Request to EPA for Clarification for Tank Inspections Under 40 CFR 63.1063(d)(1), Subpart WW
April 17, 2020
Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. MAIL CODE: 2227A
Washington, DC 20460
Environmental Protection Agency 109 T.W. Alexander Drive MAILCODE: E143-01
Research Triangle Park, NC 27709
RE: Request for Clarification for Tank Inspections Under 40 CFR 63.1063(d)(1), Subpart WW
Dear Ms. Mia and Ms. Shine:
On behalf of the members of the American Petroleum Institute (API) and the International Liquid
Terminals Association (ILTA), we respectfully submit this letter for clarification.
API represents all segments of America’s oil and natural gas industry. Its more than 600 members
produce, process, and distribute most of the nation’s energy. The industry supports
10.9 million U.S. jobs and is backed by a growing grassroots movement of millions of Americans. API
was formed in 1919 as a standards-setting organization. In its first 100 years, API has developed
more than 700 standards to enhance operational and environmental safety, efficiency and
The International Liquid Terminals Association represents more than 85 companies operating liquid
terminals in all 50 states and in over 40 countries. Our members’ facilities provide critical links
between all modes of transportation for liquid commodities, such as crude oil, petroleum products,
chemicals, renewable fuels, fertilizer, vegetable oils and other food-grade materials that are
central to the U.S. economy. Terminals provide essential logistics services that spur trade both
within the United States and connect the U.S. economy with overseas markets.
ILTA’s membership also includes about 400 companies that supply equipment and services to the
For facilities that operate internal floating roof (IFR) and external floating roof (EFR) tanks
subject to 40 C.F.R. 63, Subpart WW – National Emission Standards for Storage Vessels
(Tanks) – Control Level 2 (Subpart WW), the inspection requirement at 40 C.F.R. §63.1063(d)(1),
states, in pertinent part:
(1) Floating roof (IFR and EFR) inspections shall be conducted by visually inspecting the floating
roof deck, deck fittings, and rim seals from within the storage vessel. The inspection may be
performed entirely from the top side of the floating roof, as long as there is visual access to all
deck components specified in paragraph (a) of this section. Any of the conditions described in
paragraphs (d)(1)(i) through (d)(1)(v) of this section constitutes inspection failure.
(i) Stored liquid on the floating roof.
(ii) Holes or tears in the primary or secondary seal (if one is present).
(iii) Floating roof deck, deck fittings, or rim seals that are not functioning as designed (as
specified in paragraph (a) of this section).
(iv) Failure to comply with the operational requirements of paragraph (b) of this section.
(v) Gaps of more than 0.32 centimeters (1⁄8 inch) between any deck fitting gasket, seal, or wiper
(required by paragraph (a) of this section) and any surface that it is intended to
For purposes of the requested national alternative monitoring plan (AMP) for in-service tank seal
inspections, API and ILTA requests confirmation in its interpretation that
40 C.F.R. §63.1063(d)(1)(v) does not apply to the rim seal. While the requested AMP would not apply to Subpart WW-regulated tanks (as this regulation unambiguously allow in-service
inspections), EPA has represented in discussions that for it to issue a national AMP specifically
allowing in- service tank seal inspections the AMP would have to include more stringent criteria
from Subpart WW.
EPA representatives indicated that they believed the term “seal” is to include
“rim seals” in regard to Subpart WW’s 1/8-inch gap failure criteria. Based on the plain reading of
the rule, use of the term “rim seal” elsewhere in the rule, the rulemaking history, Subpart WW
EFR-specific rim seal inspection protocols, and statements in the new AP-42 Chapter 7: Liquid
Storage Tanks, API and ILTA believe that the 1/8 inch gap failure criteria was not intended to
apply to rim seals and asks for confirmation of this interpretation for purposes of the AMP.
The plain reading of Subpart WW suggests that the “gasket, seal, or wiper” phrase in
§63.1063(d)(1)(v) is specifically applicable to the closure of deck fittings and not to the fit of
rim seals. The “gasket, seal, or wiper” phrase is a series of nouns having similar meaning. This
phrase is preceded in the sentence by the words “deck fitting,” which are positioned
to serve as an adjective modifying the nouns that follow. Thus, the gaskets, seals, and wipers
in question are those gaskets, seals, and wipers associated with deck fittings.
The terms “liquid-mounted seal”, “mechanical shoe seal”, and “vapor-mounted seal” are each
defined at §63.1061 as referring to “rim seals”, and the term “rim seal” is defined as spanning the
annular space between the floating roof deck and the wall of the storage vessel.
