Superheater and Reheater Outlet Header Inspections Failures

8/12/2019 Superheater and Reheater Outlet Header Inspections Failures

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Thielsch Engineering, Inc.195 Frances Avenue, Cranston, RI 02910Tel. (401) 467-6454 Fax (401) 467-2398

E-mail: [email protected]

Superheater and Reheater Outlet HeaderInspections, Failures and Repairs -

Scheduled and Forced Outage

Considerations

Helmut Thielsch, P.E.PresidentThielsch Engineering, Inc.

Florence ConeSenior Metallurgical EngineerThielsch Engineering, Inc.

Presented at 8thAnnual Outage"Best Practices" Conference

August 26 to 28, 2002Clearwater, Florida


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SUPERHEATER AND REHEATER OUTLET HEADERINSPECTIONS, FAILURES AND REPAIRS -

SCHEDULED AND FORCED OUTAGE CONSIDERATIONS

Helmut Thielsch, P.E., andFlorence Cone

Thielsch Engineering, Inc.195 Frances Avenue

Cranston, Rhode Island 02910

ABSTRACT

This paper provides details of a number of failures that have occurred in Superheater andReheater Outlet headers. About one-half of these failures resulted in forced outages. Theother half were discovered during scheduled outage inspections.

This paper discusses the methods used to repair those headers, on occasion on atemporary basis. It also discusses the various inspection techniques which, if utilized aspart of a routine inspection program, are capable of identifying conditions likely to result infailures.

INTRODUCTION

Failures in Superheater and Reheater Outlet headers are relatively infrequent. Unfortu-nately, when failures do occur in these components, the necessary repairs may requireseveral weeks to complete. Due to the substantial costs associated with any forcedoutage, it is imperative to perform routine inspections of headers. In this manner, con-ditions with the potential to result in failures can be identified, monitored and addressedbefore they do result in failures.

FAILURES IN HEADERS

Failures in headers can be caused by any one or a combination of the following five factors:(1) design deficiencies, (2) manufacturing or material defects, (3) fabrication or erectiondefects, (4) service-related deterioration or (5) upset operating conditions. The majority offailures are caused by service-related deterioration, either alone or in conjunction with theother four factors. Occasionally, failures do occur solely as a result of one of these factors.

Case History No. 1

In November of 1998, after 16 years of service, a Superheater Outlet header at agenerating station located in a midwestern state began leaking steam. The subsequent


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investigation by plant personnel revealed that the leak was the result of a circumferentialcrack, Fig. 1. This crack, which was located in tube row No. 4, extended for 360 aroundthe circumference of the header. Over most of its length, this crack extended through thefull cross-sectional thickness of the header. There was pronounced separation betweenthe mating fracture surfaces, at some locations measuring as wide as 0.5".

In order to determine the feasibility of repair, two separate but concurrent courses of actionwere undertaken. This included a metallurgical evaluation of the failed header to determinethe cause of the cracking and the condition of the entire header remote from the cracking.It also included an inspection of the failed header and of a second Superheater Outletheader in the same unit to identify any other cracking or other conditions of deteriorationthat might be present in the headers and to determine the extent and severity of thatcracking.

The results of the metallurgical evaluation confirmed that the cracking was the result ofthermal fatigue and that any metallurgical deterioration was confined to the immediate

vicinity of the cracks. (Further investigation confirmed that the design of the header wasmarginal, thereby exacerbating the effects of normal operation and any upset operatingconditions, and leading to premature failure.)

The inspection of the headers included borescopic examination which is well suited toidentify ligament cracking. It also included ultrasonic examination. (The latter techniquewas utilized to size the depth of any ligament cracking.) The results of the inspectionrevealed the presence of ligament cracking in the vast majority of tube rows in bothheaders. In the failed header, the most severe cracking was located in tube rows Nos. 1to 8. In the other header, the most severe cracking was located in tube rows Nos. 37 to 47.

The extent of the cracking was such that it would take many months to repair each andevery crack by welding. (Replacement of the headers would have required a significantlylonger period, approximately six to nine months.) As such, a decision was made toinvestigate the possibility of allowing some ligament cracking to remain in place until theheaders could be replaced during a regularly scheduled plant outage.

Calculations were made to establish the size of ligament cracking that could be safely leftin place for 18 months, at which point the unit was scheduled to undergo an extendedoutage. These calculations confirmed that ligament cracking with a depth of less than 1.0"could be left in place without endangering the operating integrity of the headers during thenext 18 months of service.

