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NDT is an acronym for Non-Destructive Testing. As the term suggests, this engineering method permits for the inspection of internal and surface flaws (including cracks, porosity, and slag inclusions) in a test object (e.g., a valve, pipe, or weld) without causing any damage or destruction.
A Simple Summary Comparison
Desire to discover internal porosity or sand holes? → Choose RT or UT.
Desire to discover hairline surface cracks?
For carbon steel valves → MT is given priority to (fast and cheap).
For stainless steel valves → PT is essential.
What is the relationship between NDT and the "Shell Strength Test"?
Shell Strength Test: Employ high-pressure water (1.5 times rated pressure) to the assembled valve to confirm its macro-level pressure containment capability. It cannot search minor material flaws.
NDT: Carried out during manufacturing (e.g., on raw castings) to basically make sure the material itself is sound. A valve that fails NDT should never continue to pressure testing.
Standard Requirements
Commonly, Indispensable valve purchasing standards (such as API 6D, ISO 14313 for pipeline valves) expressly stipulate:
All pressure-containing castings must endure RT or UT sampling according to the standard.
All pressure-containing welds must bear 100% RT or UT test.
To sum up, NDT is similar to a physical check-up for the valve's material, guaranteeing its "great health" and absence of internal hidden flaws. It serves as the bedrock for a valve's long-lasting, secure, and accurate operation.
