Metallic industrial pipingBSI Standar ds Public ation... T he UK par icipatio in it preparatio w as ent us ed to Tech ical C mmit e PV E/10, Pipin sy stems.. User are resp nsible f or it
Safety
Buried piping at industrial sites poses risks to personnel, equipment, and the environment This document offers guidance on assessing these hazards and maintaining the integrity of the piping system.
NOTE 1 Attention is drawn to appropriate National or Local regulations b) The main factors to be considered are:
Design including Routing, Layout, Interaction with connecting systems;
Materials and Construction Specification and Quality Control;
External Impact Protection and Mitigation
All of these factors interact
NOTE 2 It is recommended that all buried piping be subjected to a formal hazard analysis procedure
It is important to adhere to relevant National or Local regulations Additionally, for group 1 fluids, further safety requirements may be outlined in EN 13480-1:2012, which includes the implementation of automated systems for isolating buried piping sections.
Routes
All buried piping routes must be approved by the site owner and operator The site owner is responsible for providing information on all existing or planned buried services, including cables, as well as any roadways or surface loads within the construction working width or zone of the proposed piping.
According to EN 13480-1:2012, category III piping must maintain a minimum separation distance of 0.25 meters from other pipes or services, unless it can be proven that a reduced distance is permissible.
Depth of installation
In the absence of special protection (e.g concrete slabs) buried piping shall be provided with a minimum cover of 0,8 m
Designers should enhance the cover depth beyond the minimum requirements in areas prone to penetrating cold or frost heave, as well as in locations where excavation activities may cause damage.
Pipes marking and recording
Buried pipes shall be marked by a continuous tape or other agreed means placed directly above the pipe and no closer than 0,3 m
All buried pipes must be clearly identified on as-installed drawings that accurately depict their route in relation to structures and other permanent features The site owner may also mandate the physical marking of the route using identification posts or cover slabs at suitable intervals.
Contents removal
The piping system design must ensure safe filling and removal of contents, incorporating necessary vent and drain points, as well as suitable bends and fittings.
Trench drainage
Designers must acknowledge that pipe trenches for buried piping can serve as conduits for groundwater It is essential to implement appropriate methods to ensure the trench bottom has adequate slope towards soak-aways or sumps, preventing water accumulation around the piping If these measures are unfeasible, designers should incorporate flotation considerations into their design calculations.
In addition, the drainage arrangements shall dispose of the hydrostatic test water Care shall be exercised during this operation to ensure that washout of bedding material does not occur
Materials shall conform to the requirements of EN 1 3480-2:201 2 except that the value for the specified minimum elongation after fracture for the longitudinal direction (see EN 1 3480-2:201 2, 4.1 4.) shall be 20 %
Materials with elongation values less than 20 % shall be avoided, and shall only be used subject to agreement between the purchaser and the designer
Minimum wall thickness for buried piping
Unless the pressure design calculations lead to a greater thickness, the wall thickness of the pipe shall not be lower than the value given in Table 1
Table 1 — Minimum wall thickness for buried piping
Nominal size (DN) Minimum thickness mm
Design
A basic one-dimensional model connecting buried pipes with the surrounding soil may suffice for piping designed per EN 13480-3:2012 However, more detailed analyses of pipe-soil interaction can be employed when accurate geo-mechanical data is accessible or if the conditions outlined in this annex are not satisfied.
NOTE It is assumed that the loads imposed by the piping on the soil do not exceed its load bearing capacity
The designer must account for the weight of soil or backfill above the pipe, as well as the maximum anticipated traffic and other static and dynamic loads on the ground above it A minimum immediate cover of 150 mm of sand or a similar free-flowing material is required, allowing the forces to be treated as acting over the entire 180° of the upper pipe surface.
5.2.3 In addition to calculations at the design pressure, the loadings on the unpressurized system shall be calculated
Pipe movement is largely limited by the frictional force between the pipe and the surrounding soil, particularly at buried bends and large branches In the absence of specific measures to allow for relative movement, buried pipes should be treated as fully restrained axially for calculation purposes.