The repair program ultimately implemented involved removing those sections of theheaders with the most severe cracking and replacing them. (The replacement sectionswere fabricated from pipe produced in accordance with ASME Specification SA-335,Grade P22. The pipe was furnished with an outside diameter of 16" and a nominalthickness of 3.5". Thus, it represented the same seamless pipe used in the fabrication ofthe original header.)

In those instances where the ligament cracking still in place exceeded 1.0" in depth, thecracks were excavated and the resultant cavities repaired by welding.


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The photographs provided in Fig. 2 illustrate one of the headers during in-place machining.The photograph provided in Fig. 3 illustrates the final bevel on the remaining portion of theoriginal header. The photographs provided in Fig. 4 illustrate a replacement section beingpositioned, fit up and welded.

The repairs to the Superheater Outlet headers were completed in substantially less thantwo months, thereby minimizing the length of the forced outage. The repair weldedheaders provided satisfactory service until they could be replaced 18 months later.

Case History No. 2

The previous case history is somewhat unusual in that the Superheater Outlet header inquestion experienced a guillotine-type failure after approximately 16 years of service.While ligament cracking is not uncommon in Superheater Outlet headers, it typically resultsin more gradual deterioration, i.e., the type that can be effectively monitored by periodicinspections. The header shown in Fig. 5 is a case in point. Fabricated from pipe produced

in accordance with ASME Specification SA-335, Grade P22, it had an outside diameter of11-3/4" and a wall thickness of 2-7/8".

The photographs provided in Fig. 6 illustrate the ligament cracking discovered in thisheader after 130,000 hours of service at a pressure of 1,900 psig and a temperature of1000F. As is apparent, the ligament cracking varied somewhat in severity, rangingbetween 1/8" and 3/4" in length (the full width of the available ligament). In the worst case,it was estimated to extend 30% into the available cross-sectional thickness.

The photographs provided in Fig. 7 illustrate the ligament cracking in the same header after180,000 hours of service. The cracking had not changed appreciably in severity. This

header thus has continued to be operated, with periodic inspections monitoring the integrityof the header.

Case History No. 3

At some point, ligament cracking will progress to such an extent that repair or replacementof the subject header becomes imperative. (The decision to repair or replace is dependentupon a variety of factors. However, as a general rule of thumb, it is typically impractical torepair Superheater Outlet headers subject to ligament cracking except in instances wherethe ligament cracking is of limited incidence. This is due to the fact that the ligament cracksmust be excavated from the outside diameter of the header. The heavier the wall thicknessof the header, the more welding that will be required to effect a repair.)

The header shown in Fig. 8 is a case in point. This header, placed in service in 1952, wasfabricated from pipe produced in accordance with ASME Specification SA-148, Grade P3B,a 2 Cr - 1/2 Mo low-alloy steel. The header had accumulated well in excess of 375,000hours of service. The original operating conditions involved a pressure of 1,350 psi at atemperature of 1000F. During recent years, the operating temperature has been reducedto 950F.


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The intended operating conditions for this header involved a pressure of 2,050 psi at atemperature of 1050F. Reportedly, there was some temperature variation along the lengthof the header, with the quarter points operating 20F higher.

After approximately 250,000 hours of operation, a leak developed through the seam weld

in this header. The subsequent investigation by plant personnel confirmed that the leakwas the result of a longitudinal crack. On the outside diameter surface of the header, thiscrack had an overall length of 30.5". Ultrasonic examination confirmed that this crack wassubstantially longer on the inside diameter surface of the header, approximately 7 ft. inlength.

The subsequent investigation by plant personnel also revealed that one of the hangerssupporting the header had cracked during previous operation, Fig. 18. The failure of thissupport had allowed the header to sag approximately 0.5" in the vicinity of the leak.

Several samples were removed from the cracked header in an effort to determine the

cause of the cracking and to establish the condition of the header remote from the cracking.This information would be necessary to determine the feasibility of repairs by welding.

One of the samples removed involved a plug sample, Fig. 19. This plug sample, althoughit would complicate any subsequent repair activities, was particularly useful because itpermitted the full cross-sectional thickness of the header to be evaluated.

