Bolts and Nuts for High-Temperature Applications – Ambiguities in European Standards

[Vahid.A]

Hello,

Austenitic stainless steel bolts and nuts can be used in high-temperature applications, and their maximum temperature limit is quite high in the ASME Sec II Part D standard. For example, B8 grade (SS304) is allowed up to 816°C (though some technical limitations, like relaxation, restrict its actual use at such high temperatures).

However, in European standards, these grades seem absent for high-temperature applications. ISO 3506-1 and ISO 3506-2 limit their use to 300°C, and they’re not even included in ISO 3506-5, which is specifically for high-temperature fasteners. This seems a bit odd.

have I overlooked a relevant European standard, or is this omission intentional? Any clarification would be appreciated.

 

[MintJulep]

It's right there in the abstract.

NOTE 1 Fasteners conforming to the requirements of this document are used without restriction in applications ranging from ?20 °C to +150 °C; however, fasteners conforming to this document are also used for applications outside this range down to ?196 °C and up to +300 °C. For more details, see ISO 3506-6.

Outside the temperature range of ?20 °C to +150 °C, it is the responsibility of the user to determine the appropriate choice for a given application, in consultation with an experienced fastener metallurgist and by taking into account e.g. stainless steel composition, duration of exposure at elevated or low temperature, the effect of the temperature on the fastener mechanical properties and clamped parts, and the corrosive service environment of the bolted joint.

NOTE 2 ISO 3506‑5[1] is developed in order to assist in the selection of appropriate stainless steel grades and property classes intended for use at temperatures up to +800 °C.

 

[Vectrex]

Hi,

I could not find anything related as well in ISO standards (except for the reply above), and I think they are not covered in those. You can check EN 10269, ASTM A453, or ASTM A193.

So I don't think you missed something; rather, those standards do not cover them.

 

[Vahid.A]

It's right there in the abstract.

Thank you for joining this discussion. To clarify my question: Why are austenitic stainless steels excluded from a standard intended to guide bolt selection for high-temperature applications?

Additionally, high-temperature decision-making requires extensive data, typically compiled by organizations rather than individual fastener metallurgists. Moreover, such specialists may not always be readily available.

 

[Vahid.A]

Hi,

I could not find anything related as well in ISO standards (except for the reply above), and I think they are not covered in those. You can check EN 10269, ASTM A453, or ASTM A193.

So I don't think you missed something; rather, those standards do not cover them.

Thank you for your insightful response. As you noted, EN 10269 provides high-temperature properties for fasteners, but it lacks mechanical property data for grades 1.4301, 1.4401, 1.4404, and 1.4304 at temperatures above 550–600°C, While, ASME Section II, Part D (Table 3) includes this data for similar grades up to 825°C.

The ISO/EN standards appears to exclude common austenitic grades like SS316 (A4) and SS304 (A2) for applications exceeding 600°C.

 

[MintJulep]

It doesn't seem to be an omission. It looks like the ISO committee has considered austenitic stainless and decided that the upper limit is 300C.

See ISO 3506-6:



On the spectrum of standard development, ISO tends to lean towards being supported by science and research; while ASME, ASTM etc. tend towards old farts codifying crap that they remember doing once.

It would be interesting to write to both committees with the same letter asking for their explanations of the difference.

 

[Krausen]

What is the design temperature of these bolts you're looking to use? I'm not familiar with ISO standards, but it appears they are ahead of ASME in not allowing above 300 C / 572 F, as MintJulep mentioned. I've never installed austenitic SS bolting on any high temp application I've ever designed (up to over 1000 F bolting design temps). A193 B7 & B16 studs perform just fine up to these design temps, regardless of the flange metallurgy. And B7/B16 studs/bolts don't gall like austenitic SS bolting will inevitably do.

 

[Vectrex]

I can only tell you that, based on my own experience, I avoid using SST bolts at high temperatures, especially anchor bolts in incinerator refractories that can reach 1000 degrees Celsius. I would need to research a bit deeper to determine what the issue is with SST and high-temperature intolerance. When I find out, I'll post it here. Talking about 316 and 304 here.

