DESIGN OF REPAIR CLAMP FOR ONLINE ELIMINATION OF LEAKAGE FROM BOLTED FLANGED JOINTS

Journal of Pressurized Equipment and Systems 2 (2004) 41-47

Design of repair clamp for on-line elimination of leakage from bolted flanged joint

Xin Ma a,*, Jinyang Zheng a, Zhongpei Ning b

a Institute of Chemical Process Equipment, Zhejiang University, Hangzhou 310027,China b Department of Production and Technology, LTH Natural Gas & Chemical Corporation, Luzhou 646300,China

Abstract

A new method for design of repair clamp used for on-line elimination of leakage from flanged joint is presented, where a removable inner ring is employed to compensate the gaps between the split surfaces of the clamp halves. Two independent dimensions are em-ployed respectively to eliminate two possible leakages of the sealant in different places. The problem on unit sealing pressure around the outside of the flange and the gap between the split surfaces of clamp is solved. The new method is applicable to eliminate leakages in bolted flanged joint under various working condition as long as the gap between flanges is equal to or larger than 6mm. Several practical applications in an ammonia plant with Kellogg process show that good economic benefit and satisfactory sealing were both achieved.

Keywords: Leakage; Injecting seal in service; Flanged joint; Repair clamp. 1. Introduction

Leakages at various levels are frequently found in welding joints, sealing devices and even shells (main body) of pressure vessels, piping and valves in process plant, generally due to corroding, flushing of internal working substance, fluctuation of service load, and so on. If the leakage develops to some extent without be-ing eliminated in time, it would result in serious prob-lems such as environments pollution, loss of working substance, waste of energy, toxicosis, explosion, etc. The most common method is to replace the disabled gasket in flanged joint, or change the defective valves or pipe tract, or mend the perforation or crack in the welding joint. However, doing these usually means shutting down the production system, with consequent great economic losses to the process plant for the con-tinuity of the process industry. Moreover, new leakages would often be provoked by fluctuations of pressure load and thermal load when the production system is shut down and started again. It is, therefore, very im-portant to eliminate leakage on-line in time so that high load operation of the process production with safety, economic efficiency and long production time would be maintained.

It is effective to deal with some leakages on-line by using welding, plugging or gluing [1] for certain oper-ating condition and working substance, and full encir-clements sleeves can also be employed for some per-foration in the gas pipeline as well [2-3]. But these * Corresponding author.

E-mail address: [email protected] (Xin Ma).

repair techniques may be invalid when the operating pressure or operating temperature is high, or the work-ing substance is flammable or explosive, where the injecting seal [4] is an alternatively available.

1.1. Injecting seal in service

Injecting seal in service is widely used to eliminate leakages of working substance in bolted flanged joint, welding seam and shell of pressure vessels and piping in process plants. A new seal chamber, which is used to contain the sealant, is built over the areas where the leakages are detected. A repair clamp is extensively used to build the sealing chamber. The repair clamp usually comprises two half shells, which are joined together with plate lug, bolts and nuts. Along the circumferential direction, each of the shells has some through-thickness threaded holes (typically with thread of M14×1.5), which are used to let the sealant into the seal chamber and to vent the leaking working sub-stance when the injecting seal in service are carried out. The sealant is injected into the seal chamber with a sealant gun (sealant syringe), which is connected with the clamp shell in the thread hole one by one with a connecting nut. Through the connecting nut, there is a small plug valve that is used to let the sealant into the seal chamber and prevent it from leaking out. The driving force of the piston of the sealant gun comes from oil pressure produced by an oil pump, which is connected with the gun by a high-pressure hose. Fig. 1 shows how the injecting seal in service works. After installing the clamp and connecting the sealant gun, the hose, the pump, then the sealant gun is linked with one

Xin Ma et al. / Design of repair clamp for on-line elimination of leakage from bolted flanged joint

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of threaded holes which is in the opposite direction to the leaking point, then the sealant is injected into the sealing chamber continuously from the sealant gun, and the leaked working substance is vented from the other threaded holes. As the sealing chamber is filled out gradually with the sealant, which solidifies gradu-ally under combined action of the temperature of the leaked working substance and the injecting pressure, the leaking passage of the working substance is blocked little by little, and the plug valves are closed one by one when the injected sealant arrives. When all the plug valves are closed and the leaking passage is blocked tightly with the solidified sealant, the leakage will be eliminated completely finally. The possibility of eliminating the leakage of working substance on-line without shutting down the production system is probably the unique merit of injecting seal in service over other competing techniques mentioned above.

