Introduction: What Are Piping Line Blanks?
Positive isolation keeps people safe when a piping system needs to come apart. Before a valve gets pulled, a vessel gets opened, or a line goes through hydrostatic testing, someone has to guarantee process fluid can't re-enter the work area.
A closed valve alone isn't that guarantee. Valves leak, drift, or get bumped open by mistake.
That's where line blanks come in. "Line blank" is a broad term for solid isolation components: spectacle blinds, spade blanks, paddle blinds, and the spacers that go with them. Terminology shifts by industry and even by plant, so the same part might be called a "blind," a "blank," or a "blanking plate" depending on who wrote the spec.
This guide covers the main types of line blanks, what ASME B16.48 governs, and how blind-versus-blank terminology breaks down. You'll also find what to check before ordering and where to source these components when a project needs them fast.
Key Takeaways
- A line blank creates a physical barrier that stops process fluid from entering an isolated section; closed valves alone cannot guarantee that.
- Figure-8 blanks, paddle blanks (spades), and paddle spacers each play a distinct role in the isolation sequence.
- Size, pressure class, material, facing, and gasket type all have to match the mating flanges and service conditions.
- Line blanks support lockout/tagout and isolation procedures; they don't replace them.
What Is a Line Blank in Piping?
A line blank is a pressure-retaining isolation device installed between two mating flanges to block or permit flow.
When positive isolation is required, the solid portion sits in the flow path and forms a physical barrier a valve cannot match. With a blank in place, you remove the risk of a valve being forced open, bypassed, or failing internally.
Crews rely on line blanks during:
- Maintenance and inspection work, including valve or exchanger replacement
- Hydrostatic and pneumatic pressure testing
- Equipment replacement and piping modifications
- Commissioning and decommissioning
- Planned shutdowns and turnarounds
- Temporary system modifications and tie-ins
Line Blank vs. Blind Flange
These two terms get mixed up constantly, and for good reason: they do similar jobs. A blind flange closes off the end of a pipe or an unused vessel nozzle. It's a single flanged component, bolted to one mating flange, and it isn't meant to sit between two flanges. A line blank, also called a line blind, spade, or spectacle blind, installs between two mating flanges, splitting an existing connection to isolate one side from the other. Garlock's technical bulletin on blind flanges draws this same distinction.
"Blank," "blind," and "blanking plate" are used inconsistently across projects and regions, so never assume the name alone identifies the part. Related terms worth knowing:
- Spectacle blind — one-piece assembly, solid on one end, open on the other
- Figure-8 blank — another name for the spectacle blind, based on its shape
- Spade / paddle blank — the solid disc portion, used alone or with a spacer
- Paddle spacer / ring spacer — the open-bore counterpart that maintains flange spacing when flow is needed
Confirm the exact component against the piping drawings, the line list, ASME B16.48, and the project's piping specification before ordering. A spec sheet that simply says "line blank" can mean several different parts.
Types of Piping Line Blanks
Three main component types cover most line-blank applications. All stop or allow flow; the difference is how crews handle them in the field:
- Spectacle blinds (figure-8) — solid disc and open ring joined as one piece
- Paddle blanks (spades) — solid disc with a handle for full bore block
- Paddle or ring spacers — open plate/ring that restores flange spacing and flow
Spectacle Blinds (Figure-8 Blanks)
A spectacle blind gets its name from its shape: one solid disc, one open ring, connected by a web or tie bar that resembles a pair of glasses. To switch between isolation and flow, crews unbolt the flanges, rotate the blind 180 degrees, and reinstall it. Because both positions stay attached to the same piece, there's no separate part to track or misplace.
Paddle Blanks (Spades) and Spacers
A paddle blank, also called a spade, is a solid disc with a handle that sticks out past the flange bolt circle. It blocks the bore completely.
When flow needs to resume, the spade comes out and a paddle spacer—an open-bore plate or ring with its own handle—goes in to hold the correct flange spacing. A ring spacer does the same job without the handle, which some plants prefer for tighter clearances.
Figure-8 vs. Spade-and-Spacer: Which One Fits?
| Component | Flow Condition | Typical Use | Handling Notes |
|---|---|---|---|
| Spectacle blind (figure-8) | Both positions on one part | Frequent open/closed switching | One piece to track, but heavier and bulkier at larger sizes |
| Spade (paddle blank) | Closed only | Isolation during shutdowns, tests, maintenance | Lighter individually, but needs a matching spacer stored separately |
| Paddle/ring spacer | Open only | Restoring flow after isolation | Must pair with the correct spade; easy to misplace on large jobs |
Bigger pipe sizes make this a practical decision, not just a preference. ASME B16.48 Series A lists spectacle blind weights from roughly 290 lbs at 26 inches to over 3,500 lbs at 60 inches.
