Bolting for cold service – LNG, refrigeration, cryogenic and arctic plant – must stay tough at the lowest temperature the joint will see. That is proven by impact testing, and it is the detail most often missing from a bolting enquiry. A standard ASTM A193 B7 stud is not impact tested by default.
Common Low-Temperature Bolting Grades
| Material standard | Typical grades | Notes |
|---|---|---|
| ASTM A320 (alloy and stainless bolting for low-temperature service) | L7, L43, B8 / B8M classes | Impact testing is required at the temperature stated in the standard or the order |
| ASTM A194 nuts | Grade 4, 7 (with impact testing), 8 / 8M | Nut grade and impact requirement must match the stud |
| ASTM A193 B7 / A194 2H | Standard high-temperature bolting | Not impact tested unless supplementary requirements are ordered |
What to Ask Before You Order
- Minimum design metal temperature for the joint – this sets the impact test temperature.
- Test temperature and acceptance values – the standard gives defaults, but project specifications often require a lower temperature or higher energy.
- Who is tested: studs only, or studs and nuts.
- Heat treatment condition stated on the certificate.
- Coating: confirm the coating process does not affect the tested condition.
- Documents: EN 10204 3.1 or 3.2 certificates showing the Charpy results, test temperature and heat number.
Checking the Certificate
On receipt, check that the certificate shows the impact test temperature, the individual and average absorbed energy values, the specimen size, and that the heat number matches the marking on the studs and nuts. A certificate without impact results means the material has not been proven for low-temperature service, whatever the grade name says.
Related: fastener RFQ template and how to read an EN 10204 3.1 MTC.
Frequently Asked Questions
Is ASTM A193 B7 suitable for low-temperature service?
Not by default. B7 is not impact tested unless supplementary requirements are ordered. For low-temperature service, ASTM A320 grades such as L7 are normally specified.
What test temperature should low-temperature bolting be impact tested at?
The test temperature is set by the standard and by your project specification, normally based on the minimum design metal temperature of the joint. State it on the order.
Do nuts need impact testing too?
It depends on the project specification. Many low-temperature specifications require nuts of a matching grade with their own impact testing, so state whether nuts are included.
