ASTM A312 vs ASTM A358

ASTM A312 vs A358: Choosing the Right Stainless Steel Pipe Standard

Introduction

ASTM and ASME standards on stainless steel welded tubes and pipes are ASTM A312/ASME SA312 and ASTM A358/ASME SA358. The ASTM A358 standard applies to stainless steel tubes and pipes welded with straight or spiral seams, usually used for industrial applications at high and low temperatures or in unique environments. The ASTM A312 standard applies to austenitic seamless and straight-seam welded steel tubes and pipes used for high-temperature operations and an Austenitic seamless and straight-seam welded steel pipe for general corrosive service. Regardless of the usage environment, the weld’s quality directly impacts life, property, and operational safety. This blog post explores the topic of joint efficiency and filler metals in ASTM A312 vs ASTM A358 welded stainless steel pipes.

Specifications: ASTM A312 vs A358

1. ASTM A312/A312M, hereinafter referred to as A312

A312, the full name is “Standard for Seamless (SMLS), Welded (WLD), and Heavy Cold Worked (HCW) Austenitic Stainless Steel Piping.” It is suitable for high temperatures and general corrosive conditions. TP304H, TP310H, TP316H, TP321H, TP347H, and other grades with “H” are also ideal for high-temperature service.

A312 welded pipes (WLD) are manufactured by an automatic welding process in which no filler metal is added during welding.

Heavy Cold-Worked Tubes (HCW) are manufactured from welded tubes that have passed 100% RT. They are cold-worked to a wall thickness and weld thickness reduction of ≥35%, then annealed and heat-treated. No filler is allowed for welding.

Welded pipes and HCW pipes with OD ≤ NPS 14 Inches shall have one longitudinal weld seam (two longitudinal seams are not permitted), and OD > NPS 14 Inches shall have one longitudinal seam. Still, two longitudinal seams are permitted with the approval of the Purchaser. Each weld shall be subjected to all weld tests, inspection, examination, and heat treatment.

The nominal pipe of A312 shall be free of oxidized skin and stained iron filings. Pickling, sandblasting, or surface finishing may not be mandatory if bright annealed. The Purchaser may require passivation for finished tubes.

A312 nominal tubes (SML, WLD, HCW) shall all be supplied in heat-treated conditions (see Table 2 requirements of the standard for details). Seamless tubes, or maybe after hot forming, are not less than the minimum solid solution heat treatment temperature in a medium such as water, rapid cooling, or quenching.

Mechanical tests, grain size determination, and weld corrosion tests are required. A312 steel pipe, one specimen from each batch (≤ 100 tubes) for the transverse or longitudinal tensile test; each batch to 5% and ≥ 2 for the flattening test. A transverse weld bending test can be used for the welded pipe instead of the flattening test. For high-temperature steel pipe with “H” in the grade, 5% and ≥ two specimens per batch shall be used for grain size determination. HCW welded pipe may be subjected to a weld loss test if an additional requirement is S9.

Each pipe shall be subjected to nondestructive or hydro testing, but the method used shall be at the manufacturer’s discretion (unless specified in the purchase contract). If non-destructive testing is defined in the order, each pipe shall be nondestructively tested in accordance with Gauge E213 (UT), E309, E426, or E570; the selection of nondestructive testing shall be left to the manufacturer’s discretion unless specifically requested by the Purchaser; and by agreement between the Purchaser and the manufacturer, Gauge E273 (UT of weld zone) shall be utilized in addition to a single, complete external surface inspection. The range of pipe sizes that can be inspected by each method shall be limited by the scope of the respective gauge.

Weld Repair: Welded pipe with OD ≥ NPS 6 Inches and nominal wall thickness WT ≥ 5.08 mm may be weld repaired with the addition of a matching filler metal. Weld repair shall not exceed 20% of the length of the weld; weld repair is only permitted to use tungsten grade gas shielded welding; when corrosion resistance or other properties are required, subject to the approval of the Purchaser, weld repair can be tungsten grade gas shielded welding and the use of alloy filler metal of a higher alloy composition than the base metal. The corresponding filler metal grades for steel pipe are provided in Table 6.

