{"id":593,"date":"2019-01-13T17:12:53","date_gmt":"2019-01-13T17:12:53","guid":{"rendered":"http:\/\/johnbrear-plantintegrity.com\/?page_id=593"},"modified":"2019-01-14T09:53:35","modified_gmt":"2019-01-14T09:53:35","slug":"ligament-cracking-in-a-13crmo44-superheater-header","status":"publish","type":"page","link":"https:\/\/johnbrear-plantintegrity.com\/?page_id=593","title":{"rendered":"Ligament cracking in a 13CrMo44 superheater header"},"content":{"rendered":"\r\n<figure id=\"attachment_598\" aria-describedby=\"caption-attachment-598\" style=\"width: 300px\" class=\"wp-caption alignright\"><img fetchpriority=\"high\" decoding=\"async\" src=\"http:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack-2.jpg\" alt=\"\" width=\"300\" height=\"225\" class=\"size-full wp-image-598\" srcset=\"https:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack-2.jpg 1023w, https:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack-2-300x225.jpg 300w, https:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack-2-768x576.jpg 768w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><figcaption id=\"caption-attachment-598\" class=\"wp-caption-text\">Superheater header, with end-caps removed for inspection<\/figcaption><\/figure>\r\n\r\n<p><strong>Component:<\/strong><\/p>\r\n<li>Superheater outlet headers, fabricated from  13CrMo44 (1Cr0.5Mo) steel, in two identical 60MW units<\/li>\r\n<\/ul>\r\n<p><strong>Problem:<\/strong><\/p>\r\n<ul>\r\n    <li>Extensive ligament cracking after 4 years service (~400 starts).  This lay predominantly in the circumferential direction in the bottom pair of each set of four ligaments.   Crack depths were up to 80% of wall.<\/li>\r\n<\/ul>\r\n<p><strong>Approach:<\/strong><\/p>\r\n<ul>\r\n    <li>Fracture mechanics assessment<\/li>\r\n<\/ul>\r\n<figure id=\"attachment_595\" aria-describedby=\"caption-attachment-595\" style=\"width: 300px\" class=\"wp-caption alignright\"><img decoding=\"async\" src=\"http:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack.jpg\" alt=\"\" width=\"300\" height=\"225\" class=\"size-full wp-image-595\" srcset=\"https:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack.jpg 599w, https:\/\/johnbrear-plantintegrity.com\/wp-content\/uploads\/2019\/01\/LigCrack-300x225.jpg 300w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><figcaption id=\"caption-attachment-595\" class=\"wp-caption-text\">Ligament cracking<\/figcaption><\/figure>\r\n<p><strong>Results:<\/strong><\/p>\r\n<ul>\r\n    <li>A leak-before break analysis showed that, under the pressure stress alone, a through-wall crack spanning the bottom pair of ligaments would be stable - with a reserve factor greater than 2.  Even a crack spanning all four ligaments would be stable with a 10% reserve.<\/li>\r\n    <li>The strong directionality of the cracking implied the presence of significant additional system loading.<\/li>\r\n    <li>A simple fatigue crack growth calculation indicated that a stress range of around 150MPa was required to explain the observed crack history.<\/li>\r\n    <li>Under loads compatible with the crack development, a crack spanning the bottom pair of ligaments would be unstable, failing by collapse.<\/li>\r\n<\/ul>\r\n<p><strong>Conclusions:<\/strong><\/p>\r\n<ul>\r\n    <li>The headers could not continue in service<\/li>\r\n    <li>Replacement should include a measure of redesign to reduce the system loads<\/li>\r\n<\/ul>\r\n","protected":false},"excerpt":{"rendered":"<p>Component: Superheater outlet headers, fabricated from 13CrMo44 (1Cr0.5Mo) steel, in two identical 60MW units Problem: Extensive ligament cracking after 4 years service (~400 starts). This lay predominantly in the circumferential direction in the bottom pair of each set of four ligaments. Crack depths were up to 80% of wall. Approach: Fracture mechanics assessment Results: A &hellip; <a href=\"https:\/\/johnbrear-plantintegrity.com\/?page_id=593\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Ligament cracking in a 13CrMo44 superheater header<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":114,"menu_order":5,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-593","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/pages\/593","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=593"}],"version-history":[{"count":4,"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/pages\/593\/revisions"}],"predecessor-version":[{"id":599,"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/pages\/593\/revisions\/599"}],"up":[{"embeddable":true,"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=\/wp\/v2\/pages\/114"}],"wp:attachment":[{"href":"https:\/\/johnbrear-plantintegrity.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=593"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}