13.5 B31.3 Bending, Forming, Assembly & Records

13.5 B31.3 Bending, Forming, Assembly & Records

The last two slices of the AWS blueprint that B31.3 supplies are Fabrication beyond welding — bending, forming, assembly, and erection — and Reports and Records. Both are short paragraphs with hard numbers, which makes them efficient points on an open-book exam if you have them tabbed.

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1. Bending (Para 332.1 and 332.2)

Para 332.1 sets the general permission: pipe may be bent and components formed by any hot or cold method suitable for the material, the fluid service, and the severity of the bending or forming process. Three outcome requirements attach:

• The finished surface shall be free of cracks and substantially free from buckling.
• Thickness after bending or forming shall be not less than that required by the design — the link back to $t_m$ from Para 304.
• PFI Standard ES-24 may be used as a guide for pipe bending.

Bend Flattening (Para 332.2.1)

$\text{Flattening} = D_{\max} - D_{\min} \text{ at any cross section}$

And a prohibition that generates exam items on its own: removal of metal shall not be used to achieve these requirements. Grinding the high spots off an out-of-round bend to make the caliper reading pass is a Code violation, not a repair.

Bending Temperature (Para 332.2.2)

• Cold bending of ferritic materials shall be done at a temperature below the transformation range.
• Hot bending shall be done at a temperature above the transformation range, and in any case within a temperature range consistent with the material and the intended service.

Corrugated and Other Bends (Para 332.2.3)

Dimensions and configuration shall conform to the design qualified in accordance with Para 306.2.2.

2. Forming (Para 332.3)

The temperature range for forming shall be consistent with material, intended service, and specified heat treatment. B31.3 does not enumerate forming methods; it constrains the thermal window and then imposes the heat treatment rules below.

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3. Required Heat Treatment After Bending and Forming (Para 332.4)

Para 332.4 states that heat treatment shall be performed in accordance with Para 331.1.1 when required by Para 332.4.1 or 332.4.2, and recommends the process and temperature control methods of ASME B31P.

After Hot Bending and Forming (Para 332.4.1)

Heat treatment is required for P-Nos. 3, 4, 5, 6, and 10A materials in all thicknesses. Durations and temperatures are in accordance with Para 331 — that is, the Table 331.1.1 holding range and soak schedule for the material.

After Cold Bending and Forming (Para 332.4.2)

Heat treatment is required for all thicknesses, with temperature and duration as given in Table 331.1.1, when any of the listed conditions exist. The leading condition is the fiber-elongation test:

(a) for P-Nos. 1 through 6 materials, where the maximum calculated fiber elongation after bending or forming exceeds 50% of the specified basic minimum elongation (in the direction of severest forming) for the applicable specification, grade, and thickness.

This requirement may be waived if it can be demonstrated that the selection of pipe and the choice of bending or forming process provide assurance that the finished product meets the design intent.

+-----------------------------------------------------------------------------------------+
|             B31.3 PARA 332.4 HEAT TREATMENT AFTER BENDING AND FORMING                   |
+-----------------------------------------------------------------------------------------+
| HOT bending / forming (332.4.1)                                                         |
|   P-Nos. 3, 4, 5, 6, and 10A --> heat treatment required in ALL thicknesses,            |
|   duration and temperature per Para 331 (Table 331.1.1 ranges)                          |
|                                                                                         |
| COLD bending / forming (332.4.2)                                                        |
|   P-Nos. 1 through 6 --> heat treatment required in ALL thicknesses, per Table 331.1.1,  |
|   when max calculated fiber elongation > 50% of the specified basic minimum elongation  |
|   in the direction of severest forming                                                  |
|                                                                                         |
| Note the asymmetry: the HOT rule starts at P-No. 3; the COLD rule starts at P-No. 1.     |
+-----------------------------------------------------------------------------------------+

[!IMPORTANT] The hot and cold lists are not the same. Hot work triggers heat treatment for P-Nos. 3, 4, 5, 6, and 10A; cold work reaches down to P-No. 1 but only through the 50% fiber-elongation gate. Options that apply one list to the other operation are the standard distractor.

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4. Assembly and Erection (Para 335)

Alignment (Para 335.1)

• (a) Piping Distortions: Any distortion of piping to bring it into alignment for joint assembly that introduces a detrimental strain in equipment or piping components is prohibited.
• (b) Cold Spring: Before assembling any joints to be cold sprung, guides, supports, and anchors shall be examined for errors that might interfere with desired movement or lead to undesired movement. The gap or overlap prior to assembly shall be checked against the drawing and corrected if necessary. Heating shall not be used to help close the gap, because it defeats the purpose of cold springing.
• (c) Flanged Joints: Unless the engineering design specifies otherwise, flanged joints shall be aligned as follows:

Flanged Joints (Para 335.2)

• 335.2.1 Preparation for Assembly: Any damage to the gasket seating surface that would prevent gasket seating shall be repaired, or the flange shall be replaced.
• 335.2.2 Bolting Torque: Governs how the gasket is compressed and how bolt load is applied during assembly.