When this plug sample was examined visually, it was apparent that the inside diametersurface did not parallel the outside diameter surface. Rather, it had a much greater degreeof concavity than would be typical. It was subsequently determined that the concavity wasintroduced during fabrication of the header. Specifically, the longitudinal seam weldpresent in this header was machined to remove any reinforcement. The machiningperformed along the inside diameter surface of the header resulted in the removal ofexcessive metal. The wall thickness values recorded on the plug sample ranged between3.140" and 3.559". The minimum wall thickness value recorded at the seam weld locationwas 5% below the design minimum wall thickness, and 12% less than the maximumrecorded wall thickness of the header base metal.

When the samples removed from the header were evaluated metallurgically, it wassubsequently determined that the crack was located at the approximate centerline of thelongitudinal seam weld, Fig. 20. Advanced creep deterioration was observed immediatelyadjacent to the crack. This included void formation, void linkage and microfissuring. At aslight distance from the primary crack, the creep damage was limited to isolated voidformation.

The base metal was also examined. It did exhibit microstructural transformations asso-ciated with the prior years of high-temperature service including carbide spheroidizationand agglomeration. There was, however, no evidence of creep deterioration.

The results of the metallurgical evaluation confirmed that repairs by welding were possibleand that they could be considered permanent in nature. (Any material subject to advancedcreep deterioration would be removed during the excavation of the crack.)


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The results of the metallurgical evaluation also confirmed that the cracking in the seamweld was the result of several factors. This included the 12% reduction in wall thicknesscreated by the cosmetic machining of the seam weld. It also included the fact that the weldhad been completed using a low-carbon filler material. (The carbon content of a low-alloysteel weld deposit has a direct influence on its resistance to creep deterioration; the lower

the carbon content, the lower will be the creep resistance.) The third factor contributing tothe failure of the header was the bending stresses introduced into the header when thehanger supporting it failed, allowing it to sag 0.5".

The repairs to the header were completed in accordance with a proprietary low-stresswelding procedure. It involved excavating the crack in its entirety using both arc airgouging and grinding. Due to the width of the resultant root gap, it was considered prudentto utilize backing bar segments. The welding was performed utilizing the shielded metalarc (SMAW) or "stick" welding process. The final weld, Fig. 21, was postweld heat treatedat a temperature of 1250F. It should be noted also that a final weld reinforcement of 3/8"was provided to compensate for the original counterbore on the inside of the header.

This header has now been in service for about 13 years subsequent to the repair of theseam weld. No further cracking has occurred at the location of the seam weld.

Case History No. 6

The photographs provided in Fig. 22 illustrate a Superheater Outlet header installed at amidwestern utility. These photographs were taken after the fillet weld securing aninspection cap to the west end of the header had failed catastrophically. Fortunately, the3,600 psi steam escaping from the 3-1/4" hole was contained within the penthouse abovethe boiler.

During the course of the investigation, it was determined that the inspection caps on thisand the other Superheater Outlet header in this unit were installed several years after theunit had been placed in service. The Original Equipment Manufacturer directed that thefillet welds attaching these inspection caps to the header have a throat measurement of3/4".

Measurements performed on the fillet weld that failed, Fig. 23, confirmed that it was grosslyundersized, having a throat measurement of 3/8". This fabrication deficiency resulted inthe weld being subject to stresses substantially higher than intended by the designer. Thisin turn resulted in accelerated creep deterioration in the weld. Amazingly, despite beinggrossly undersized, this fillet weld was in service for 15 years before it ultimately failed.

Case History No. 7

A similar failure occurred in a Superheater Outlet header owned and operated by a north-eastern utility, Fig. 24. The inspection cap, shown in Fig. 25, was installed as part of OEMrecommended modifications to the header. The metallurgical evaluation confirmed that thefailure was the combined result of an undersized weld (1" throat versus the recommended1.5" throat) in conjunction with the use of a low-alloy steel filler material with a low carboncontent to complete the fillet weld in the chromium-molybdenum alloy steel header.


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Case History No. 8

The header shown in Fig. 26 is located in the High Temperature Superheater of a boilerowned and operated by a northeastern utility. This header, which was forged and boredfrom a 2-1/4 Cr - 1 Mo low-alloy steel billet, was placed into commercial operation in 1955.

The operating conditions involve a pressure of 2,460 psi at a temperature of 1050F.

In 1977, the High Temperature Superheater was retubed. The tube stubs were supposedto be replaced at that time. However, it appears that the contractor neglected to do this,electing instead to build up the existing header-to-tube welds by a process of weldoverlaying.