The axial stress due to combined pressure and temperature change effects shall be calculated as follows:
SL is the longitudinal stress 0,90 x yield strength at design temperature;
Sp is the circumferential stress due to pressure alone;
T is the maximum temperature range;
In cases where a detailed analysis is not performed, the maximum temperature range, including installation temperature, must not exceed 35 °C Additionally, restraining features like buried bends and tees should maintain a separation of at least 5 DN If a detailed analysis is conducted, it must adhere to the specified guidelines.
EN 1 3480-3:201 2 supplemented by Annex A (normative)
5.2.6 Where seismic events are to be considered, the pipe shall be treated as if rigidly connected to the ground and following the imposed displacements Dynamic amplification may be ignored
NOTE The surrounding soil can be considered to effectively dampen all harmonic excitations of the pipe
5.2.7 The designer shall consider the interface between buried and above ground sections of the piping for all design conditions
In static analysis, the buried section is treated as clamped for thermal expansion, ensuring that the above-ground portion has adequate flexibility to keep the loads at the connection between the two sections within acceptable limits.
The designer must evaluate the impact of expected settlement of buried piping on the connected aboveground or ducted piping, ensuring adherence to the specified requirements It is important to consider that when gaseous fluids are transported through the piping, there may be an increase in temperature in the compressor discharge lines, along with a corresponding decrease in temperature at the outflow from pressure reducing equipment.
Where such in-line items are close to a buried section, the designer shall consider the effects of the temperature change
Trenches
The standard installation method involves excavating trenches, while an alternative approach includes using thrust boring or similar trenchless techniques to install sections of underground pipe within casings.
The trench bottom must be compacted and clear of sharp objects, rocks, or stones It should have an adequate slope to ensure proper drainage for the pipe, reducing the risk of flotation and corrosion Additionally, soak-aways or sumps should be installed where necessary.
The piping shall be laid on an even bed of sand or similar material and consequently the longitudinal bending stress due to weight may be discounted
6.1 3 A bedding base of free-flowing material such as rounded sand or fine gravel shall be provided with sufficient depth to support the pipe and assist drainage.
Pipe laying
6.2.1 The trench shall be substantially free of water before the pipe is placed in position
Sufficient access must be ensured for joints to allow proper examination during hydrostatic or other testing operations, along with the necessary wrapping or protection of pipe joints in the trench Additionally, adequate measures should be in place for the removal of hydrostatic test water from both the pipe and the trench.
6.2.3 The bore of the piping shall be clean to the required standard before laying in the trench
To prevent damage to pipes and their coatings during storage and laying, all practical measures must be implemented Lifting should not involve wire ropes or chains Additionally, protective coatings on the pipes should undergo visual inspection or high voltage testing after installation and before backfilling the excavation.
Back filling
6.3.1 All tie and examination operations shall be completed before backfilling
The initial cover of the piping must consist of free-flowing materials, applied to a minimum depth of 150 mm, ensuring complete contact of the filling with the entire circumference of the pipe.
The backfilling must consist of the same material excavated from the trench or materials with similar properties, ensuring that no organic or waste materials are included Compaction should only begin after a minimum cover of 0.3 meters has been established.
When buried piping is exposed to regular overhead traffic or occasional heavy loads, it is essential to consider the installation of an external protective sleeve or casing This protective measure is also recommended for sections installed using thrust boring or similar methods.
Casings shall be of steel, concrete or plastic composition with a diameter providing a minimum of 1 00 mm clearance from the carrier pipe
The construction must be designed to support all anticipated external loads, independent of the carrier pipe and any internal supports Additionally, the thickness of the steel tubing should meet or exceed the specified minimum requirements.
EN 1 3480-3:201 2 according to the loads applied (with a minimum of 9,5 mm)
Not less than 3 supporting centralising spacers shall be installed around the pipe at intervals not exceeding the span requirements with a maximum of 4 m
Casings must be sealed at both ends to prevent water and foreign matter from entering When filling the annulus between carrier and sleeve pipes with fluid, the seal only needs to withstand the pressure of the filler, unless the purchaser specifies otherwise.
General 1 0
To prevent external corrosion of buried piping caused by water, ground contaminants, and stray electrical currents, it is essential to implement protective measures This protection involves applying a coating to the pipe surface and utilizing cathodic electrical protection.
Piping specifications typically outline essential requirements for the corrosion protection of buried pipes, which include preparation, coating, and cathodic protection specifications.
