異徑管大小端的面積壓力差產(chǎn)生的彎矩引起大端相對(duì)張開(kāi)、小端相對(duì)收縮的現(xiàn)象。大小頭以材質(zhì)可劃分以下幾種：

1、碳鋼異徑管: ASTM/ASME A234 WPB、WPC

2、合金異徑管: ASTM/ASME A234 WP 1-WP 12-WP 11-WP 22-WP 5-WP 91-WP911、15Mo3 15CrMoV、 35CrMoV

3、不銹鋼異徑管:ASTM/ASME A403 WP 304-304L-304H-304LN-304N
ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti
ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H

4、低溫鋼異徑管:ASTM/ASME A402 WPL3-WPL 6

5、高性能鋼異徑管: ASTM/ASME A860 WPHY 42-46-52-60-65-70