Spectacle Blind, Flange Spade, Ring Spacer (ASME B16.48)

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Author: Projectmaterials
Posted: September 20, 2017
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Spectacle blind, flange spade, and ring spacer are forged products used to blind pipelines (temporarily or permanently). These devices are cost-effective alternatives to isolation valves. A spectacle blind combines, in one single product, a flange spade and a ring spacer. Flange spades and ring spacers, as separate products, are used when the rotation of a spectacle blind would be difficult due to space constraints. ASME B16.48 covers the dimensions and specifications of these isolation devices.

SPECTACLE BLIND OPERATION

Spectacle blinds, spades, and ring spacers are installed between flanges to sections of a pipeline permanently or temporarily as shown in this Youtube video:

Source: Sure Flow Equipment Inc.

Spectacle blinds are available in standard sizes up to 24 inches and in forged material grades like ASTM A105 (high-temperature carbon), A350 low-temperature carbon), and various ASTM A182 grades (alloy, stainless steel, duplex). Click on the link to learn about the chemical and mechanical properties, and the selection criteria, of these common spectacle blind grades (which are the same as flanges).

Where to buy spectacle blinds? Generally, flange factories are also spectacle blind manufacturers.

The reference specification for pipeline isolation devices (including spectacle blind, ring spacers, and line blanks) is ASME B16.48.

Spectacle blinds (also defined “spectacle flanges”) are manufactured from steel plates and are basically two interconnected discs: one is actually a ring (i.e. a disc with a hole of the same bore size of the pipeline), the other is a solid disc.

In normal conditions, spectacle blinds are installed in the open position and do not interrupt the flow of the fluid conveyed by the pipeline.

To blind the pipeline, and interrupt the flow, the site staff has simply to unscrew the flange bolts and rotate the spectacle blind to its closed position.

It is easy to understand if a spectacle blind is in an open or closed position, as one of the two discs is always outside the pipe (so when the ring is visible, the pipeline is closed; when the solid disc is visible outside, the pipeline is open). For spades and ring spacers, holes on the hangers inform the staff.

Spectable blinds for pipelines opening and closing

Spectacle blind in an open position: the conveyed fluid can flow through the pipeline. As the disc is rotated, the flow is interrupted.

These products are available in most diameters, from 1/2 to 36 inch generally, and in pressure classes from 150 to 600 pounds (for RTJ flanges, the common pressure ranges are between 300 and 2500 pounds).

Carbon steel spectacle blinds are manufactured out of a single piece of steel, whereas alloy / stainless steel blinds can be manufactured by welding more pieces together (generally up to three).

SPECTACLE BLIND TYPES

There are three types of spectacle blinds:

Flat face spectacle blind (FF): similar to a flat face flange, the surface of the disc is flat (suited for flat face gaskets, for low-pressure applications).
Raised face spectacle blind (RF): likewise raised face flanges, there is an additional thickness on the surface of the disc. This type fits semi-metallic gaskets, as the spiral wound type.
Ring joint face spectacle blind (RTJ): a groove is inscribed on the surface of the disc. This type is used in conjunction with ring joint gaskets.

types of spectable blinds

SPECTACLE BLIND DIMENSIONS in MM ASME B16.48

Spectable blind sizes

CLASS 150

Class 150 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 150	A	B	C	t	W
1/2	45	16	60	3	38
3/4	54	21	70	3	38
1	64	27	80	3	38
1¼	73	42	90	6.4	38
1½	83	48	100	6.4	38
2	102	61	120	6.4	51
2½	107	73	140	6.4	51
3	133	89	150	6.4	64
3½	159	102	175	9.7	64
4	172	114	190	9.7	64
5	194	141	215	9.7	76
6	219	168	240	12.7	76
8	276	219	300	12.7	76
10	337	273	360	15.7	102
12	406	324	430	19.1	102
14	448	356	475	19.1	108
16	511	406	460	22.4	108
18	546	457	580	25.4	114
20	603	508	635	28.4	121
24	714	610	750	31.8	140

CLASS 300

Class 300 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 300	A	B	C	t	W
1/2	51	16	65	6.4	38
3/4	64	21	80	6.4	38
1	70	27	90	6.4	38
1¼	79	42	100	6.4	38
1½	92	48	115	6.4	38
2	108	61	125	9.7	51
2½	127	73	150	9.7	51
3	146	89	170	9.7	64
3½	162	102	185	12.7	64
4	178	114	200	12.7	64
5	213	141	235	15.7	76
6	248	168	270	15.7	76
8	305	219	330	22.4	76
10	359	273	385	25.4	102
12	419	324	450	28.4	102
14	483	356	515	31.8	108
16	536	406	570	38.1	108
18	594	457	630	41.1	114
20	651	508	685	44.5	121
24	772	610	810	50.8	140