All appropriate information in respect of the corrosion hazards likely to be encountered on site shall be provided.
Coatings 1 0
All coatings shall be suitable for the underground environment and have mechanical and electrical properties to suit the specified conditions
In the absence of any other specification, the manufacturer shall consider the relevant European Standards for the selection of suitable coatings
Coatings shall bond strongly to the pipe surface and be resistant to loss of bonding at geometrical discontinuities and damaged sites areas exposed to external impact
Maximizing offsite coating application is essential for optimal conditions, while site coating can utilize alternative methods like tape wrapping for joints and small areas It is crucial to choose a bonding method that adequately adheres to the main pipe body coating and is suitable for the specific installation conditions.
Cathodic protection .1 1
Cathodic protection of buried piping shall be applied to reduce the risk of aggressive localised corrosion at points where the protective coating is or could become defective
Protection shall be either by the connection of sacrificial anodes or the use of an impressed current Protection shall be applied as soon as practicable after installation
It is crucial to address the risks associated with stray earth currents in complex industrial environments, and the protection system designer must take into account potential interactions with nearby electrical networks Additionally, the designer must guarantee electrical continuity for all buried piping.
NOTE Flanges and other in line components may require specific continuity connections
Electrical connections to piping must utilize fully welded pads that are compatible with the pressure shell material, as direct connections to the pipe wall are not allowed.
Buried piping shall be electrically isolated from above ground sections through the use of isolating flanges or similar arrangements
Buried piping shall be examined and tested in accordance with EN 1 3480-5:201 2
Buried sections of piping should be pressure tested before installation in the trench, and all final connections must undergo leak testing or other approved non-destructive testing methods.
Annex A (normative) Calculations for buried piping
This annex describes the applicable requirements for buried piping, supplementing those of
Thus, it is proposed to deal with the calculations for buried piping taking account of the following:
weight of the soil or backfill above the pipe according to the different types of installation;
static and dynamic loads imposed on the ground above the pipe (e.g traffic loads);
flexibility and stability of the piping subjected to combined pressure and temperature change effects
The requirements specified in EN 1 3480-2:201 2 apply without any restriction
Corrosion in buried piping differs significantly from that in above-ground piping found in ducts or tunnels.
The calculation procedure involves several key steps: first, determining the required thicknesses based on the equations provided in EN 13480-3:2012 for piping subjected solely to internal pressure; second, assessing the loads from backfill and live loads; third, verifying the thicknesses established in the first step against various operating conditions relevant to the loads identified; and finally, ensuring the overall stability of the buried piping system.
A.3.2 Determination of the loads due to backfill
The installation methods for buried piping covered are as follows:
piping in wide trench or in positive projecting embankment condition
For the purposes of this annex the following notations shall apply:
C dyn Coefficient for taking into account the dynamic effect of the live loads;
D o External piping diameter For standardized tubes, D o is the theoretical external diameter, tolerances excluded; eord Ordered wall thickness;
E Modulus of elasticity for the piping material (see EN 1 3480-3:201 2);
H t Total height from the top of the piping to natural ground surface (cover);
H e Distance from the plane of equal settlement to the top of pipe; k Ratio of lateral pressure to vertical pressure for the backfill material (Rankine coefficient):
L t Width of the trench in the horizontal plane containing the top of the piping;
t Unit weight of backfill material;
Angle of internal friction for the material used to fill the trench;
Coefficient of internal friction of backfill material;
' Coefficient of sliding friction between the backfill material and the trench walls;
'is always less than or equal to and 'may be taken asprovided that backfilling material of proper quality (homogeneity) is used;
In the absence of specific data, the values given in the table hereafter may be used for the design and calculation of buried piping
Table A.3.2.3 — Soil properties and backfill material
Type of soil Density = tan () k ' = tan ( ' ) k k ' daN/m 3 °
Yellow clay, moist and partially compacted b 1 600 0,330 0,400 0,1 30
Saturated yellow clay or loam b 2 080 0,370 0,300 0,1 1 0
Table A.3.2.3 (concluded) Type of soil Density = tan () k ' = tan ( ' ) k k ' daN/m 3 °
Moist-loamy backfilling material is essential for the stability of buried pipelines, as outlined in the calculations of external loadings acting on these conduits (CERIB, 1970) The theory of external loads on closed conduits has evolved based on recent experiments (MARSTON, 1930) Additionally, the stability of buried pipelines has been extensively studied by E.M Yassine and V.I Tchernikine in Moscow, highlighting the importance of proper backfilling techniques.
