The distance between each slot and any end of the test block or other slots is not less than T or 25mm, whichever is larger. 2, the minimum length of the test block L should be 200mm or 8T, whichever is larger. 3. When the inner diameter is equal to or less than 100mm, the minimum radian is 270°. When the inner diameter is greater than 100mm, the minimum arc length is 200mm or 3T, whichever is greater. 4, each groove groove depth 11%T≥h≥8%T, groove width ≤6mm, groove length ≥25mm.