Floating roof inspections: an inside job

Robert L. Ferry, Trinity Consultants,

USA, looks at the recent revisions to the US Environmental Protection Agency’s NSPS Kb tank inspection requirements.

Along-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 fl oating 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 fi nal 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 (Refi nery 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 Refi nery MACT. The signifi cance 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 specifi ed 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 specifi ed 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 fl oating 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 specifi ed 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

up-close inspection for compliance with air regulations is required on a 10-year cycle.

In that API 653 internal inspections are conducted with the tank out-of-service, air regulation up-close inspections will also be conducted whenever the tank is out-of-service for the API 653 inspection. The question, then, has been whether the up-close inspections of IFRs that become due between API 653 inspections may be conducted with the tank in-service, thereby avoiding unnecessary tank cleaning and degassing events.

Subpart WW vs NSPS Kb

Subpart WW has clearer language

In the preamble to the proposal for revising NSPS Kb, the EPA characterised the difference between Subpart WW and NSPS Kb as follows: “The storage vessel design, operation, inspection frequency, inspection procedure, and repair requirements are largely the same between NESHAP Subpart WW and NSPS Subpart Kb. However, the organisation and phrasing of the two rules is different. Where they differ, the requirements in NESHAP Subpart WW are clearer and more stringent than the requirements in NSPS Subpart Kb.” [85 FR 65779, 16 October 2020 – fi rst column, second paragraph.]

By virtue of having clearer language, Subpart WW is less prone to adverse misinterpretation than is NSPS Kb.

Subpart WW is more stringent

The provisions of Subpart WW that are more stringent than NSPS Kb include the following requirements for specifi c deck fi ttings: Whereas NSPS Kb requires the covers for access hatches and gauge float wells to be bolted closed only for IFRs,

Subpart WW requires these covers to be bolted or fastened closed for external floating roofs (EFRs) as well. Whereas NSPS Kb requires roof drains to have a cover over at least 90% of the area of the opening only for EFRs,

Subpart WW requires IFR drains to have these covers as well.

However, under Subpart WW, it is possible to wait until the next time the tank is emptied and degassed to complete these deck fi tting upgrades, as long as the upgrades are accomplished within the next 10 years.

Figure 1. Cable-suspended aluminum IFR (courtesy of Allentech). Clarification of Subpart WW gap limit

A question that has sometimes arisen with respect to Subpart WW has been whether the 1/8 in. gap limit specifi ed at §63.1063(d)(1)(v) is applicable to rim seals or only to deck fi ttings. The EPA addressed this issue in a footnote to the preamble for the proposed revisions to NSPS Kb as follows: “EPA does not apply this 1/8-inch maximum gap width criteria to rim seals.” [85 FR 65779, 16 October 2020 – footnote 10.]

Conducting the inspection in-service

Safety considerations

A concern that arises when considering in-service inspection of IFRs is whether it is safe to do so. Conducting the inspection in-service necessarily involves sending personnel into the tank which, of course, would constitute a confi ned-space entry. Safety issues, however, are beyond the purview of the EPA and thus evaluation of the safety concerns is a separate consideration from whether the requirements of the air regulation can be met by inspecting the IFR while the tank is in-service. Individual companies make their own determination of whether a given IFR can be inspected safely in-service.

Robotic inspections

The question arises as to whether the up-close inspection of the IFR can be conducted robotically, thereby avoiding human entry into the tank. When evaluating the suitability of a robotic option, it should be kept in mind that the requirement in Subpart WW reads as follows: “Floating roof (IFR and EFR) inspections shall be conducted by visually inspecting the fl oating roof deck, deck fi ttings, and rim seals from within the storage vessel. The inspection may be performed entirely from the top side of the fl oating roof, as long as there is visual access to all deck components specifi ed in paragraph (a) of this section.” [40 CFR Part 63 Subpart WW, paragraph §63.1063(d)(1).]

Thus any robot or drone used as a means of conducting the up-close inspection must be able to gain visual access to gaskets that may be located beneath lids or covers as well as primary rim seals that may be located beneath secondary rim seals.