One or more of the supplementary requirements of A312 are used as additional tests only when specified in the order. Supplementary requirements are S1 (finished product analysis), S2 (transverse tensile test), S3 (flattening test), S4 (immersion test), S5 (radiographic inspection), S6 (stabilizing heat treatment), S7 (intergranular corrosion test), S8 (supplied with minimum wall thickness), S9 (weld loss test).

As can be seen, A312 welded pipe (WLD and HCW), supplied in heat treatment (solution), but stabilized stainless steel stabilization treatment, needs to be ordered to mention the additional requirements of S6; the default is also no RT test unless to mention the additional requirements of S5 (RT test for the entire length of each double seam welded pipe); UT test is not necessarily available (the default is customized by the steel mills of the water pressure or NDT) unless the order is UT is specified.

In accordance with ASME B31.3, Table 302.3.4 or Table A-1B, the longitudinal weld joint quality factor Ej for A312 welded pipe without additional RT requirements is 0.80 (for single-sided welds) or 0.85 (for double-sided welds); if only partial RT is available, the longitudinal weld joint quality factor Ej is 0.90 in accordance with Table 302.3.4 (not listed in Table A-1B) [Note 1]; If there is 100% RT, the longitudinal weld joint quality factor Ej is taken as 1.0. Table 302.3.4 is the general rule, while Table A-1B is specific to the refinement of the steel pipe standard, and both are consistent.

[Note 1] Table A-1B does not list the value of Ej at localized RT, and the value of 0.90 is taken to be determined according to the rules in Table 302.3.4.

ASTM A312

ASTM A312

2. ASTM A358/A358M, hereinafter referred to as A358

A358 is a standard for Cr-Ni austenitic stainless steel electrofusion-welded steel pipe for corrosive service conditions, high-temperature service conditions, and so on. EFW commonly means electrofusion welding, electric arc welding, or submerged arc welding. SAW is a kind of electrolytic welding. Steel pipe is usually Grade (316, 316L, 321, 347H, 304L, 310S, etc.) or UNS indicated.

A358 specifies 5 Class categories based on the weld (single or double-sided), RT test condition, filler metal condition, etc.
Class 1, double-sided welds, all weld passes by adding filler metal and 100% RT.
Class 2, double-sided welding, all weld passes by adding filler metal, no RT.
Class 3, single-sided, all weld passes with filler metal added and 100% RT.
Class 4, Single Side Welding with filler metal added to the outer passes and no filler metal added to the inner passes with 100% RT.
Class 5 is double-sided; all passes have filler metal and partial RT.

If there are additional testing requirements, see additional requirements S1 through S8 for details.

Table 1 for A358 lists the corresponding raw steel plates and their filler metal grades for each welded pipe, which is very good. The steel plates for A358 welded pipe in Table 1 are primarily from ASTM A240.

ASTM A358

ASTM A358

Manufacturing Process: ASTM A312 vs A358

ASTM A312:

Covers seamless and welded (without filler metal) stainless steel pipes.
Pipes are typically produced by extrusion (for seamless) or automated welding processes.

ASTM A358:

Covers electric-fusion-welded (EFW) austenitic stainless steel pipes.
Welding is done using filler metal, enhancing the strength and making it suitable for thicker walls.

In-depth Analysis of ASTM A358

A358 Specifies for Welded Joints:

(1) The joints thereof shall be full penetration double-sided or single-sided butt welded joints by the fusion welding process. The difference in the quality factor for welded joints is not specified in the single-sided or double-sided welding process. If a backing ring or strip is used, the ring or strip shall be of the same P-Number material as the plate being joined. After welding, the backing ring or strip shall be removed entirely, and the exposed weld surface will be visually inspected for conformance before any required radiographs are taken. Welding with backing strips or rings left in place is prohibited. Welding procedures and operators shall conform to the requirements of ASME BPVC IX.
(2) For Class 4 welded pipe utilizing multiple passes, the root weld pass may be made without adding filler metal. Class 4 welded pipe: the weld surface inside the pipe may be due to a single pass (without adding filler metal) made from the inside. Except in the case of Class 4, Class 1, 2, 3, and 5 welds shall be made exclusively by a process involving the deposition of filler metal. All single-sided welded pipes shall be 100% RT (radiographic testing).
(3) The surface of the weld shall be permitted to be flush with the substrate or to have a projection not exceeding 3 mm; no depressions shall be allowed unless the thickness of the weld metal is ≥ the minimum thickness of the adjacent neighboring base metal.
(4) Welding defects shall be repaired by removing the intact metal and rewelding. Subsequent heat treatment and inspection (i.e., visual, radiographic, and dye penetration) shall conform to the requirements of the original weld.

