{{Short description|Pressure vessel with a non-structural liner wrapped with a structural fiber composite}} [[Image:Copv tank close out prior to flight.png|thumb|A COPV inside a sounding rocket]] A '''composite overwrapped pressure vessel''' (COPV) is a vessel consisting of a thin, non-structural liner wrapped with a structural fiber composite, designed to hold a fluid under pressure. The liner provides a barrier between the fluid and the composite, preventing leaks (which can occur through matrix microcracks which do not cause structural failure) and chemical degradation of the structure. In general, a protective shell is applied for shielding against impact damage.<ref>{{Cite web |url=http://findarticles.com/p/articles/mi_qa3957/is_200002/ai_n8886150 |title=Protective shells for composite overwrapped pressure vessels |access-date=2008-10-20 |archive-date=2021-10-01 |archive-url=https://web.archive.org/web/20211001043146/http://findarticles.com/?noadc=1 |url-status=live }}</ref><ref name="mfs-31814">{{Cite tech report |last=Delay |first=Tom |url=https://ntrs.nasa.gov/api/citations/20110014768/downloads/20110014768.pdf |title=Making a Metal-Lined Composite-Overwrapped Pressure Vessel |date=March 2005 |publisher=NASA |hdl=2060/20110014768 |access-date=1 October 2021 |archive-url=https://web.archive.org/web/20240830204328/https://ntrs.nasa.gov/api/citations/20110014768/downloads/20110014768.pdf |archive-date=30 August 2024 |url-status=live }}</ref> The most commonly used composites are fiber reinforced polymers (FRP),<ref>{{Cite thesis |last=Lung |first=Bryan C. |date=2005 |title=A structural health monitoring system for composite pressure vessels |url=https://harvest.usask.ca/items/06def5fb-8821-4046-9eaa-8d3bcc14c962 |url-status=live |archive-url=https://web.archive.org/web/20240830204845/https://harvest.usask.ca/items/06def5fb-8821-4046-9eaa-8d3bcc14c962 |archive-date=30 August 2024 |access-date=15 January 2024 |publisher=University of Saskatchewan |oclc= |docket= |degree=Master's |hdl=10388/etd-04042005-133006 |chapter= }}</ref> using carbon and kevlar fibers. The primary advantage of a COPV as compared to a similar sized metallic pressure vessel is lower weight; COPVs, however, carry an increased cost of manufacturing and certification. [[File:Altair X248-A2 rocket stage.jpg|thumb|350px|Casing of the Altair rocket stage, essentially a fiberglass composite overwrapped pressure vessel]]
==Overview== A composite overwrapped pressure vessel (COPV) is a pressure-containing vessel, typically composed of a metallic liner, a composite overwrap, and one or more bosses.<ref name="srtp2">{{Cite tech report |last1=Russel |first1=Rick |last2=Flynn |first2=Howard |last3=Forth |first3=Scott |last4=Greene |first4=Nathanael |last5=Kezirian |first5=Michael |last6=Varanauski |first6=Don |last7=Leifeste |first7=Mark |last8=Yoder |first8=Tommy |last9=Woodworth |first9=Warren |url=https://ntrs.nasa.gov/api/citations/20110003996/downloads/20110003996.pdf |title=Composite Overwrapped Pressure Vessels (COPV) Stress Rupture Test. Part 2 |date=10 May 2010 |publisher=NASA |hdl=2060/20110003996 |access-date=25 May 2018 |archive-url=https://web.archive.org/web/20211031040702/https://ntrs.nasa.gov/api/citations/20110003996/downloads/20110003996.pdf |archive-date=31 October 2021 |url-status=live }}</ref> They are used in spaceflight due to their high strength and low weight.<ref name=frss/>
During operation, COPVs expand from their unpressurized state.<ref>{{cite journal |title=Design and Manufacture of a Composite Overwrapped Pressurant Tank Assembly |last=Tam |first=Walter H. |journal=AIAA |via=Orbital ATK |url=https://www.orbitalatk.com/commerce/Technical_Paper_Library/AIAA2002-4349%20Astrolink%20Pres.pdf |access-date=May 24, 2018 |url-status=dead |archive-url=https://web.archive.org/web/20180525132844/https://www.orbitalatk.com/commerce/Technical_Paper_Library/AIAA2002-4349%20Astrolink%20Pres.pdf |archive-date=May 25, 2018}}</ref>
==Manufacturing==
COPVs are commonly manufactured by winding resin-impregnated high tensile strength fiber tape directly onto a cylindrical or spherical metallic liner.<ref name="Grun2025">{{cite journal |last1=Grün |first1=V. A. |last2=Dyagilev |first2=A. |last3=Greb |first3=C. |last4=Gries |first4=T. |title=Inline Quality Control of Filament Wound Composite Overwrapped Pressure Vessels |journal=Journal of Composites Science |date=2025 |volume=9 |issue=12 |page=690 |doi=10.3390/jcs9120690 |doi-access=free }}</ref> A robot places the tape so that the fibers lay straight and do not cross or kink, which would create a stress concentration in the fiber, and also ensures that there are minimal gaps or voids between tapes. The entire vessel is then heated in a temperature controlled oven in order to harden the composite resin.
