PMI on Duplex Stainless Steel and Stainless Steel

Positive Material Identification (PMI) is essential for the various types of stainless steels and corrosion-protection steel alloys.
Hence, PMI is essential for:
Stainless Steel 316, 304, 410, etc;
Duplex Stainless Steel (22% Cr);
Super Duplex Stainless Steel (25% Cr);
Hastelloy;
Inconel;
Monel.

For Duplex Stainless Steel and Stainless Steel valves, PMI is conducted by using PMI XRF portable test gun, pointed at the external surface of completed valves.  Parts of valves to be PMI tested are:
a)  Body,
b)  Bonnet;
c)  Stem (for all valves having externally-exposed stems).

For Duplex Stainless Steel and Stainless Steel, which are the more common materials used for oil and gas industry, the main material composition to be PMI tested are Chromium (Cr), Nickel (Ni) and Molybdenum (Mo).

Composition to be tested are as follows:

Material type	Steel Grade	Cr	Ni	Mo
Stainless Steel Casting	ASTM A351 Gr CF8M	18.0% - 21.0%	9.0% - 12.0%	2.0% - 3.0%
Duplex Stainless Steel Casting	ASTM A890 Gr 4A	21.0% - 23.5%	4.5% - 6.5%	2.5% - 3.5%
Stainless Steel Forging	ASTM A182 Gr F316L	16.0% - 18.0%	10.0% - 15.0%	2.0% - 3.0%
Duplex Stainless Steel Forging	ASTM A182  Gr F51	21.0% - 23.0%	4.5% - 6.5%	2.5% - 3.5%

The above are the most common types of stainless steel and duplex stainless used in valves for petrochemical, oil and gas industry.

For me, as a Quality Control Consultant for the past 2 decades, PMI (positive material identification) is the most important Quality Control practice for ensuring correct valve material, hence, the strength and properties of the specific types of steel.

 

My email contact:  valve4oem@gmail.com

Facebook Page:  www.facebook.com/ValvesForOilAndGas

Facebook Personal:  www.facebook.com/Michael.Valves

Positive Material Identification - PMI

PMI is abbreviation for Positive Material Identification.

PMI is actively applied in the oil and gas industry.
Purpose of PMI includes:
1)  Check the correctness of material used for making a certain equipment.
2)  Check the content of alloying elements for a specific type of steel.
3)  Check the type of steel used, e.g. Stainless Steel 316, Stainless Steel 304, Stainless Steel 410, Duplex Stainless Steel 22% Cr, Super Duplex Stainless Steel 25% Cr.

How to do PMI?

PMI can be done using XRF or OES methods.

XRF is X-Ray Fluorescence.  XRF can be done using a portable analyzer or a desktop analyzer.  Desktop XRF analyzer is  suiable for test samples and small-sized products, tested in a lab or office environment.  Portable XRF analyzer is suitable for products as well as test samples, tested anywhere.  That's the beauty of portable XRF analyzer; it can be easily carried around for testing to be done anywhere, i.e. at site, at plant, at platform, at vendor's warehouse, at vendor's factory.

OES is Optical Emissions Spectroscopy.  OES is often used in test labs.  OES have an advantage over XRF, because OES can detect and measure Carbon (C) and Nitrogen (N).  Disadvantage is OES will create a "burn mark" on product tested, so it is  not truly non-destructive.  

ExxonMobil does not permit PMI using OES for testing the real products.

PMI for Valves

PMI is often used for checking the valve materials used, especially for the body and bonnet.  PMI is often used as a Quality Control practice if the body/bonnet material is made of stainless steel, duplex stainless steel, or super duplex stainless steel.