Effect of Surface Preparation Grades of

Weld Seam on the Coating Performance in

Marine Structures
1. BACKGROUND
2. RESULTS
3. RESULTS & DISCUSSION
4. CONCLUSIONS
1. Background
Ø In ISO 8501-3, brief expressions and one general picture about preparation
grades of weld ripple/profile are given without specificity.

[ ISO 8501-3 ]

1
 1. Background

Ø Issue about interpretation of P3 criteria for surface treatment has a possibility of

repeated controversy and made incessant delay of overall production process
during building a offshore structure.
Ø The buyer has required that the ripples made by multiple welding shall be removed
to flat surface in accordance with ISO 850103, P3 grade.

[ Surface treatment guidance for weld ripple and profile ]

(a) ISO 8501-3(Multi pass) (b) ISO 12944-3(Single pass)

2
 1. Background

Ø In this study, surface preparation condition and paint film thickness

distribution on the welded joint lines were investigated. The crack and
corrosion resistance by the 5 types of the surface treatment were also
evaluated to identify the effect of surface treatment on the coating
performance.

Removal of ripple
Multi pass to flat surface
welding

3
2. Experimental methods

[ Blast cleaning to Sa2.5 ]

[ Welding ] [ Grinding to 5 grades ]

Without With
Coat 1. Effect of blasting
stripe coat stripe coat
Coating A - Bronze Coating A - Bronze
1st coat 2. Film distribution
(160μm) (160μm)
Stripe
- Coating A - Grey
coat 3. Corrosion resistance
Coating A - Grey Coating A - Grey
2nd coat
(160μm) (160μm)
4. Crack resistance
Thickness: 900μm and 1,200μm
<Evaluation items>
<Coating application>
4
3. Results and discussion
3.1 Effects of power tool and blast cleaning
Ø It was found that blast cleaning made the irregular shape of smoothness due to
high impact energy of numerous abrasive particles.
Ø Therefore, all specimens after abrasive blasting have smooth surfaces enough to
wet by applied coating materials.
[ The appearance of specimens with 5 grades of surface preparation ]
Grade G1 G2 G3 G4 G5
(No Grinding) (Soft) (Medium) (Hard) (Very Hard)

After
grinding

After
Blasting
(Sa 2.5)

Enough smooth surfaces without irregular shape 5

 3. Results and discussion

3.2 Film thickness distribution

Ø The epoxy coating materials were applied by airless spray and cured at ambient
condition for three weeks.
Ø For measurement of the film thickness distribution of T-bar specimen, the cross-
sections of coated film were observed using the microscope with the 50 and 150
times scale, respectively.

[ Paint specification ]

Coat System 1 System 2

Coating A - Bronze Coating A - Bronze

1st coat
(160μm) (160μm)
Stripe coat - Coating A - Grey
Coating A - Grey Coating A - Grey
2nd coat
(160μm) (160μm)

6
 3. Results and discussion

Ø It can be generally supposed that the paint film thickness at the valley location, 2, 4
and 6, is extremely higher than others (location 1, 3, 5 and 7) due to its concave
configuration.
[ System 1_without stripe coat ]
Sector G1 G2 G3 G4 G5
1 272 200 252 259 230
2 314 346 349 343 303
3 326 343 351 349 323
4 423 371 398 383 325
5 329 435 376 350 310
6 357 294 483 392 340
7 236 417 322 442 245
Average 322 344 362 360 297

Sectional
view

7
 3. Results and discussion

Ø It can be generally supposed that the paint film thickness at the valley location, 2, 4
and 6, is extremely higher than others (location 1, 3, 5 and 7) due to its concave
configuration.
[ System 2_with stripe coat ]
Sector G1 G2 G3 G4 G5
1 228 240 328 286 263
2 443 362 447 424 343
3 369 358 410 437 323
4 485 401 399 441 378
5 358 313 395 516 331
6 463 422 560 468 347
7 344 299 468 490 327
Average 384 342 429 437 330

Sectional
view

8
 3. Results and discussion

Ø However, the average film thicknesses at the valley locations were merely
50~100μm higher than others.
Ø This means that there was no necessary to grind the weld bead with the excessive
grade equal to G2~G5 before 2nd surface preparation to achieve a uniform film
thickness.
[ DFT of system 1 ]
[ Cross-sectional view ] Sector G1 G5
1 272 230
G1 G5
2 314 303
3 326 323
4 423 325
5 329 310
6 357 340
7 236 245
Avg. 322 296

9
 3. Results and discussion

3.3 Corrosion resistance

Ø Seawater immersion test (ISO 20340)
§ The coating performance such as blistering, corrosion creep from a scribe line were
evaluated after exposure of the coated panels in the seawater immersion for
4,200hours in accordance with ISO 20340.