1.2. Problems with repair clamp over flanged joint

The main reasons for leakages in bolted flanged joint are the defected gasket and damaged sealing face, due to fluctuation of the operating pressure or initial tiny flaws, where initial minute leakage will soon de-velop into ejecting heavily resulted from highly speed attack of the working substance, especially in operating condition where high temperature and high pressure are both present.

Caulking, steel strip and repair clamp can all be used in the injecting seal in service to eliminate the leakage in the bolted flanged joints [4]. The first two methods are applicable only for leakages in operating condition of low pressure and small gap between flanges, while the third one, i.e., the repair clamp, is almost applicable for leakages in all kinds of operating condition. On

account of extensive using of the repair clamp, it is important to design an appropriate repair clamp in or-der to carry out injecting seal in service effectively.

Spot repair on-line of leakage in the bolted flanged joint is usually a hard job, due to short time, the for-midable natural conditions and the tough work envi-ronment. How to design a repair clamp over bolted flanged joint properly seems, therefore, to be a subtle work even for experienced engineers, especially in operating conditions where high temperature and high pressure are both present or the leaking working sub-stance is explosive or flammable.

1.3. Previous work

Previous work in this field focused mainly on fol-lowing: analysis and experimental validation of the additional force of bolts caused in bolted flanged joint when the injecting seal was carried out [5], and how to design a repair clamp over bolted flanged joint with reasonable structure under severe operating conditions [6-8]. To ensure safety of bolts, Zhao [5] advised the initial injecting pressure should not be larger than 6.0 MPa, and the final injecting pressure, 10.0 MPa. Hu [8] and other researchers [1,4] developed 3 kinds of rein-forced repair clamp over bolted flanged joint:

. Repair clamp with caulking, in which a convex Ⅰis designed along the inner side of the clamp, and large plastic deformation is produced along the edges of both flanges by caulking in order that the edge of the flange can contact tightly with the convex (see Fig. 2 for de-tail). The flanges should be made of plastic materials or this kind of repair clamp will fail. On the other hand, it will be a tough job to strike the edges when the flanges are large.

bolted flanged joint

repair clamp shell

connecting nut and plug valve

seal chamberoil pump

high pressure hose

sealant gun (sealant syringe)

Fig. 1. Schematics of how a repair clamp over bolted flanged joint in injecting seal works.


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flange

gasket

repair clamp

the convex of the repair clamp

caulked edge of the flanged joint

Fig. 2. Repair clamp with caulking.

copper wire

repair clamp

injecting hole


Fig. 3. Repair clamp with copper wire.

repair clampsoft stuffingthe gap c

between flanges

thin steel strip


Fig. 4. Repair clamp with soft stuffing.

. Repair clamp wiⅡ th copper wire which is shown

in Fig. 3. Two slots are designed in the clamp, and four sections of copper wire are put into the slots individu-ally. The plastic deformation of the copper wire results from the bolt force, and a sealant-tight chamber is built with the gap of the flanges, the clamp and the de-formed copper wire.

. Repair clamp with soft stuffing, in which a thin Ⅲsteel strip and some soft stuffing such as asbestos rope are placed in the slots instead of the copper wire (Fig. 4). The steel strip and soft stuffing are pushed by the pressurized sealant, which is injected into gap between the thin steel strip and the slot with the sealant gun so that the soft stuffing can contact tightly with outside edges of the flanges, thus the seal chamber is built.

These repair clamps are effective for certain cases, which mainly include low or medium working pressure,

or leaking substance which is difficult to burn or ex-plode, or the leakage is not so heavy. 1.4. Present study

The object of the present study is to find out a new structure of the repair clamp over bolted flanged joint so as to eliminate leakage in severe operating condi-tions more easily and reliably where high temperature and high pressure are both present, the leaking working substance is explosive or flammable, or serious leakage may occur, and to validate the usefulness and effectiv-ity of this structure by applications in engineering.

2. The new method for design of repair clamp 2.1. Difficulty the conventional method faced with

Experience in engineering shows that the key of in-jecting seal in service is how to build a sealant-tight chamber properly and select suitable sealant. In prac-tice, the sealant can be selected according to the leak-ing substance and its temperature and pressure. Cer-tainly, requirements on liquidity, stability and time of solidification for the sealant should all be considered as well. On the other hand, the seal chamber needs to contain the sealant and prevent it from escaping under pressure of leaking substance and injecting pressure before the sealant solidified. Hence, it is important for the seal chamber that certain strength, stiffness and especially, effective sealant-tightness, which is also the most important for the repair clamp, should all be sat-isfied at the same time.

