acid immersion test - doxsteel fasteners€¦ · the acid immersion test is one of the quickest...

Acid Immersion TestASTM G31 STANDARD GUIDE FOR LABORATORY IMMERSION CORROSION TESTING OF METALS

The acid immersion test is one of the quickest ways to see how well Doxsteel Fasteners hold up to corrosive environments. Our bolts are submerged in an acid solution for seven days and monitored to see how much mass is lost. We often perform this test for visitors to our lab, placing an immersed Doxsteel Fastener side by side with a bolt from a leading competitor. The competitor’s bolt reacts immediately while the Doxsteel Fastener stands strong.

COATINGS EVALUATIONS INMERSION TEST ASTM G31

281-298-1500 | [email protected] | doxsteel.com1544 Sawdust Rd #301 | The Woodlands, TX 77380

COATING CORROSION RATE (g)

BEST RESULTS

CORROSION RATE (g)

AVERAGE (200 TESTS)

Cadmium Plating 2.3820 3.0290

Hot Dip Zinc 2.0250 4.0120

Zinc Plating 1.8380 3.2500

Zinc Plating + PTFE 0.0930 0.6320

Ceramic + PTFE 0.1260 0.7450

Zn-Ni Plating 1.1210 2.1430

doxsteelfasteners 0.0037 0.0100

Stork Testing & Metallurgical Consulting

222 Cavalcade Street, 77009-3213 P.O. Box 8768, Houston, Texas 77249-8768

Tel: (713) 692-9151 Fax: (713) 696-6205 Attention: Miguel Angel Rodriguez Aguilar Doxsteel, LLC 6 South Berryline SPRING, TX 77381 P: / F:

W/O. No.: P.O. No.: Report Date:

PRO002-04-21-80450-1 23 4/21/2011

Testing Laboratory Certificate Number 1480-05

Respectfully Submitted:

Our letters and reports are for the exclusive use of the client to whom they are addressed and shall not be reproduced except in full without the approval of the testing laboratory. The use of our name must receive our written approval. Our letters and reports apply only to the sample tested and/or inspected, and are not indicative of the quantities of apparently identical or similar products. Unless otherwise noted all test methods and specifications are to the most current revision. Material submitted to our metals department will be discarded after a period of 30 days unless otherwise directed. Stork Testing & Metallurgical Consulting is an operating unit of Stork Materials Technology B.V., Amsterdam, The Netherlands, which is a member of the Stork group

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Acid Immersion Test of Coated Nuts and Bolts

This report is a compilation of data generated for STMC work orders; PRO002-02-22-78042 and PRO002-03-31-79691 and covers testing of studs and nuts using various protective coatings and of various typical materials used in bolting.

This document contains technical data whose export and re-export/re-transfer is subject to control by the U.S. Department of Commerce under the Export Administration Act and the Export Administration Regulations. The Department of Commerce’s prior written approval is required for the export or re-export/re-transfer of such technical information to any foreign person, foreign entity or foreign organization whether in the United States or abroad.


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Index 1. Introduction ....................................................................................................................................3

1.1. Studs ......................................................................................................................................3 1.2. Nuts........................................................................................................................................3

2. Testing............................................................................................................................................4

2.1. Solution..................................................................................................................................4 2.2. Test Regime ...........................................................................................................................4

3. Test results......................................................................................................................................5

3.1. Stud Test Data ........................................................................................................................5

3.1.1. Results Analysis.............................................................................................................5

3.2. Nuts Test Data........................................................................................................................6

3.2.1. Results analysis ..............................................................................................................6

4. Discussion ......................................................................................................................................7

4.1. Studs ......................................................................................................................................7 Figure 1 Left to right, un-tested sample and tested samples...........................................................8 Figure 2 Zinc coating as received and after test (lower) ................................................................9 Figure 3 Zinc coated stud at liquid/air interface .......................................................................... 10 Figure 4 Fluropolymer as received and after test (lower) ............................................................ 11 Figure 5 DOX ® as received and after test (lower) ..................................................................... 12 Figure 6 Cadmium coated as received and after test (lower) ....................................................... 13 Figure 7 Cadmium plated stud at liquid/air interface showing red rust in oxygenated region....... 14

4.2. Nuts...................................................................................................................................... 15 Figure 8 Zinc plated nut showing pitting attack as well as total removal of external plating ........ 16 Figure 9 Cadmium plated nut showing pitting as well as plating removal ................................... 17 Figure 10 A representative fluroplymer coated example showing no visual changes (PCI 3P)..... 18 Figure 11 Dox ® example showed some slight discoloration ...................................................... 19 Figure 12 B5 nuts had a lightly adherent black deposit on the whole surface............................... 20 Figure 13 NiCu400 showed a cleaning effect after immersion .................................................... 21 Figure 14 C276 sample showed slight cleaning of the blackened nuts recieved. ..........................22

5. Conclusions .................................................................................................................................. 23


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1. Introduction Stork Testing & Metallurgical Consulting, Inc. was asked to carry out acid immersion tests on a variety of studs and nuts covering 6 different coating types on threaded stud and 12 nuts with various coatings and of various material types. Testing was to provide a qualitative assessment of the coatings ability to withstand immersion in the test solution.

1.1. Studs The coatings on six studs were examined:

1) Zinc 2) Fluropolymer 3) DOX ® 4) Fluropolymer topcoat with Zinc plate basecoat 5) Fluropolymer topcoat with Ceramic metallic basecoat 6) Cadmium

All samples were supplied by the client or direct from various reputable industrial vendors to STMC.

1.2. Nuts 12 different nuts were testing covering a range of coatings and materials types. 3 nuts of each type were tested to provide an average, and rule out possible anomalous results due to damage or coating variations

1) Zinc 2) Cadmium 3) PCI3 - Fluropolymer only 4) PCI 3P - Fluropolymer with zinc base coat 5) PCI 3 Plus - Fluropolymer with ceramic base coat 6) DOX ® 7) B8M - 316 SS 8) B8T - 321 SS 9) B8C - AISI 347 SS 10) B5 - AISI 501 martensitic stainless steel 11) NiCu400 - Monel 12) C276 - Hastealloy

All nuts were 5/8”-11 and were supplied by the client or direct from various reputable industrial vendors to STMC.


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2. Testing

2.1. Solution A test solution was made up in accordance with client requirements consisting of: 1% H2SO4 - Sulfuric Acid 0.15% HNO3 - Nitric Acid 0.1% HCl - Hydrochloric acid - (Muriatic acid) Sufficient solution was made up to test all items to ensure consistent conditions between the tests

2.2. Test Regime All samples were washed and dried before commencement of testing, no solvents were used to ensure that no damage occurred to the coatings, and care was taken to ensure that threads etc. were not damaged to reveal the base material to the acid exposure. The stud samples were tested immersed to 2/3rds of their length in the solution a period of 1 week (7 days). The nut samples were tested fully immersed attached to studs of identical material type and or coating method. The samples were weighed before immersion and after the immersion period to give approximated weight losses and hence corrosion rates. Weighing after the immersion was carried out on washed and dried samples, but without any cleaning to remove adhered material etc. Care was taken at every step to prevent damage to the coatings, ensuring that the effects seen were those of the coatings reactions to the solution. Samples were photographed at the start and finish of the test. The stud samples were not consistent in diameter and thread pitch and different lengths of studding were used as available these differences were allowed for by rough calculations of immersed lengths and surface area.


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3. Test results

3.1. Stud Test Data

Pre test weight

Weight After

Immersion

Weight loss Sample

(g) (g) (g)

1- Zinc 114.8870 109.9600 4.9269

2- Fluropolymer 124.5930 124.0980 0.4947

3- DOX ® 57.2085 57.0190 0.1895

4- Fluropolymer topcoat with Zinc plate basecoat 44.2707 43.8823 0.3884

5- Fluropolymer topcoat with Ceramic metallic basecoat 127.1330 126.6440 0.4899

6- Cadmium 126.0900 121.2410 4.8490

3.1.1. Results Analysis Approximate corrosion rates for the stud were calculated per unit length of studding multiplied by the outer circumference of the studs (i.e. treating the stud as a smooth cylinder). It should be noted that these values are nominal as they are not based on actual surface area (the end of the stud plays a significantly larger part in total surface area on the shorter studs), and the actual surface to the threads. It also makes no allowances for potential increased corrosion rates at the liquid air interface. The values can however be used for comparison purposes to rank the tests relative to each other, more stringent corrosion rate calculations would require more rigorous testing methodology.

