GB/T 3098.8 Bolts for -200°C to +700°C Use

Introduction to GB/T 3098.8 Standard

This standard outlines mechanical properties, materials, inspection, identification, and marking for bolted connection parts operating in extreme temperatures from -200°C to +700°C. It ensures reliability in applications such as pressure vessels, boilers, and high-temperature machinery, supplementing standards like GB/T 3098.1, GB/T 3098.6, and DIN EN 10269.

Scope

GB/T 3098.8-2010 specifies requirements for fasteners made of austenitic steels for low temperatures down to -200°C and steels/nickel alloys for high temperatures up to +700°C. It covers mechanical performance grades, testing methods, and material matching to guarantee structural integrity under thermal stresses. This is crucial for industries requiring resistance to creep, relaxation, and brittle failure.

Applies to bolts, screws, studs, and nuts in bolted connections.
Focuses on full load-bearing capacity for safe operation in extreme environments.
References related standards for comprehensive compliance.

Materials and Mechanical Properties

Materials are selected based on temperature ranges to maintain mechanical integrity. For low temperatures, austenitic steels provide ductility; for high temperatures, steels and nickel alloys offer strength and creep resistance. Properties must meet specified hardness, tensile strength, and proof loads.

Low-Temperature Materials

Table 1 lists austenitic steel groups for minimum working temperatures to -200°C, with properties per GB/T 3098.6 and GB/T 3098.15. Copper content ≤1%. Higher temperatures have no impact; lower require performance tests per conditions.

Minimum Continuous Working Temperature (Approximate)	Steel Group^เอ	Performance Grade
Minimum Continuous Working Temperature (Approximate)	Steel Group^เอ	Bolt	Nut
-60°C^ข	A2L	50	50
	A2		50
	A3		70
-200°C^c	A4L	70	70
	A4		80
	A5		80

^เอ Copper content ≤1% (per GB/T 3098.6 and GB/T 3098.15).
^ข Headed bolts.
^c Studs.

High-Temperature Materials

Table 2 specifies steels and nickel alloys for up to +700°C, with properties per DIN EN 10269 Table 4 for heat treatment. Reference data for yield strength, creep strength, and relaxation from DIN EN 10269 Tables 5, C.1, D.1. Related to AD 2000-W2, W7, W10, and VdTUV sheets.

Working Temperature Range per DIN EN 10269			วัสดุ				Bolt and/or Nut Hardness/HV
นาที	Short-term^เอ สูงสุด	Long-term^ข สูงสุด	Abbreviation	ตัวเลข	Grade	Condition	นาที	สูงสุด
-120°C	/	/	KB	1.568	X12Ni5	+NT	157	203
-120°C	/	/	KB	1.568	X12Ni5	+QT	173	235
/	400°C	500°C	Yd	1.1181	C35E	+N	150	200
/	400°C	500°C	YK	1.1181	C35E	+QT	165	210
/	400°C	/	YB	1.5511	35B2^จี	+QT	165	210
-60°C	500°C	550°C	KG	1.7218	25CrMo4	+QT	195	240
-100°C	500°C	/	GC	1.7225	42CrMo4	+QT	275	337
/	500°C	550°C	GA	1.7709	21CrMoV5-7	+QT	225	272
/	600°C	550°C	GB	1.7711	40CrMoV46	+QT	272	320
/	550°C	600°C	Ve	1.4923	X22CrMoV12-1	+QT 1^อี	256	303
/	550°C	600°C	VH^f	1.4923	X22CrMoV12-1	+QT 2^f	287	367
/	600°C	600°C	VW	1.4913	X19CrMoNbVN11-1	+QT	287	367
/	650°C	670°C	เอส	1.4986	X7CrNiMoBNb16-16	+WW+P	210	272
-196°C	650°C	650°C	SD	1.498	X6NiCrTiMoVB25-15-2	+AT+P	287	367
-196°C	650°C	800°C	เอสบี	2.4952	NiCr20TiAl	+AT+P	320	417

^เอ Temperature limit for yield and tensile strength.
^ข Temperature limit for creep and rupture strength.
^c Conditions per DIN EN 10269 Table 4: +N (normalized), +NT (normalized and tempered), +QT (quenched and tempered), +WW (warm worked), +AT (solution annealed), +P (precipitation hardened).
^ง For nuts only.
^อี V per DIN EN 10269, Rp0.2 ≥600 N/mm² (+QT1).
^f VH per DIN EN 10269, Rp0.2 ≥600 N/mm² (+QT2).
^จี See VdTUV WB 490.

