AMP_04_May_June_2021_Digital_Edition

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 1 2 9 ism, promoting rapid material damage or loss. Degradation may not be appar- ent over the period of extended shut- down but may only manifest in the future after delayed operational re- start. There is potential for initiation of a degradation mechanism that may take time to manifest, or the degrada- tion may be sufficiently tolerable within the design envelope of a system. Nev- ertheless, engineers must remain vig- ilant to identify potential degradation paths and how they can be prevent- ed. In adverse or unusual operational Fig. 2 — Walkdowns and augmented inspections provide opportunities to mitigate adverse or unexpected conditions. Fig. 1 — Stagnant or altered flow patterns can contribute to the degradation of systems or individual parts. LIST OF EXAMPLE OPERABILITY MODIFICATIONS • Equipment running longer or at expanded temperatures, pres- sures, or speeds. • Equipment shutdown for times longer than expected. • A contaminant or unusual envi- ronmental exposure. • Damage or accident occurrence modifies the equipment’s re- maining life. • Processing not up to industrial standards, leaving abnormal or unexpected condition. • Alternate processing request or substitution. circumstances, additional mechanisms may be postulated. ENGINEERING ASSESSMENT Many of these extended shutdown conditions do not introduce issues that are as insidious, acute, or dangerous relative to events postulated and ana- lyzed for normal operation accidents, but still present the potential to make additional repair or replacement nec- essary. When unplanned, this need for repair or replacement can present ex- treme economic challenges, possibly putting scheduled operation at risk. An additional consideration is that normal procedures can require ex- tra scrutiny if performed before an ex- tended shutdown condition, as typical assumptions can become invalid. For example, a cleaning operation might assume that a subsequent operation fulfills the rinse step, or that a rinse step is abandoned due to legacy experience, but the disruption to normal proce- dures may create some risk for residues or other contaminants to remain on the surfaces of parts and systems. In an- other example, an inspection of a di- mensional surface may be based on operational time, when in reality a deg- radation mechanism may depend on calendar time (even when not operat- ing) as a potential contributing factor. In this case, delayed reinspection of parts may allow for additional degradation to occur before the inspection can be per- formed (Fig. 2). Fortunately, the risk for adverse conditions resulting from changes in operating procedures is minimal due to policies and procedures in place and be- cause of the skilled personnel who eval- uate the potential effects of changes in environment, shutdown timeframes, and operational parameters. Engineers carefully consider these effects and ap- ply a conservative bias toward the eval- uation of adverse conditions.