# 316L vs 317L Pipe: When Is a Material Change Worth Reviewing?

Canonical: https://jundapipe.com/en-GB/blog/316l-vs-317l-pipe

Compare the material basis of 316L and 317L, then assess corrosion evidence, fabrication and quotation scope before approving a substitution.

317L is worth comparing with 316L when the corrosion assessment identifies a reason to consider additional alloying. A larger grade number is not enough to justify substitution. Compare the actual exposure, product standard, fabrication requirements and supporting corrosion evidence before approving the change.

[IMOA’s reference table](https://www.imoa.info/molybdenum-uses/molybdenum-grade-stainless-steels/austenitic-stainless-steel.php) identifies 316L as S31603 and 317L as S31703, with a higher molybdenum range for 317L. This is a screening distinction, not a service-life prediction or a certificate for supplied pipe.

## What does the composition comparison show?

| Reference grade | UNS designation | Reference molybdenum, mass % |
| --------------- | --------------- | ---------------------------- |
| 316L            | S31603          | 2.00–3.00                    |
| 317L            | S31703          | 3.00–4.00                    |

Source: [IMOA, Austenitic stainless steel, Table 1](https://www.imoa.info/molybdenum-uses/molybdenum-grade-stainless-steels/austenitic-stainless-steel.php), accessed 25 October 2026. IMOA describes these compositions as taken from plate, sheet and strip specifications where available, or company data sheets. Use the selected pipe standard and edition for acceptance limits.

The ranges touch at 3.00% molybdenum. Comparing that one element cannot establish grade equivalence. The complete chemistry, ordered designation, condition and product requirements must be checked against the applicable standard and certificate.

## What evidence would justify a change?

Identify the mechanism the change is intended to address. Collect fluid composition, normal and upset temperatures, cleaning exposures and failure observations. Distinguish general corrosion, localized attack and fabrication-related problems.

For an existing installation, record whether damage is in base metal, a joint, a crevice, a stagnant branch or an externally contaminated area. A material change may be relevant, but a local design condition can remain after the alloy changes.

Use corrosion data that match the service closely enough to support the decision. Label differences in concentration, temperature and test condition. A qualitative material comparison cannot substantiate a numerical lifetime multiplier.

## How should quotations be compared?

Prepare a common basis covering:

1. Identical product form, dimensions, wall basis and lengths.
2. The exact grade and product specification edition.
3. The same condition, examination and documentation scope.
4. Differences in approved welding and accessories.
5. Confirmed commercial terms for the actual quantity.

For austenitic pipe, [ASTM A312/A312M-25](https://store.astm.org/a0312_a0312m-25.html) is a specification to evaluate where the project requires it. Its public scope does not confirm the grade, size or inspection offered by an individual supplier.

Compare installed cost after resolving technical differences. Keep material price, fabrication, inspection and maintenance assumptions separate. Without current quotations and service evidence, a fixed price premium or payback period would be speculative.

## Where do Junda products enter the review?

Junda lists [316L seamless pipe](https://jundapipe.com/products/316l-seamless-pipe) and [317L seamless pipe](https://jundapipe.com/products/317l-seamless-stainless-steel-pipe). [Catalogue source](https://jundapipe.com/products) Request comparable offers through the [contact page](https://jundapipe.com/contact), explaining why the alternative is being considered.

If neither candidate addresses the service, broaden the assessment. The [904L and 254SMo comparison](https://jundapipe.com/blog/904l-vs-254smo-pipe) covers a different material decision with its own evidence requirements.