To ensure the sealant-tightness of the repair clamp, two gaps are crucial (see Fig. 5). One is the radial gap d between outer surface of the flange and inner surface of the repair clamp; the other is the gap t between clamp halves. When the pressure of the leaking sub-stance is low, for example, Pw ≤ 1.6 MPa, the satisfy-ing gaps (as a matter of experience from engineering, no gap should be larger than 0.5mm in this case) can be arrived by designing the repair clamp precisely or using one of the repair clamps mentioned in 1.3. But when the pressure of the leaking working substance is higher, for example, Pw≥ 2.5 MPa, especially when Pw≥ 10.0 MPa, and severe leakage occurs at the same time, even a very minute gap will result in that the sealant is forced out along the gap t or d, thus the in-jecting seal in service fails. To solve this problem, soft stuffing materials mentioned in 1.3 can be used to eliminate the radial gap d, and the gap t should be de-creased to some extent as small as possible (according to our experience from engineering, usually the gap t should not be larger than 0.05 mm in the case Pw≥ 10.0 MPa). The stuffing corresponds to the gasket in bolted flanged joint; therefore, enough unit pressure in radial direction between the flanges and the stuffing is needed, just as what the gasket in a bolted flanged


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joint does, to prevent the sealant from being forced out along the axial direction at out circle surface of the flange. The unit pressure can be provided through bolts force of the repair clamp as long as the gap t>0, i.e. the split surfaces of the repair clamp does not contact each other tightly. But when doing this, another difficulty arises: how can we ensure enough radial unit pressure between the flange and the stuffing and a gap t minute enough at the same time just with a single dimen-sion—the proper inner diameter of the repair clamp. Usually, the radial unit sealing pressure between the flange and the stuffing is still low but difficult to be increased, because the split surfaces of the repair clamps have contacted each other tightly (the contact pressure between the split surfaces of the clamp other than the radial unit pressure between the flange and the stuffing will be increased if the bolts force is increased later in this case), thus the sealant would be forced out along the circumferential surface of the flange if the injecting seal were carried out; or the radial unit pres-sure between the flange and the stuffing has been large enough and the stuffing material almost can not be compressed any more, while the gap t between the split surfaces of the repair clamp is still large, as would lead to that the sealant be forced out from the gap t. Both of the above cases would result in failure of injecting seal in service. 2.2. New method for design of repair clamp over bolted flanged joint

The structure of the repair clamp can be changed according to the above analysis. That is, two dimen-sions can be employed to meet the different require-ments of the leak-tightness of the sealant in repair clamp in two different locations. A new design method on repair clamp over bolted flanged joint as follows was developed.

(1) Only the radial unit pressure between the flange and the stuffing is taken into account when design a repair clamp, and two slots where stuffing material is put can be grooved in the inner side of the repair clamp. With the bolts at the plate lug, the adequate radial unit pressure between the flange and the stuffing can be achieved. Thus possible leakage of the sealant along the circumferential surface of the flange can be pre-vented. As to the gap t between the split surfaces of the repair clamp, it may be controlled at 0.5~5 mm loosely.

(2) An inner ring which is split into two halves is set at the inner side of the repair clamp and in the gap of bolted flanged joint as well (Fig. 6). The split sur-faces of the half ring are stagger with those of the half shell of the clamp approximately in a 90º angle, and the thickness B of internal ring is designed strictly. The thickness B equals to the gap of the flanged joint, and the deviation should be not larger than 0.05 mm. This can be archived easily.

(3) A tongue (an inner convex, see Fig. 7) can be

employed along the inside surface of the repair clamp as an alternative. In this case, the tongue should be removed partly near the split surface of the clamp and a section of the inner ring, which is taken from that designed as mentioned above in (2) and is also used to prevent the sealant from being forcing out near the split surfaces of the clamp, should be employed just at the breach of the tongue instead of an inner ring half in (2). See Fig. 7 for detail. The tongue can be used as a facility in position finding when the repair clamp is being mounted on the leaking bolted flanged joint.

