When does Carbon Equivalent CE become an essential variable in Welding Process (PQR)?

𝐀𝐫𝐭𝐢𝐜𝐥𝐞 𝐍𝐨.𝟎𝟏

The 𝐰𝐞𝐥𝐝𝐚𝐛𝐢𝐥𝐢𝐭𝐲 of 𝑐𝑎𝑟𝑏𝑜𝑛 𝑎𝑛𝑑 𝑙𝑜𝑤 𝑎𝑙𝑙𝑜𝑦 𝑠𝑡𝑒𝑒𝑙 is significantly influenced by 𝑐𝑎𝑟𝑏𝑜𝑛 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 𝑎𝑛𝑑/𝑜𝑟 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡, and various standards provide specific thresholds where welding restrictions apply:• 𝐀𝐒𝐌𝐄 𝐁𝐏𝐕𝐂 𝐕𝐈𝐈 𝐃𝐢𝐯 𝟏, 𝐏𝐚𝐫𝐭 𝐔𝐅 (𝐔𝐅-𝟓), stipulates that the heat analysis of forgings intended for welding must not exceed 𝟎.𝟑𝟓% 𝐜𝐚𝐫𝐛𝐨𝐧.•   𝐀𝐏𝐈 𝟓𝟏𝟎 explicitly prohibits welding of carbon or alloy steel with a carbon content exceeding 𝟎.𝟑𝟓%.Nevertheless, the 𝐂𝐚𝐫𝐛𝐨𝐧 𝐄𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) is a more optimal 𝑚𝑒𝑡𝑟𝑖𝑐 for evaluating metal 𝐡𝐚𝐫𝐝𝐞𝐧𝐚𝐛𝐢𝐥𝐢𝐭𝐲 and 𝐰𝐞𝐥𝐝𝐚𝐛𝐢𝐥𝐢𝐭𝐲.The definition of 𝐂𝐚𝐫𝐛𝐨𝐧 𝐄𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) is given by the following formulas CE= C+ (Cr+ Mo+ V)/5+ Mn/6 + (Ni+Cu)/15 (API 577 , ASME BPVC IX) • 𝐀𝐏𝐈 𝟓𝟕𝟕 defines preheat and post-weld heat treatment (PWHT) requirements based on the carbon equivalent (CE) of the steel: 1. 𝐂𝐄 ≤ 𝟎.𝟑𝟓: No preheat required. 2. 𝟎.𝟑𝟓 < 𝐂𝐄 ≤ 𝟎.𝟓𝟓: Preheating is typically necessary. 3. 𝐂𝐄 > 𝟎.𝟓𝟓: Both preheating and PWHT are required.• 𝐀𝐒𝐌𝐄 𝐁𝐏𝐕𝐂 𝐕𝐈𝐈 𝐃𝐢𝐯 𝟏, 𝐏𝐚𝐫𝐭 𝐔𝐂𝐒, employs the 𝐂𝐚𝐫𝐛𝐨𝐧 𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) to determine certain restrictions on post-weld heat treatment (𝐓𝐚𝐛𝐥𝐞 𝐔𝐂𝐒-𝟓𝟔-𝟏).Returning to the question: under which conditions does the 𝐜𝐚𝐫𝐛𝐨𝐧 𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) become an 𝐞𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥 𝐯𝐚𝐫𝐢𝐚𝐛𝐥𝐞?All 𝐞𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥, 𝑠𝑢𝑝𝑝𝑙𝑒𝑚𝑒𝑛𝑡𝑎𝑟𝑦 𝐞𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥, and 𝐧𝐨𝐧-𝐞𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥 variables are listed in 𝐀𝐒𝐌𝐄 𝐁𝐏𝐕𝐂 𝐈𝐗, 𝐓𝐚𝐛𝐥𝐞 𝐐𝐖-𝟐𝟓𝟐 , but 𝐂𝐄 is not among them.• The 𝐂𝐚𝐫𝐛𝐨𝐧 𝐄𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) becomes an 𝐞𝐬𝐬𝐞𝐧𝐭𝐢𝐚𝐥 𝐯𝐚𝐫𝐢𝐚𝐛𝐥𝐞 for Welding Procedure Qualification (WPQ) when the 𝐭𝐞𝐦𝐩𝐞𝐫 𝐛𝐞𝐚𝐝 𝐭𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞 is used, as specified in 𝐴𝑆𝑀𝐸 𝐵𝑃𝑉𝐶 𝐼𝑋, 𝑇𝑎𝑏𝑙𝑒 𝑄𝑊-290.4.What is the 𝐭𝐞𝐦𝐩𝐞𝐫 𝐛𝐞𝐚𝐝 𝐭𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞?• The 𝐭𝐞𝐦𝐩𝐞𝐫 𝐛𝐞𝐚𝐝 𝐰𝐞𝐥𝐝𝐢𝐧𝐠 technique was developed to mitigate the deterioration of the metallurgical properties of the 𝐇𝐞𝐚𝐭 𝐀𝐟𝐟𝐞𝐜𝐭𝐞𝐝 𝐙𝐨𝐧𝐞 (𝐇𝐀𝐙) by carefully managing welding bead deposition, overlapping, and heat input. This process tempers the base metal 𝐇𝐀𝐙, reducing hardness and improving fracture toughness, especially in hardenable materials. Since 𝐜𝐚𝐫𝐛𝐨𝐧 𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐭 (𝐂𝐄) 𝑖𝑠 𝑡ℎ𝑒 𝑏𝑒𝑠𝑡 𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑜𝑟 ℎ𝑎𝑟𝑑𝑒𝑛𝑎𝑏𝑖𝑙𝑖𝑡𝑦, it is evident why CE is considered an essential variable (with increasing CE) in this context. The technical details are provided in 𝐀𝐒𝐌𝐄 𝐁𝐏𝐕𝐂 𝐈𝐗, 𝐐𝐖-𝟐𝟗𝟎 paragraph, Figure 𝐐𝐖-𝟒𝟔𝟐.𝟏𝟐, 𝐚𝐧𝐝 𝐅𝐢𝐠𝐮𝐫𝐞 𝐐𝐖-𝟒𝟔𝟐.𝟏𝟑.