In 1986, a firm performing inspection of the header recommended its replacement, citingaccelerated creep deterioration. The owner chose to delay replacement of the header,instead instituting a program of periodic inspection and repair. The most recent inspection,approximately 16 years after the recommendation for replacement, did reveal cracking in

a number of header-to-tube welds. This cracking, the typical appearance of which isillustrated in Figs. 27 and 28, was caused by bending stresses, thermal fatigue associatedwith cyclic service as well as residual welding stresses introduced during the weldoverlaying of the header-to-tube welds performed in 1977.

All of the cracks were removed by grinding. Only four of the resultant cavities weresufficiently deep to require repairs by welding.

Using this approach of periodic inspection and maintenance, the owner considerablyextended the life expectancy of this header without experiencing an unacceptable numberof forced outages. (Of course, the owner probably spent somewhat more money on

inspection and maintenance than he otherwise would have.) Nevertheless, the continuedoperation of the header was considered to be safe and cost effective.

Case History No. 9

In some instances leaks in header-to-tube welds, in addition to resulting in forced outages,may also result in damage to the body of the header itself. The Reheater Outlet headershown in Fig. 29 is a case in point. A leak in a header-to-tube weld had gone undetectedfor some period of time. The steam escaping from the header, at a pressure of 475 psigand a temperature of 1000F, eroded the header along the outside surface. The resultantgrooves, oriented radially, were present over an arc of approximately 120. The mostsevere groove had an overall length of approximately 6" and a maximum depth in excessof 1". The depth of the grooves was such that after repairs by welding, it was necessaryto subject the header to a postweld heat treatment.

Case History No. 10

The header-to-tube weld shown in Fig. 30 had failed catastrophically after approximately10 years of service. The failure was unusual in that the header-to-tube weld had pulledcompletely free of the header, leaving behind a "donut-shaped" cavity. The shape of the


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cavity indicated that the cracking that produced the catastrophic failure paralleled closelythe fusion line of the header-to-tube weld.

The inspection of the remaining header-to-tube welds on this header confirmed that over50 header-to-tube welds were subject to similar cracking, albeit not as severe.

(Interestingly, when exploratory grinding was performed on header-to-tube welds that werefree of surface cracking, cracking was discovered approximately 1/8" below the surface.This subsurface cracking followed the same pattern exhibited by the header-to-tube weldscontaining visible cracking. It followed the header side toe of the header-to-tube weld.)

A metallurgical evaluation performed on samples removed from the header-to-tube weldsconfirmed that the cracking was the result of advanced creep deterioration. The creep, thetypical appearance of which is illustrated in Figs. 31 and 32 was confined predominantlyto the fine-grained, low-temperature heat-affected zone. The results of the metallurgicalevaluation further confirmed that the creep was due to the fact that the header had notbeen supplied in accordance with the chemical composition requirements of the specified

material grade. It was supposed to be a 2-1/4 Cr - 1 Mo low-alloy steel. Instead, itcontained less than 0.5% chromium and less than 0.25% molybdenum. The header alsocontained surprisingly large amounts of nickel (0.5%) and copper (0.3%).

The material discrepancy was significant in that the strength and therefore the creepresistance of a steel is heavily influenced by alloy content. Thus, the creep resistance ofthe header as furnished would have been significantly less than that of a header of thespecified material grade. The effect on the creep-rupture properties of the header was ofsufficient magnitude that the header-to-tube welds cracked, and in one case failed, in only10 years of service.

Although material discrepancies of this type are uncommon, they do occur. It is for thisreason that owners and operators of power plants should give consideration to performingPositive Material Identification (PMI) for any new construction or major repair.

Case History No. 11

The header shown in Fig. 33 was fabricated from ASME Specification SA-335, Grade P22pipe. The pipe was furnished with a nominal thickness of 5.0". (The actual wall thicknesswas 5-1/4".)

The header was placed in service in 1969. The operating conditions involved atemperature of 1005F and a pressure of 3,800 psi.

