1.1    This edition of IGEM/TD/12, which supersedes Edition 2 (which is now obsolete), has been drafted by a Panel appointed by the Institution of Gas Engineers and Managers' (IGEM's) Gas Transmission and Distribution Committee, subsequently approved by that Committee and published by the authority of the Council of IGEM. It reflects improvements and developments through calculation and analysis.

1.2    In 1975, the Institution of Gas Engineers (IGE) published IGE/TD/9 ‘Offtakes and pressure regulating installations for inlet pressures between 7 and 70 bar’. Within IGE/TD/9, Section 9 and the associated Appendix 4 on pipework design and stressing outlined methods for the calculation of stresses within a piping system. IGE/TD/9 has been superseded by IGEM/TD/13.

In 1985, IGE published IGE/TD/12 (Edition 1), extending the scope of these methods to cover a wider application than those given in IGE/TD/9. Amendments to IGE/TD/12 (Edition 1) were issued in 1990. 

IGE/TD/12 (Edition 2) was published in 2003, and amendments were issued in 2005. Edition 2 ‘Reprint with Amendments’ was published in 2012.

1.3    The aim of this Standard is to ensure that piping systems are designed to withstand the stresses within them and to ensure that forces and moments applied to connected equipment and support structures are considered.

1.4    Materials and methods of analysis are subject to continuous evolution and it is intended to review this Standard in line with IGEM’s policy. Regard will be paid to the publications and findings of appropriate organisations with which IGEM maintains liaison.

1.5    This Standard reflects the need to ensure adequate reliability and continuity of supply at pressures that are safe for the downstream system and equipment.

1.6    This Standard makes use of the terms “must”, “shall” and “should” when prescribing particular requirements. Notwithstanding clause 1.9:

• the term “must” identifies a requirement by law in (Great Britain) GB at the time of publication.
• the term “shall” prescribes a requirement which, it is intended, will be complied with in full and without deviation.
• the term “should” prescribes a requirement which, it is intended, will be complied with unless, after prior consideration, deviation is considered to be acceptable.

Such terms may have different meanings when used in Legislation, or Health and Safety Executive (HSE) Approved Codes of Practice (ACoPs) or Guidance, and reference needs to be made to such statutory Legislation or official Guidance for information on legal obligations.

1.7    The primary responsibility for compliance with legal duties rests with the employer. The fact that certain employees, for example (e.g.) “responsible engineers”, are allowed to exercise their professional judgement does not allow employers to abrogate their primary responsibilities. Employers are required to:

• have done everything to ensure, so far as is reasonably practicable, that there are no better protective measures that can be taken other than relying on the exercise of professional judgement by “responsible engineers”
• have done everything to ensure, so far as is reasonably practicable, that “responsible engineers” have the skills, training, experience and personal qualities necessary for the proper exercise of professional judgement
• have systems and procedures in place to ensure that the exercise of professional judgment by “responsible engineers” is subject to appropriate monitoring and review
• not require “responsible engineers” to undertake tasks which would necessitate the exercise of professional judgement that is beyond their competence. There should be written procedures defining the extent to which “responsible engineers” can exercise their judgement. When “responsible engineers” are asked to undertake tasks that deviate from this, they should refer the matter for higher review.

1.8    It is now widely accepted that the majority of accidents in industry generally are in some measure attributable to human as well as technical factors. People who initiated actions that caused or contributed to accidents might have acted in a more appropriate manner to prevent them.

To assist in the control of risk and proper management of these human factors,
due regard should be taken of HSG48, HSG65 and IGEM/G/7. 

1.9    Notwithstanding clause 1.6, this Standard does not attempt to make the use of any method or specification obligatory against the judgement of the responsible engineer. Where new and better techniques are developed and proved, they should be adopted without waiting for modification to this Standard. Amendments to this Standard will be issued when necessary, and their publication will be announced in the Journal of IGEM and other publications as appropriate.

1.10    Requests for interpretation of this Standard in relation to matters within their scope, but not precisely covered by the current text, should be either: 
•    addressed to Technical Services, IGEM, IGEM House, 26-28 High Street, Kegworth, Derbyshire, DE74 2DA; or
•    emailed to [email protected].

These will be submitted to the relevant Committee for consideration and advice, but in the context that the final responsibility is that of the engineer concerned. 
If any advice is given by or on behalf of IGEM, this does not imply acceptance of liability for the consequences and does not relieve the responsible engineer of any of their obligations. 

1.11    This Standard was published in October 2021.
 

2.1    This Standard covers the stress analysis and calculation of loadings for welded and flanged pipework used in gas industry installations on or connected to pipelines. 

In general, an installation on a pipeline comprises one or more of the following:

• compressor station
• line valve 
• branch connection
• meter installation (see also IGEM/G/1, IGEM/GM/8 and/or IGEM/GM/4, as appropriate)
• multi-junction station with or without in-line metering and which may include pig traps and/or line valves
• overhead pipe crossing
• pigging station
• PRI controlling gas flow and/or pressure from one system to another
• terminal
• other offtakes.

2.2    This Standard applies to pipework (as outlined in Sub-Section 2.1) on land. For pipework offshore, additional or alternative guidance may be required. However, many of the requirements in this Standard will remain valid.

Note:    Offshore pipework is on the seaward side of the low water mark or special boundaries drawn at bays and estuaries.

2.3    This Standard is entirely dependent upon the application of other relevant codes and standards, appropriate to the system being designed, e.g., IGEM/TD/1, IGEM/TD/13, etc., to ensure overall plant integrity.

Note:    The information covering materials (pressure testing and construction) is included to qualify the stress analysis recommendations and draw attention to important areas of consideration.

2.4    This Standard is entirely dependent upon the correct selection of materials compatible to the appropriate duty. This Standard is not intended for general application to pipelines, which are covered by IGEM/TD/1, IGEM/TD/3 and IGE/TD/4 respectively. Where larger diameter pipework is above ground for a significant distance, these requirements may be relevant. 

2.5     This Standard covers stress analysis for pipework carrying gas at a maximum operating pressure (MOP) not exceeding 100 bar and at a temperature between -25 oC and 120 oC inclusive. Some pipework such as venting pipework could be subjected to lower than -25 oC in certain conditions. IGEM/TD/12 can still be used for the assessment of this pipework, but the designer is to ensure that the material remains ductile under these lower temperatures.

Note:    Specifically, this Standard applies to the range of conditions expected to be encountered in the types of plant specified in Sub-Section 2.1. 

2.6    This Standard covers pipework handling 1st and 2nd family gases as defined in BS 1179, odorised or unodorised.
 
2.7    This Standard applies only to carbon and austenitic steels whose permanent elongation at tensile fracture at room temperature is greater than 14% when measured using the method outlined in BS EN ISO 6892-2. 

Note 1:    The use of pipe manufactured from non-metallic, cast metallic or other brittle material is not within the scope of this Standard. 

Note 2:    Materials operating above their creep threshold are not covered.

2.8    This Standard applies to pipework containing gas at a positive gauge pressure, i.e., internal pressure not less than external pressure.

2.9    Pipes with a diameter to wall thickness ratio (D/t) of less than 10 require special consideration. 

For pipes of D/t greater than 96, the possibility of buckling of the pipework needs to be considered.

2.10    All pressures are gauge pressures unless otherwise stated.

2.11    Italicised text is informative and does not represent formal requirements.

2.12  Appendices are informative and do not represent formal requirements unless specifically referenced in the main sections via the prescriptive terms “must”, “shall” or “should”.