[ ISO 20340 ]

Corrosion creep, M=(C-W)/2

M: Corrosion creep (mm)
C: Average of the nine measurements (mm)
W: The original width of the scribe (mm)

C1~C9(Corrosion creep)

10
 3. Results and discussion

Ø Salt spray test (ISO 12944)

§ The coating performance such as blistering, rust breakthrough from the un-
scribed line and the corrosion creep from the scribed lines were evaluated after
exposure of the coated panels in the salt spray chamber for 1,440 hours in
accordance with ISO 12944-2 & 6(C5-M very high, salt spray test).

Corrosion creep, M=(C-W)/2

M: Corrosion creep (mm)
[ ISO 12944-6, Assessment of test panels]
C: Max. of corrosion creep (mm)
Assessment W: The original width of the scribe (mm)
Requirement after qualification testing
method
After artificial ageing in accordance with ISO 7253
Corrosion from a any corrosion of the substrate from the scratch shall
W
scribed line not exceed 1mm when calculated using the equation
in annex A.
Max. C1(Corrosion creep)

11
 3. Results and discussion

[ Results of corrosion resistance ]

Grade G1 G2 G3 G4 G5

Seawater
Immersion
(4,200 hrs)

Corrosion creep: below 1mm (criteria: ≤ 8.0mm)

Salt spray
exposure
(1,440 hrs)

Corrosion creep: below 1mm (criteria: ≤ 1.0mm)

12
 3. Results and discussion

3.4 Crack resistance

Ø T-bar specimens with 5 different grinding grades were blasted to Sa2.5 grade and
coatings were applied on panels with the thickness of 900μm and 1,200μm in order
to evaluate the paint film’s crack resistance in terms of film thickness and surface
preparation methods.
Ø Crack resistance test (thermal cycles: 4hours at -20℃, ramp to 60℃ for 2hours,
4hours at 60℃ and drop to -20℃ for 2hours) was carried out in a humidity controlled
chamber in accordance with HHI’s crack resistance test method.
80
60

40
Temp.(℃)

20
0

-20
-40
0 2 4 6 8 10 12 14 16 18 20 22 24
Hour
[ Thermal cyclic test condition ] [ Humidity controlled chamber ] 13
 3. Results and discussion

<Crack resistance test result>

Grade G1 G2 G3 G4 G5

Film
thicknes
s (900μm)
Crack

Film
thicknes
s
(1200μm)

14
 3. Results and discussion

Ø All cracks were found out at the borderline between welding bead and
steel plate, not at the valley of weld ripple.
Ø Therefore, it can be concluded that the coating crack on the welded joints is not
affected by the surface preparation methods such as the P3 grinding and blast
cleaning.

<Crack resistance test(crack initiation)>

80
900㎛ <The location of crack generation>
1,200㎛
60
Cycles

40 Crack

20 HHI acceptance criteria: > 30cycles

0
G1 G2 G3 G4 G5
Surface treatment grade 15
4. Conclusion
1) Considering the fact that the basic background for the request of application of P3 on the welding
lines is securing the specified paint film thickness on the welding bead surface, it is reasonably
certain that the existence of local points lower than target film thickness and the possibility of
crack
occurrence due to localized over film thickness should be a standard of judgment in clearing the
interpretative problem of ISO 8501-3(Multi pass) and ISO 12944-3(Single pass).

2) Based on film thickness distribution, corrosion and crack resistance tests, it was found that all test
specimens after 2nd surface preparation have enough smooth surfaces, which could be completely
wetted by commercially available paint regardless of steel preparation (P3) grade, and coating
performance including corrosion resistance is governed by 2nd surface preparation stage not by
steel
preparation (P3).