1 2 3 4 5 6 Sample

Zinc Fluropolymer DOX®

Fluropolymer topcoat with Zinc plate basecoat

Fluropolymer topcoat with

Ceramic metallic basecoat

Cadmium

Stud Diameter cm 1.580 1.551 1.243 1.245 1.562 1.538 Total length cm 9.94 10.10 7.24 5.72 10.31 10.23 Immersed length (2/3) cm 6.62 6.73 4.83 3.81 6.88 6.82 Weight loss (g) 4.9269 0.4947 0.1895 0.3884 0.4899 4.8490 Weight loss g/cm2 0.150 0.015 0.010 0.026 0.015 0.147


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3.2. Nuts Test Data

Weights are in g

Pre test Weight

Weight After

Immersion

Weight Loss

Pre test Weight

Weight After

Immersion

Weight Loss

Pre test Weight

Weight After

Immersion

Weight Loss

Average

Sample 1 2 3 1 Zinc 48.8416 47.1644 1.6772 48.6662 46.6809 1.9853 48.9243 47.0714 1.8529 1.8385 2 Cadmium 51.0178 48.9386 2.0792 51.2124 48.6001 2.6123 51.3148 48.858 2.4568 2.3828 3 PCI3 48.2080 48.1562 0.0518 49.0025 48.6344 0.3681 47.8662 47.8377 0.0285 0.1495 4 PCI 3P 48.9573 48.7498 0.2075 49.1623 49.1388 0.0235 48.9591 48.9116 0.0475 0.0928 5 PCI 3 Plus 48.8359 48.7442 0.0917 48.7075 48.5361 0.1714 49.1774 49.0615 0.1159 0.1263 6 DOX ® 48.9283 48.9218 0.0065 48.8921 48.8917 0.0004 49.1062 49.102 0.0042 0.0037 7 316 SS 51.2224 51.2158 0.0066 51.1109 51.0964 0.0145 51.2842 51.2675 0.0167 0.0126 8 321 SS 51.2322 51.0975 0.1347 50.6927 50.5674 0.1253 51.0208 50.8658 0.1550 0.1383 9 347 SS 50.7478 50.6301 0.1177 49.6556 49.5347 0.1209 49.5422 49.4247 0.1175 0.1187 10 B5 53.2621 51.1220 2.1401 53.1472 51.1382 2.0090 53.4065 51.1603 2.2462 2.1318 11 NiCu400 58.3724 58.3637 0.0087 57.8617 57.8590 0.0027 58.2947 58.2900 0.0047 0.0054 12 C276 59.6686 59.6565 0.0121 58.1077 58.0944 0.0133 58.1045 58.0913 0.0132 0.0129

3.2.1. Results Analysis Rank Sample (g)

1 DOX ® 0.0037 2 NiCu400 - Monel 0.0054 3 316 SS 0.0126 4 C276 - Hastealloy 0.0129 5 PCI 3P Fluropolymer with Zinc base 0.0928 6 347 SS 0.1187 7 PCI 3 Plus - Fluropolymer with ceramic base 0.1263 8 321 SS 0.1383 9 PCI3 Fluropolymer 0.1495 10 Zinc 1.8385 11 B5 Martensitic Stainless 2.1318 12 Cadmium 2.3828

Samples ranked by average weight loss show the DOX® coated nuts to give nearly 2/3 the weight loss of the next nearest nut type tested. For the cadmium and zinc coated samples there was residual coating present in the thread area of the nut where it had been protected from attack by being mounted on a stud.


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4. Discussion

4.1. Studs The DOX coated stud showed the lowest total corrosive attack closely followed by the Fluropolymer topcoat with Ceramic metallic basecoat. The table below shows the coatings ranked from lowest to highest corrosion rates.

Coating method g/cm2 DOX® 0.010 Fluropolymer topcoat with Ceramic metallic basecoat 0.015 Fluropolymer 0.015 Fluropolymer topcoat with Zinc plate basecoat 0.026 Zinc 0.150 Cadmium 0.147

The Cadmium and Zinc gave the worst overall corrosion rates, at 15 times the rate of the DOX ® samples. The Fluropolymer/Zinc sample showed a mid way corrosion between the highest and lowest rates seen. The rate of attack was very clear on the Cadmium and Zinc coated studs, examining the samples for the first few hours showed a steady and heavy stream of bubbles being generated at the immersed surfaces. After 2 days this evolution became less obvious however the liquid steadily took on a “rust” color and by the end of the first test period the studs were almost completely obscured by the dissolved material. The remaining four samples showed some surface bubbles but these typically adhered to the surface and did not stream away. After the immersion it was noted that the immersed section of the Cadmium and Zinc plated studs showed no evidence of remaining deposit and that the immersed area was all “rust” colored. For the Cadmium plating the area in the ”splash zone”, where the air was in contact with the surface of the liquid showed rusting at the liquid surface but a different corrosion product in the bulk liquid. The DOX ® showed the lowest corrosion rate with the Fluropolymer and Fluropolymer/Ceramic samples tying. The Fluropolymer/Zinc coating showed early signs of its lowered protection levels over the other two Fluropolymers, any perforation of the external coating allowing direct access to the zinc of the acid solution, which would be attacked. The Zinc and Cadmium samples showed similar corrosion rates, but at rates 10 to 15 times higher than DOX ® and the Fluropolymers.


