What Is Flange Spreading?

Flange spreading is the controlled separation of two bolted flanges to create enough gap for gasket removal, inspection, or insertion of a paddle blind or spectacle blind. Dedicated flange spreading tools—mechanical or hydraulic—apply force evenly without damaging the flange faces. Prying flanges apart with crowbars or wedges risks gouging the sealing surface, which leads to leaks on reassembly.

Property	Detail
Purpose	Separate bolted flanges safely for maintenance
Tool types	Mechanical (wedge), hydraulic (cylinder-driven)
Typical spread	5-50 mm depending on tool and flange size
Standards	No specific flange spreader standard; use per ASME PCC-1 assembly guidelines
Sizes	Tools available for NPS 1 through NPS 48+ flanges
Force	Hydraulic units: 5-50 tons; mechanical: up to 10 tons

Types of Flange Spreaders

Type	Mechanism	Advantages	Limitations
Mechanical wedge	Threaded bolt drives a wedge between flanges	Simple, no power source needed	Limited force; slow
Hydraulic wedge	Hydraulic cylinder pushes wedge	High force, fast	Requires hydraulic pump
Bolt-hole spreader	Pins insert into bolt holes; hydraulic ram separates	Even force distribution	Requires two adjacent empty bolt holes
Integrated spreader	Mounts on flange studs	Keeps hands clear of gap	Higher cost

Common Mistake

Never use screwdrivers, chisels, or pry bars between flange faces. These tools concentrate force on small areas, gouging the flange face finish and creating leak paths. Even a 0.1 mm scratch across the gasket seating surface can prevent a proper seal with spiral wound gaskets.

Typical Procedure

1. Depressurize and drain the line
2. Loosen all stud bolts but leave two diametrically opposite bolts finger-tight for safety
3. Insert flange spreader in an open bolt hole or between flange faces
4. Spread flanges gradually—check gap at multiple points for even separation
5. Remove old gasket and inspect flange faces for damage
6. Insert new gasket, blind, or spacer as required
7. Remove spreader, install all bolts, and torque per bolt torque chart

Pro Tip

For RTJ flanges, the metal ring gasket sits in a groove and can be difficult to extract. Use a flange spreader to open the joint enough to pry the ring out without damaging the groove. Inspect the groove for dents or corrosion before installing a new ring.

Safety Considerations

Flange spreading on live or recently depressurized systems carries residual pressure risk. Always verify zero energy isolation (bleed valves open, pressure gauge at zero) before inserting any tool between flanges. Use appropriate PPE, including face shields, for breaking flanged joints in hazardous service.

Read the full guide to flanges