Section 4 Pipework
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 11 Production, Storage and Offloading of Liquefied Gases in Bulk - Chapter 5 Process Pressure Vessels and Liquids, Vapour and Pressure Piping Systems and Offshore Arrangements - Section 4 Pipework

Section 4 Pipework

Parent topic: Chapter 5 Process Pressure Vessels and Liquids, Vapour and Pressure Piping Systems and Offshore Arrangements

4.1 Piping fabrication and joining details

4.1.1  General
  1. The requirements of this Section apply to piping inside and outside the cargo tanks. Relaxation from these requirements may be accepted, in accordance with recognised Standards for piping inside cargo tanks and open-ended piping.

4.1.2  Direct connections

The following direct connection of pipe lengths, without flanges, may be considered:
  1. Butt welded joints with complete penetration at the root may be used in all applications. For design temperatures colder than –10°C, butt welds shall be either double welded or equivalent to a double welded butt joint. This may be accomplished by use of a backing ring, consumable insert or inert gas back up on the first pass. For design pressures in excess of 1 MPa and design temperatures of –10°C or colder, backing rings shall be removed.
  2. Slip-on welded joints with sleeves and related welding, having dimensions in accordance with recognised Standards, shall only be used for instrument lines and open ended lines with an external diameter of 50 mm or less and design temperatures not colder than –55°C.
  3. Screwed couplings complying with recognised Standards shall only be used for accessory lines and instrumentation lines with external diameters of 25 mm or less.
4.1.3  Flanged connections
  1. Flanges in flange connections shall be of the welded neck, slip-on or socket welded type.
  2. Flanges shall comply with recognised Standards for their type, manufacture and test. For all piping except open ended, the following restrictions apply:
    1. For design temperatures colder than –55°C, only welded neck flanges shall be used.
    2. For design temperatures colder than –10°C, slipon flanges shall not be used in nominal sizes above 100 mm and socket welded flanges shall not be used in nominal sizes above 50 mm.

4.1.4  Expansion joints

Where bellows and expansion joints are provided in accordance with Pt 11, Ch 5, 3.1 Installation design requirements 3.1.1, the following requirements apply:
  1. If necessary, bellows should be protected against icing.
  2. Slip joints shall not be used except within the cargo tanks.

4.1.5  Other connections

Piping connections shall be joined in accordance with Pt 11, Ch 5, 4.1 Piping fabrication and joining details 4.1.2 to Pt 11, Ch 5, 4.1 Piping fabrication and joining details 4.1.4, but for other exceptional cases the Administration may consider alternative arrangements.

4.2 Welding, post-weld heat treatment and non-destructive testing

4.2.1  General
  1. Welding shall be carried out in accordance with Pt 11, Ch 6 Materials of Construction and Quality Control

4.2.2  Post-weld heat treatment

Post-weld heat treatment shall be required for all butt welds of pipes made with carbon, carbon manganese and low alloy steels. LR may waive the requirements for thermal stress relieving of pipes with wall thickness less than 10 mm in relation to the design temperature and pressure of the piping system concerned.

4.2.3  Non-destructive testing

In addition to normal controls before and during the welding, and to the visual inspection of the finished welds, as necessary for proving that the welding has been carried out correctly and according to the requirements of this paragraph, the following tests shall be required:
  1. 100 per cent radiographic or ultrasonic inspection of butt-welded joints for piping systems with design temperatures colder than –10°C, and with inside diameters of more than 75 mm, or wall thicknesses greater than 10 mm;
  2. When such butt-welded joints of piping sections are made by automatic welding procedures approved by LR, then a progressive reduction in the extent of radiographic or ultrasonic inspection can be agreed, but in no case to less than 10 per cent of each joint. If defects are revealed the extent of examination shall be increased to 100 per cent and shall include inspection of previously accepted welds. This approval can only be granted if well-documented quality assurance procedures and records are available to assess the ability of the manufacturer to produce satisfactory welds consistently; and
  3. For other butt-welded joints of pipes not covered by Pt 11, Ch 5, 4.2 Welding, post-weld heat treatment and non-destructive testing 4.2.3.(a) and Pt 11, Ch 5, 4.2 Welding, post-weld heat treatment and non-destructive testing 4.2.3.(b), spot radiographic or ultrasonic inspection or other non-destructive tests shall be carried out depending upon service, position and materials. In general, at least 10 per cent of butt-welded joints of pipes shall be subjected to radiographic or ultrasonic inspection.

4.3 Installation requirements for cargo piping outside the cargo area

4.3.1  Bow and stern loading arrangements
  1. The following provisions apply to cargo piping and related piping equipment located outside the cargo area:
    1. Cargo piping and related piping equipment outside the cargo area shall have only welded connections. The piping outside the cargo area shall run on the weather decks and shall be at least 0,8 m inboard, except for cargo transfer connection piping. Such piping shall be clearly identified and fitted with a shutoff valve at its connection to the cargo piping system within the cargo area. At this location it shall also be capable of being separated, by means of a removable spool piece and blank flanges, when not in use.
    2. The piping is to be full penetration butt-welded and subjected to full radiographic or ultrasonic inspection, regardless of pipe diameter and design temperature. Flange connections in the piping shall only be permitted within the cargo area and at the cargo transfer connections.
4.3.2  Turret compartment transfer systems
  1. The following provisions apply to liquid and vapour cargo piping where it is run outside the cargo area:
    1. Cargo piping and related piping equipment outside the cargo area shall have only welded connections.
    2. The piping shall be full penetration butt-welded, and subjected to full radiographic or ultrasonic inspection, regardless of pipe diameter and design temperature. Flange connections in the piping shall only be permitted within the cargo area and at connections to cargo hoses and the turret connection.
4.3.3  Gas fuel piping
  1. Gas fuel piping, as far as practicable, shall have welded joints. Those parts of the gas fuel piping that are not enclosed in a ventilated pipe or duct according to Pt 11, Ch 16, 2.1 Supply requirements 2.1.3, and are on the weather decks outside the cargo area, shall have full penetration butt-welded joints and shall be subjected to full radiographic or ultrasonic inspection.
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