Choosing Between ASTM A358 and ASTM A312 for Your Project

Stainless steel pipes have many international standards, among which ASTM A358 and ASTM A312 are two commonly used standards. Today, we will analyze these two standards to see which one best suits your usage conditions, testing requirements, and budget.

lASTM A312 is a standard for austenitic stainless steel pipes, covering seamless pipes, welded pipes, and heavily cold-worked welded pipes.  It is frequently used in high-temperature and general environments.

lBesides ASTM A312 being a commonly used standard, ASTM A358 is also frequently used. This standard applies to EFW austenitic chromium-nickel stainless steel pipes and has welding/non-destructive testing grades (Class 1-5). This standard screenshot can help you address welding quality issues.

The key to choosing the right standard is not about which one is better, but rather finding a reasonable balance between usage conditions, testing requirements, diameter, and budget.

Difference Between ASTM A358 and ASTM A312

We'll start by summarizing the results in a table for your quick reference

How do I control weld integrity expectations at PO stage?

The ASTM A358 standard divides pipe materials into five main categories and clearly links the pipe material to the welding method and radiographic inspection level. This standard also includes test methods for tensile testing, guided bend welding, and hydrostatic testing.

I need flexibility—seamless or welded—while staying inside a widely accepted piping standard

If you need a standard that covers both seamless and welded pipes, ASTM A312 is clearly a better fit for you. It covers seamless, straight-seam, and cold-worked welded austenitic stainless steel pipes for high-temperature and general corrosive environments.  It also emphasizes that certain H-grade steels, such as TP304H and TP316H, are suitable for environments with high creep and stress rupture performance requirements. 

ASTM A358 Overview

Electric-Fusion Welded Process

1. Prepare stainless steel plates or coils and verify that they meet the cutting specifications.

2. Place the steel plates into a U-shaped or O-shaped bending machine for forming.

3. Weld the steel plate seams using arc welding.

4. Configure the welding according to standards and project requirements: Class 1/5 requires double-sided welding, and Class 3/4 requires single-sided welding.

RT requirements vary with the Class: Class 1/3/4 requires full radiographic testing.

Class 5 requires spot radiographic testing, while Class 2 has no mandatory radiographic testing.

5. Determine whether solution annealing/heat treatment is required; this is usually decided by the project.

6. Perform pickling, passivation, and surface treatment, such as removing scale and improving corrosion resistance.

7. Perform NDT testing: RT/UT, dimensional inspection, and visual inspection.

8. Conduct tests: pressure testing, weld testing, hydrostatic testing, etc.

9. Compile report documents: MTC, NDE, heat treatment records.

ASTM A312 Overview

Seamless and Welded Pipe Types

1. Steel bars are placed in the furnace for heating.

2. After heating to a stable temperature, they are transferred to the piercing mill for piercing.

3. The tubes are rolled to the target size.

4. Heat treatment is performed according to requirements.

5. Pickling and passivation are carried out.

6. Straightening, cutting, and beveling are performed.

7. The steel pipes are inspected (NDT, hydrostatic testing, dimensions, and appearance).

8. The outgoing documents are compiled and issued.

Welded Pipe Types

1. Incoming inspection of steel plates or steel strips; proceed to cutting if qualified.

2. Bending and forming (same as ASTM A358)

3. Welding of seams (TAW/SAW)

4. Seam shaping

5. Solution heat treatment (depending on project requirements)

6. Pickling and passivation

7. Inspection

8. Marking and documentation

Comparing Specifications and Uses

l If you are using it in a high-pressure environment, ASTM A312 seamless steel pipe might be a good option, as this standard avoids problems associated with welds.

l For some projects requiring large diameter/high flow/plant utility/piping, it is recommended to use the ASTM A358 standard, with the Class level depending on the inspection and criticality of the application.

Cost Factors

Based on actual market conditions, for the same material and dimensions, the price of welded steel pipes is usually lower than that of seamless steel pipes, with seamless steel pipes being 20-40% more expensive than welded steel pipes.

Important procurement nuance

l The difference between A358 Class 1 and Class 2 pipes lies in their pricing. The price of Class 1 pipes can differ significantly from that of Class 2 pipes because Class 2 includes not only the pipe itself but also radiography and more stringent quality control and inspection mechanisms, making it more expensive.

l The A312 HCW process includes additional process controls (cold rolling and heat treatment before cold working), which may affect delivery times and pricing.

Selecting the Right Standard for Your Project

l There is no inherent "superiority" between ASTM A358 and ASTM A312; the choice depends on factors such as manufacturing process, inspection strategy, and procurement risks.

l TORICH Group can help you determine and select the most suitable stainless steel pipes for your project (A358 or A312 SML/WLD/HCW).  We can also provide quotations that match your specific inspection and documentation requirements (MTC, PMI, NDE records, ITP support). Simply send us your email address, pipe specifications, and project details, and our team will develop a solution for you. Contact us today!