gate valves which the stem has pulledfree of the gate.

Until recently, line-stopping has been restricted to:1. Low temperature, (below 650JF) (343'Q.2. Low pressure (750 Ib/in2 gauge, or 5.2 MPa).3. Products which would not attack the sealing cup.4. Lines with relatively little or no flow.5. Lines free of excessive corrosion and deposits.Equipment and techniques have been developed which

permit line-stopping most all process piping systems. Thenew techniques use a tapered metal plug which goes com-pletely across the line. The plug is made from material com-patible to the system. It is now possible to line-stop anypiping system of 16 in (40.64 cm) pipe size or smaller, onwhich a line-stop fitting can be installed. New techniqueshave also been developed to permit stopping off branch con-nections at the branch to main line joint.

Feasibility of on-stream repair

We must now look at determining the feasibility ofthese services. In terms of safety considerations we must ask:

1. What is the physical condition of the equipment?2. Is it in danger of imminent failure?3. Are the service company personnel equipped with the

necessary safety devices (full acid suits, breathing air, firesuits, air conditioned suits, safety belts, etc.)?

4. Are the service company personnel required to attendregular scheduled safety meetings?

5. Are the service company personnel traned to do thejob?

6. Are the service company personnel backed up with en-gineering and research facilities?

Under engineering considerations we must ask:1. Has the clamp or enclosure been designed to the appli-

cable section of the ASME code?2. Are materials used ASTM grade?

3. Are mill test reports available on the materials used?4. Are the welders qualified under Section XI of the

ASME code?5. Are the clamps or enclosures designed to line speci-

ficationor vessel specifications?6. Do drilled and tapped holes meet ANSI B 31.3?7. When contact with stainless steel, do the sealants con-

tain chlorine or other halogens?8. Has the sealant been certified for the intended service,

or will it cause a chemical reaction?9. What is the pH of the sealant?10. Will the sealant encourage caustic embrittlement?11. When an enclosure or clamp is used, is the void com-

pletely filled and the annular around the studs filled to reducethe chances of hydrogen entrapment and possibly, hydrogenattack?

12. Are the repair means non-destructive?13. Will the personnel work from a crane, if necessary?14. What is the response time?Lastly, let's look at the rationale for on-stream services.

The justifications for using reformer tube crimping, hot-tapping, and line-stopping are straightforward. These ser-vices eliminate unscheduled shut-downs and all costs associ-ated with shutdown, e.g., lost production, decontamination,the need for other repairs necessitated by the shutdown.

Figure 9. A crimping block on the inlet pigtail.

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Figure 10. Chlorine storage tank damaged in anexplosion.

Figure 11. Plugging a large puncture in the shell ofthe chlorine storage tank.

On-stream leak elimination services are important in theelimination of unscheduled shutdowns. The elimination ofprocess leaks not only reflects a savings in product, but re-duces possible fire and health hazards. In many cases, plantshave been able to come within air pollution compliance onlyafter eliminating numerous small leaks, from flange and/orvalve packings. With quick response of service personnel,major spills have been contained, and even evacuation ofpersonnel has been averted by the use of on-stream leakrepair methods. Figure 10 illustrates a chlorine storage tankwhich was damaged in an explosion; the manway nozzle isshown after repairs were effected. Figure 11 illustrates theplugging of a large puncture in the shell of the same chlorinestorage tank as in Figure 10.

It is much easier to illustrate the savings realized by elimi-nating steam leakage. Utilizing Grashof's formulas (figureson saturated steam conditions) at an optimum 100% boilerefficiency, a 1/32 in (0.794 mm) diameter hold at 450 Ib/in2gauge (3.1 MPa) will permit the loss of 420 Ib (191 kg) ofsteam per day, that's 154,000 Ib (6,954 kg) of steam peryear. Using the same pressure, a 1/87 in (3.175 mm) diam-eter hole will lose 6,760 Ib (3,066 kg) per day or 2.468,million Ib ( 1,119,485 kg) per year. At steam costs approach-ing $3/1,000 Ib (454 kg), it is easy to see the need to elimi-nate leaks.

In addition to these savings, using non-destructivemethods to repair leaks saves the cost of replacing valves,flanges or other fittings damaged by welding or peening.

DISCUSSION *FEELDERS, UKF Holland: Can you tell me whatmaterial you are using to seal that pigtail in betweentwo clamps?GEORGE HARRISON, Leak Repairs, Inc.: I cannotgive you the chemical composition of the sealant, asit is proprietary. I am sorry that I can't go beyondthat.BOB PRESCOTT, C.F. Braun and Co.: When youcome in and repair a leak in a vessel or whatever,does your company assess the equipment involvedto determine whether it's mechanically safe tocontinue operating that piece of equipment after therepair? Or is this left up to the operator?HARRISON: When we install a clamp or enclosureon a piece of equipment, the leak repair technicianobtains the measurements, operating data, anddesign conditions from the operator. This informa-tion is forwarded to our engineering group whodesigns the necessary device. If the design of thedevice increases the bolt loading, then the device isdesigned with a clamping means and/or strong-back to maintain the equipment design conditions.If we are unable to achieve these conditions, thenwe go back to the operator and explain to what pointthe safety factor will be reduced. It is then the opera-

tor's decision whether to go forward or not.Now, a lot of times, when installing a clamp or

enclosure or a simple wire and cable, you canimpose adverse conditions on the equipment, con-ditions which permit the entrapment of hydrogenand/or other materials which can adversely affectthe materials of construction. In the slide I showed,the clamp on an ammonia synthesis converter, therewas great concern about hydrogen attack on thebolting. To monitor the condition at-the bolts, wechecked weekly by drilling out the injection pointsat each stud and taking pressure measurements todetermine if any hydrogen was getting into the studarea. Several times, the pressure would build toaround 10% of the operating pressure, in theseinstances we would reinject the clamp, and in allcases the pressure would then drop back to zero.

It is our company policy to completely fill the voidarea, forcing the sealing media into the annularspace around the bolting and back into the point ofleakage. This accomplishes two things: First, it dis-places any chemical from around the bolting, andsecond, it drops the bolt loading by reducing theeffective area on which the contained pressure canact.

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