These are inspection points a CWI can check with a straightedge, a feeler gauge, and a drift pin, and they are among the few B31.3 assembly requirements with hard numbers attached.

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5. Records (Para 346)

B31.3's records clause is short enough to read in full during the exam, and every line is examinable.

• Para 346.2 Responsibility: It is the responsibility of the piping designer, the manufacturer, the fabricator, and the erector, as applicable, to prepare the records required by the Code and by the engineering design. Note who is not named: the Owner's Inspector does not prepare these records — the Inspector verifies them.
• Para 346.3 Retention of Records: Unless otherwise specified by the engineering design, the following shall be retained for at least 5 years after the record is generated for the project:
  1. Examination procedures
  2. Examination personnel qualifications
  3. Examination reports

Two related record obligations sit outside Para 346 and are easy to forget:

• Para 328.2.4 (Qualification Records): The employer shall maintain copies of the procedure and performance qualification records specified by Section IX, available to the Inspector at the location where welding is being done. Keeping the PQR binder in a head office two states away does not satisfy this.
• Para 341.4.1(c) (Certifications and Records): The examiner shall be assured, by examination of certifications, records, and other evidence, that materials and components are of the specified grades and have received the required heat treatment, examination, and testing — and shall provide the Inspector with a certification that all the quality control requirements of the Code and of the engineering design have been carried out.

+-----------------------------------------------------------------------------------------+
|                     WHO OWNS WHICH B31.3 RECORD OBLIGATION                              |
+-----------------------------------------------------------------------------------------+
|  Designer / manufacturer / fabricator / erector --> PREPARE the records (346.2)         |
|  Employer                                       --> MAINTAIN Section IX PQ and WPQ      |
|                                                     records at the welding location     |
|                                                     (328.2.4)                            |
|  Examiner                                       --> CERTIFY to the Inspector that QC    |
|                                                     requirements were carried out        |
|                                                     (341.4.1(c))                         |
|  Owner's Inspector                              --> VERIFY; does not prepare or perform |
|  Retention                                      --> AT LEAST 5 YEARS for examination    |
|                                                     procedures, personnel qualifications,|
|                                                     and examination reports (346.3)      |
+-----------------------------------------------------------------------------------------+

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6. Field Scenario and Exam Traps

Field Scenario: The Ground-Down Bend

A fabricator produces a cold-formed 90° bend in NPS 8 ($D = 8.625\text{ in.}$) A106-B pipe for a Normal Fluid Service hydrocarbon line. Caliper readings across the bend give a maximum diameter of 9.05 in. and a minimum of 8.28 in. The shop foreman proposes grinding the high side down to bring the reading into tolerance.

The CWI's Finding: Two separate nonconformances.

1. Flattening. $D_{\max} - D_{\min} = 9.05 - 8.28 = 0.77\text{ in.}$ Against a nominal outside diameter of 8.625 in., that is $0.77 / 8.625 = 8.9%$, which exceeds the 8% limit for internal pressure in Para 332.2.1. The bend is rejectable as produced.
2. The Proposed Fix. Para 332.2.1 states that removal of metal shall not be used to achieve these requirements. Grinding is expressly prohibited as a means of meeting the flattening limit, and it would also attack the Para 332.1 requirement that thickness after bending be not less than that required by the design.

The bend must be re-made. And because this is a cold bend in a P-No. 1 material, the fabricator must also evaluate Para 332.4.2(a): if the maximum calculated fiber elongation exceeds 50% of the specified basic minimum elongation in the direction of severest forming, a Table 331.1.1 heat treatment is required in all thicknesses.

Common Exam Traps to Avoid

• 8% and 3% Are Not Interchangeable: 8% flattening for internal pressure, 3% for external pressure. The tighter number goes with the less intuitive loading.
• Grinding Is Not a Remedy: Removal of metal shall not be used to meet the flattening limits.
• The Hot List vs. the Cold List: Hot bending and forming triggers heat treatment for P-Nos. 3, 4, 5, 6, and 10A; cold bending and forming reaches P-Nos. 1 through 6 but only through the 50% fiber elongation gate.
• Heating a Cold-Spring Gap: Para 335.1(b) prohibits using heat to help close a cold-spring gap, because heating defeats the purpose of cold springing.
• Flange Alignment Numbers: 1 mm in 200 mm (1/16 in./ft) across any diameter for gasket contact surfaces; 3 mm (1/8 in.) maximum bolt hole offset. These are the two numeric flange tolerances in B31.3.
• The 5-Year Retention Rule: Para 346.3 covers exactly three record types — examination procedures, examination personnel qualifications, and examination reports — for at least 5 years, unless the engineering design says otherwise. Do not extend the list to MTRs or PQRs from memory; those are governed elsewhere.
• Who Prepares vs. Who Verifies: Para 346.2 places record preparation on the designer, manufacturer, fabricator, and erector. The Owner's Inspector verifies.