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Figure 1 Left to right, un-tested sample and tested samples

1) Zinc coating 2) Fluropolymer coating 3) DOX ® coating 4) Fluropolymer topcoat with Zinc plate basecoat 5) Fluropolymer topcoat with Ceramic metallic basecoat 6) Cadmium coating

1 5 3 4 2 6


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Figure 2 Zinc coating as received and after test (lower)

The un-immersed section of the stud is clearly visible at the left of the figure. The area immediately above the immersion line shows a limited attack from the vapor above the solution. The complete length of the immersed sample is free of any evidence of the coating and shows a uniform corrosion attack over the full surface.

Vapor area above liquid


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Figure 3 Zinc coated stud at liquid/air interface

Even in the area above the liquid surface the Zinc coating can be seen to be almost completely lost

Traces of coating in vapor area above liquid


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Figure 4 Fluropolymer as received and after test (lower)

The Fluropolymer only coated sample showed some coating loss at the immersed end of the stud, and even at the low magnification above breaks in the coating surface can be seen.


PRO002-04-21-80450-1 Page 12 of 23

Figure 5 DOX ® as received and after test (lower)

There was some discolorization of the immersed section of the stud and nut, and a matting of the surface in the vapor area. No attempt of cleaning was made other than washing so it is not known if this is a deposit or material loss

Discolored area in vapor above liquid


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Figure 6 Cadmium coated as received and after test (lower)

Complete removal of the coating is clearly seen in the photograph. The vapor area does not show the attack seen on the Zinc sample but there is a marked difference in the surface appearance in the area immediately below the surface of the liquid. This is the only one of the samples that appeared to show “normal” red rust attack on the underlying bolt material. As the depth below the surface increased the rust color disappeared and a darker rough general corrosion appears to have taken place.

Oxygenated Liquid surface area


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Figure 7 Cadmium plated stud at liquid/air interface showing red rust in oxygenated region

Three distinct zones, the almost undamaged Cadmium plate, a layer of red rust corrosion products, followed by general corrosion with no obvious adhered corrosion products


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4.2. Nuts Overall average weight losses during the test ranged from 0.0037g for the DOX ® coated material to 2.38 g fro the cadmium plated materials. Individual weight losses ranged from 0.0004g for a DOX ® treated nut to 2.6123g for a cadmium plated one. Obviously in the case of the cadmium and zinc coated nuts the weight loss is most probably primarily driven by the coating deposit which is stripped by the reaction. The DOX ® coated nut showed the least average weight loss during the test period with a weight loss of only about 25% of the C276 - Hastealloy material known for its corrosion resistance. The B5 martensitic stainless steel nuts showed a corrosion loss between the zinc and cadmium plated nuts, in this case the material is ferritic and does not have the corrosion resistance properties of an austenitic stainless, such as the 316SS nuts which showed corrosion losses similar to the C276 - Hastealloy nuts. Shown below are some of the tested samples compared with un-tested nuts, these are chosen to show those nuts that were affected by the immersions. Most of the stainless steel nuts showed a cleaning effect after immersion, with the darker coloration seen on the nuts being removed or loosened. The B5 martensitic stainless nuts were covered with a lightly adherent black deposit. While the zinc and cadmium plated nuts showed no only plating loss but pitting on the surface of the nuts as well as the base material was attacked by the acid solution.


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Figure 8 Zinc plated nut showing pitting attack as well as total removal of external plating


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Figure 9 Cadmium plated nut showing pitting as well as plating removal


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Figure 10 A representative Fluropolymer coated example showing no visual changes (PCI 3P)


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Figure 11 DOX ® example showed some slight discoloration


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Figure 12 B5 nuts had a lightly adherent black deposit on the whole surface


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Figure 13 NiCu400 (Monel) showed a cleaning effect after immersion


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Figure 14 C276 (Hastealloy) sample showed slight cleaning of the blackened nuts received.


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5. Conclusions The DOX® coated stud gave the highest resistance to the corrosive environment in this test, particularly over galvanic protection coatings which were rapidly removed by the acidic solution. The same is true of the DOX® coated nuts which gave virtually no measurable weight loss during the immersion.

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