3) By evaluating the influence of surface preparation (steel preparation (P3) & abrasive blasting) and
paint film thickness distribution on coating performance, it was identified that a primary factor in
determining the lifetime of coated film of marine structure is the 2nd surface preparation(abrasive
blasting) process rather than steel preparation (P3). This means that there was no necessary to
16
grind
Thank you
Any Questions?
 “Effect of Surface Preparation Grades of Weld Seam on the Coating
Performance in Marine Structures”

By Sangmoon Shin

Presented at SSPC 2018

January 15 – 18 , 2018
New Orleans, LA

Notice: This paper was presented by the author(s) or assigned speakers at the SSPC 2018 conference as indicated above. SSPC:
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 Effect of Surface Preparation Grades of Weld Seam
on the Coating Performance in Marine Structures

Sang-Moon Shin*, Chung-Seo park, Seung-Gon Choo, Eun-Ha Song and Han-Jin Bae

Protective coating Research Department Hyundai Heavy Industries

1000 Bangeojinsunhwan-doro, Dong-gu, Ulsan, South Korea

ABSTRACT: According to the international surface preparation standard for welds

(ISO8501-3), the preparation grades before the application of paints are divided into 3
levels, P1, P2 and P3. These grades are described with rough qualitative representations,
not description of surface treatment methods or measurable conditions. Because of the
ambiguous wordings on the standard, there have been a lot of arguments for the surface
preparation grades and abraded condition during the construction.
In this study, coating thickness, the corrosion resistance and crack tendency of the
coated films on the welds were evaluated for the grinding range in 5 levels from mild to
severe. Each grinded specimen was blasted to Sa 2.5 and coated with 2 coats of epoxy
paints. The performances of coatings on welds with the grades of grinding condition were
not significantly different, satisfying the criteria of ISO 12944 (C5-M medium). After
blasting, all of grinded specimens showed smooth surface which can not make a sharp
edge or excessive film thickness.
 Introduction

Proper surface preparation is essential to ensure the coating performance. The

performance of coatings applied to steel is significantly affected by the condition of the
substrate prior to painting. Imperfection in the substrate should be rectified with proper
surface preparation method. Preparation grades on welds are described in ISO 8501-3.

Ÿ P1: No preparation
Ÿ P2: Surface shall be dressed to remove
irregular and sharp edged profiles
Ÿ P3: Surface shall be fully dressed, i.e. smooth

Figure 1 Preparation grades on welds (ISO 8501-3)

P3 grade of the ISO 8501-3 on the welding line is required to achieve a specified coating
thickness and prevent a coating crack in the irregular shape of the substrates. However, due
to the ambiguity of expression in international standard (ISO 8501-3), there are a lot of
arguments on the surface preparation grade and criteria for the acceptance or refusal in a
working stage.
In this study, coating performance and defects were evaluated on the various condition
of surface treatment, to verify the effect of the surface treatment grade if the welding
beads and clarify the criteria of the surface treatment.
Visual Inspection of Surface Treatment on the Welding Line
T-bar specimens were made by welding with typical bead sequence as shown in Figure 2.
Prior to coating application, weld seams and sharp edges of the T-bar specimens were
ground into five different grades (No treatment, Soft, Middle, Hard and Very hard), and
followed by blasting process.
As shown in Table 1, abrasive blasting as a secondary surface preparation makes the
irregular welding bead smooth. After blasting, even the G1 (No treatment) specimen did not
show the sharp edges or irregularity.

(a) T-bar (b) Weld image

Figure 2 Configuration of test specimens

Table 1 The appearance of specimens with 5 grades of surface preparation

Surface treatment
Grade
Step 1 : Grinding Step 2 : Blasting (Sa 2.5)

No Grinding
G1

Soft
G2

Medium
G3
 Hard
G4

Very hard
G5

Measurement of Coating Film Thickness on the Welding Line

After blasting to Sa 2.5 (surface profile; 30~75 μm), two kinds of coating system (Table 2)
were applied by airless spray pump. Coating thickness of the welding area was analyzed
using an electro-microscope with the 50 times scale. As shown in Table 3, coating film
thicknesses at the valley location (1, 3 and 5) were higher than others (location 2 and 4) due
to its concave configuration. However, average coating thickness for each surface treatment
grade was not significantly different.

