Request to EPA for Clarification for Tank Inspections Under 40 CFR 63.1063(d)(1), Subpart WW
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Cathy Landry

Request to EPA for Clarification for Tank Inspections Under 40 CFR 63.1063(d)(1), Subpart WW

April 17, 2020

Marcia Mia
Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. MAIL CODE: 2227A
Washington, DC 20460

Brenda Shine
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 
terminal industry.

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 
fitting closures.

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

Peter Lidiak
Vice President of Government Affairs International Liquid Terminals Association 1005 N. Glebe Road, 
Suite 600
Arlington, VA 22201 USA

Cc:        Cary Secrest - Maria Malave - Larry Starfield -

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