Flipping that much mass takes real rigging. On large jobs, separate spades and spacers are often easier to handle piece by piece—even if it means keeping two components straight instead of one.
Most spades and spectacle blinds carry an indicator handle or tab that shows at a glance whether the line is open or isolated. That cue helps crews on the ground, but it is not a substitute for formal isolation verification—a handle position reflects what someone believes is true, not what a locked, tagged, and confirmed procedure has verified.
Critical: Installation and removal always require controlled depressurization, flange separation, correct gasket replacement, and reassembly under an approved procedure. Skipping any of those steps defeats the point of using a line blank.
ASME B16.48, Materials, Ratings, and Facing
The Standard That Governs Line Blanks
ASME B16.48 is the primary standard for line blanks used with ASME B16.5 flanges. It covers NPS ½ through NPS 24 and Classes 150, 300, 600, 900, 1500, and 2500.
The standard sets pressure-temperature ratings, dimensions, tolerances, materials, marking, and testing requirements. Always use the current edition—not figures from an older project spec or outdated supplier catalog.
Larger sizes and higher pressures fall under extended tables and API ratings. Twinco's paddle blind inventory, for example, runs from ½ inch to 72 inches, Classes 150 through 2500, with API ratings up to 15,000 PSI—well beyond the base B16.48 size range for oversized and high-pressure work.
Matching Pressure-Temperature Ratings
The blank's rating has to line up with:
- The mating flanges on both sides
- The piping class specified for that line
- Design pressure and design temperature for the service
- Test pressure during hydrotesting, which often exceeds normal operating pressure
A blank rated for Class 150 service must not isolate a Class 600 line, even temporarily.
Material Selection
Material choice depends on the process fluid, temperature range, and corrosion conditions, not just what's sitting on the shelf. Common options include:
- Carbon steel (A516 Gr. 70, A36, A105) for general service
- Stainless steel (304/316, A182 F304/F316) for corrosive or high-purity service
- Alloy steel (F11, F22, F91) for elevated temperature service
- Duplex and super duplex for chloride-heavy or offshore environments
- Nickel alloys (Inconel, Monel, Hastelloy) for severe corrosion or extreme temperature
Every blank should carry a permanent stamp showing size, pressure rating, material grade, heat number, and standard reference, so the part stays traceable in the field.
Facing Must Match the Mating Flange
Line blanks come in flat face (FF), raised face (RF), and ring-type joint (RTJ) configurations. Whatever facing the mating flanges use, the blank and its gasket need to match. A mismatched facing won't seal properly no matter how good the gasket is.
Before ordering, confirm each of these details:
- Nominal size and pressure class
- Material specification and flange standard
- Facing, bore/ID, and thickness
- Handle orientation
- Project-specific marking or inspection requirements
Where Line Blanks Are Used
Line blanks show up anywhere a piping system needs guaranteed isolation, including:
- Refineries and petrochemical plants
- Pipeline construction and midstream infrastructure
- Power generation facilities
- Manufacturing and utility plants
- Industrial construction sites
Hydrostatic and Pressure Testing
During hydrotesting, a line blank separates the section under test from the rest of the system. It keeps test fluid off equipment that isn't rated for the pressure, and out of any connected line that should stay dry.
Paddle blinds built to hydrotest thickness handle this job. Thinner isolation-only blanks are used once a line is depressurized.
Maintenance, Turnarounds, and Construction
Common scenarios include:
- Replacing a valve or exchanger without draining the entire unit
- Inspecting or cleaning a section of pipe
- Modifying piping ahead of a planned shutdown
- Isolating a section during a turnaround
- Supporting construction tie-ins, commissioning, and decommissioning
Duration and pressure conditions both matter here. A blank sized for a two-week turnaround isolation isn't automatically right for a tie-in that will sit blanked for months awaiting a future connection. Check both before deciding.
Isolation Within a Lockout Program
OSHA classifies blank flanges and bolted slip blinds as lockout devices under 29 CFR 1910.147. The regulation is clear: a physical isolation device works within a documented energy-control program, not instead of one.
Install and remove blanks only after qualified personnel confirm the line is isolated and depressurized, following the site's approved procedure.
How to Select the Right Piping Line Blank
Picking the right line blank comes down to matching the part to the system, not just grabbing a size off the shelf. Start by pulling the piping specification and design documents, then confirm:
- Line size and pressure class
- Design temperature and process medium
- Exact isolation point in the system
Match the Flange, Gasket, and Material
The blank has to fit the mating flange dimensions and facing exactly:
- Compatible gasket type: spiral wound, RTJ, or compressed fiber, depending on service
- Matching bolt circle and bolt hole count
- Correct bore or spacer dimensions for spade-and-spacer combinations
Material selection follows the same logic. Cross-reference the process fluid, required metallurgy, temperature range, corrosion allowance, and project material specification before locking in a grade. Skipping this step is how the wrong alloy ends up in a corrosive line.
