Material Certificate versus Positive Material Identification (PMI)

PMI stands for Positive material Identification basically we check the material content, Material Certificate as the name suggests also describes the material content

Contents

so what is the difference between them?

When we have especially Higher Grade materials like Alloy C-276 etc. we ask for both WHY??

Example – Milkshake

Suppose you need milkshake of 1000 liters from a milkshake vendor

And you want the sugar to be used of Grade A in the milkshake.

But in order to be sure that the milkshake vendor uses Grade A sugar and not the cheap sugar you do two things

STEP 1:- You ask the Vendor to submit the Detail bill (like a material certificate) of sugar purchased from wholesaler (D-MART etc) to ensure the vendor has bought Grade A sugar.

Now:- When you receive 1000 tons of milkshake there could be a chance that vendor bought the Grade A sugar from D-MART but did not use it in your milkshake and used some cheap quality

STEP 2:- So you run a test (like PMI) in milkshake sample or entire lot to know whether grade A sugar was put in it or not.

Same is with PMI the PMI could be done on a few tags or an entire lot of tags ( Also referred to as 100% of Tags) or 10% of tags etc depending on criticality etc.

Example in one of my project for Bolts only 10% of the lot would undergo PMI was finalized and agreed by the client so cost could be minimized.

Example:-

Suppose we want 100 Valves of Grade A so when the vendor buys the Material from the supplier, the supplier produces a Certificate called material certificate 3.1 and after the Valve is manufactured to ensure that the same material is used and no mixing has taken place PMI test is done.