What Is Stock Finish?

Stock finish refers to the standard flange face surface finish as delivered by the manufacturer without any special machining requirements beyond ASME B16.5 specifications. For RF flanges, the stock finish is a phonographic (spiral serrated) finish with a surface roughness of 3.2 to 6.3 micrometers Ra. This is the default finish on all standard raised face flanges and is suitable for the vast majority of process piping applications.

Stock Finish Specifications

Parameter	Standard Stock Finish (RF)
Pattern	Spiral serrated (phonographic)
Ra range	3.2 to 6.3 micrometers (125-250 AARH microinches)
Standard	ASME B16.5, ASME SP-6
Groove pitch	~0.9-1.5 mm/revolution
Applicable to	RF flanges, Class 150-2500
Gasket compatibility	Spiral wound, compressed fiber, graphite, PTFE
Additional cost	None (standard manufacturing)

Stock Finish vs Special Finishes

Finish Type	Ra Range (micrometers)	When Specified	Extra Cost
Stock finish	3.2-6.3	Default (no special specification needed)	None
Smooth finish	0.8-1.6	Rubber gaskets, PTFE envelope gaskets	Moderate
Concentric serrated	3.2-6.3	Operator preference for critical service	Slight
Cold water wash	0.8-3.2	Food/pharma (sanitary applications)	Moderate
RTJ groove	1.6 max (groove surface)	RTJ flanges	Higher

Common Mistake

Over-specifying the flange face finish adds cost and lead time. For standard process piping with spiral wound gaskets, the stock finish (3.2-6.3 Ra) is optimal. Requesting a smoother finish (<3.2 Ra) actually reduces gasket grip and increases blowout risk with serrated gaskets. Only specify a non-stock finish when the gasket type or service genuinely requires it.

When Stock Finish Is NOT Acceptable

Situation	Required Finish
Mating with rubber gaskets	Smooth (0.8-1.6 Ra)
PTFE envelope gaskets	Smooth (0.8-3.2 Ra)
RTJ flanges	RTJ groove (1.6 Ra max in groove)
Corroded or damaged flange faces	Re-machined to stock or better
Operator/project specification requires concentric	Concentric serrated (3.2-6.3 Ra)
Food or pharmaceutical service	Cold water wash or polished finish

Inspecting Stock Finish

Method	Tool	Acceptance
Visual	Surface comparator (ASME SP-6)	Grooves visible, uniform, no damage
Quantitative	Profilometer / surface roughness tester	Ra within 3.2-6.3 micrometers
Damage check	Flashlight at low angle across face	No radial scratches, pits, or corrosion

Pro Tip

Stock finish flanges should be stored with flange face protectors (plastic caps or wooden covers) to prevent damage during shipping and storage. A single radial scratch across the serrations creates a direct leak path from bore to atmosphere. Inspect every flange face immediately before gasket installation, not just at goods receipt.

Flanges with damaged stock finish can be re-machined on a portable flange facing machine in the field, provided sufficient material remains to maintain the minimum flange thickness per ASME B16.5. For RTJ flanges, groove re-machining requires tighter tolerances and is typically performed in a machine shop.

Read the full guide to flanges