Carbon Steel Spectacle Blind Flanges Manufacturer & Supplier

Carbon Steel Spectacle Blind Flanges Manufacturer and Supplier

A carbon steel spectacle blind flange is a figure-8-shaped plate, one solid blank disc joined by a short web to one open ring, built to ASME B16.48 in ASTM A105 and A694 grades for Class 150 through 2500 duty. The open ring end sits in the line during normal operation and lets the process fluid pass through exactly as if a spacer plate were there. When a section of pipe needs to be positively isolated for maintenance, the joint bolts are removed, the whole plate is swung around its web, and the solid blank end is bolted back into the same joint, sealing the line completely. Because the same piece of steel carries both the open and the blank position, there is no chance of confusing which state the line is in, the shape itself tells you at a glance whether that joint is open or closed. Solitaire Overseas manufactures carbon steel spectacle blind flanges with full mill test certification and hydrostatic testing or third-party inspection can be arranged on request.

Request a quote

Technical Data

Specifications Chemical Composition Mechanical Properties Pressure Class Class 150 Dimensions Weight Chart

ASME B16.48 Carbon Steel Spectacle Blind Flange Specifications

Parameter	Specification
Standard	ASTM A105, ASTM A694, ASME B16.48, MSS SP44
Size Range	NPS 1/2 inch to 24 inch
Pressure Class	Class 150, 300, 600, 900, 1500, 2500
Facing	Raised Face or Flat Face
Construction	Forged or plate cut figure 8 plate, supplied with matching paddle spacer on request
Testing	Hydrostatic test, third party inspection on request
Certification	Mill Test Certificate EN 10204 3.1, 3.2 on request

Carbon Steel Spectacle Blind Flange Chemical Composition (%)

Grade	C max	Mn	P max	S max	Si
ASTM A105	0.35	0.60 to 1.05	0.035	0.040	0.10 to 0.35
ASTM A350 LF2	0.30	0.60 to 1.35	0.035	0.040	0.15 to 0.30

Mechanical Properties for Carbon Steel Spectacle Blind Flanges

Grade	Tensile Strength min	Yield Strength min	Elongation min (%)
A105	485 MPa (70 ksi)	250 MPa (36 ksi)	22
A694 F60	586 MPa (85 ksi)	415 MPa (60 ksi)	18

Pressure Class Reference Carbon Steel Spectacle Blind Flange

Class	Approximate Rating at Ambient (psi)	Approximate Rating at Ambient (bar)
150	285	20
300	740	51
600	1480	102
900	2220	153
1500	3705	255
2500	6170	425

For Class 600 and above, see our Carbon Steel High Pressure Flanges range for the full grade selection guidance at that duty.

Class 150 CS Spectacle Blind Flanges Dimensions and Weights

NPS	Outside Diameter (mm)	Center to Center (mm)	Thickness (mm)	Web Width (mm)	Spectacle Blind Weight (kg)	Paddle Blank Weight (kg)	Paddle Spacer Weight (kg)
1/2 inch	45	60	3.0	38	0.07	0.03	0.03
1 inch	64	80	3.0	38	0.14	0.07	0.06
2 inch	102	120	6.4	51	0.68	0.41	0.26
4 inch	172	190	9.7	64	2.81	1.80	1.01
6 inch	219	240	12.7	76	5.39	3.82	1.57
8 inch	276	300	12.7	76	8.32	6.07	2.25
12 inch	406	430	19.1	102	26.95	19.77	7.18

For sizes, classes or weights beyond this reference table, use our Flange Weight Calculator.

ASME B16.5 CS Spectacle Blind Flange Weight Chart

Temperature (°F)	150#	300#	400#	600#	900#	1500#	2500#
-20 to 100	285	740	985	1480	2220	3705	6170
200	260	680	905	1360	2035	3395	5655
300	230	655	870	1310	1965	3270	5450
400	200	635	845	1265	1900	3170	5280
500	170	605	805	1205	1810	3015	5025
600	140	570	755	1135	1705	2840	4730
650	125	550	730	1100	1650	2745	4575
700	110	530	710	1060	1590	2655	4425
750	95	505	675	1015	1520	2535	4230
800	80	410	550	825	1235	2055	3430
850	65	320	425	640	955	1595	2655
900	50	230	305	460	690	1150	1915
950	35	135	185	275	410	685	1145
1000	20	85	115	170	255	430	715

Applications of Carbon Steel Spectacle Blind Flanges

Positive line isolation ahead of confined space entry or hot work
Unit turnaround and planned shutdown isolation points
Permanent isolation between two process systems that must never mix
Isolation of a section of line for hydrotest without affecting the rest of the system
Safety critical isolation on oil, gas and petrochemical process piping

Frequently Asked Questions

What is a carbon steel spectacle blind flange?

It is a figure-eight shaped plate with a solid blank end and open ring end, connected by a web. It rotates within a bolted pipe joint to provide visible open or closed isolation.

How does a spectacle blind flange isolate a pipeline?

After the pipeline is valved off and depressurized, the joint is opened and the spectacle plate rotated. The solid end is then positioned between flanges and bolted securely to isolate flow.

What is the difference between a paddle blank and a paddle spacer?

A paddle blank is a solid disc without a bore that blocks flow. A paddle spacer is an open ring, maintaining the required joint gap, bolt length, and alignment during open operation.

Which standard covers spectacle blind flange dimensions?

ASME B16.48 governs spectacle blind dimensions, including thickness, outside diameter, and bolting details. It covers line blanks for pipeline isolation across pressure classes commonly used in process and industrial piping.

Which carbon steel grades are used for spectacle blind flanges?

ASTM A105 is commonly specified for carbon steel spectacle blinds. ASTM A694 suits higher pressure applications, while ASTM A350 LF2 is selected for low-temperature service requiring suitable impact properties. Grade selection depends on service conditions.

Contact Solitaire Overseas for expert guidance and the right flange solution for your application.

Carbon Steel Spectacle Blind Flanges