Figure-8 or Spade-and-Spacer?
How often the line will open and close—and how hard the blank is to handle—drives the choice:
- Choose a figure-8 blank for lines that switch between open and isolated repeatedly; one part means less to track.
- Choose separate spades and spacers when size, weight, or site layout make handling a single large assembly impractical.
Ordering Checklist
Before submitting a quote request, have these details ready:
- Quantity, size, and pressure class
- Material and face type (FF, RF, or RTJ)
- Governing standard, such as ASME B16.48 or a project spec
- Delivery date and project location
- Documentation and inspection requirements
- Whether installation accessories or rental equipment are needed
Have the responsible engineer, plant authority, or qualified piping professional review final selection before the order goes out, especially on high-pressure, high-temperature, hazardous, or unusual services.
Twinco Industrial's Line Blank and Piping Support
Twinco Industrial has supplied industrial components and rental equipment since 1977. Based in Houston, the company serves pipeline, petrochemical, and construction customers across the Gulf Coast and throughout the USA, Canada, and Mexico.
What Twinco Carries for Line Blank Applications
Twinco's paddle blind inventory covers a wide range of project needs:
- Spade-and-spacer sets, spectacle blinds, and ported paddle blinds
- Sizes from ½ inch to 60+ inches
- Pressure Classes 150 through 2500, with API ratings up to 15,000 PSI
- Materials including carbon steel, stainless steel, alloy steel, duplex/super duplex, and nickel alloys
- Face types in RF, FF, and RTJ
Every paddle blind carries a permanent stamp with size, pressure rating, material grade, and heat number for traceability.
Twinco also supplies blind flanges, bolting, gaskets, valves, fittings, and pipe, plus specialty or hard-to-find components. Confirm current availability and specs with the sales team.
Rental Equipment for Testing and Turnarounds
For crews that need gear for the length of a job rather than the life of a plant, Twinco rents isolation and tooling equipment for hydrostatic testing, maintenance shutdowns, and turnarounds:
- Blind flange kits with matching studs, nuts, and gaskets as needed
- Paddle blind racks
- Hydraulic and torquing tools for installation and removal
Rental paddle blinds are inspected for dimensional accuracy and surface condition, then cleaned and stored so they're field-ready when a project needs them.
Getting a Quote
When requesting a quote, have these details ready:
- Line size, pressure class, and material
- Facing and service conditions
- Required date and project location
That lets Twinco's inside sales team, including specialists like Al Waters and Shane Holmes, match the right product or rental solution to the job.
Conclusion: Choosing Line Blanks for Safe, Controlled Isolation
A line blank is an engineered isolation component. It has to match the piping system's size, pressure class, temperature, material, and flange arrangement. Getting any one of those wrong undermines the isolation it is supposed to provide.
Before ordering, review the piping specification and isolation requirements for the job. Then request a technically complete quote from a qualified industrial supplier such as Twinco Industrial. That quote should cover:
- Size and pressure class
- Material and facing
- Service conditions
Getting the details right before the part ships is far cheaper than finding out they are wrong once the blank is on the flange.
Frequently Asked Questions
What is a flange blank?
A flange blank is a solid, non-bored plate used to block flow or close a flanged connection. The term overlaps with "blind flange" and "line blank" depending on the industry and specific application.
What is a line blank?
A line blank is a pressure-retaining isolation device installed between two mating flanges to create a physical barrier against flow. Common examples include spectacle blinds, spades (paddle blanks), and paddle spacers.
What is the difference between blind flanges and blank flanges?
A blind flange typically closes off the end of a pipe or an unused nozzle, bolted to a single mating flange. A blanking plate or line blank installs between two flanges for isolation, though naming conventions vary by industry and plant.
What is the purpose of blind flanges?
Blind flanges close pipe ends, contain pressure, support temporary testing setups, and cap connections left open for future use. They also serve as isolation and lockout devices when correctly rated and installed.
What is the purpose of a spade in piping?
A spade, or paddle blank, is the solid disc inserted between two flanges to stop flow and provide positive isolation. It's removed and replaced with a spacer once flow needs to resume, following approved site procedures.
What are the two types of flanges?
There isn't one universal pair; flange classifications vary by design and application. Common types include blind, weld neck, slip-on, threaded, socket-weld, and lap-joint flanges.
