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Studding of Furnace Tubes|Studded tubes

 1.0 Studding of Furnace Tubes General

- This specification concerns studded tubes for which cylindrical studs are fixed on bare tubes by an automatic electric resistance welding process.

- This specification concerns the tolerances, tests and acceptance criteria .

- The manufacturer hereafter mentioned ensures the studding operations with the particular requirements of the order.

- The order includes the technical requisitions (FN) and eventually addenda to the present specification.

2.0 Studding of Furnace Tubes Ordering Information

The requirement and/or the purchase order shall specify the following:

2.1 For the tubes

- Quantity, (Except otherwise specified , tubes are delivered in free issue by HPF)

- Name (Except otherwise specified, tubes are seamless pipes etc ..),

- Specification (A 106,.A 312 etc …),

- Grade or type (B, A, TP 304 etc …),

- Dimensions (Diameter, wall thickness),

- Length in one length except if butt welding is required to the manufacturer

- Over length shall be foreseen to take into account the dimensional variations during the studding,

- A 1000 mm length per grade shall be foreseen for tests and operating adjustments

- Tubes will be in accordance with the applicable standard of tubes (Straightness, concentricity etc. …)

2.2 For the studs configuration and material grade

- Height,

- Diameter,

- Pitch (Generally 16mm : distance between 2 adjacent circular studs rows),

- Total quantity, quantity per row, longitudinally quantity depending on the pitch

- Stud material (carbon steel, AISI 304 , AISI 409 …)

- Bare end dimensions and intermediate bare sections,

- Dimensions per studded length (length and location of studded section),

2.3 Particular requirements

- Cutting to length,

- Bevelled ends according to tube standards or order,

- Heat treatment depends on the tube grade,

- Hydraulic tests, not required except otherwise specified,

- Protection against corrosion per § 8 and order requirements

3.0 Studding of Furnace Tubes Fabrication

3.1 Electric resistance welding performs the connection between stud and tube. The welding procedure specification shall be submitted to HPF for approval

3.2 Studs are arranged in staggered rows.

3.3 Studs are considered to be a non-pressure attachment having essentially no load carrying function. They only have to support the operation of introduction of studded tube in the tube sheet holes of convection coils

3.4 Exception for stainless steel or nickel alloyed tubes, tubes have to be scraped clean with abrasive sheet or shot peened (For example, on a special machine by projection of cast iron grain) in order to assist the current flow during studding and eliminating any oxidation or scale trace .

Degreasing shall be done on studs and on stainless steel or nickel alloy tubes

3.5 The manufacturer operator checks for each tube the good quality of work by visual control

3.6 In case of low alloyed (Cr Mo) steel base tube and whatever the nature of studs, its circumference has to be preheated on a minimal length of 200mm on both sides of studding point. The preheating temperature shall be to 200 at 250°C. If welding process is stopped during more than 15 minutes, the tube will be preheated once more on 200mm length from interruption point before starting again studding.

3.7 In case of low alloyed steel (Cr Mo) tube and whatever studs grade, a post-studding heat treatment is required except particular agreement. In this case, a procedure of heat treatment shall be submitted to confirmation.

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