What are Stainless Steel Tubes?

Stainless steel tubes are usually made in accordance to ASTM A269/A213. ASTM A269 is the standard specification for seamless and welded austenitic stainless steel tubing for general service. While for ASTM A213, it is a standard specification for seamless ferritic and austenitic alloy-steel boiler, super heater and heat-exchanger tubes. They are also commonly made to dual grade which is SS316/316L with seamless quality.

Figure 1: Stainless Steel Tube Bundle

Stainless Steel Tube Attributes:
The minimum yield strength for stainless steel tube is 515 N/mm² and with maximum 90 HRB of hardness. Maximum 80 HRB is specified so that compression fittings can work well with the tubes. Stainless steel tubes contain at least 10.5% of chromium and it will react with the oxygen to form an invisible chrome-oxide layer. The layer is strong enough to prevent further oxygen from rusting the surface.

SS316/316L is molybdenum-bearing austenitic stainless steel with molybdenum content ranging from 2.0 to 3.0%. The high nickel and molybdenum content provides resistance in highly corrosive surroundings such as salt water or chloride environments. In addition, SS316/316L also provides excellent elevated temperature tensile, outstanding formability and weld-ability.

Figure 2: Stainless Steel Tube Bundle

The means of “L” designation after the grade number is the carbon content is restricted to a maximum of 0.03% where the normal level of carbon content of stainless steel are maximum of 0.08%. The lower level of carbon content stainless steel tubes are used where welding will be performed. This lower level carbon content prevents the chromium from being depleted and thus it can still form the chrome-oxide layer on the tube surface.

Stainless Steel Tube Finishing:
Tubes are supplied in 3 type of finishing as Annealed and Pickled, Polished 320 Grit, and Bright Annealed.

Figure 3: Annealed & Pickled Tube(Top), Polished 320 Grit Tube (Bottom)

Usually stainless steel tubes are supply in anneal and pickle condition. Anneal is a heat treatment that will alter the physical and chemical properties of the material. It increases the ductility and reduces the hardness of stainless steel tube. Pickling is a metal surface treatment that contains strong acid to remove the impurities on the tube surface.

Polished 320 Grit are produced for applications where a smoother finishing is required for aesthetic application. Bright Annealed is produced by heat treating (annealing) steel with a controlled atmosphere. After the heat treatment, the steel has reflective, mirror-like appearance.

Stainless Steel Tubes are also suitable for flaring and cold bending. For cold bending, a bend radius of 3x the external tube diameter is recommended with tube benders or by hand. Tubes made of SS316/316L are suitable for arc welding according to usual techniques. The welding filler should be selected in accordance with DIN EN 1600 and DIN EN 12072 part 1 taking into account the type of application and the welding technique.

Outer Diameter and Tube Thickness Specifications:
The tubes outer diameter (OD) are according to ASTM A269/A213. However, for hydraulic applications, a tighter tolerance is usually specified to work well with compression fittings. Tolerance specifications are as per below:


For tubes thickness, A269 and A213 has 2 different type of wall thickness tolerance. For ASTM A269, the permissible variations in wall thickness is +/− 10%. However for ASTM A213, there are 2 options for the wall thickness tolerance. The 1st option is minimum wall thickness which is + 20%, − 0% of wall thickness. The 2nd option is average wall thickness which is +/− 10% of wall thickness.

Our usual option for tubing products wall thickness of tubing are +/− 10% and it will comply to both A269 and A213 standards.

Stainless steel tubes manufacturing process is illustrated below.

Manufacturing Process:


Chuan Kok Hardware maintains a large stock of stainless steel tube to be needed in high performance hydraulic line application. Seamless cold drawn tubes are being constantly offered to clients due to its quality and cleanliness. Seamless cold drawn tubes are precision in dimension and free of scale.

To find out more about stainless steel tubes, please watch the video below:

For more information, please visit our site at www.chuankok.com/stainless-steel-tubes.html

What are Pressure Gauges?


Figure 1
Figure 1: Material of pressure gauge casing (stainless steel) and connection (brass)

Pressure gauges are devices used to measure pressures in hydraulic systems and made in accordance to EN 837-1 European standards. It is applicable for hydraulic oil and gaseous media. The reading measurements are shown on the face of the gauge. Measuring pressure on equipment is essential for monitoring and providingthe smooth functioning and operating safety of the system.

Material and size:

A pressure gauge has two parts, the casing and the connection point. Usually, the material for the casing is stainless steel (1.4301) and the material for the bottom or back connection is brass (Figure 1). The lenses are made of acrylic sight glass. The size of the casing is usually available in 63mm (2 1/2 Inches) and 100mm (4 Inches).