A358 Heat Treatment Provisions for Butt Weld Welds:

All pipes shall be heat treated in accordance with Table 2.

However, if the buyer does not desire the heat treatment of Table 2, provision shall be made for it in the purchase order.

Solid solution annealing temperatures above 1950°F [1065°C], Grade 321, 321H, 347, 347H, 348 may impair resistance to intergranular corrosion upon subsequent exposure to sensitized service conditions. When the Purchaser specifies, a lower temperature stabilization or re-solution annealing shall be used after the initial high-temperature solution annealing (see Supplementary Requirement S5).

Chemical Composition of A358 Welded Pipe and Welded Filler Metals:

(1) The chemical composition of all plates of A358 welded pipe shall conform to ASTM A240/A240M.
(2) The chemical composition of welded filler metals other than Gr. S34751 shall conform to the requirements of the applicable AWS specification for the corresponding grade shown in Table 1 or shall conform to the chemical compositions specified for the plate in A240/A240M, or where corrosion resistance or other properties are required, and subject to approval by the Purchaser, shall be a filler metal that is alloyed to a higher degree than the base metal. The use of filler metals other than those listed in Table 1 or those conforming to the chemical composition specified for the sheet in Specification A240/A240M shall be reported, and the filler metal shall be identified on the test certificate. When nitrogen and cerium are specific to the grade ordered, the analysis method for these elements shall be determined by agreement between the Purchaser and the manufacturer.
(3) The chemical composition of Gr. S34751 weld filler metal shall conform to the chemical composition specified for the plate in A240/A240M. The method of nitrogen analysis shall be determined by agreement between the Purchaser and the manufacturer.

Allowable Deviations in Dimensions of A358 Welded Pipe:

(1) Deviation in outside diameter: ± 0.5%.
(2) Out-of-roundness – difference between large and small OD, 1%.
(3) Alignment: Use a 3-meter straightedge to make both ends in contact with the pipe, with a deviation of 3 mm from the pipe.
(4) Negative deviation of wall thickness: 0.3mm.

Melting Analysis of A358 Welded Pipe and Raw Materials:

(1) The plate manufacturer shall analyze each steel furnace, and the chemical composition (elemental percentage) shall conform to the requirements specified in A240/A240M.
(2) Product analysis shall be made.

A358 Tensile Requirements for Raw Materials for Welded Pipe:

(1) The plate used in pipe fabrication shall conform to the tensile property requirements of the applicable codes listed in Table 1. The plate manufacturer shall qualify it through tensile tests.
(2) The tensile strength of a transverse tensile test performed on a welded joint specimen shall not exceed the minimum tensile strength specified for the plate.
(3) A358 welded pipe shall be subjected to a transverse guided bending weld test.

Radiographic Testing Provisions for A358 Welded Pipe

(1) For Class 1, 3, and 4 welded pipes, all welded joints shall be 100% RT tested.RT testing shall conform to the requirements of ASME BPVC VIII-1 Para. UW-51.
(2) Class 5 welded pipe, welded joints shall be locally RT tested with a radiographic length of not less than 12 inches [300 mm] per 50 feet [15 m] of weld.RT testing shall conform to the requirements of ASME BPVC VIII-1 Para. UW-52.
(3) Radiographic inspection before heat treatment is permitted.

Additional Requirements for A358

S1 (product analysis), S2 (tensile and flexural testing), S3 (penetrating oil and powder inspection), S4 (fusion-deposited ferrite control), S5 (stabilizing heat treatment), S6 (intergranular corrosion testing), S7 (process heat treatment), S8 (ASME III or VIII-1 requirements)

In accordance with ASME B31.3, Table 302.3.4 or Table A-1B, for A358 welded pipe Class 1, Class 3, and Class 4, the longitudinal weld joint quality factor Ej is taken to be 1.0; for Class 5, the longitudinal weld joint quality factor Ej is taken to be 0.90; and for Class 2, the longitudinal weld joint quality factor Ej is taken to be 0.85. Table 302.3.4 is the general rule, while Table A-1B is specific to refining the steel pipe standard; the two are identical.