Table 2 Test coating system

Coat System 1 System 2
st
1 coat Epoxy 160 μm Epoxy 160 μm
Stripe Coat N/A Epoxy 50 ~ 80 μm
2nd coat Epoxy 160 μm Epoxy 160 μm

Table 3 Results of coating film thickness measurements

(a) System 1 (μm)
Sector G1 G2 G3 G4 G5
1 314 346 349 343 303
2 326 343 351 349 323
3 423 371 398 383 325
4 329 435 376 350 310
5 357 294 483 392 340
Avg. 322 344 362 360 296

Sectional
view

(b) System 2 (μm)

Sector G1 G2 G3 G4 G5
1 443 362 447 424 343
2 369 358 410 437 323
 3 485 401 399 441 378
4 358 313 395 516 331
5 463 422 560 468 347
Avg. 384 342 429 437 330

Sectional
view

Corrosion Resistance
T-bar specimens with 5 different grinding grades with two coats of epoxy paint for dry
film thickness of 320 μm (160 μm × 2) were cured for 4 weeks at 25℃. After curing of
the test panels, salt spray test was conducted to evaluate corrosion resistance in
accordance with ISO 12944-2 & 6 (C5-M very high, salt spray test for 1,440 hours).
After the salt spray exposure, any corrosion-related defects (Blistering, Delamination and
Rust creepage) were not found in all of the test specimens. Also, degree of undercutting
from the scribed line was below 1mm as shown in Table 4.
From these results, it can be concluded that the corrosion resistance of the test panels
prepared with 5 different grinding grades is almost the same, satisfying the ISO 12944 C5-M
criteria.

Table 4 Rust creepage from the scribe line after salt spray exposure for 1,440 hours
Grade Configuration Rust creepage

G1 < 1mm

G2 < 1mm

G3 < 1mm

G4 < 1mm
 G5 < 1mm

Crack Resistance
T-bar specimens with 5 different grinding grades were blasted to Sa 2.5 and selected
coatings were applied to 900 μm and 1,200 μm, respectively.
After curing of test panels, crack resistance test were carried out by means of thermal
cyclic test (4hours at -20℃, ramp to 60℃ for 2 hours, 4hours at 60℃ and down to -20℃
for 2 hours).
From the crack resistance test, it was found that crack resistance results of the test
panels with 5 different grinding was almost similar, as shown in Figure 3. The number of
cycles of crack initiation was 58 ~ 60 at 900 μm dry film thickness and 54 ~ 58 at 1,200 μm
dry film thickness, which are much higher than HHI’s acceptance criteria (> 30 cycles).

80
900㎛
※HHI acceptance criteria: > 30cycles 1,200㎛
60
Cycles

40

20

0
G1 G2 G3 G4 G5
Surface treatment grade
Figure 3 Crack resistance test results (the number of cycles of crack initiation)
 CONCLUSIONS

To verify the effect of surface treatment grade on the welding beads and clarify the
criteria of the surface treatment, paint film thickness distribution, crack resistance and anti-
corrosion performance were evaluated for the grinding range in 5 levels from mild to severe.
Based on the paint film thickness measurement results, it was found that all test
specimens after 2nd surface preparation (abrasive blasting) had enough smooth surfaces,
which could be completely wetted by coating materials regardless of steel preparation grade.
Also, coating performance of all test specimens satisfied the ISO 12944 C5-M criteria with
uniform film thickness. That means a primary factor in determining the lifetime of coated
film of marine structure is the 2nd surface preparation process rather than steel grinding
preparation (P3). Thus, it is not necessary to grind the excessively before the 2nd surface
preparation to achieve a uniform film thickness on the welding beads.
Sang Moon Shin, Hyundai Heavy Industries

Sang Moon is currently employed at HYUNDAI HEAVY INDUSTRIES within the Protective Coating Research
Department, some current project include: the epoxy coating development of the discoloration resistance
for the ship, and the optimization of the painting process about marine and engine.

Previous employment includes: KCC Corporation. While with KCC, he worked on a number of projects,
some coating formulation design, performance evaluation of films and some improved film performance-
including drying time and corrosion resistance for marine and heavy duty.