Difference Between Weldolet Sockolet And Threadolet

While Weldolets, Sockolets, and Threadolets all connecting a branch line to a run pipe, they differ in design, application, and installation.

Per MSS SP-97 and ASME piping codes, distinct application parameters dictate which fitting is required. Below is the technical comparison of these three forged fittings.

Difference in Connection Geometry and Method

The primary distinction lies in the branch interface: Weldolets utilize a beveled butt-weld, Sockolets employ a recessed socket-weld, and Threadolets use a tapered screw connection.

Weldolet: This fitting has a beveled end that matches the bevel of the branch pipe. It requires a full penetration butt weld, ensuring a smooth transition between the fitting and the branch pipe.

Sockolet: This fitting features a counterbore (socket) into which the branch pipe is inserted. The connection is secured using a fillet weld around the exterior of the fitting/pipe interface.

Threadolet: This fitting contains internal female threads (typically NPT or BSP). The branch pipe is screwed into the fitting, requiring no welding at the branch interface, although the fitting itself is still welded to the header.

Difference in Pressure Capabilities and Criticality

Weldolets are used for critical, high-pressure, and high-temperature applications requiring radiography, whereas Sockolets and Threadolets are generally restricted to lower-criticality or small-bore lines.

Weldolet: Because it utilizes a butt-weld, the Weldolet minimizes stress concentrations and allows for radiographic inspection. This makes it the standard choice for high-pressure steam, corrosive chemical lines, and large-bore piping where fatigue resistance is paramount.

Sockolet & Threadolet: These are typically defined by pressure classes. While capable of handling significant static pressure, the geometry of a fillet weld (Sockolet) or thread root (Threadolet) creates stress risers that make them less suitable for cyclic service or systems subject to severe vibration or crevice corrosion.

Difference in Installation and Welding Requirements

Weldolets require precise alignment and bevel preparation for a butt weld, while Sockolets and Threadolets use simpler fillet welds for installation onto the header.

Weldolet: The installation requires the branch pipe to be beveled. The welder must perform a butt weld, which is technically more demanding and time-consuming but offers superior joint strength.

Sockolet: No beveling of the branch pipe is required; the pipe is cut square. However, the installer must ensure a strict expansion gap (typically 1/16 inch) at the bottom of the socket to prevent thermal expansion failure before fillet welding.

Threadolet: This requires no welding on the branch side. It allows for easy assembly and disassembly of the branch connection, making it ideal for instrument connections or temporary lines, provided leakage via threads is not a safety concern.

Difference in Nominal Pipe Size Limitations

Weldolets are available for all branch sizes, including large-bore piping, while Sockolets and Threadolets are universally used for smaller branch sizes.

Weldolet: There is no upper limit to the size of a Weldolet; they are commonly manufactured for branch sizes ranging from 2 inches up to 48 inches and larger.

Sockolet & Threadolet: These fittings are almost exclusively used for small-bore branching. They are generally manufactured for outlet sizes of NPS 4 and smaller, as the mechanical stresses on fillet welds and threads become unmanageable in larger diameters.

Difference in Flow Characteristics

Weldolets offer the least resistance to flow due to a smooth bore transition, whereas Sockolets and Threadolets introduce flow disruption due to internal steps or crevices.

Weldolet: When properly installed, the internal bore of the Weldolet aligns with the ID of the branch pipe, minimizing turbulence and erosion-corrosion.

Sockolet: The gap between the pipe end and the socket bottom creates a cavity that can trap fluid or cause turbulence, potentially leading to crevice corrosion in stainless steel.

Threadolet: Similar to the Sockolet, the threaded interface creates discontinuities in the pipe wall that can disrupt laminar flow.

Difference in Maintenance, Durability, and Cost

Weldolets and Sockolets offer superior long-term durability with minimal maintenance needs, whereas Threadolets provide easier disassembly but may incur higher ongoing inspection costs due to potential leak points.

The welded nature of Weldolets and Sockolets results in a monolithic structure resistant to corrosion and fatigue, aligning with nickel alloy's high-performance attributes and reducing lifecycle costs in harsh environments, though initial fabrication is more expensive.

Threadolets facilitate maintenance by allowing unscrewing for repairs or replacements without cutting the pipe, but they demand regular checks for thread corrosion or sealant degradation, potentially elevating operational expenses in corrosive stainless steel applications despite lower upfront costs.

Conclusion

For critical piping systems involving stainless steel or nickel alloys, the choice between these fittings is driven by the piping specification.

Use Weldolets for critical, large-bore, or high-cyclic service. Select Sockolets for permanent small-bore connections where radiography is not required. Utilize Threadolets for small-bore instrumentation or maintenance connections where welding the branch is not feasible.

FAQs

When to use weldolet and sockolet?

Weldolet: When piping systems are under high pressure, high temperature, large diameter, or critical operating conditions, Weldolet should be the preferred choice. It is the standard choice for transporting hazardous media, enduring severe cyclic loads, or long-distance pipelines.

Sockolet: Sockolet is typically used when branch pipelines are small diameter (usually NPS 4 and below) and do not require internal radiographic inspection. It is mainly used for general process pipelines or applications without severe vibration.