Further review of the rule text reveals that the only usage of the word “seal” that is not
expressly qualified as referring to “rim seals” is in the deck fitting design requirements of
§63.1063(a)(2) and the inspection requirement of §63.1063(d)(1)(v) suggesting this condition does
not apply to the rim seal. Specifically, §63.1063(d)(1) quoted in whole above requires the
visual inspection of “deck fittings, and rim seals.”
The rulemaking history of Subpart WW suggests that the 1/8-inch gap failure criteria was only
intended to apply to deck fittings. The proposed rule published in the Federal Register read as
follows under the listing of conditions constituting an inspection failure:
Gaps of more than 0.32 centimeters (1⁄8 inch) between any deck fitting gasket (required by
paragraph (a) of this section) and any surface that it is intended to seal.
63 FR 55257.
The final rule language augmented the reference to “gasket” with “seal, or
wiper” in acknowledgement that the specified controls for certain deck fittings were described as
seals or wipers:
Gaps of more than 0.32 centimeters (1⁄8 inch) between any deck fitting gasket, seal, or
wiper (required by paragraph (a) of this section) and any surface that it is intended to seal.
There is no explanation of the addition of “seal, or wiper” in the rulemaking, but if the addition
was designed to significantly increase the stringency of Subpart WW by applying a 1/8 inch gap
failure criteria to rim seals as compared to comparable storage tank rules, such change would have
warranted explanation. To now read the word “seal” to apply to seals beyond deck fittings neglects
the history of the rule that §63.1063(d)(1)(v) was originally drafted to solely apply to deck
Additionally, as Section 63.1063(d)(1) applies to both “IFR and EFR” floating roofs, interpreting
this section to impose a 1/8-inch rim seal gap limit renders Subpart WW’s specific EFR rim seal gap
inspection protocol (§63.1063(d)(3)) superfluous. Subpart WW’s EFR rim seal inspection
criteria has a specific primary rim seal gap maximum of 3.81 centimeters (1.5 inches).
§63.1063(d)(3)(ii). For the EFR secondary seal, “the maximum gap width shall not exceed 1.27
centimeters (0.5 inches), except when the secondary seal must be pulled back or removed to inspect
the primary seal.” §63.1063(d)(3)(iii).
Subpart WW also requires that for the inspection of EFR rim seals, inspectors use a 1/8-inch diameter probe to identify gaps and calculate the area of all gaps
over 1/8 inch. Thus, a 1/8-inch gap in an EFR rim seal does not necessarily indicate inspection
failure. If the 1/8-inch gap failure criteria applied to rim seals, then EPA would have had no
reason to include additional EFR rim seal gap inspection protocols for gaps larger than 1/8
inches. As interpreting the 1/8-inch gap failure criteria to apply to rim seals
renders a significant portion of Subpart WW useless, it is fair to assume that EPA
did not intend this interpretation.
Finally, EPA’s new AP-42, Fifth Edition, Volume I, Chapter 7: Liquid Storage Tanks indicates that
“average” tanks currently in service would not pass Subpart WW’s 1/8-inch gap failure criteria is
applied to rim seals. AP-42 defines a new category of especially tight rim seals called
“tight-fitting seals.” Table 7.1-8 . “Tight-fitting” is defined as meaning “that the rim seal is
maintained with no gaps greater than 1/8 in. wide between the rim seal and the tank shell.”
Referencing a value in the “average-fitting seal” category, the guidance further states
that “If no specific [rim seal] information is available, this value can be assumed to
represent the most common or typical rim- seal system currently in use for internal floating roof
tanks.” In other words, EPA’s own guidance suggests that the “typical rim-seal system currently in
use” for IFRs does not fit its 1/8-inch rim seal limit category.
For purposes of the requested AMP to specifically allow for in-service tank seal inspections, API
and ILTA asks for confirmation that the term “seal” does not include “rim seals” in
regard to Subpart WW’s 1/8 inch gap failure criteria and that an AMP incorporating Subpart WW’s
more stringent provisions would not include this misinterpretation.
David Murk Manager, Pipeline
American Petroleum Institute 200 Massachusetts Avenue NW Suite 1100
Washington, DC 20001-5571
Vice President of Government Affairs International Liquid Terminals Association 1005 N. Glebe Road,
Arlington, VA 22201 USA
Cc: Cary Secrest - Secrest.Cary@epa.gov Maria Malave - Malave.Maria@epa.gov. Larry Starfield - firstname.lastname@example.org