In 1991, after 121,000 hours of service, the Original Equipment Manufacturer (OEM)performed an inspection to monitor the ligament cracking known to exist in the header. Theremote visual (borescopic) inspection confirmed the presence of the ligament cracking, Fig.34. It also revealed a linear indication extending approximately 8 ft. along the insidediameter surface of the header, Fig. 35. The OEM performed an ultrasonic examinationin the area of the linear indication and recorded ultrasonic signals or reflectors which wereinterpreted as progressive cracking extending 3-1/2" or 70% through the available cross-


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sectional thickness, Fig. 36. The OEM recommended replacement of the header to beaccomplished within 6 months of the inspection.

The utility, in the interest of prudence, requested a second opinion. The videotapedocumenting the cracking that existed in the header was carefully reviewed. At that time,

it was noted that the cracking had not progressed in the ligaments between adjacent tubeholes. Rather, it "skimmed" the edges of the tube holes in a tangential fashion, Fig. 37.This is not typical of cracking produced by hoop stresses, making it extremely unlikely thatthe cracking was in fact 3-1/2" deep. To further confirm this, the header was inspectedusing the radiographic examination technique. This inspection revealed slight fissuringextending off the tube holes in a "starburst" pattern typical of ligament cracking. There was,however, no additional longitudinal cracking between adjacent tube holes. Based upon theresults of this inspection, the utility was advised that the longitudinal cracking wassuperficial in nature, probably less than 1/4" in depth, and related strictly to thermal fatigue,i.e., intermittent wetting and drying of the inside diameter surface of the header, most likelyas a result of condensate flashing to steam during start-up.

Due to conflicting opinion, the Authorized Inspector requested the utility to remove athrough-wall plug sample from the header. This was accomplished using a magnetic-baseddrill equipped with a 4" diameter hole saw, Fig. 38.

The visual and nondestructive examinations of the plug sample, shown in Figs. 39 and 40,confirmed that the cracking was superficial "craze-type" cracking that related to thermalfatigue. It extended less than 1/8" into the available cross-sectional thickness.

The "reflectors" or indications initially interpreted as cracks actually represented laminationsand/or stringer inclusions present in the pipe from which the Superheater Outlet header hadbeen fabricated. The photographs provided in Fig. 41 illustrate these indications asrevealed by liquid penetrant examination. The photographs provided in Fig. 42 illustratethese indications as revealed by optical microscopy.

The 4" diameter 5-1/4" deep through-wall hole saw cavity was subsequently reweldedthrough the full cross section. After a stress relief heat treatment and a completenondestructive examination, the header was returned to service. (The total scheduledoutage period involved a period of 7 days from the initial shut down to the return tooperations.)

Subsequent inspections have confirmed the continued soundness of the header at thelocation of the laminations and of the repair weld areas.

Case History No. 12

An ultrasonic examination of another Superheater Outlet header in a southwestern stateperformed in 1994 resulted in a report of progressive cracking extending 50% into the 4.10"wall thickness of the 26.75" OD header. The header represented a 2-1/4 Cr - 1 Mo alloysteel subject to an operating temperature of 1000EF and a pressure of 450 psi. The headerwas fabricated from plate produced in accordance with ASME Specification SA-387,Grade D.


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The shell section was rejected by the initial inspection contractor. Repairs by welding weresubsequently scheduled by the plant operator. Subsequent re-evaluations by the perfor-mance of ultrasonic, radiographic and borescopic examinations and comparisons of theresults against extensive crack identification standards, confirmed that the indicationsinitially identified as cracks actually represented patterns significantly different from

progressive cracks that have been evaluated by sectioning pressure vessels, headers,drums and piping.

The initial inspection results thus were accepted as inconsequential material defectsrepresenting nonmetallic inclusions or laminations in the header material. Subsequentreinspections have confirmed that there have been no changes in the position of theseindications.

A scheduled long repair outage thus was shortened by several weeks. This SuperheaterOutlet header continues to provide satisfactory service.

Case History No. 13

Fig. 43 illustrates parallel Superheater Outlet headers installed at a midwestern utility. Theunit in which these headers was installed had been brought off line due to leaks. Thesubsequent investigation by plant personnel confirmed that the initial leak was the resultof transverse cracking in a header-to-tube weld, Fig. 44. Additional transverse andcircumferential cracking was present in varying degrees in approximately 70% of theheader-to-tube welds, Fig. 45.

The transverse cracking was the result of unusually high residual welding stressesintroduced during prior repair welding of the header-to-tube welds. The circumferential

cracking occurred during normal operation (although residual stresses may have playeda contributory role).

The high-pressure fluid escaping through the transverse cracks caused erosion damageon various other tubes, Fig. 46, and the body of the header.

