EN18-e

Distribution of nominal, structural and notch stress at a structural discontinuity

Key:

1 Nominal stress

2 Structural stress

3 Notch stress

4 Extrapolation to give structural stress at potential crack initiation site.

Fig. 18-1 — Distribution of nominal, structural and notch stress at a structural discontinuity

Extrapolation to obtain structural stress from FEA or strain gauge results

Fig. 18-3 - Extrapolation to obtain structural stress from FEA or strain gauge results (in Annex N)

Locations of stresses for determination of structural stress by extrapolation to point of stress concentration (weld toe in this case):

a) low bending stress component, gauge length ≤ 0,2e, linear extrapolation;

b) high bending stress component, stiff elastic foundation, gauge length ≤ 0,2e, quadratic extrapolation;

c) gauge length > 0,2e, linear extrapolation

where "gauge length" refers to size of strain gauge or FE mesh.

Typical example of stress variation when the principal stress directions remain constant

(a) Typical variation with time of the structural principal stresses

(b) Variation with time of the principal stress differences and the resulting Δσ_eq

Fig. 18-4 - Typical example of stress variation when the principal stress directions remain constant

Deviations from design shape at seam welds

(a) Axial misalignment

(b) Ovality

Figure 18-10 — Deviations from design shape at seam welds

Variables

Variable 83 – Class of weld

Table 18-4 — Class of weld details for use with structural equivalent stress range a) - Seam welds

Detail No.	Joint type	Sketch of detail	Comments	Class
Detail No.	Joint type	Sketch of detail	Comments	Testing group 1 or 2	Testing group 3
1.1	Full penetration butt weld flush ground, including weld repairs	Fatigue cracks usually initiate at weld flaws	Weld to be proved free from surface-breaking flaws and significant sub-surface flaws (see EN 13445-5:2014) by non-destructive testing. Use fe instead of few.	90	71
1.2	Full penetration butt weld made from both sides or from one side on to consumable insert or temporary nonfusible backing	1:3	Weld to be proved free from significant flaws (see EN 13445--5:2014) by nondestructive testing and, for welds made from one side, full penetration*.	80	63
1.3		e 1:3 e	Weld to be proved free from significant flaws by nondestructive testing (see EN 13445--5:2014). Effect of centre-line offset to be included in calculated stress.	80	63
1.4			Weld to be proved free from significant flaws (see EN 13445-5:2014) by nondestructive testing
			a £ 30°	80	63
			a > 30°	71	56
*In case of misalignment, see 18.10.4.

Table 18-4 — Class of weld details for use with structural equivalent stress range a) - Seam welds

Detail No.	Joint type	Sketch of detail	Comments	Class
				Testing group 1 or 2	Testing group 3
1.5	Full penetration butt welds made from one side without backing		If full penetration can be assured*.	63	40
			If inside cannot be visually inspected and full penetration cannot be assured*.	40	40
1.6	Full penetration butt welds made from one side onto permanent backing.		Circumferential seams only (see 5.7) Minimum throat = shell thickness
			Weld root pass inspected to ensure full fusion to backing.	56	40
			Single pass weld.	40	40
1.7	Joggle joint		Circumferential seams only (see 5.7) Minimum throat = shell thickness.
			Weld root pass inspected to ensure full fusion to backing.	56	40
			Single pass weld.	40	40
*In case of misalignment, see 18.10.4.

Table 18-4 — Class of weld details for use with structural equivalent stress range

b) — Shell to head or tubesheet

Detail No.	Joint type		Sketch of detail		Comments			Class
								Testing group 1 or 2	Testing group 3
2.1	Welded-on head				Head plate shall have adequate through-thickness properties to resist lamellar tearing.
			(a)		Full penetration welds made from both sides (detail a):
					- as-welded			71	63
					- weld toes dressed (see 18.10.2.2).			80	63
			(b)		Partial penetration welds made from both sides (detail b):
					- fatigue cracking in weld*			32	32
					- fatigue cracking in shell from weld toe.			63	63
			(c)		Full penetration welds made from one side without back-up weld (detail c):
					- if the inside weld can be visually inspected and is proved to be free from overlap or root concavity.			63	40
					- if the inside cannot be visually inspected and full penetration cannot be assured.			40	40
2.2	Welded-on head with relief groove				Weld to be proved free from significant flaws (see EN 13445-5:2014) by NDT.
					Full penetration welds made from both sides, or from one side with the root pass ground flush.			80	63
					Full penetration welds made from one side:
					- if the inside weld can be visually inspected and is proved to be free from weld overlap and root concavity.			63	40
					- if the inside cannot be visually inspected.			40	40
*To be considered only if weld throat < 0,8 x shell thickness
2.3		Set-in head		(a)		Full or partial penetration welds made from both sides (detail a). (Refers to fatigue cracking from weld toe in shell) :
						- as-welded	71			63
						- weld toes dressed (see 18.10.2.2).	80			63
				(b)		Partial penetration welds made from both sides (detail b):
						- refers to fatigue cracking in weld, based on weld throat stress range.	32			32
						- weld throat ≥ 0,8 x head thickness.	63			63
				(c)		Full penetration weld made from one side without back-up weld (detail c):
						- if the inside weld can be visually inspected and is proved to be free from overlap or root concavity.	63			40
						- if the inside cannot be visually inspected.	40			40

