WELDED HYDRAULIC TUBING
NFPA STD T188.8.131.52
This specification covers cold worked and annealed electric resistance welded low carbon steel pressure tubing with outside diameter 3/8 inch to 2-1/2 inch, inclusive, for use as hydraulic lines for industrial equipment or other applications requiring flaring and bending.
CHEMICAL COMPOSITION (percentage by weight)
|Manganese||0.30 – 0.60|
The tubing shall conform to the following requirements:
|Tensile Strength||45,000 psi minimum|
|Elongation in 2 inch||35 percent* minimum|
|Rockwell Hardness||B65 maximum|
* For tubes with OD of 3/8 inch and/or wall thickness of 0.035, a minimum elongation of 30 percent is permitted.
FLATTENING TEST — A section at least three inches in length shall be taken from every 1500 feet or less of finished tubing and shall be flattened between parallel plates to three times the wall thickness of the tube. The weld shall be placed at a point of 90 degrees from the direction of applied force. Any cracking or flaws revealed by this test shall be cause for rejection. Superficial ruptures resulting from minor surface imperfections shall not be cause for rejection.
REVERSE FLATTENING TEST — A section at least four inches in length shall be taken from every 1500 feet or less of finished tubing and split longitudinally 90 degrees on each side of the weld and the sample opened and flattened. There shall be no evidence of cracks or lack of penetration or overlaps resulting from flash removal in the weld.