A piping is considered as piping in narrow-trench condition (Figures A.3.2.4.1 -1 to A.3.2.4.1 -4) if one of the following conditions is satisfied:
If neither of these conditions is satisfied, the piping is considered as piping in wide-trench condition
A.3.2.4.2 Calculation of the load due to backfill
The load per unit length the piping is subjected to is given by the Equations A.3.2.4.1 -1 and -2:
The value of C 1 may be derived directly from Figure A.3.2.4.2 as a function of the ratio H t / L t and of the product k '.
A.3.2.5 Piping in wide-trench conditions or positive projecting embankment conditions
The projection ratio, qr, is defined in Figures A.3.2.5.1 -1 and A.3.2.5.1 -2 and the most commonly used values are given in Table A.3.2.5.1 -1
Table A.3.2.5.1 -1 — Values for the projection ratio qr
The settlement ratio, C tass , is defined as follows:
S 1 settlement of the backfill adjacent to the piping, measured between the natural ground plane and the horizontal plane containing the top of the piping;
S 2 settlement of the natural ground under the backfill adjacent to the piping;
T 1 settlement of the piping into the natural ground;
T 2 deflection of vertical height of the pipe
NOTE Two cases may be envisaged after back-filling:
The backfill placed above the piping experiences less settlement compared to the surrounding backfill In the case of rigid piping, the shearing forces at the boundaries increase the load on the piping, resulting in a positive settlement ratio.
The backfill placed above the piping experiences greater settlement compared to the surrounding backfill In the case of semi-rigid or flexible piping, the shearing forces at the boundaries reduce the load on the piping, resulting in a negative settlement ratio.
Table A.3.2.5.1 -2 gives a set of values recommended for this settlement coefficient for the most current cases:
The settlement coefficients for various types of piping are as follows: Rigid piping on rock or firm soil has a coefficient of +1.0, while on ordinary soil it ranges from +0.8 to +0.5 For rigid piping on unconsolidated soil, the coefficient is between +0.5 and 0 Flexible piping with non-compacted backfill on each side has a coefficient ranging from -0.4 to -0.2, and with slightly compacted backfill, it ranges from -0.2 to 0 When flexible piping has well-compacted backfill on each side, the coefficient is between 0 and +0.4, and with optimally compacted backfill, it ranges from +0.4 to +0.8.
NOTE 1 A piping may be considered as a ôrigidằ piping if:
In the scenario of rigid piping that remains undeformed and when the foundation soil is incompressible, the settlement coefficient is determined to be 1, indicating a uniform plane of equal settlement.
The plane of equal settlement is the level at which the settlement of backfill over the piping matches that of the adjacent backfill The distance, denoted as \$H_e\$, from this plane to the top of the pipe can be calculated using specific equations.
NOTE The value of He may be derived directly from Figure A.3.2.5.1 -4
21Figure A.3.2.5.1 -4 — Plane of equal settlement – Determination of H e
A.3.2.5.2 Calculation of the load due to backfill
The load per unit length the piping is subjected to is given by Equation A.3.2.5.2-1
The coefficient C 2 is given by the following equations: a) H e H t : virtual plane of equal settlement
(A.3.2.5.2-3) b) H e H t : real plane of equal settlement
The value of C 2 may be derived directly from Figure A.3.2.5.2 for different values of k
A.3.3 Determination of the loads due to live loads
In the case of a concentrated live load Fc in Newton, the load per unit length the piping is subjected to is given by Equation A.3.3.1 -1 : c dyn 7
The coefficient C 7 may be obtained directly from Figures A.3.3.1 -1 and -2 with:
L Piping length, loaded by Fc (equal to 1 if the actual length of the piping under consideration exceeds 1 )
For an area load of pr in N/m², the load per unit length the piping is subjected to is given by Equation A.3.3.2-1 :
The coefficient C 8 may be derived directly from Figures A.3.3.1 -1 and -2 with:
Dimensions of the projection area affected by the area load
1 Static loads p r Surface pressure due to distributed live load
A.3.4 Determination of the moments acting upon the piping
The equations presented allow for the calculation of moments at any point along the piping wall under various loading conditions By superimposing these different cases, we can effectively analyze the behavior of the piping system.
