U Bend Stainless Steel Tubes For Heat Exchanger Specification

Reference standards and steel grades

“U” bent tubes for heat exchanger can be supplied in accordance with the following norms and steel grades :

“U” Bent tubes in accordance with the standards detailed in table 1, part A can be requested.

The bent area can be subject to stress relieving heat treatment by joule effect in inert atmosphere.

Minimum radius treated = 1.5 × Outside Diameter.
Maximum radius treated = 1500 mm.

2. Dimensions and lengths

Tubes with the following external diameters in mm can be bent a upon agreement: 15,8 - 16,0 - 17,0 - 18,0 - 19,05 - 20,0 - 21,3 - 25,4 -26,7 - 31,8 -38,1.

The minimum feasible radius is :
1,5 × Outside Diameter
The maximum feasible radius is 1500 mm.

3. Tolerances

Tolerances (diameter and wall thickness) according to ASTM A556 or given in the standards detailed in table 1 point A are respected.

Bending tolerances.

The tolerances stipulated in ASTM A556 are respected.

Minimum wall thickness tolerances in the bent area conforming to the TEMA standard "Class R heat exchangers" can be requested or in accordance with specific requests.

4. Checks and test

All the mechanical and technological tests stipulated in the cited standards are carried out. Leak tightness test: electromagnetic test (Eddy Current) is performed on straight tubes. Hydrostatic test on bent tubes is performed only if expressly requested, specifying the test pressure (option d).

Additional tests and checks can be agreed upon.

5. Surface protection

“U” bent tubes for exchangers are supplied unprotected or with a temporary external oil protection to prevent from rust if stored in a covered area. (Tenaris code : PT9).

Other types of protection can be agreed upon.

6. Certification

The product is supplied with a 3.1. certificate, in compliance with EN 10204 and ISO 10474 3.1.B.

Certification according to 3.2 can be agreed upon at time of order. In the event that one of these certificates is requested, the customer must designate, at time of order, the inspection authority.

7. Identification and marking

Tube identification is by indelible ink marking. The data determined by the product norms are continuously marked along the entire length of the tube.

Data in addition to that of the product norms can also be marked on the tube, upon request.

8. Packaging

Suitable packaging should be agreed upon before ordering.Such as Wooden cases, bundle or plastic bags, plywood boxes

9. Minimum quantity supplied

To be agreed upon, at time of order, on the basis of dimensions and stainless steel grade.

10. U Bend requirements

When U-Bends are formed, it is normal for the tube wall at the outer radius to thin, the minimum tube wall thickness in the bent portion before bending shall be:

T0=T1[1+D0/4R]

Where: T0= Original Wall thickness Inches (mm)
T1= Minimum Wall thickness calculated by code rules for a straight tube subject to the same pressure and metal temperature, inches (mm)
D0= Outside tube diameter, inches (mm)
R= Mean radius of bend, inches (mm)

More than one tube gage tubes, may be used in a tube bundle

When U-bends are formed from tube material which are relatively non-work-hardening and of suitable temper, Tube wall thickness in the bend should not exceed a normal 17% of original tube wall thickness.

Flattening at the bend tube shall not exceed 10% of the normal tube outside diameter.

U-bends formed from tube material having low ductility, or materials which are susceptible to work hardening may require special consideration.

11 Bend Spacing

11.1.Center-To Center Dimension

The center to center dimensions between parallel legs of U-tubes shall be such that they can be inserted into the baffle assembly without damage to the tubes

11.2.Bend Interference

The assembly of bend shall be of workmanlike appearance .Metal-To-Metal contact between bends in the same
Plane shall not be permitted

12. Heat treatment

Cold work in forming U-bends may induce embrittlement or susceptibility to stress corrosion in certain material and/or environments. Heat treatment to alleviate such conditions may be performed by agreement between manufacturer and purchaser.

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