Met-L-Chek® VP-31A — Visible Post Emulsifiable Inspection Penetrant

Type 2 | Methods B & C | 1 Gallon / 3.7 LSKU: 29235-0001

Overview

The Met-L-Chek® VP-31A is a professional-grade visible (red dye) post emulsifiable inspection penetrant designed for the reliable detection of surface-breaking flaws and through-leaks in metallic and non-metallic components. A Type 2 (visible), Method B (post emulsifiable) and Method C (solvent removable) penetrant, VP-31A is the high-performance visible LPI solution of choice for general metalworking, weld inspection, nuclear, and automotive applications where the sensitivity advantages of the post emulsifiable technique are required — but UV-A lighting is unavailable, impractical, or not specified by the inspection procedure.

Supplied in a 1-gallon (3.7 L) bulk container, VP-31A is ideally suited for penetrant testing benches, immersion tanks, flow-on application systems, and high-volume inspection operations where individual aerosol cans are impractical. The 1-gallon format delivers significant cost savings per unit volume compared to aerosol packaging, while maintaining the same trusted Met-L-Chek® formulation chemistry and code compliance that inspectors rely on worldwide.

Manufactured by Met-L-Chek — a brand of McGean — VP-31A is rated at ISO Level 2 sensitivity and is approved against a comprehensive list of international standards including ASME, ASTM, AMS-2644, ISO-3452, and NAVSEA — making it a versatile, compliant choice across virtually every industrial inspection sector.

Key Specifications

Box Dimensions & Shipping Weight (Estimated)

Dimensions and weight are estimates based on typical packaging for 1-gallon penetrant containers of this class. Please verify with your freight forwarder prior to shipping.

Post Emulsifiable Technique (Method B) — Why Higher Sensitivity

The defining characteristic of VP-31A is its post emulsifiable (Method B) formulation — a significantly more sensitive penetrant removal technique than simple water washing (Method A). Understanding why Method B achieves higher sensitivity is key to understanding when VP-31A is the correct product choice.

With water washable penetrants (Method A), the penetrant is inherently designed to wash off with water — which means it can also be inadvertently washed out of tight, shallow defects during the excess removal step if water pressure or dwell time is not carefully controlled. Post emulsifiable penetrants do not wash off with water alone. VP-31A remains firmly in place — both on the surface and within discontinuities — until the E-50 emulsifier is deliberately applied to the surface for a controlled contact time, which then renders the surface penetrant water washable. The penetrant inside tight discontinuities, however, is protected from the emulsifier by the geometric confinement of the crack — remaining in place while excess surface penetrant is washed away cleanly.

The result is a cleaner background with more complete penetrant retention in fine discontinuities — translating directly into more sensitive, more reliable indication formation and fewer missed defects, particularly on rough or porous surfaces that tend to retain penetrant.

Used with Met-L-Chek® E-50 Emulsifier: VP-31A is processed in Method B by applying E-50 lipophilic emulsifier by spray, which quickly renders the surface penetrant water washable. E-50 is a fast-acting emulsifier requiring only a short contact time — making it efficient for production inspection workflows. E-50 is also effective as a pre-wash cleaner for tough-to-clean surfaces including rough castings and components with significant oily surface contamination.

Method C (Solvent Removable) — Field and Spot Inspection Flexibility

In addition to the Method B post emulsifiable technique, VP-31A is fully compatible with Method C solvent removal — making it equally suitable for field inspection, spot checks, and applications where water rinsing facilities are unavailable. For Method C processing, excess surface penetrant is removed by wiping with a lint-free cloth moistened with Met-L-Chek® E-59A, R-503, or R-504 solvent remover — a completely self-contained technique requiring no water supply or drainage.

This dual-method compatibility gives the inspector maximum procedural flexibility — VP-31A can be used at a fixed inspection station with Method B processing for maximum sensitivity on complex batches, or taken to the field with Method C remover for portable spot inspection without any change to the penetrant itself.

Material Safety — Safe for Critical Alloys

VP-31A's low halogen and sulfur content makes it safe for use on the most sensitive engineering materials encountered in aerospace, medical, and nuclear applications:

• Titanium — chloride, fluoride, and sulfur contents are all well below the limits that cause stress corrosion cracking in titanium alloys
• High-nickel alloys — safe for Inconel, Hastelloy, and other nickel superalloys used in turbine and nuclear applications
• Aluminum — non-corrosive to aluminum alloys per physical property test data
• Carbon steel — non-corrosive
• Magnesium — non-corrosive
• Stainless steel — non-corrosive

Combined with a VOC content of 0 g/L and a high flash point exceeding 93°C (200°F), VP-31A presents a favorable environmental, health, and safety profile for both operator welfare and regulatory compliance.

Sensitivity

Visible penetrants are not assigned sensitivity levels under AMS-2644 (which applies only to fluorescent penetrants), but VP-31A's performance characteristics have been assessed against available standards:

• ISO-3452-2005 Level 2 — the highest sensitivity rating available for visible penetrants under this standard
• AMS-2644 equivalent — approximate to Level 1 fluorescent penetrant sensitivity
• 50 µm discontinuities are readily detected under standard conditions
• 30 µm discontinuities can be detected under controlled conditions

Compliance & Standards

VP-31A meets the requirements of the following codes and standards:

• AMS-2644E — Inspection Material, Penetrant (Qualified Products List)
• ASME Boiler & Pressure Vessel Code — Section V, Article 6
• ASTM E165 — Standard Practice for Liquid Penetrant Examination
• ASTM E1417 — Standard Practice for Liquid Penetrant Testing
• ISO-3452-2005 — Non-destructive testing: Penetrant testing
• NAVSEA T9074-AS-GIB-010/271 — U.S. Navy requirements for penetrant inspection materials
• RCC-M Rev. 2000 — French nuclear industry code

Compatible Products

For a complete Method B or Method C visible penetrant inspection system using VP-31A, the following complementary Met-L-Chek® products are recommended:

Met-L-Chek® Visible Penetrant Family

Ideal Applications

• Weld inspection — detection of surface-breaking cracks, porosity, and undercut
• Casting and forging inspection — cold shuts, seams, shrink cracks, and laps
• Pressure vessel and piping fabrication quality control
• In-service inspection of structural components and pressure equipment
• Nuclear component inspection — NAVSEA and RCC-M compliant
• Automotive powertrain and structural component inspection
• General metalworking acceptance testing and in-process inspection
• Any application requiring Method B post emulsifiable or Method C solvent removable visible penetrant inspection

About Met-L-Chek

Met-L-Chek, a brand of McGean, is one of the most established names in penetrant inspection materials — with over 70 years of experience developing and manufacturing high-quality liquid penetrant testing products for the aerospace, defense, oil and gas, power generation, nuclear, and industrial manufacturing sectors. Met-L-Chek products are trusted by NDT professionals worldwide and appear on the Qualified Products Lists of leading aerospace OEMs and government specifications globally.