Load Capacities

Load values ensure fasteners withstand operational stresses. Use for design verification.

Minimum Tensile Loads for Coarse Thread Bolts

Table 4a: A_s,nom × R_m,min /kN

Thread Size d	Stress Area A_s,nom /mm²	Austenitic Stainless Steel Grade		Steel and Nickel Alloys
		50	70	KB	YK	KG	GA	GB	GC	วี	VH	เอส	SD	เอสบี
		50	70	KB	YB	KG	GA	GB	GC	วี	VW	เอส	SD	เอสบี
เอ็ม3	5.03	2.52	3.52	2.67	2.52	3.02	3.52	4.28	4.33	4.02	4.53	3.27	4.53	5.03
ม3.5	6.78	3.39	4.75	3.59	3.39	4.07	4.75	5.76	5.83	5.42	6.1	4.41	6.1	6.78
เอ็ม4	8.78	4.39	6.15	4.65	4.39	5.27	6.15	7.46	7.55	7.02	7.9	5.71	7.9	8.78
เอ็ม5	14.2	7.1	9.94	7.53	7.1	8.52	9.94	12.1	12.2	11.4	12.8	9.23	12.8	14.2
เอ็ม6	20.1	10.1	14.1	10.7	10.1	12.1	14.1	17.1	17.3	16.1	18.1	13.1	18.1	20.1
เอ็ม7	28.9	14.5	20.2	15.3	14.5	17.3	20.2	24.6	24.9	23.1	26	18.8	26	28.9
เอ็ม8	36.6	18.3	25.6	19.4	18.3	22	25.6	31.1	31.5	29.3	32.9	23.8	32.9	36.6
เอ็ม10	58	29	40.6	30.7	29	34.8	40.6	49.3	49.9	46.4	52.2	37.7	52.2	58
เอ็ม12	84.3	42.2	59	44.7	42.2	50.6	59	71.7	72.5	67.4	75.9	54.8	75.9	84.3
เอ็ม14	115	57.5	80.5	61	57.5	69	80.5	97.8	98.9	92	104	74.8	104	115
เอ็ม16	157	78.5	110	83.2	78.5	94.2	110	133	135	126	141	102	141	157
เอ็ม18	192	96	134	102	96	115	134	163	165	154	173	125	173	192
เอ็ม20	245	123	172	130	123	147	172	208	211	196	221	159	221	245
เอ็ม22	303	152	212	161	152	182	212	258	261	242	273	197	273	303
เอ็ม24	353	177	247	187	177	212	247	300	304	282	318	229	318	353
เอ็ม27	459	230	/	243	230	275	321	390	395	367	413	298	413	459
เอ็ม30	561	281	/	297	281	337	393	477	482	449	505	365	505	561
เอ็ม33	694	347	/	368	347	416	486	590	597	555	625	451	625	694
เอ็ม36	817	409	/	433	409	490	572	694	703	654	735	531	735	817
เอ็ม39	976	488	/	517	488	586	683	830	839	781	878	634	878	976

Bearing Capacity of Bolt Connections

For full capacity: Matching full-capacity bolts and nuts with appropriate heights (Type 1 for coarse, Type 2 for fine), thread tolerances, and strength ratios. Fracture in tensile tests must occur in unthreaded sections per GB/T 3098.1 or 3098.6. Waisted studs per GB/T 13807.2/3 with tolerances per GB/T 3103.4.

Perform tensile tests to verify minimum loads.
Ensure nut height meets type requirements for load distribution.
Match materials to avoid weak links in the assembly.

คำถามที่พบบ่อย

What materials are suitable for -200°C applications?

Austenitic steels like A4L, A4, A5 with grade 70 or 80, ensuring ductility and toughness per Table 1.

How to select matching bolts and nuts for high temperatures?

Use Table 3 for rational pairings, ensuring nut strength >70% of bolt and proper thread tolerances for full capacity.

What if operating temperature exceeds +700°C?

The standard limits to +700°C; for higher, conduct specific creep and relaxation tests per DIN EN 10269 guidelines.

Why higher proof stress for austenitic nuts?

To account for manufacturing variations in small batches, ensuring reliability when matched with softer bolts (see Table 3 note b).

How to test for full load-bearing capacity?

Conduct tensile tests per GB/T 3098.1 or 3098.6, verifying fracture location and minimum loads from Tables 4a/5a.

Are there restrictions on copper content?

Yes, ≤1% for austenitic steels to prevent embrittlement in low-temperature service.