Fatigue: A phenomenon in which a metal material is below the ultimate strength and is subjected to an alternating load (that is, a load whose shape and direction are repeatedly changed) for a long period of time, and suddenly breaks without significant plastic deformation, and is called fatigue. The fatigue index includes fatigue limit and fatigue strength.

ERW pipe standard are as follows:
API 5L, ASTM A53 B, ASTM A178, ASTM A500/501, ASTM A691, ASTM A252, ASTM A672

(1) Domestic casing according to SY/T6194-96, the length of the casing is not fixed, and its range is 8-13m. However, casings not shorter than 6 m can be supplied, and the number must not exceed 20%.
(2) The inner and outer surfaces of the casing shall be free from folding, hairline, separation, cracking, rolling and crusting. These defects should be completely removed and the depth of removal should not exceed 12.5% of the nominal wall thickness.

Standard basis and content of A106B American standard seamless pipe acceptance
First, the basis for acceptance
The basis for the acceptance of the A106B American standard seamless pipe is mainly the contract signed by the supplier and the buyer (that is, the agreement with legal functions). Therefore, the acceptance work is carried out according to the following documents: