Wafer Check Valves

Wafer check valve is one category of check valve which has a more compact design, a shorter face-to-face dimension.

There are wafer swing check valves and wafer lift check valves.  Wafer swing check valves are more commonly used.

Advantages of wafer swing check valve as compared to regular swing valve:
1)  Wafer swing check valve has a shorter face-to-face dimension.
2)  Wafer swing check valve is lighter in weight than the regular swing check valve.
3)  Wafer swing check valve consume less space and less weight in a skid or oil and gas platform.

Wafer swing check valve could be dual-disc or single-disc.  Variation of the single-disc is the tilted single-disc.

Disadvantages of wafer swing check valve as compared to regular swing valve?
1)  Wafer swing check valves is generally more expensive than regular swing check valve on per kg basis.
2)  There are less valve factories manufacturing wafer swing check valves.

Wafer swing check valve could be dual-disc or single-disc.  Variation of the single-disc is the tilted single-disc.


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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.

 

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Forged Steel Ball Valves

Forged Floating Ball Valves are used mainly in Oil, Gas Transmission and Distribution Pipeline, Petroleum ,Chemistry, Chemical Fiber, Metallurgy, Paper Pulp etc. The forging material can ensure sufficient rigidity and strength under maximum rated operation pressure without inherent flaw of cast. The Forged Steel Body assures uniform fine grain structure and toughness free from inevitable casting defects such as porosity, abscess, crackle, gas hole. Enough wall thickness of separate Body and Adapters and high strength tie bolts are convenient for valve maintenance and sufficient to bear the stress of pipe.

Standards:

Design and manufacture -  API 6D / BS 5351

Pressure-temperature rating - ASME B16.34

Face to face dimensions - ASME B16.10

Flange type and dimensions – ASME B16.5

Butt-welded end – ASME B16.25

Inspection and test – API 598, ASME B16.34

Size range – NPS ½”  up to  NPS 8”

Pressure rating – 150 lb  to 300 lb

Fire Safe.  Forged Steel Floating Ball Valves fire safe is designed in compliance with API 607-4^th, API 6FA and BS 6755 Part 2. Each possible leakage parts between body and ball, middle flange, body and stem is designed as metal-to-metal contact, when non-metal resilient seats are damaged in a fire or unusual temperature increasing, the upstream medium pressure push the ball into the downstream metal seat lip to cut off the line fluid and prevent the internal leakage due to a secondary metal-to-metal seals.

Blow-out Proof Stem Design.  The stem is designed with integral T-type shoulder to provide blow-out proof effectively. The lower end of stem is terraced and installed from the lower internal part of stem. It is internally inserted as the back seat function to assure stem sealing safety at all pressures.

Locking Devices (on request). To prevent wrong operations of valve switch and improper actions by unpredictable, vibration of the line, the valve is equipped with locking hole at the full open and full close position of the valve, and the valve can be locked with a pad lock. Especially this locking device is uniquely advantageous when the valve is installed outdoors or on the production line of flammable petroleum or chemicals.

Handle Indicating Open/Closing Status of Valve.  Flat square structure is adopted for the head of valve stem which enables the correct connection with the handle and ensures the handle to be in the same direction with flow hole of the ball. When the handle is horizontal with pipeline of the valve, the valve is in the state of opening, when the handle is vertical with pipeline of valve, valve is in the status of closing.

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.