The stresses ( ) may be derived from the values of the resultant moments M () using the following equation: v I
A.3.4.2 Moments due to backfill and live loads
Q is the total load per unit length with Q F 1 F 7 (where A.3.3.1 is applicable) F 8 (where A.3.3.2 is applicable), if A.3.2.4 is applicable; or Q F 2 F 7 (where A.3.3.1 is applicable) F 8 (where A.3.3.2 is applicable), if A.3.2.5 is applicable
In order to take account of backfill and live loads, a less conservative method is given hereafter
M (A.3.4.2.2-2) where q is the load per unit length, related to the mean diameter
A.3.4.3 Dead load of the pipe
M cw (A.3.4.3-1 ) where pcw is the weight of the pipe per circumferential unit length
M w (A.3.4.4-1 ) where pw is the unit weight
A.3.4.5 Taking account of the bedding condition (e.g continuous supporting on sand bed)
K sin cos (A.3.4.5-4) where qtotal is the distributed total load (backfill load, dead load and hydrostatic pressure)
A.3.5 Global stability of a buried piping system
The procedure outlined hereafter allow to check the stability of a buried piping affected by operating pressure and operating temperature changes, for service temperature above 35 °C
For the purpose of the following paragraphs the notations hereafter shall apply in addition to those in A.3.2.2:
t Change in temperature between mounting temperature (backfilling) and operating temperature
c Circumferential stress in a pipe caused by internal positive pressure
D m Mean diameter of the pipe
W p Weight per unit length of the pipe
S Cross section of the pipe
E Young modulus of the material of the pipe
Rultim Allowable deformation factor of the soil
A.3.5.3 Load due to pressure and temperature on a straight part of a piping
A.3.5.5 Determination of the effective length
The effective length of a straight part of a piping is given by the following equation: eff eff aF
For a straight section of piping, if the total effective lengths measured at both ends are less than the actual length, specific checks must be conducted.
A.3.5.6.1 Stability of the restrained part
0 and 0,8 and 0,9 are safety coefficients
The design is acceptable if:
This verification shall be performed with or without pressure in the pipe and with or without backfilling
A.3.5.6.2 Longitudinal compressive stress in the restrained part
L is the circumferential stress due to pressure
The design is acceptable if:
R eHt as defined in EN 1 3480-3:201 2, Table 3.2-1
A.3.5.6.3 Stability of the effective length of the pipe
Critical load for a radius elbow/bend 1 ,5 D
The design shall be acceptable if:
A.3.5.6.4 Stress in the effective length of the pipe
A.3.5.6.3 Stability of the effective length of the pipe
Critical load for a radius elbow/bend 1 ,5 D
The design shall be acceptable if:
A.3.5.6.4 Stress in the effective length of the pipe
Elongation of the effective length taking account of friction (for information)
The design is acceptable if: t f eH f 0 R,9 v
When the total effective lengths of a straight piping section exceed its actual length, the procedure outlined in A.3.5.6.4 must be followed, utilizing Equation (A.3.5.6.4-2) to determine Leff, which can be either the calculated value or L.
Annex Y (informative) History of EN 1 3480-6
Y.1 Differences between EN 1 3480-6:2004 and EN 1 3480-6:201 2
The 201 2 edition of EN 1 3480-6 contains the 2004 edition of the standard and the Amendment(s) and/or correction(s) issued in the meantime
Revision of 5.2 related to the design of the buried piping
Addition of the new Annex A related to the calculations for buried piping
NOTE The changes referred include the significant technical changes but is not an exhaustive list of all modifications
Y.2 List of corrected pages of Issue 2 (201 3-08)
Y.3 List of corrected pages of Issue 3 (201 4-08)
Relationship between this European standard and the essential requirements of EU Directive 97/23/EC
This European Standard was developed under a mandate from the European Commission to ensure compliance with the Essential Requirements of the New Approach Directive 97/23/EC, which pertains to the harmonization of laws among Member States regarding pressure equipment.