The document summarizes international standards regarding weld proximity. Several standards specify minimum distances between weld toes, generally 4 times the thickness of the welded parts. BS 2633 states weld toes of adjacent butt welds on ferritic steel pipework should be at least 4 times the pipe thickness and to avoid attachment welds crossing existing welds closer than twice the thickness or 40mm. BS 4515 also specifies a minimum toe-to-toe distance of 4 times the pipe thickness for steel pipelines. BS 2971 notes appropriate precautions shall be agreed upon if more than two welded seams cannot be avoided on carbon steel pipework.

1. Weld proximity is covered by a number of international standards. Extracts from these standards are
shown below and summarised in the following table:
Standard Applies to
Minimum distance
between weld toes
Notes
BS 2633:1987
Ferritic steel
pipework
4t
t= nominal thickness of the
pipe
See below for notes on
attachment welds.
BS 4515:2009 C-Mn pipelines 4t t= pipe thickness
BS 2971:1991
Carbon steel
pipework
Agreed by parties -
PD 5500:2012 Pressure vessels
4e or 100mm
whichever is greater
e= design thickness
Refers to staggering of
longitudinal welds
ASME B&PV
Boilers and
pressure vessels
Not specified -
BS 2633 ‘Class I arc welding of ferritic steel pipework for carrying fluids’ (Section 11), states that the
toes of adjacent butt welds shall, whenever possible, be no closer than four times the nominal
thickness of the pipe.
It also states that attachments of non-pressure parts by welds which cross existing main welds or for
which the minimum nominal distance between the toe of the attachment weld and the toe of the
existing main welds or branch welds is less than the smaller of twice the thickness of the pressure part
or 40mm should be avoided.
If such welds cannot be avoided, they should cross the main weld completely rather than stop
abruptly near the main or branch weld in order to avoid stress concentrations in these areas. Non-
destructive testing of main welds should be carried out before attachment welds which cross are
deposited.
BS 4515 ‘Specification for welding of steel pipelines on land and offshore’ (Section 11), states that
the proximity of weld toe-to-toe distance shall not be less than four times the pipe thickness
BS 2971 ‘Class II arc welding of carbon steel pipework for carrying of fluids’ (Section 10), states that
if design factors are such that the meeting of more than two welded seams cannot be avoided, then
appropriate precautions shall be taken which shall be agreed between the contracting parties.
PD5500 ‘Specification for Unfired fusion welded pressure vessels’ (Section 4.1.3), states that where
any part of a vessel is made in two or more courses, the longitudinal seams shall be completed before
commencing the adjoining circumferential seam(s) and, where practicable, the longitudinal seams of
the adjacent courses shall be staggered by 4e or 100mm, whichever is the greater, measured from
the toe of the welds. (where e = nominal thickness).
ASME Boiler and Pressure Vessel Code Section VIII Division 1, the only mention of proximity of
welds is in UG-82 ‘Lugs and fitting attachments’:
All lugs brackets, saddle type nozzles, manhole frames, reinforcement around openings, and other
appurtenances shall be formed and fitted to conform reasonably to the curvature of the shell or
surface to which they are attached.

2. 1. When pressure parts, such as saddle type nozzles, manhole frames and reinforcement around
openings extend over pressure retaining welds, such welds shall be ground flush for the portion
of the weld to be covered.