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Technical datasheet ASTM A320 — Alloy steel bolting for low-temperature service

Reference only — for design, verification or contractual purposes refer to the current issue of the original standard. MF Fastener Industries LLC · sales@mfindllc.com · +971 6 767 2469 · mfindllc.com

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Dimensional datasheet

ASTM A320 low-temperature stud

Alloy steel bolting for low-temperature service. Grade L7 is the common specification for cryogenic and cold-climate flanged joints, impact tested to prove toughness at temperature. The cold-service counterpart to A193 B7.

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d nominal thread diameterP thread pitchL stud length

Dimensions

inches

Imperial sizes, 8 UN thread above 1 inch as standard for flange bolting. Studs are supplied cut to length with chamfered ends, normally with two A194 Grade 4 or 7 nuts.

Size	Threads/in	Tensile stress area	Weight per inch	Tensile min	Yield min
1/2"	13 UNC	0.142 in²	0.019 lb	125 ksi	105 ksi
5/8"	11 UNC	0.226 in²	0.030 lb	125 ksi	105 ksi
3/4"	10 UNC	0.334 in²	0.043 lb	125 ksi	105 ksi
7/8"	9 UNC	0.462 in²	0.059 lb	125 ksi	105 ksi
1"	8 UN	0.606 in²	0.077 lb	125 ksi	105 ksi
1-1/8"	8 UN	0.790 in²	0.098 lb	115 ksi	95 ksi
1-1/4"	8 UN	1.000 in²	0.121 lb	115 ksi	95 ksi
1-1/2"	8 UN	1.492 in²	0.175 lb	115 ksi	95 ksi
1-3/4"	8 UN	2.082 in²	0.238 lb	100 ksi	75 ksi
2"	8 UN	2.771 in²	0.311 lb	100 ksi	75 ksi

Charpy impact testing is the point of A320

A320 differs from A193 not in strength but in verified toughness at low temperature. Grade L7 is impact tested at −101 °C (−150 °F), with acceptance criteria on absorbed energy and lateral expansion.

Without the impact test result on the certificate, the material is not A320. Always ask for the Charpy values, not just the tensile figures.

Nuts must also be qualified for low temperature

A320 L7 studs are used with ASTM A194 Grade 4 or Grade 7 nuts. Where the specification calls for it, the nuts are impact tested too.

An ordinary 2H nut on an L7 stud defeats the purpose of the specification in a cold joint.

L7 and L7M are different products

L7 — 125 ksi tensile, standard cold service. L7M — tempered to a maximum hardness of 235 HBW for sour service, with correspondingly lower strength (100 ksi).

L7M is specified where NACE MR0175 / ISO 15156 applies. It is not a substitute for L7 where full strength is required, and the reverse is also true.

Grades

ASTM A320

Grade	Material	Tensile min	Impact test	Service
L7	AISI 4140 / 4142, Q&T	125 ksi	−101 °C	General low temperature
L7M	AISI 4140, Q&T, 235 HBW max	100 ksi	−101 °C	Sour service, NACE
L43	AISI 4340, Q&T	125 ksi	−101 °C	Larger diameters
B8 Class 1	304 stainless	75 ksi	−254 °C	Cryogenic
B8M Class 2	316 stainless, strain hardened	95 – 110 ksi	−254 °C	Cryogenic, corrosive

Grade selection is a design decision. Where the piping specification names a grade, supply that grade — the grades are not interchangeable.

Related specifications

—

Standard	Covers	Relationship to A320
ASTM A193 B7	High temperature bolting	Same alloy family, no impact testing
ASTM A194 Gr 4 / 7	Nuts for A320	The matching nut specification
ASTM A182	Flanges and forged fittings	The joint the stud serves
NACE MR0175	Sour service materials	Drives the choice of L7M

A193 B7 and A320 L7 look identical and are often the same base alloy. The difference is the impact test and the certificate. They are not interchangeable.

At a glance

Standard	ASTM A320
Common grade	L7
Material	AISI 4140 / 4142, quenched and tempered
Impact test	Charpy V-notch at −101 °C
Thread	UNC to 1 in · 8 UN above
Matching nut	ASTM A194 Grade 4 or 7
High temperature equivalent	ASTM A193 B7
Sour service grade	L7M, 235 HBW max
Cryogenic grades	B8 · B8M stainless

Supply

A320 stud bolts are manufactured at our own plant — cut to length, threaded, chamfered and supplied with matching nuts.

Bar stock is sourced from certified mills with the impact test results traceable to the heat number.

Finish

Plain	Black, oiled — the normal supply
PTFE / Xylan	Common for offshore and subsea flanges
Cadmium / zinc	Where the specification permits
Certification	Mill certificate with Charpy results against heat number

Testing

Dimensional and thread inspection is carried out in our own plant on calibrated instruments. Tensile, hardness and chemical testing is carried out by independent UAE-accredited laboratories.

Reference only

This datasheet is published for reference. Dimensions and property values are reproduced in good faith from published standards, but for design, verification or contractual purposes always refer to the current issue of the original standard.

If a figure here conflicts with the standard, the standard governs.

Need a quotation?

Send the size, length, grade, nut grade, coating and quantity. Confirm the design temperature — it determines whether L7, L7M or a stainless grade applies.