Author experience 10 years HRSG inspection, did two shift operation HRSG and base load HRSG inspection , this paper is to share some experience to inspection the HRSG.
- Generation inspection prepare
crawl-through Visual inspection by experienced eyes is the first and foremost method of HRSG checkupproactively scheduling inspections to find and correct minor problems before they become major inspections into specific areas: inlet duct areas; superheaters, reheaters, evaporators and economizers; header crawl space enclosure; firing ducts; selective catalytic reduction and carbon catalyst (if installed); stack; high- intermediate- and low-pressure steam drums; tube internals; casings; casing pipe penetration seals; module supports; and drain systems. “crawl-through” of the complete gas path, accessible components above and below the gas path (the interconnecting piping such as jumpers, risers, drains and vents), the gas baffles, all piping hangers and the drum internals
when the outage comes, the plant management make huge time to do outage planing, the stage the spare parts and prepare manpower, and procedures and work order line up, operation busy on build LOTOT, so everything is going somthly then outage will successfully to reach the goal, but all this prepare is depends on find job, and past experience. The unfound job should to know as early as possilbe maybe it will change outage schedule and budget.
HRSG Insepection is important, which depends the operation mode, the two shitft operation HRSG specially, before inspection the confined space entry permit and necessary tool with inspector is import.
- Fuel gas patch inspetion
- Gas turbine exhaust inspection
Form this suction, inspector can inspect the last stage of the gas turbine blade, and gas turbine exhaust cylinder, exhaust strut and the blade path tempertue and exhaust gas temperautre probe, for the siemens 501F machine due to design issue, there is a lot of crack at the exhaust cyclinder, welding repair always necessary, so mark up the cracks in sharp pen and carfully review the side wall at exhasut tunnal not have any damage. The expansion join all need pay enough attention no leakage.
Crack found on Siemens 501F struts
Welder repair cracks
some HRSG install the flow distrubution grid, the gird is located at high temperature and area, so inspection the supports and expanshion movement is improant, high vibration maybe cause the connection bolts and nuts sheared , Voget HRSG installed flow dirtrubution grid install at ESEC experienced crash on lower secution as figure 1 and also has connet bolts broken
Flow distribution grid crash down
Connection bolts is sheared
Support for the distribution grid
- HP superheater and Hot reheater suction
Inspection side baffle not damage, if it is damage it will bypass the hot gas then cause the efficiency decrease, inspection the drain line peneration bellow, and expension, steam leaking sign at the bottom and top welding. Check the tube bundle overheating sign, tube bowing is over heating sign. At GEC experienced the top superheater leakage as below repair pictures
Repair the superheated tubes
Evaporator overheating cause tube bowing
- Duct burner bay inspection
Duct burner bay is most problem find place which is due to the hotest area, and frequency cycle, so inspector duct burner is critial step for the HRSG inspection, see more detail at this paper 2.0
- Heating surface bundle inspection
For the fins tube, watch the color
Lower side baffle broken
- SCR inspection
SCR inspection is import to check the amonnia not cristal to plug the distribution holes, check the SCR surface not coverd the insulation piarticles, take some samples of SCR catylist to test the performance degradation
SCR surface covered by insulation particles
- Stack inspection
If not installed stack damper make sure check the bottom drain is not have plugged by dust and corrosion iron, inspection the sign of the economizer tube no sulfure aicd corrosion due to due point low and aicd condensation.
- Duct burner inspection
it is crucial to maintain proper flame shape, to ensure a uniform vertical distribution of flue-gas, and to prevent flames from overextending and impinging on downstream tube panels.
For HRSGs with supplementary firing, the highest tube-metal temperatures and heat fluxes typically occur on the tube banks immediately downstream of the duct burners. Tube- overheating failures typically occur in this area
flame should extend no more than half to two-thirds of the length of the firing duct, Flames should be independent of each other, and should be completely horizontal
Be sure flames never contact the tubes! Tube damage resulting from an elongated upper-level duct-burner flame
Inspect the flow disbution panel and set support, inspect fuel nozzle not been plugged, inspect the grid, each runner to inspect shape not sagged down , also check the flame pinchment with side wall, flow no spinning washer.
Inspect the support movement is smoothly due to expansion, no restriction and welds no crack, use skyclaimber to access the top runner to do more close inspection.
If the side wall is installed, carfully review the insulation intergirty which not pill off.
Duct burner perforated plate cracked
Duct burner runner bowing
- water side inspction
- Drum inspection
Drum is most plant staff want to first to see when the unit shutdown
HP drum
Inspect the cycle seperator, watch the iron accumuclation and grip some sample, check the belly band and internal structure crack indication, bolts and nuts no missing, the downcome need clearful review the support sturcture, on the two shift plant, old deltak design was sucked down cause million dollar lost, in the meaning time watch inside surface color and find operation water level line is imprortant to expalin the water carrier over.
HP drum downcomer vortex breaker design issue
HRSG HP drum inside review
IP drum
IP drum unsually is samller than HP and drum, but for the steam cooling gas turbine, IP size almost same with HP drum. Most IP drum has cascade tube connect to the HP drum inspection the water chemistriy sign is important in this drum
LP drum:
Inspection the steam misture seperator mesh intergrity, for Vogt boiler, inspect the condensate sprary nozzle wear signs and replace if the gap is too big, replce it as neccesary if there is damage.
LP drum condensate spring nozzle
- Blowdown tank inspection
Blowdown tank inspection is also imports, due to water drains is flashed to steam so two FAC corrosion is possible in the blow down tank, using UT to test the thickness, carfully inspect the drain line to check the corrosion sign.
- HRSG External Inepction
- Inspection boiler exterinal includes the pipe system expansion, bottoem peneration seals and all hanger cold and hot positon and expansion situation
Penetration bellow damaged
- Inspection the attic and bottom box of the HRSG
- corrosion inspection
Inspection the corrosion is important for inspector to gather information regards under deposit corrosion, FAC corrosion, stress crack corrosion and pit corrosion and generatal corrosion, FAC is major failuare mechnizam on the HRSG when the carbion steel with temperature less than 300 degree C, before inspection to check the iron log to understand the average iron level, specialty to monitory the HP, IP, LP drum accumucaltion on the bottom and combined with UT test the thickness.
LP economizer tube leaking due to FAC
STG lube oil leakage due to pit corrosion
Blowdown tank bottom leaking due FAC
CTG Kattle boiler expansion joint leakage
- Conculsiton
Inspection is important and challenge work, after the unit stop before outage, inspection plant as early as possible, find the operation defeact to understand outage scope, some big find maybe dramaticly to impact outage schedule and cost, some parts and engiener support maybe need more time to prepare, inspector make good pictures and mark up the location is key, most advance inspection use the NDE technical maybe necessary.