In this new method, the potential possible leakages of the sealant when injecting seal is carried out are prevented by following means: on the one hand, possi-ble leak passage 1 (see Fig. 5) is prevented through adequate radial unit pressure between the flange and the stuffing. The radial unit pressure is supplied by bolts force of the repair clamp, and the bolt force can be ensured through a suitable gap t (about 0.5~5 mm, which could be attained easily), which would be satis-fied only by a proper inner diameter Di of the clamp. In other words, the diameter Di is only used to get ade-quate radial unit pressure. On the other hand, possible leak passage 2 is prevented through strictly designed inner ring other than inner diameter Di in traditional methods. Therefore, the requirement for the gap t, as mentioned above, can be very low in this new structure. The effect of the inner ring, which almost contact with both flanges tightly, is similar to that of labyrinth gland: increase the fluid resistance if the sealant were leaking out. The inner ring, the split surfaces of which are staggered with those of the clamp, can compensate the large gap t between the split surfaces of the clamp. Moreover, an additional differential pressure of the flowing sealant would be caused across the inner ring, as can be helpful for the soft stuffing to seal flowing sealant. That is to say, possible leakage 1 is prevented finally through a proper inner diameter Di of the repair clamp, while possible leakage 2 is prevented finally through a suitable thickness B of the inner ring. Two independent dimensions Di and B are employed re-spectively to eliminate two possible leakage of the sealant in different place. Therefore, the potential leakages of the sealant would be prevented completely as a result, and design of a repair clamp over bolted flanged joint would be an easy job as well.

2.3. Scope of application

According to the fundamentals of the new method, it is important for a bolted flanged joint to have a gap C which is wide enough to put in an inner ring, and the clearance between the inner ring and the two flanges should be as small as possible. The smaller the clear-ance is, the better the effect of the injecting seal in ser-vice would be. If the inner ring could contact tightly with both of the two flanges, the best sealing would be archived.


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the gap t between split surfaces of repair clamp(the possible leak passage 2)

the gap d between flange and repair clamp(the possible leak passage 1)

repair clamp

blind flange

the bolts of repair clamp

the bolts of the flanged joint

Fig. 5. Schematics of the gaps (d and t) and possible leak passages.

the inner ring halves

one of through-thickness holes in the inner ring

the soft stuffing in the repair clamp

inner ring

(b)

the gap t between the split surfaces of the repair clamp

the gap between inner ring halves

t

repair clamp

the plate lug welded to the repair clamp

soft stuffingbolted flanged joint

one of injecting holesin the repair clamp

(a)

(a) The repair clamp, the inner ring halves and the soft stuffing. (b) A flanged joint mounted with a repair clamp with inner ring. Fig. 6. How a repair clamp with inner ring works.

partial inner ring

tongue(inner convex)

bolts in flanged joint

Fig. 7. Repair clamp with partial inner ring.

As for the thickness of the inner ring, it should not

be thinner than 6mm according to our experience in engineering. It would be difficult to machine an inner ring if it is too thin, for there are some radial through-thickness holes in the inner ring to let the sealant in. Therefore, the gap C between the flanges of

a leaking flanged joint should be equal to or larger than 6 mm to employ this method with good sealing result. This gap size would be satisfied in most cases, that is, the new method could be applied when a leaking bolted flanged joint is composed of a pair of raised face flanges, ring joint flanges, or some of tongued and grooved flanges, or some of Male & Female flanges. 3. Validation in practical engineering

Dozens of repair clamps which were designed ac-

cording to the new method mentioned above have been used successfully to eliminate leakages in bolted flanged joints of various working substances, operating conditions and different levels of leakage occurred in actual production of process plants. The results are all satisfactory. Here are some examples in a synthesis ammonia plant with Kellogg process with a product of 300,000 tons per year in LTH Natural Gas & Chemical Corporation, Luzhou, Sichuan province:


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. A heavy leakage occurred in the bolted flanged Ⅰjoint of the outlet check valve of 114-C，which is an important heat-exchanger in the plant. The leaking sub-stance is boiler feed water with a high pressure of 10.5 MPa at 314 . The diameter of the valve ca℃ p, i.e., a blind flange, is about 350 mm, and the gap C between the flanges of the valve cap and the valve body is 8.0 mm. In this case, a repair clamp with a partial inner ring was employed (see Fig. 7). The gap t between the split surfaces of the clamp was 1.0 mm after the repair clamp was mounted on the leaking bolted flanged joint, while the leakage was eliminated successfully after the sealant was injected into the seal chamber with a labor of 3 hours. Good sealing had been remained till the major repairs of the synthesis ammonia installation about a year later, during which several large fluctua-tions of pressure and temperature load were occurred, due to shutting down and restarting of the installation.