Through the above several stainless steel welded pipe standard comparisons and learning, the pipeline designers in the pipe material grade table for the ASTM A358 standard can be Class 1, 2, 3, 4, 5 to simplify the account of the manufacturing method used and RT testing requirements. ASTM A312 welded pipe uses no filler metal added to the manufacturing of automatic welding, so only additional RT requirements can be proposed.

Size Range and Wall Thickness: ASTM A312 vs A358

ASTM A312:

Standard sizes are commonly used, with normal wall thickness.
More focused on standard applications where extreme wall thickness is not required.

ASTM A358:

Typically applies to larger diameter and heavier wall thickness pipes.
Specifically designed for applications requiring robustness in higher pressures or corrosive environments.

Joint Efficiency and Filler Metals: ASTM A312 vs A358

ASTM A312:

Purpose: Covers seamless and welded austenitic stainless steel pipes.
Joint Efficiency: Typically, the joint efficiency for welded joints is around 60% to 85%, depending on the type of weld and inspection methods used.
Filler Metals: ER308L or ER316L filler metals are generally recommended for welding. These fillers are suitable for most applications involving austenitic stainless steels.

ASTM A358:

Purpose: Specifically covers electric-fusion-welded (EFW) austenitic stainless steel pipes.
Joint Efficiency: The controlled welding process can increase joint efficiency for EFW pipes, often around 85% to 100%.
Filler Metals: Similar to A312, ER308L or ER316L are commonly used. However, the choice may vary based on specific service conditions and corrosion resistance requirements.

Testing Requirements: ASTM A312 vs A358

ASTM A312:

Includes nondestructive tests such as hydrostatic testing and eddy current testing.

ASTM A358:

Requires more stringent testing due to the welded nature, such as radiographic inspection and enhanced mechanical testing for welded joints.

Intended Applications: ASTM A312 vs A358

ASTM A312:

General-purpose applications in industries like petrochemical, food processing, and power generation.
Suitable for moderate pressure and temperature conditions.

ASTM A358:

Designed for high-pressure and high-temperature applications, often in chemical plants, power plants, and industrial boilers.
Ideal for corrosive environments due to its fusion welding with filler metal.

Cost: ASTM A312 vs A358

ASTM A312:

Generally more cost-effective due to simpler manufacturing processes.

ASTM A358:

Higher cost due to the use of filler material, fusion welding, and additional quality controls.

Summary: ASTM A312 vs A358

(1) Pipe OD <DN400, can not be realized double-sided welding, only single-sided welding; pipe OD ≥ DN400, only double-sided welding.
(2) Pipe WT <6mm, no wire (no filler metal added).
(3) 100% RT cannot be realized for small-size welded pipes.
(4) Crew electrofusion welded pipe [Note 3], formed on a crew using rows of rolls to form steel strip or strip coils, continuously welded; no filler metal added, single-sided weld, weld seam can be straight or spiral. The welded pipe of ASTM A312 is of this type. The advantage of its output is efficiency; the disadvantage is that it has large dimensional tolerances (approximately the same seamless steel pipe).
(5) plate welded pipe [Note 4] is the use of a single sheet of steel as a billet, longitudinal rolled or pressed to shape, using a straight seam welding process (automatic, semi-automatic, or manual) welded into a single steel pipe. Subject to increased pipe diameter, there may be one longitudinal seam, two longitudinal seams, etc.; the welded seam may or may not have filler metal added. ASTM A358 welded pipe is of this type.

ASME B31.3 is interpreted as a pipe made from one or two straight-seam butt joints or one helical-seam butt joint in which fusion is produced in a preformed pipe by manual or automatic arc welding.

The welds may be single-sided (welded from one side) or double-sided (welded from both the inside and outside), with or without the addition of filler metal. Typical electrofusion welding processes used for piping include self-fusion welding, combination welding (COW), and submerged arc welding (SAW). Submerged Arc Welding (SAW) pipe electrofusion welded pipe made by the submerged arc welding process; there is at least one submerged arc weld channel on the outside of the pipe, and when SAW is also used for welding the inside of the pipe, the pipe is referred to as Double Submerged Arc Welding (DSAW) pipe; it can be classified as straight seam (SAWL) and spiral seam (SAWH) according to the seam condition.