During manufacturing, COPVs undergo a process called autofrettage. The unit is pressurized and the liner expands and plastically (permanently) deforms, resulting in a permanent volume increase. The pressure is then relieved and the liner contracts a small amount, being loaded in compression by the overwrap at near its compressive yield point. This residual strain improves cycle life. Another reason to autofrettage a vessel is to verify that the volume increase across pressure vessels in a product line remain within an expected range. Larger volume growth than usual could indicate manufacturing defects such as overwrap voids, a high stress gradient through the overwrap layers, or other damage.<ref name="frss">{{Cite conference |last1=Kezirian |first1=Michael T. |last2=Johnson |first2=Kevin L. |last3=Phoenix |first3=Stuart L. |date=27 September 2011 |title=Composite Overwrapped Pressure Vessels (COPV): Flight Rationale for the Space Shuttle Program |url=https://ntrs.nasa.gov/api/citations/20110015972/downloads/20110015972.pdf |conference=AIAA SPACE 2011 Conference and Exposition |location=Long Beach, Ca. |publisher=AIAA |hdl=2060/20110015972 |archive-url=https://web.archive.org/web/20240317225827/https://ntrs.nasa.gov/api/citations/20110015972/downloads/20110015972.pdf |archive-date=17 March 2024 |access-date=24 May 2018 |url-status=live }}</ref><ref>{{cite web|url=http://ston.jsc.nasa.gov/collections/trs/_techrep/SP-2011-573.pdf|author1=Pat B. McLaughlan|author2=Scott C. Forth|author3=Lorie R. Grimes-Ledesma|title=Composite Overwrapped Pressure Vessels, A Primer|publisher=NASA|date=March 2011|url-status=dead|archive-url=https://web.archive.org/web/20150421081326/http://ston.jsc.nasa.gov/collections/trs/_techrep/SP-2011-573.pdf|archive-date=2015-04-21}}</ref>
==Testing== Various tests and inspections are performed on COPVs, including hydrostatic tests, stress-rupture lifetime, and nondestructive evaluation.<ref>[http://www.agingaircraftconference.org/all_files/3/3c/3c-ppt.pdf Vessel Testing] {{webarchive|url=https://web.archive.org/web/20080905122843/http://www.agingaircraftconference.org/all_files/3/3c/3c-ppt.pdf |date=2008-09-05 }}</ref><ref name="asc-astm-20170917">{{Cite conference |last1=Grimes-Ledesma |first1=Lorie |last2=Phoenix |first2=S. Leigh |last3=Beeson |first3=Harold |last4=Yoder |first4=Tommy |last5=Greene |first5=Nathaniel |date=17 September 2017 |title=Testing of Carbon Fiber Composite Overwrapped Pressure Vessel Stress-Rupture Lifetime |url=https://dataverse.jpl.nasa.gov/api/access/datafile/10821 |conference=ASC/ASTM 21st Annual Technical Conference of the American Society for Composite |location=Dearborn, Mi. |publisher=ASTM International |hdl=2014/39869 |archive-url=https://web.archive.org/web/20240830210004/https://dataverse.jpl.nasa.gov/api/access/datafile/10821 |archive-date=30 August 2024 |access-date=20 October 2008 |url-status=live }}</ref>
== Aging ==
Three main components affect a COPVs strength due to aging: cycle fatigue, age life of the overwrap, and stress rupture life.<ref name=srtp2 />
== Failures == COPVs can be subject to complex modes of failure. In 2016, a SpaceX Falcon 9 rocket exploded on the pad due to the failure of a COPV inside the liquid oxygen tank:<ref>{{Cite news|url=https://www.compositesworld.com/blog/post/spacex-announces-copvs-role-in-sept-rocket-explosion|title=SpaceX announces COPV's role in September rocket explosion|work=01/02/2017|access-date=2018-11-30|archive-date=2018-06-14|archive-url=https://web.archive.org/web/20180614043910/https://www.compositesworld.com/blog/post/spacex-announces-copvs-role-in-sept-rocket-explosion|url-status=live}}</ref> the failure resulted from accumulation of frozen solid oxygen between the COPV's aluminum liner and composite overwrap in a void or buckle. The entrapped oxygen can either break overwrap fibers or cause friction between fibers as it swells, igniting the fibers in the pure oxygen and causing the COPV to fail. A similar failure occurred in 2015 on CRS-7 when the COPV burst, causing the oxygen tank to overpressurize and explode 139 seconds into flight.<ref>{{cite web |date=July 20, 2015 |title=CRS-7 INVESTIGATION UPDATE |url=https://www.spacex.com/news/2015/07/20/crs-7-investigation-update |url-status=dead |archive-url=https://web.archive.org/web/20150721152601/https://www.spacex.com/news/2015/07/20/crs-7-investigation-update |archive-date=July 21, 2015 |access-date=June 15, 2020 |publisher=SpaceX}}</ref> On June 18, 2025, a SpaceX Starship prototype, S36 was destroyed by the failure of a COPV.<ref>{{Cite web |date=June 19, 2025 |title=Starship Static Fire Update |url=https://www.spacex.com/updates/ |access-date=June 19, 2025 |website=SpaceX}}</ref>
==See also== *{{annotated link|Gas cylinder}} *{{annotated link|Fuel tank}} *{{annotated link|Hydrogen tank}} *{{annotated link|Graphite-Epoxy Motor}}
==References== {{reflist}}
Category:Pressure vessels