1. What is the primary application and scope of ASTM A139 steel pipe?
Answer: ASTM A139 is a standard specification for electric-fusion (arc)-welded steel pipe in sizes NPS 4 and above. Its primary application is for pipeline transmission systems for water, oil, gas, and other fluids. It is commonly used in municipal water supply lines, sewer force mains, and industrial process piping where high-pressure capability is required. The standard covers pipes suitable for field bending, provided appropriate bending practices are followed.
2. How does the manufacturing process of A139 pipe affect its properties?
Answer: A139 pipes are manufactured using the electric resistance weld (ERW) or electric fusion weld process. This involves forming the pipe from coiled steel plate and welding the seam without the addition of filler metal. This continuous process allows for high production rates and long pipe lengths, which can reduce installation costs. However, the weld seam is a critical area. It must be meticulously controlled and is often tested non-destructively to ensure it is free of defects that could become failure points under pressure.
3. What are the key mechanical properties to verify for A139 pipe, and how are they tested?
Answer: The two key mechanical properties are Tensile Strength and Yield Strength.
Tensile Strength: Minimum 48,000 psi (Grade A) or 60,000 psi (Grade B).
Yield Strength: Minimum 30,000 psi (Grade A) or 35,000 psi (Grade B).
These are verified through destructive tests performed on specimens cut from production pipes. A test is conducted for each lot of 400 pipes or less. The test involves stretching a sample coupon in a tensile testing machine until it fractures to measure the force it can withstand.
4. Is post-weld heat treatment (PWHT) required for A139 pipes?
Answer: No, post-weld heat treatment is not a mandatory requirement under the ASTM A139 standard. The pipe is generally used in the as-welded condition. However, the specifier (e.g., the project engineer) may require normalized or stress-relieved pipe for specific applications involving severe cold bending, low-temperature service, or to enhance dimensional stability and relieve residual stresses from the welding process. This would be an additional requirement specified in the purchase order.
5. What are the standard hydrostatic test requirements for A139 pipe?
Answer: Every length of A139 pipe must undergo a non-destructive hydrostatic test. The test pressure is calculated using a specific formula provided in the standard: P = 2St / D, where:
P = Minimum Test Pressure (psi)
S = Allowable Fiber Stress, which is 50% of the specified minimum yield strength (psi)
t = Nominal Wall Thickness (in)
D = Nominal Outside Diameter (in)
This test verifies the soundness of the pipe body and the weld seam by subjecting it to a pressure significantly higher than its intended operating pressure, ensuring it can safely perform in service.