Table 18-4 — Class of weld details for use with structural equivalent stress range

c) — Branch connections

Detail No.	Joint type	Sketch of detail	Comments	Class
Detail No.	Joint type	Sketch of detail	Comments	Testing group 1 or 2	Testing group 3
3.1	Crotch corner	1 1 Crack radiates from corner into piece, sketches show plane of crack.	Assessment by the method for unwelded parts is the normal approach. However, simplified assessment using class 100 according to Annex Q is allowed. Use f_e instead of f_ew	100	100
3.2	Weld toe in shell		Full penetration welds:
			- as welded	71	63
			- weld toes dressed (see 18.10.2.2)	80	63
			Partial penetration welds:
			- weld throat ≥ 0,8 x thinner thickness of connecting walls, as welded	63	63
			- weld throat < 0,8 x thinner thickness of connecting walls	32	32
			- weld toes dressed (see 18.10.2.2)	71	63
3.3	Stressed weld metal		Fillet and partial penetration welds.	32	32
3.4	Weld toe in branch		- As-welded.	71	63
3.4	Weld toe in branch		- Weld toes dressed (see 18.10.2.2) e_n = branch thickness in Equation (18.10-6).	80	63

Table 18-4 — Class of weld details for use with structural equivalent stress range

d) Jackets

Detail No.	Joint type	Sketch of detail	Comments	Class
				Testing group 1 or 2	Testing group 3
4.1	Jacket connection weld with shaped sealer ring		Full penetration weld to be proved free from significant flaws (see EN 13445-5:2014) by non-destructive testing
			Welded from one side:
			- multi-pass weld with root pass inspected to ensure full fusion;	63	40
			- single pass weld.	40	40
			Welded from both sides or from one side with back-up weld.	71	56

Table 18-4 — Class of weld details for use with structural equivalent stress range

e) — Attachments

Detail No.	Joint type	Sketch of detail	Comments	Class
				Structural equivalent stress	Nominal equivalent stress
				Testing group 1, 2, 3	Testing group 1, 2, 3
5.1	Attachment of any shape with an edge fillet or bevel buttwelded to the surface of a stressed member, with welds continuous around the ends or not		For details with welds continuous around ends, one class increase if weld toes dressed (see 18.10.2.2)
			L ≤ 160 mm, t ≤ 55 mm	71	56
			L > 160 mm	71	50
5.2	Attachments of any shape with surface in contact with stressed member, with welds continuous around ends or not		For details with welds continuous around ends, one class increase if weld toes dressed (see 18.10.2.2)
			L ≤ 160 mm, W ≤ 55 mm	71	56
			L > 160 mm, W ≤ 55 mm	71	50
			L > 160 mm, W ≤ 55 mm	71	45
5.3	Continuous stiffener		For full penetration welds, one class increase if weld toes dressed (see 18.10.2.2)
			t £ 55mm	71	56
			t > 55mm	71	50

Table 18-4 — Class of weld details for use with structural equivalent stress range (continued)

f) Supports

Detail No.	Joint type	Sketch of detail	Comments	Class
				Testing group 1 or 2	Testing group 3
6.1	Support on either horizontal or vertical vessel	1 Fillet welded to vessel all round 2 Backing plate	As-welded.	71	71
			Weld toe in shell dressed (see 18.10.2.2)	80	80
6.2	Trunnion support	1 Backing plate	As-welded.	71	71
			Weld toe in shell dressed (see 18.10.2.2)	80	80
6.3	Saddle support	1 Fillet welded to vessel all round	As-welded.	71	71
			Weld toe in shell dressed (see 18.10.2.2)	80	80
6.4	Skirt support		Welded from both sides:
			as-welded;	71	71
			weld toe in shell dressed (see 18.10.2.2).	80	80
			Welded from one side	56	56
6.5	Leg support (with or without reinforcing pad) with fillet weld to vessel continuous all around.			71	71

Table 18-4 — Class of weld details for use with structural equivalent stress range

g) Flanges and pads

Detail No.	Joint type	Sketch of detail	Comments	Class
Detail No.	Joint type	Sketch of detail	Comments	Testing group 1 or 2	Testing group 3
7.1	Full penetration butt welded neck flange or compensation flange with welding lug.		Weld to be proved free from surface-breaking and significant sub-surface flaws (see EN 13445-5:2014) by nondestructive testing.
			Weld made from both sides or from one side with back-up weld or onto consumable insert or temporary backing.	80	63
			Weld made from one side:
			- if full penetration can be assured	63	40
			- if the inside cannot be visually inspected	40	40
7.2	Welded flange		Full penetration welds:
			- as-welded	71	63
			- weld toe dressed (see 18.10.2.2);	80	63
			Partial penetration welds:
			- weld throat ≥0,8 x shell thickness;	63	63
			- weld throat < 0,8 x shell thickness.	32	32
7.3	Set-in flange or pad		Full penetration weld:
			- as-welded	71	63
			- weld toe dressed (see 18.10.2.2).	80	63
			Weld made from one side:
			- if full penetration can be assured	63	40
			- if the inside cannot be visually inspected	40	40
			Fillet welded on both sides:
			- weld throat ≥ 0,8 x shell thickness;	63	32
			- weld throat < 0,8 x shell thickness.	32	32
7.4	Set-in flange or pad, welded from both sides		- weld throat ≥ 0,8 x shell thickness;	63	32
7.4	Set-in flange or pad, welded from both sides		- weld throat < 0,8 x shell thickness.	32	32

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EN18-e

Distribution of nominal, structural and notch stress at a structural discontinuity

Extrapolation to obtain structural stress from FEA or strain gauge results

Typical example of stress variation when the principal stress directions remain constant

Deviations from design shape at seam welds

Variables

Variable 83 – Class of weld