The headers were then repaired by welding. The repairs included replacing those tubessubject to erosion, weld overlaying the body of the header, and repair of those with thepotential to produce leaks within one year of additional service.

Case History No. 14

In 1988 after 250,000 hours of operation the high-temperature Superheater tube pendantson a Secondary Superheater Outlet header were being replaced. The header had originallybeen placed in service in 1957, Fig. 47. It consisted of a forging produced to ASMESpecification SA-182, Grade F22, representing a 2-1/4 Cr - 1 Mo alloy steel. Until 1988 theoperating conditions involved a temperature of 1050F and a pressure of 2700 psi.

When the tube stubs were removed from the header, cracking was observed in a numberof tube holes.


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header had been fabricated from 24" diameter by 4.875" wall pipe produced to ASMESpecification SA-335, Grade P11. This represented a 1-1/4 Cr - 1/2 Mo alloy steel. Thisheader originally had been placed in service in 1961. At the time of the inspection in 1987,the header had been in service for 177,000 hours at a temperature of 1005F and apressure of 2200 psi.

The initial inspection resulted in the conclusion that the header had experienced creep andneeded to be replaced.

Subsequently, a 4" diameter plug sample was removed from the header with a hole saw,Fig. 52, for a detailed metallurgical evaluation. Inspection through the hole where the plugsample had been removed revealed very minor fissuring on the inside of the tube holes,Fig. 53.

Metallurgical examination of the header plug sample across the 4.875" wall thicknessconfirmed the absence of creep. The satisfactory condition of the header material was also

confirmed by stress rupture testing and the comparison of the test results with publishedLarson-Miller data.

GENERAL COMMENTS

The case histories discussed herein illustrate the potential for failures to occur inSuperheater and Reheater Outlet headers. Due to the potential for failure, this type ofequipment should be subjected to periodic inspections. Although scheduled outages aremost cost effective, about one-half of header failures causing steam leaks through theheaders cause forced outages. However, if header-to-tube welds are included in forced

outage statistics (as described in Case Histories 10 and 15), then the majority ofSuperheater Outlet failures represent forced outages.

The initial inspection should be performed before the header is placed in service (andpreferably before it is installed in the boiler). This inspection should include materialverification. It should also include visual examination of the welds on the header to confirmthat they are of adequate size and free of visible defects.

The subsequent in-service inspection program for headers should include several non-destructive examination techniques. These include wet fluorescent magnetic particleexamination of the header-to-tube welds, any other attachment welds, and all girth andseam welds, to detect any cracking and/or fissuring that might be present in the welds, theadjacent heat-affected zones or the adjacent base material. (The girth and seam weldsshould also be subjected to ultrasonic examination to detect the presence of anysubsurface cracking or defects.)

The inspection program for headers should also include metallurgical evaluation usingreplication, hardness testing, and if warranted, sample removal to determine the materialcondition of the header and to identify any evidence of microstructural degradationassociated with the prior years of high-temperature service. (It should be recognized,however, that the microstructure along the outside surface of the header, because of


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decarburization, frequently differs from the microstructure 1/8" to 1/4" below the headersurface.)

Header inspections should also include remote visual (borescopic) examination of theinside diameter surface of the header. If ligament cracking is discovered, ultrasonic

examination may be necessary to size the depth of the cracking.

Of course, any condition revealed by an inspection must be evaluated carefully todetermine its cause and significance. Some conditions may lead to leaks and potentiallycatastrophic ruptures. In the majority of instances, however, the conditions observed arenoncritical.

If a condition is determined to be noncritical, it should be left in place and monitored on anas-needed basis. If a condition is determined to be critical, the feasibility of repair versusreplacement should be evaluated.

Headers can generally be repaired by welding. Repair welding, if performed properly, canvery significantly extend the life of a header. Moreover, in most cases, repair welding isgenerally more attractive than replacement with respect to both cost and schedule. Manyheaders after well planned and executed repair welding programs have now providedentirely safe and satisfactory service for periods of 10, 20 and even more years of service.

Despite this, repair welding of headers should not be undertaken lightly. In a number ofinstances, seemingly minor repairs have produced major cracking in a very short period oftime because of inappropriate welding procedures, inexperienced welders, or inadequatecontrol over the repair welding process.


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Documents

Superheater and Reheater Outlet Header Inspections Failures