Agenda Item 620-1002, REV 0
Title:
Lower DMT Limit Annex S Tanks
Date:
May 23.2014
Contact:
Name
: John Lieb (Primary) / Joshua Coots (Secondary)
Company : Tank Industry Consultants (TIC) / Storage Tank Products, LLC
Phone
:630-841-9014 / 225-490-0539
E-mail
:Lieb@TankIndustry.com / JCoots@stpllc.com
Purpose: Clarify Lower Limit of DMT for Annex-S Tanks
Source:
E Mail from Bhana Mistry
Revision: 0
Impact:
The business impact of this item is neutral.
Rationale: As currently worded, API 620 states in S.1.2 that the minimum design metal
temperature for Annex-S non-refrigerated tanks is not limited. It has been
proposed that either a lower limit on DMT be defined for non-refrigerated
tanks or that this statement be removed from the standard. There is no
similar statement in Annex S of API 650.
Proposal:
S.1.2 This annex applies only to tanks in non-refrigerated service. For
stainless steel tanks in refrigerated service, refer to Annex Q of this
standard. Minimum design metal temperature of the non-refrigerated
tanks in the scope of the annex is not limited. Maximum design metal
temperature shall be limited as given in 1.2.2. For the purposes of this
annex, the design temperature shall be the maximum operating
temperature as specified by the Purchaser. Ambient temperature tanks
(non-heated) shall have a design temperature of 40 °C (100 °F). It is
cautioned that exothermic reactions occurring inside unheated storage
tanks can produce temperatures exceeding 40 °C (100 °F).
Notes:
1) Wording to be deleted is shown in red strike-through font.
2) At the Spring 2014 meeting, Don Comire of Eastman Chemical
indicated that he may vote negative if the sentence is removed as
proposed herein. Don’s argument is that materials 304, 304L, 316,
316L, 317, and 317L are intrinsically safe for use to extremely low
service temperatures and he did not want to see an artificial low
temperature limit on these materials. Don stated that his company
typically has minimum design metal temperatures in the -20 F to -55
F range, but does not want to preclude the use of the subject
materials without impact testing all the way down to -320 F.
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3) In response to Don’s comments in item 2: Removing the sentence in
S.1.2 as proposed herein would not preclude the use of the subject
materials without impact testing for extremely low ambient
temperatures.
4) The arguments in favor of removing the sentence as proposed herein
are: a) The sentence adds no value to the standard – i.e. the
requirements of the standard are clear without the sentence; b) The
inclusion of the sentence is not consistent with API 650; and c) The
sentence is technically not correct and could be misinterpreted – i.e.
in practice, the MDMT for non-refrigerated tanks would be limited to
the lowest possible ambient temperature the tank would experience in
service. Any means to further cool the tank or its contents would take
it out of the category of non-refrigerated and the sentence would no
longer apply.
5) The argument against removing the sentence is is that the standard
should not preclude the use of the subject materials down to -320 F.
6) The preparers of this agenda item conclude that removal of the
sentence as proposed would not preclude the use of the subject
materials without impact testing down to MDMTs for refrigerated
tanks. With reference to Q.2.2.1, the standard already allows that
“Impact testing is not required for primary components of austenitic
stainless steel, nickel alloy, and aluminum”. Annex Q of API 620
applies to tanks with MDMTs down to -270 F.
7) Based on the above discussion, the preparers of this agenda item
recommend that the sentence in S.1.2 of API 620 be deleted as
proposed.
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