CLASS 600

Class 300 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 600	A	B	C	t	W
1/2	51	16	65	6.4	38
3/4	64	21	80	6.4	38
1	70	27	90	6.4	57
1¼	79	37	100	9.7	57
1½	92	43	115	9.7	67
2	108	55	125	9.7	57
2½	127	67	150	12.7	67
3	146	83	170	12.7	67
3½	159	96	185	15.7	76
4	191	108	215	15.7	76
5	238	135	265	19.1	86
6	264	162	290	22.4	86
8	318	212	350	28.4	95
10	397	265	430	35.1	105
12	454	315	490	41.1	105
14	489	346	525	44.5	114
16	562	397	605	50.8	124
18	610	448	655	53.8	133
20	679	497	725	63.5	133
24	787	597	840	73.2	152

CLASS 900

Class 900 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 900	A	B	C	t	W
1/2	60	16	80	6.4	38
3/4	67	21	90	6.4	41
1	76	27	100	6.4	57
1¼	86	37	110	9.7	57
1½	95	43	125	9.7	67
2	140	55	165	12.7	57
2½	162	67	190	12.7	67
3	165	83	190	15.7	67
4	203	108	235	19.1	76
5	244	135	280	22.4	86
6	286	162	320	25.4	86
8	356	212	395	35.1	95
10	432	265	470	41.1	105
12	495	315	535	47.8	105
14	518	346	560	53.8	114
16	572	397	615	60.5	124
18	635	448	685	66.5	133
20	696	497	750	73.2	133
24	835	597	900	88.9	152

CLASS 1500

Class 1500 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 1500	A	B	C	t	W
1/2	61	16	80	6.4	38
3/4	67	21	90	9.7	41
1	76	27	100	9.7	64
1¼	86	35	110	9.7	64
1½	95	41	125	12.7	70
2	140	53	165	12.7	70
2½	162	63	190	15.7	76
3	172	78	205	19.1	76
4	206	102	240	22.4	89
5	251	128	290	28.4	89
6	279	154	320	35.1	89
8	349	203	395	41.1	102
10	432	255	480	50.8	114
12	518	303	570	60.5	114
14	575	333	635	66.5	127
16	638	381	705	76.2	133
18	702	429	775	85.9	146
20	752	478	830	95.3	152
24	899	575	990	111.3	178

CLASS 2500

Class 2500 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 2500	A	B	C	t	W
1/2	67	16	90	9.7	38
3/4	73	21	95	9.7	41
1	83	27	110	9.7	64
1¼	102	35	130	12.7	64
1½	114	41	145	15.7	70
2	143	53	170	15.7	70
2½	165	63	195	19.1	76
3	194	78	230	22.4	76
4	232	102	275	28.4	89
5	276	128	325	35.1	89
6	314	154	370	41.1	89
8	384	198	440	53.8	102
10	473	248	540	66.5	114
12	546	289	620	79.2	114

ASME B 16.48 spectacle blinds dimension and weight.pdf

This norm covers the dimensions, marking, pressure-temperature ratings, materials, dimensional tolerances and testing for line blanks in sizes between NPS 1/2 and NPS 24 for installation between ASME B16.5 flanges in the classes from 150 to 2500.

FLANGE SPADE AND RING SPACER

A flange spade, otherwise called steel “blanking spade”, or “single-blind”, “blank” or “paddle blind”, is a metallic ring used to isolate a pipe (it has the same scope as a spectacle blind). To close the pipe, the blanking spade is inserted between the flanges; to open the pipe, the spade is removed, and the ring spacer takes its place.

Field staff understands if a pipe is open or closed, as blanking spades have one single signaling hole on the device holder, and ring spacers have instead two holes (look at the image).

Flange spades and ring spacers are manufactured according to the ASME B16.48 specification and belong to the family of pipeline isolation devices.

Flange spade and ring spacer — Ring spacer (left) and blanking spade (right)

FLANGE SPADE VS SPECTABLE BLINDS

A spectacle blind combines a flange spade and a ring spacer in a single device (this is the reason why flange spades are called “single-blinds” or “blanks”). The difference is that spectacle blinds may need some space to be rotated, and this space is not always available due to the routing of the piping system. This is when two separate devices are used, as they do not require rotation to be installed.

Spades, ring spacers, and spectacle blinds are available in multiple sizes (from 1/2 inch to 24 inches, and pressure rating from 150 to 2500#) and material grades (the same available for standard flanges) depending on the fluid conveyed by the pipeline.

The difference between spades/ring spacers and spectacle blinds is shown in the image:

difference spade and spectable blind