| Abstract | Pouzdanost sustava je vjerojatnost da on izvršava funkcije za koje je predviđen u željenom
razdoblju bez kvara i u predviđenoj okolini. Postoji mnoštvo metoda za povećanje pouzdanosti
sustava kroz smanjenje tehničkih rizika. Pored metoda koje vrše direktnu analizu tehničkih
rizika, postoje i tehnike za procjenu vjerojatnosti rizika. U ovom radu, primijenjena je RAMI
(engl. reliability, availability, maintainability, inspectability) analiza, koju je definirala ITER
organizacija a uključuje kombinaciju IDEF0 (engl. Integration definition for function
modelling) funkcijsku analizu koja pruža osnovu za provedbu FMECA-e (engl. Failure mode,
effects and criticality analysis) kao analize tehničkih rizika i RBD analize (engl. reliability block
diagrams) kao tehnike za procjenu vjerojatnosti rizika. Prvo je proučena zbog upoznavanja sa
prednostima i nedostacima ovih metoda, ali i drugih koje nisu primijenjene u radu, u svrhu
postizanja boljih rezultata i točne primjene metoda. Nakon toga, u radu je opisana primjena
RAMI analize na uređaju za servisnu inspekciju, koji trenutno razvija tvrtka INETEC. Uređaj
za servisnu inspekciju se kreće po tračnicama koje su pričvršćene na vanjsku stranu vakuumske
posude ITER tokamaka kako bi ispitivao obližnje zavare. Prilikom provedbe analize, poseban
naglasak je stavljen na pravilnu dekompoziciju funkcija uređaja i formulaciju IDEF0
funkcijskog modela. Sljedeći korak analize je FMECA u kojoj su definirani mogući načini
otkazivanja definiranih funkcija, te pripadajući uzroci i učinci, na temelju prijašnjeg iskustva
tvrtke. Prijašnje iskustvo i stručna prosudba su pomogli i pri kvantificiranju ozbiljnosti i
učestalosti učinaka i uzroka načina otkazivanja. Posljednji korak je provedba RBD analize za
koju su korištene vrijednosti iz FMECA tablice i dekompozicija prikazana u IDEF0 funkcijskoj
analizi. FMECA analizom, na temelju vrijednosti kritičnosti, otkrivena su 2 velika rizika, 57
srednjih i 40 malih rizika. RBD analizom dobivena je vrijednost pouzdanosti od 0% nakon 8
sati i dostupnosti od 16,5%. Otkriveno je da na učestalost najveći utjecaj imaju softverske i
operatorske greške, a na ozbiljnost, greške koje propagiraju kroz uređaj, poglavito vezane uz
tok zraka, vode i struje. Na kraju je izvršena usporedba dobivenih rezultata sa drugim
pristupima pronađenih u literaturi i predložene su radnje za smanjenje rizika, odnosno
povećanje pouzdanosti i dostupnosti sustava, prema rezultatima opisanih analiza. U daljnjem
radu, preporuča se prikupljanje veće količine informacija vezanih u pouzdanost sličnih sustava. |
| Abstract (english) | Reliability is the probability that the system will perform its required functions for desired
periods of time without failure, in a specified environment. There are many methods aimed at
increasing systems reliability through mitigation of technical risks. Next to methods for direct
technical risk analysis, there are also probabilistic risk assessment techniques. In this paper,
RAMI (Reliability, availability, maintainability, inspectability) analysis, which was devised by
the ITER Organization as a combination of IDEF0 (Integration definition for function
modelling) functional analysis to provide the basis for FMECA (Failure mode, effects and
criticality analysis) as technical risk analysis and RBD (Reliability block diagrams) as a
probabilistic assessment technique, is used. Literature was studied to examine the advantages
and disadvantages of these methods, as well as others, to obtain the best possible results and
ensure correct application. Afterwards, this paper presents the application of the RAMI analysis
to in-service inspection device, which is currently being developed by the INETEC company.
In-service inspection device travels inside rails fixed on the outer shell of the ITER tokamak's
vacuum vessel in order to inspect adjacent welds. During application, great emphasis was
placed on the correct decomposition of functions and formulation of IDEF0 functional model.
Next step of the analysis was the FMECA which includes the definition of failure modes for
said functions, as well as their causes and effects, based on the company's previous experience.
Previous experience combined with expert judgment also helped in quantifying the severity and
occurrence of effects and causes of failure modes, respectively. The last step is the RBD
analysis which used values from FMECA as an input and the decomposition shown in IDEF0
functional analysis as its basis. FMECA analysis indicated, based on criticality values, 2 major
risks, 57 medium and 40 minor risks. RBD analysis showed that the device’s reliability achieves
0% after 8 hours and constant availability of 16,5%. The biggest impact on risks occurrence is
due to software and operator errors, and on severity is from failures propagating throughout the
device, these are mainly air, water and electricity failures. Lastly, a comparison between
obtained results and other approaches found in literature was made, and risk mitigations actions
were suggested according to the results of the analyses. For future work, more reliability data
should be collected from similar systems to get a better reliability model of the device. |