ASME B16.11 weldolet size chart

Run pipe nominal size		Branch pipe nominal size		Lengths			Diameter of fitting			Hole diameter
DN	NPS	DN	NPS	A			D2min			d1nom
				STD	XS	Sch160	STD	XS	Sch160	STD	XS	Sch160
8-900	1/4-36	6	1/8	16	16	一	24	42	一	16	16	一
10-900	3/8-36	8	1/4	16	16	一	26	26	一	16	16	一
15-900	1/2-36	10	3/8	19	19	一	30	30	一	19	19	一
20-900	3/4-36	15	1/2	19	19	28	36	36	36	24	24	14
25-900	1-36	20	3/4	22	22	32	43	43	46	30	30	19
32-900	11/4-36	25	1	27	27	38	55	55	51	36	36	25
40-900	11/2-36	32	11/4	32	32	44	66	66	63	45	45	33
50-900	2-36	40	11/2	33	33	51	74	74	71	51	51	38
65-900	21/2-36	50	2	38	38	55	90	90	82	65	65	43
80-900	3-36	65	21/2	41	41	62	104	104	98	76	76	54
90-900	31/2-36	80	3	44	44	73	124	124	122	93	93	73
100-900	4-36	90	31/2	48	48	一	138	138	一	113	113	一
125-900	5-36	100	4	51	51	84	154	154	154	120	120	98
150-900	6-36	125	5	57	57	94	187	187	188	141	141	122
200-900	8-36	150	6	60	78	105	213	227	222	170	170	146
250-900	10-36	200	8	70	99	一	265	292	一	220	220	一
300-900	12-36	250	10	78	94	一	323	325	一	275	265	一
350-900	14-36	300	12	86	103	一	379	381	一	325	317	一
400-900	16-36	350	14	89	100	一	411	416	一	357	351	一
450-900	18-36	400	16	94	106		465	468	一	408	403
500-900	20-36	450	18	97	111	一	522	525	一	459	455	一
550-900	22-36	500	20	102	119	一	573	584	一	508	509	一
650-900	26-36	600	24	116	140	一	690	708	一	614	612	一

ASME B16.11 thredolet dimensions

Run pipe nominal size		Branch pipe nominal size		Face of fitting to crotch		Diameter of fitting		Diameter a tend of branch pipe		Length of thread	Hole diameter
DN	NPS	DN	NPS	A		D1min		D2min		L2min	d1 nom
				3000	6000	3000	6000	3000	6000		3000	6000
8-900	1/4-36	6	1/8	19	一	27	一	22	一	6.7	16	一
10-900	3/8-36	8	1/4	19	一	27	一	22	一	10.2	16	一
15-900	1/2-36	10	3/8	21	一	30	一	25	一	10.4	19	一
20-900	3/4-36	15	1/2	25	32	38	45	33	42	13.6	24	19
25-900	1-36	20	3/4	27	37	47	52	39	48	13.9	30	25
32-900	11/4-36	25	1	33	40	56	63	48	58	17.3	36	33
40-900	11/2-36	32	11/4	33	41	66	72	58	67	18.0	45	38
50-900	2-36	40	11/2	35	43	75	83	64	77	18.4	51	49
65-900	21/2-36	50	2	38	52	90	104	77	93	19.2	65	59
80-900	3-36	65	21/2	46	一	105	一	94	一	28.9	76	一
100-900	4-36	80	3	51	一	124	一	114	一	30.5	94	一
125-900	5-36	100	4	57	一	154	一	140	一	33.0	121	一

ASME B16.11 sockolet dimensions

Nominal size		Branch pipe nominal size		Depth of socket	Face of fitting to crotch		Diameter of fitting		Socket wall thickness		Hole diameter
DN	NPS	DN	NPS	Jmin	Amax		Dmax		Cmin		d1 nom
					3000	6000	3000	6000	3000	6000	3000	6000
8-900	1/4-36	6	1/8	9.5	10	一	27	一	3.18	一	16	一
10-900	3/8-36	8	1/4	9.5	10	一	27	一	3.78	一	16	一
15-900	1/2-36	10	3/8	9.5	13	一	30	一	4.01	一	19	一
20-900	3/4-36	15	1/2	9.5	16	24	38	47	4.67	5.97	24	19
25-900	1-36	20	3/4	12.5	16	25	47	53	4.90	6.96	30	25
32-900	11/4-36	25	1	12.5	22	29	56	63	5.69	7.92	36	33
40-900	11/2-36	32	11/4	12.5	22	30	66	74	6.07	7.92	45	38
50-900	2-36	40	11/2	12.5	24	32	75	83	6.35	8.92	51	49
65-900	21/2-36	50	2	16.0	24	37	90	104	6.93	10.92	65	59
80-900	3-36	65	21/2	16.0	25	一	105	一	8.76	一	76	一
100-900	4-36	80	3	16.0	30	一	124	一	9.52	一	94	一
125-900	5-36	100	4	19.0	30	一	154	一	10.69	一	121	一