ISO-28300 / API-2000 Deflagration Venting/Mitigation

Brad OtisApril 28, 2010

2010 API Spring Refining and Equipment Standards Meeting

The companies in which Royal Dutch Shell plc directly or indirectly owns investments are separate entities. In this presentation the expressions "Shell", "Group" and "Shell Group" are sometimes used for convenience where references are made to Group companies in general. Likewise the words "we", "us" and "our" are also used to refer to Group companies in general or those who work for them. The expressions are also used where there is no purpose in identifying specific companies.

Shell Global Solutions is a network of independent technology companies in the Shell Group. In this presentation the expression ‘Shell Global Solutions’ is sometimes used for convenience where reference is made to these companies in general, or where no useful purpose is served by identifying a particular company.  The information contained in this presentation contains forward-looking statements, that are subject to risk factors which may affect the outcome of the matters covered. None of Shell International B.V., any other Shell company and their respective officers, employees and agents represents the accuracy or completeness of the information set forth in this presentation and none of the foregoing shall be liable for any loss, cost, expense or damage (whether arising from negligence or otherwise) relating to the use of such information.

The information contained in this presentation is intended to be general in nature and must not be relied on as specific advice in connection with any decisions you may make. Shell Global Solutions is not liable for any action you may take as a result of you relying on such material or for any loss or damage suffered by you as a result of you taking this action. Furthermore, these materials do not in any way constitute an offer to provide specific services. Some services may not be available in certain countries or political subdivisions thereof.

Copyright © 2010 Shell Global Solutions (US) Inc. All copyright and other (intellectual property) rights in all text, images and other information contained in this presentation are the property of Shell International B.V. or other Shell companies. Permission should be sought from Shell International B.V. before any part of this presentation is reproduced, stored or transmitted by any means, electronic or mechanical including by photocopy, recording or information storage and retrieval system.

 

Agenda Four Areas of Proposed Work

o Clarify “Emergency Venting”o Review deflagration venting and applicable industry

standardso Understand API-650 frangible roof performanceo Clarify tank deflagration causes and prevention

measures Conclusion

Emergency Venting Section 3.4 states:

“venting required when an abnormal condition, such as ruptured internal heating coils or an external fire, exists either inside or outside a tank.”

o An external fire inside the tank??o Other abnormal conditions should be referenced

Proposed 3.4: “venting required when an abnormal condition exists, such as external fire or other overpressure circumstances (see 4.2.5)”

Deflagration Venting Section 4.2.5.15 states:

“Tank contents can ignite, producing an internal deflagration with overpressures that develop more rapidly than some venting devices can handle. For explosion venting, see NFPA 68 and EN 13237. For inerting, see Annex F.”

o This was not in 5th edition of API-2000

Deflagration Venting Placement of this paragraph under the section “other

overpressure circumstances” makes it mandatory to consider and evaluate storage tank internal deflagration overpressure protection (or prevention).

o Recommendation: The ISO-28300 working group

should review that language to confirm if this is appropriate.

Deflagration Venting Unclear if EN-13237 and NFPA 68 are the most

appropriate references for hydrocarbon storage tank deflagration venting

EN-13237 was not reviewed due to insufficient time

NFPA 68 was reviewed in detail and the following issues were identified:

o Clearly covers deflagration ventingo Covers hydrocarbon storage tanks but it does not

provide direct guidance

Deflagration Venting

Closest guidance is section 8.6 “bins, hoppers and silos” (NFPA 68-2002):

“The entire enclosure top can be made to vent deflagrations. In such cases, design and operating conditions (internal and external pressure, wind loads, and snow loads) can cause the mass of the roof to exceed that prescribed for deflagration vent closure. Roof panels are to be as lightweight as possible and are not to be attached to internal roof supports. API 650, Welded Steel Tanks for Oil Storage, should be referenced for guidelines for the design of a frangible, welded roof joint. Although frangible roof design in accordance with API 650 is not intended to serve as deflagration venting, experience shows that such roofs have successfully vented deflagrations. A frangible roof design is not recommended for use as the inner roof on enclosures that have a headhouse or penthouse.”

Deflagration Venting The latest (2007) edition of NFPA 68 does NOT include

the previous language in red.

It states in 8.6.3.4: “The remaining portions of the enclosure, including anchoring, shall be designed to resist the calculated Pred, based on the vent area provided.“

Extensive work was done to assess frangible roof designs (see API Publications 937 and 937A)

It is not clear whether the API-650 frangible roof design complies with the NFPA-68 criteria or whether it should comply.

Deflagration Venting API Publication 937 states:

“API-650 (API, 1993) provides design criteria for fluid storage tanks with frangible roof joints. The rules are intended for fluid storage tanks used to store flammable liquids which could be subjected to sudden over-pressurization. Over-pressurization can occur due to the ignition of flammable vapors and can exceed the capabilities of the pressure relief vents specified in storage tank design.”

Neither API-650 or API Publications 937 and 937A reference NFPA-68.

Deflagration Venting It appears that this was intentional and that API-650

frangible roof design may be an alternative to NFPA-68 design.

Recommendation: the API Sub-Committee on Atmospheric Storage Tanks (SCAST) should confirm whether API 650 frangible roof design meets NFPA-68 or if this is an alternative to NFPA-68.

Deflagration Venting

API 650 Frangible Roof Performance What is considered good frangible roof performance?

o Tank shell/bottom seam fails?o Tank shell/roof seam tears but roof is held?o Tank shell/roof seam fails but roof is thrown?

Video Examples

Recommendationso API SCAST summarize to the ISO-28300 working

group the intended design performance of API-650 frangible roofs.

o ISO-28300 language to be updated to reflect that expectation

Causes of Tank Internal Deflagration

Deflagration Prevention Measures

ISO-28300 (2008) paragraph 4.5.2 discusses design options for explosion prevention. Consider modifying the 2nd sentence as follows:

“…The user is cautioned that the use of a flame arrester within the tank's relief path introduces the risk of tank damage from overpressure or vacuum due to plugging if the arrester is not maintained properly. The user is also cautioned that a sustained fire on the outlet of the flame arrestor or on other parts of the tank/fittings may result in temperature high enough to ignite internal flammable vapors….”

Conclusion

A number of issues dealing with tank internal deflagration exist in the current edition of ISO-28300.

A bit more investigation is needed to resolve some of

the questions.

Revisions to some of the ISO-28300 language is recommended to clarify the requirements.