Remaining questions

While the 19 January 2021 revisions to NSPS Kb brought certainty to the issue of up-close inspections of fl oating roofs being allowed to be conducted with the tank in-service, the wording of the revisions left a few questions unanswered. Industry groups submitted comments to the proposed revisions raising these questions, but the EPA responded in the preamble to the fi nal rule that these questions were outside the scope of this rulemaking and may be considered in the future. These questions are: Can the Subpart WW option be made available to other regulations that reference NSPS Kb? As worded, the

Subpart WW option added to NSPS Kb is available to tanks

EHS & Engineering EHS & Engineering Support for Tanks Support for Tanks & Terminals & Terminals

EHS Support Emissions Estimating MI and Inspections

Trinity provides terminal operators with a wide range of services to help ensure compliance with applicable environmental rules and regulations.

Permitting and compliance assistance Environmental Justice assessments and assistance NSPS and NESHAP/MACT support Transportation fuel compliance Air dispersion modeling programs and support BREEZE TankESP of fers powerful productivity enhancements to ef fectively manage tank emission calculations.

Select either old or new

AP-42 equations Adjust for mid-month changes in service Calculate emissions from floating roof landing and tank cleaning events Account for changes in tank construction Trinity/Provenance support all aspects of implementing and executing a Fixed Equipment Mechanical Integrity (MI) and Inspection program.

Risk analysis and recommendation support Engineering design Construction management API-certified inspections including NDE, NDT, and UT Full FEMI program support

that meet the applicability criteria of NSPS Kb. However, there are certain regulations (e.g. BWON6, GD MACT7) that invoke NSPS Kb requirements for tanks that do not meet the applicability criteria specified in NSPS Kb itself.

It would be helpful if the EPA would further revise

NSPS Kb to expressly extend the Subpart WW option to tanks that become subject to NSPS Kb requirements through another rule. Can reporting under the Subpart WW option be on a semi-annual basis? NSPS Kb specifies different deadlines for different types of reports. In rules promulgated by the EPA since the early 1990s, however, it has transitioned to requiring all reports to be submitted on a semi-annual basis. It would be helpful if the EPA would further revise NSPS Kb to accommodate semi-annual reporting. What is the actual deadline for the up-close inspections? While NSPS Kb requires the up-close inspections to be conducted at least every 10 years, the rule does not specify when within the tenth year the inspection would become past due. The EPA has specified in other rulemaking that compliance tasks which are required at a specified frequency are due at some point within the specified calendar period. It would be helpful if the EPA would further revise

NSPS Kb to specify that these 10-year up-close inspections must be conducted prior to the end of the calendar year in which the deadline occurs.

Conclusion

The 19 January 2021 revisions to NSPS Kb expressly provide for conducting the 10-year up-close inspection of fl oating roofs while the tank is in-service. The mechanism for doing so is to elect to comply with Subpart WW in lieu of NSPS Kb. The EPA further clarifi ed that the 1/8 in. gap limit in Subpart WW is applicable only to deck fi ttings and not to rim seals. While this rulemaking brought certainty to the resolution of these two issues, certain other questions were deferred for future consideration.

References

1. 'Standards of Performance for Volatile Organic Liquid Storage

Vessels (including Petroleum Liquid Storage Vessels) for Which

Construction, Reconstruction, or Modification Commenced After

July 23, 1984,', US Environmental Protection Agency, 40 CFR Part 60,

Subpart Kb. 2. 'National Emission Standards for Storage Vessels (Tanks) – Control

Level 2,' US Environmental Protection Agency, 40 CFR Part 63,

Subpart WW. 3. 'National Emission Standards for Hazardous Air Pollutants From

Petroleum Refineries,' US Environmental Protection Agency, 40 CFR

Part 63, Subpart CC. 4. Preamble to 40 CFR Part 60 Subpart Kb proposed rule, 49 FR 29708-09, 23 July 1984. 5. API Standard 653, 'Tank Inspection, Repair, Alteration, and

Reconstruction', Fourth Edition, April 2009, Addendum 1, (August 2010). Paragraph 6.4.2.2 specifies a maximum interval of 20 years if certain corrosion rate procedures are used, and up to 30 years if other specified measures are taken. 6. 'National Emission Standard for Benzene Waste Operations,',

US Environmental Protection Agency, 40 CFR Part 61, Subpart FF. 7. 'National Emission Standards for Gasoline Distribution Facilities (Bulk Gasoline Terminals and Pipeline Breakout Stations),'

US Environmental Protection Agency, 40 CFR Part 63, Subpart R.

Your Specialist for PRESSURE RELIEF SOLUTIONS

Consulting. Engineering. Products. Service. T +49 2961 7405-0 hello@rembe.de