Robert L. Ferry, Trinity Consultants, USA, looks at the recent revisions to the US Environmental Protection Agency’s NSPS Kb tank inspection requirements.
A
long-standing interpretation issue for storage tanks subject to US Environmental Protection Agency (EPA) regulation 40 CFR part 60 Subpart Kb1 (NSPS Kb) has been whether the tank must be removed from service and cleaned in order to conduct the 10-year up-close inspection required for internal floating roofs (IFRs). This up-close inspection of the IFR is required each time the tank is emptied and degassed, but in any case at intervals not greater than 10 years [§60.113b(a)(4)]. The question has been: if an IFR tank subject to NSPS Kb comes to the 10-year milestone without having been emptied and degassed, is it acceptable to conduct the up-close inspection with the tank in-service, or does the tank have to be emptied and cleaned to conduct the inspection? A final revision to NSPS Kb was posted to the Federal Register on 19 January 2021 [86 FR 5013] that resolves this issue. This revision adds a paragraph at §60.110b(e)(5) titled “Option to comply with part 63, Subpart WW, of this chapter.” The option to comply with Subpart WW2 in lieu of NSPS Kb had already been available in multiple rulemakings, such as 40 CFR part 63 Subpart CC3 (Refinery MACT), but the provisions for opting to comply with Subpart WW rather than NSPS Kb under those rules are applicable only to storage tanks that are subject to those rules. This revision to NSPS Kb now extends the Subpart WW option to any storage tank subject to NSPS Kb and not just those that are also subject to another rule such as Refinery MACT. The significance of the Subpart WW option with respect to the 10-year IFR inspections is that it expressly allows these 10-year up-close inspections of IFRs to be conducted with the tank in-service.
Background The rationale for the specified inspection frequency in NSPS Kb was the expectation that tanks, on average, would be emptied and degassed once every 10 years for structural inspection of the tank. The specified frequency, then, was intended to allow the up-close IFR inspection to be conducted when the tank had been cleaned and gas-freed for inspection of the tank itself, thereby avoiding a cleaning and degassing of the tank solely for the purpose of conducting the floating roof inspection. The express concern was to avoid unnecessary degassing of the tank, because the degassing process involves emissions to the atmosphere.4 The intention of avoiding degassing of the tank solely for purposes of conducting the up-close inspection of the IFR for air regulation compliance has been frustrated by the frequency subsequently specified in API Standard 653 (API 653) allowing up to 20 years between internal inspections for tank integrity purposes.5 Thus, an internal inspection of the tank for structural integrity purposes is often conducted on a 20-year cycle, per API 653, but an 2 23 Autumn 2021
