Bri-Steel Seamless Pipe Manufacturer

Seamless Pipe Low-Temperature
( ASTM A333 / ASME SA333 )

Standard Specification for Seamless Steel Pipe for Low-Temperature Service and Other Applications with Required Notch Toughness

ASTM Scope:
This specification covers nominal (average) wall carbon and alloy steel pipe intended for use at low temperatures and in other applications requiring notch toughness. Several grades of ferritic steel are included as listed in Table 1. Some product sizes may not be available under this specification because heavier wall thicknesses have an adverse effect on impact properties.

Product Knowledge:
This ASTM specification is written so that the end user and the manufacturer can agree upon, and clearly understand, the properties and capabilities of the piping product being supplied. In contrast with national codes (like API, ASME or CSA), ASTM A333 is rarely stipulated by national or state-level legal requirements.

There are several grades in A333, each with different steelmaking approach to improve the steel’s impact properties at lower temperatures. Several grades have nickel (Ni) additions, and are capable of high toughness at cryogenic temperatures as low as -320F (-195C). Many of these grades would be considered rare, and in the experience of Bri-Steel, they are expensive to procure and may be difficult to find a capable fabricator with an proven weld procedure. The exception to this is Gr6, which is quite common and is regularly stocked in colder regions of North America. A333 Gr6 has proven impact toughness at -50F (-45C), and is commonly used in applications where the piping is exposed directly to cold environments during construction and/or in operation.

A333 Gr6 is also commonly used for pressure piping of compressed gas, where a crack would be expected to have catastrophic consequences.

Beginning with the 2013 edition, the title of this spec included “other applications with required notch toughness”. This could include applications where cyclic loading and fatigue cracking are concerns, or where corrosion may be expected to contribute to notching of the metal. In these applications, the proven notch toughness of the material would be expected to deter crack initiation and growth.

Note that A333 Gr 6 allows seamless and long-seam pipe manufacturing techniques. That being said, for pipes with long seams, impact toughness of the base metal, weld metal and weld heat-affected zone must be proven and documented.

Rather than “re-invent the wheel”, ASME has recognized the widespread use of this product, and has adopted the A333 standard for use in pressure vessel (BPVC) and pressure piping (B31.X) applications. The details of this can be found in ASME Boiler and Pressure Vessel Code (BPVC) Section IIA, and is identified as SA333. Note that there may be minor exceptions in the SA version of ASTM standards, and the engineers, end users, purchasers and Manufacturer must comply. Note also that there is often a 5 to 10 year lag between the approved ASTM edition and the approved ASME edition. This means that there can be minor differences between the two specifications. Most engineers who spec SA333 product will also prefer to follow the requirements of the more recent ASTM version (which is usually also more strict), resulting in the common notation ASTM/ASME A/SA106 on the product documentation.

Note that there is a lower limit on manganese (Mn) in ASTM A333 Gr6 of around 0.30% Mn, though you will typically see around three times this much (around 0.90% Mn). For products that are hot rolled, it will be more common to see values of above 1.20% Mn, as the increased alloying is necessary to attain the impact toughness requirements of the standard. Because of these considerations, this product will commonly have a Mn/C ratio of 4 to 8 depending on the production method. Therefore, ASME B31.3 limits the low temp application of SA333 Grade 6 products to above -50F (-45C).

There is also a limitation on Niobium Nb (in the USA, this element is referred to as Columbium Cb). It seems that this limitation was an attempt to reduce the demand for worldwide Niobium, since the ore is generally mined in Africa and has become a conflict mineral. From the engineering perspective, Niobium is still preferred to other microalloying elements for its ability to increase the ductility of the steel during an impact (i.e, the % shear increases with Niobium content).

A106 does not have its own table of pipe dimensions. Rather, like A333 and API 5L, it reverts to ASME B36.10 for the nominal pipe dimensions. Therefore, A106 pipe products are often multi-certified to similar ASTM A53, A333 and API 5L grades, where the requirements of all these specifications are met.

Note that for welding SA333 products, ASME BPVC Section IX considers SA333 Gr6 to be in the P1G1 alloy grouping (along with SA53 GrB, SA106 GrB).

It is interesting that hydrotesting is not required for this standard, provided that non-destructive testing has been performed, such as ultrasonics or eddy current inspection, and was determined to be capable of full-thickness inspection (i.e., it must have been volumetric NDT). When the hydrotesting option is chosen instead of NDT, the test pressure will be at 60% of the burst pressure of the pipe.

Basic Product Properties:
A333 Grade 6:
35 ksi (240 MPa) min. YS
60 ksi (415 MPa) min. UTS
Impact Tested to meet
Minimum 18J (13 ft-lb) at
-45°C (-50°F)

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