Figure 2
Figure 2: Standard dual scales with bar and psi

There are two different connection directions, stem (bottom) mounting and panel (back) mounting. The connection direction is dependent on the system design. Connection wise, 1/4″BSPP & 1/4″NPT are usually used for gauges with size diameter 63mm, while 1/2″BSPP and 1/2″NPT are available for size diameter 100mm.

Reading range:

Pressure gauges come with standard dual scales with pressure indication in kilopascal (bar) and poun ds per square inch (psi) (Figure 2). The gauges are available in different measuring ranges to suit different installation needs.


There are two types of gauges are available; dry dial gauge (Figure 3) and glycerine filled gauge. Glycerine gauges reduce the effects of vibration and oscillation for needle reading accuracy. It also lubricates the movement and internal parts. In general, it improves reliability and extends the life of pressure gauges. Gauges are made to accurately read only the middle values. The accuracy range is ±1.6% of the full-scale for dial size 63mm, and ±1.0% of the full-scale for dial size 100mm. In order to make sure the readings on the gauge are accurate, a calibration test can be done by a laboratory. A certificate of calibration will be issued by a laboratory to confirm that the gauge accuracy. There are also many panel mounting options available for installation of gauges. The options include u-bolt assembly, front flange assembly, rear flange assembly and u-bolt with front flange assembly.

Permissible Temperatures:

Pressure gauges work well within a temperature range of -20°C to +60°C / -4°F to +140°F. Out of this temperature range, the gauge readings will be inaccurate.

Brands and Manufacturers:

A highly recommended manufacturer for gauges is Walter Stauffenberg GmbH & Co. KG. Walter Stauffenberg GmbH & Co. KG is a German manufacturer that has more than 50 years of specialized experience in manufacturing Stauff branded pressure gauge. Other reputable manufacturers include WIKA GmbH from Germany and Parker Hannifin from USA.

Based in Singapore, Chuan Kok Hardware & Machinery Pte Ltd is an international distributor of Pressure Gauges. To find out more about Pressure Gauges, do visit us at www.chuankok.com/stauff-pressure-gauges.html


Stauff Brand

What are Square Flanges?

Introduction to Flanges:

A pipe flange is used in the assembly of pipe to pipe or other components like valves, tees, elbows etc. The flanges are bolted together, creating several lengths of pipes or other assemblies. There are many different flange standards to be found worldwide. Common world standards include ASA/ANSI/ASME (USA), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean). Flanges in each standard are divided into “pressure classes”, allowing flanges to be capable of taking different pressure ratings.

Square Flanges:

Square Flange made in accordance to JIS B2291 standard is a connecting piece that links JIS (Japanese Industrial Standards) nominal bore size pipes together and has a working pressure of up to 210kgf/cm2. This is equivalent to 210 Bar, or 21MPa. They are usually used in high pressure systems such as hydraulic and steam lines for up to 3,000 PSI working pressure.

There are three types of Square Flanges under this standard:

  1. SHAB – Used with hexagon hex bolts, larger flange body size (Figure 1)
  2. SSAB – Used with socket cap screw, smaller flange body size than SHAB (Figure2)
  3. LSA – Oring side only, L shaped internal flow (Figure 3)Untitled

A complete set of square flanges consist of the female flange (oring side), male flange (flat side), oring, and bolts. The female flange is identified as part A. The male flange is identified as part B. And the complete set is AB.

Figure 4 – Left : SHAB Square Flange using Hexagon bolts (larger flange body), Right: SSAB Square Flange using Socket Cap Screw (smaller Flange body)

Blind Flanges:

Another type of flange available are Blind Flanges. These are used to seal the end of a piping system or pressure vessel openings to prevent flow.  Blind pipe flanges are commonly used for pressure testing the flow of liquid or gas through a pipe or vessel.  They also allow easy access to the pipe in the event that work must be done inside the line.  Only one side of a blind flange is used for the termination of the piping system. Either the female blind flange (oring side), or male flange (flat side) will be connected to the component to close off the pipe line  (Figure 5).

Figure 5:  Oring and Flat Square Blind Flanges


Material, Size Range and Connection:

Square Flanges are available in either carbon steel (SF440A) or stainless steel (SS316) material. The size range from 1/4″NB to 6”NB and the connection type is Socket Welding.

Brands of Square Flanges:

A highly recommended manufacturer for square flanges is KPL Industry Co., Ltd. KPL Industry Co., Ltd is a Korean manufacturer that specializes in producing various forged products in the field marine & offshore, seawater desalination plant, nuclear power plant and industrial sites.

To find out more about how to assemble Square Flanges, please watch:


Chuan Kok Hardware & Machinery is a stockist of KPL JIS B2291 Square Flanges in Singapore. To find out more about square flanges do visit us at www.chuankok.com/square-flanges.html

03 KPL