 

[Vahid.A]

Thank you for sharing your thoughts. I believe material selection depends on the specific application, and austenitic stainless steels are not universally prohibited. For instance, some boiler manufacturers use them for components like connecting baffles in applications up to 650°C. Additionally, ASTM F2281 provides guidance on service conditions, stating that the safe scaling temperature for continuous service in SS304 and SS316 is 871°C.

That said, I’ve identified a few limitations that could influence material selection, though I’m uncertain about their overall impact:

Stress Relaxation: B8M bolts experience a significant decline in their residual stress due to stress relaxation, a creep-like phenomenon. (Attachment from Handbook of Reliability Prediction Procedures for Mechanical Equipment by Naval Surface Warfare Center)

Some designers use tack welding as a supplementary installation method—would this help mitigate the issue? Additionally, galling can occur even at lower temperatures—could this also affect stress relaxation behavior?

Sigma Phase Formation: This occurs at temperatures above 1000°F (~538°C). I’m unsure whether this poses a limitation for stainless steel bolting applications.

Sensitization: This can occur between 700–1500°F (370–815°C), but I’m not certain if it’s a concern in non-corrosive environments.

Are there any insights on alternative grades like B8C or B8T? I’d appreciate any opinions or experiences with these materials.

 

[mfgenggear]

OP
Maybe you should discuss with specialty fastener manufacture.

What are high-temperature fasteners and how do you choose the correct one for your application? - UC Components, Inc.

High-temperature fasteners are used extensively in critical industries such as semiconductor, aerospace, automotive, and oil/gas. They are specially designed to be able to withstand high temperatures and extreme environments. On top of that they are designed to withstand the alternate phases of...

www.uccomponents.com

 

[Trestala]

Why are austenitic stainless steels excluded from a standard intended to guide bolt selection for high-temperature applications?

I'm fairly certain majority of Owners/Contractors exclude austenitic SS bolts mainly due to Chloride SCC, galling, and it being an intermediate/low strength bolting for pressure retaining components such as flanges. If you're near the shore or the bolts being exposed to rainwater, that can cause Cl- SCC if you have higher operating temperatures >140°F.

It is captured in the abstract of ISO 3506 which mentions "corrosive service environment" as well

Outside the temperature range of ?20 °C to +150 °C, it is the responsibility of the user to determine the appropriate choice for a given application, in consultation with an experienced fastener metallurgist and by taking into account e.g. stainless steel composition, duration of exposure at elevated or low temperature, the effect of the temperature on the fastener mechanical properties and clamped parts, and the corrosive service environment of the bolted joint.

 

[WKTaylor]

SAE aerospace [ASxxxxx] parts bolts/nuts/washers/cotter-pins/lockwire/etc for turbine engine service might be just what you need... alloy-quality-strength-heat/fatigue/erosion-corrosion resistance, etc

 

[TugboatEng]

It sounds like the fastener you are looking for is covered under ASTM A286 or EN 1.4980. These have double the initial strength of your B8 and B8M fasteners, hold it to higher temperatures, and are much more resistant to galling.

When AS**** fasteners were recommended, the CRES or corrosion resistant extra strength fasteners are typically A286. It's also known as Inconel 660.

Tack welding fasteners does not prevent loss of tension due to creep.

 

[WKTaylor]

It sounds like the fastener you are looking for is covered under ASTM A286 or EN 1.4980. These have double the initial strength of your B8 and B8M fasteners, hold it to higher temperatures, and are much more resistant to galling.

When AS**** fasteners were recommended, the CRES or corrosion resistant extra strength fasteners are typically A286. It's also known as Inconel 660.

Tack welding fasteners does not prevent loss of tension due to creep.

Tug... ASTM A286 'Tentative Specification for Quenched and Tempered Alloy Steel Bars'???? Looks like your fingers were ahead of your brain [happens to me all the time]...

PS: The UNS for A286 is S66286... I never knew that A286 had a co-designation of Inconel 660... till now [I did check]... wow.