. A severe leakage occurred in the bolted flangeⅡ d joint of the inlet nozzle of 101-C, i.e., the primary waste heat boiler, which is one of critical equipments in the Kellogg process. The working substance is boiler water with a high pressure of 10.5 MPa at 314 . The ℃diameter of the flange is about 600 mm, and the meas-ured gap C between the flanges was 11.3 mm, and the eccentricity, 3.0 mm. A repair clamp with inner ring

was employed in this case. Considering that the leakage is very large and severe, dual sealing slot, between which the sealant would be injected in so that a pre-sealing could be carried out, were employed at the each side of the repair clamp (see Fig. 8 for detail), and many comb dent were also employed on the end faces of the inner ring where the effect of labyrinth seal would be more strong (see Fig. 9 for detail). The gap t between the split surfaces of the repair clamp was 3.5 mm after the repair clamp was mounted, but the leak-age was also cleared up successfully with a labor about 8 hours.

. A leakage occurred in the bolted flanged Ⅲ joint of a reformer tube of 101-B, i.e., the primary converter, which is also one of crucial equipments in the Kellogg process. The working substance is the primary re-formed gas (which is explosive and flammable) with a pressure of 2.2 MPa and a high temperature of 780 . ℃The diameter of the blind flange is about 200 mm, and the measured gap C between the flanges was 11.0 mm. A repair clamp with inner ring was employed in this case. The gap t between the split surfaces of the clamp was 1.0 mm after the repair clamp was mounted, while the leakage was eliminated successfully with a labor about 1.5 hour.

half shell of repair clamp

injecting holes

slots used to hold soft stuffing

plate lug of repair clampe=3.0

chambers for pre-sealing

Fig. 8. The repair clamp employed over the bolted flanged joint of inlet nozzle of 101-C.

1.5

Ⅰ

90°

Ⅰ

0.75

0.1

r0.3

comb dents of the inner ring

injecting hole

Fig. 9. The inner ring of the repair clamp in 101-C.


4. Conclusions

A new method for design of repair clamp over bolted flanged joint was developed, where a removable inner ring is employed to compensate the gaps t be-tween split surfaces of the clamp halves, and two in-dependent dimensions Di and B are employed respec-tively to eliminate two possible leakage of the sealant in different place. The problem on unit sealing pressure around the outside of the flange and the gap between the split surfaces of clamp is solved. The scope of ap-plication of the new method is comprehensive. It is applicable to eliminate leakages in bolted flanged joint which might be composed of a pair of raised face flanges, ring joint flanges, or some of tongued and grooved flanges, or some of M&F flanges as long as the gap C between the flanges is no less than 6mm. The engineering applications in an ammonia plant with Kellogg process shows that good economic benefit and satisfactory sealing are both achieved by using this method.

Acknowledgements

The authors would like to thank Hui Zhou, a senior

engineer in department of production in LTH, for his valuable contributions to this work.

References [1] Hu GZ. Sealing technology in chemical industry. Beijing:

Chemical Industry Press, 1995. (in Chinese). [2] Otegui JL, Rivas A, Manfredi C, Martins CF. Weld failure

in sleeve reinforcement of pipelines. Engineering failure analysis 2001; 8: 57-73.

[3] Cisilino AP, Chapetti MD, Otegui JL. Minimum thickness for circumferential sleeve repairs fillet welds in corroded gas pipelines. International Journal of Pressure Vessels and Piping 2002; 79: 67-76.

[4] Hu YW. Dynamical seal technology: leaking & sealing. Beijing: Defense Industry Press, 1998. (in Chinese).

[5] Zhao QY. An analysis and experimental validation of bolt force of flanged joint Subjected to injecting seal. Equip-ment in Petrochemical Industry 1998; 27: 36-38. (in Chi-nese).

[6] Hu YW. Research on repair clamp & sealing structure in injecting seal. Chemical Engineering & Machinery 1997; 24: 341-348. (in Chinese).

[7] Gan ZL, Zhou SY. On applications of injecting seal to the chemical fertilizer plant in Jiujiang company. Petroleum & Chemical Industry in Jiangxi 2001; 18: 18-21. (in Chinese).

[8] Hu YW. On dynamic disposal of local leakage in the flanged joint of pressure vessels. Pressure Vessels Tech-nology 2000; 17: 17-21. (in Chinese).

Documents

DESIGN OF REPAIR CLAMP FOR ONLINE ELIMINATION OF LEAKAGE FROM BOLTED FLANGED JOINTS