GOST 21858-78 Threaded Pipeline Connections. Screw-in Unions. Design

GOST 21858-78 establishes the design of screw-in unions for threaded pipeline connections with a 24° cone angle.

Mandatory product quality requirements ensuring interchangeability, safety for life and health, and environmental protection are set out in clauses 2 and 4 of the standard. The standard may be used for certification, with the scope and methods of certification testing per GOST 15763-91.

The standard does not specify the surface roughness of the hexagon.

The design and basic dimensions of screw-in unions must comply with those shown in the drawing and table.

Dimensions in mm
Group	Nominal size (bore)	Outer tube diameter	for thread			Thread		for thread		(tolerance ±0.3)	for thread		Weight per 1000 pcs, kg
			metric	pipe		metric	pipe	metric	pipe		metric	pipe
1	2.5	4	3	3	M8×1	M8×1	1/8	13.8	16.2	21.5	12	14	7.2
	3.0	5			M10×1								8.6
	4.0	6	4.5	4.5		M10×1		16.2	16.2		14	14	10.5
	6.0	8			M12×1.5					22.5			11.0
2	4.0	6	4	4	M12×1.5	M10×1	1/8	16.2	16.2	23.5	14	14	14.0
	6.0	8	6	7	M14×1.5	M12×1.5	1/4	19.6	21.9	29.0	17	19	22.0
	8.0	10	7	7	M16x1.5	M14×1.5		21.9		30.0	19		30.0
	10.0	12	9	9	M18×1.5	M16x1.5	3/8	25.4	25.4	31.5	22	22	40.0
	12.0	15	11	14	M22×1.5	M18x1.5	1/2	27.7	31.2	35.0	24	27	53.0
	12.0	(16)	12	14	M24×1.5	M22×1.5		31.2	31.2	35.0	27	27	76.0
	15.0	18	14	14	M26×1.5 (M27×2)	M22×1.5				36.0			75.0
	20.0	22	18	18	M30×2	M26×1.5 (M27×2)	3/4	36.9	36.9	40.0	32	32	106.0
	25.0	28	23	23	M36×2	M33×2	1	47.3	47.3	43.0	41	41	168.0
	32.0	(34)	30	30	M45×2	M42×2	1 1/4	57.7	57.7	48.0	50	50	282.0
	32.0	35			M45×2	M42×2		57.7	57.7	48.0	50	50	310.0
	40.0	42	36	36	M52×2	M48×2	1 1/2	63.5	63.5	52.0	55	55	355.0
3	3.0	6	4	5	M14×1.5	M12×1.5	1/4	19.6	21.9	32.0	17	19	30.0
	4.0	8	5		M16×1.5	M14×1.5		21.9		34.0	19		41.0
	5.0	10	7	8	M18×1.5	M16×1.5	3/8	25.4	25.4	34.5	22	22	53.0
	6.0	12	8		M20×1.5	M18×1.5		27.7		36.5	24		69.0
	8.0	(14)	10	12	M22×1.5	M20×1.5	1/2	31.2	31.2	41.0	27	27	94.0
	10.0	16	12		M24×1.5	M22×1.5							100.0
	12.0	20	16	16	M30×2	M27×2	3/4	36.9	36.9	47.0	32	32	155.0
	15.0	25	20	20	M36×2	M33×2	1	47.3	47.3	53.0	41	41	276.0
	20.0	30	25	25	M42×2	M42×2	1 1/4	57.7	57.7	57.0	50	50	441.0
	25.0	38	32	32	M52×2	M48×2	1 1/2	63.5	63.5	64.0	55	55	611.0

Notes:

1. Values given in parentheses are non-preferred.

2. Pipe thread shall not be used in new designs.

3. Mass is given for reference.

Example of designation for a group 1 union with metric thread M10 on the screw-in part, for connection with d=6 mm:

Union 1-6-M10 GOST 21858-78

Same, with pipe thread 1/8 on the screw-in part:

Union 1-6-1/8 GOST 21858-78

Same, group 2 with metric thread M10 on the screw-in part:

Union 2-6-M10 GOST 21858-78

Same, with pipe thread 1/8 on the screw-in part:

Union 2-6-1/8 GOST 21858-78

Same, group 3 with metric thread M12 on the screw-in part:

Union 3-6-M12 GOST 21858-78

Same, with pipe thread 1/4 on the screw-in part:

Union 3-6-1/4 GOST 21858-78

Recommended nominal (rated) pressure values for each group of screw-in unions, depending on the type of connection, are given in GOST 15763-91, Annex 3; assembly examples are given in GOST 22525-77, Annex 2.

Technical requirements, acceptance, test methods, packaging, transportation, storage, and installation recommendations for various types of connections are given in GOST 15763-91.