Study 1: Metallurgical Evaluation Report

Analysis of Weld Insert Rings for Use with AL-6XN
This is a summary of a confidential report in regards to the use of three (3) different shapes of weld insert rings for use when welding AL-6XN alloy.

The reason for the commissioning of this report was to determine the best shape of insert ring for use in regards to alloy mixture and weld finish profile. We studied three (3) styles of rings fabricated from alloy 625 material. The geometric styles were:

1. Inverted "T" or internal ring
2. Conventional "T" or external ring
3. Flat washer style with no shoulder

The findings supported the use of the flat washer style ring for alloy mixture and weld quality. For additional information or discussion, please contact CSI at 800.654.5635.

Responsible Testing Party: Metals and Materials Consulting Engineers LLC
Mr. John Tverberg, P.E. is the managing partner of Metals & Materials Consulting Engineers and the former Vice President of Technology for Trent Tube, E. Troy, WI. He has both a B.S. and M.S. in Metallurgical Engineering, and a minor in Physical Chemistry from the University of Arizona. He was an exchange scientist with EURATOM in Germany. His career includes nuclear power, heat transfer, alloy design and industrial systems design. He is a member of ASME, ASM International, NACE and ISPE. He served as chairman of the ASME Heat Exchanger Committee, and is past chairman of the Columbia Basin Chapter of ASM. He is a licensed professional engineer, and the author of numerous technical papers.

Study 2: Metallurgical Evaluation Report

Analysis of AL-6XN Weld Discoloration
This is a summary of a confidential report in regards to the discoloration typically found in and around the welds when welding AL-6XN material. This discoloration consists of areas of "white" and "dark" on both the inside and outside.

The reason for commissioning this report was to determine: 1) the origin and composition of the contaminants, and 2) the impact, if any, the contaminants have upon the integrity and subsequent corrosion resistance of the material.

Our report answers the questions above in detail, however in summary:

1. The weld discoloration has its origins from inclusions in the steel that are obtained from the steel-making process or enter as tramp elements from the use of scrap at the mill.
2. The weld discoloration appears to have no effect on corrosion resistance of the weld or surrounding area.
3. It appears nothing can be done to eliminate the discoloration in the welds.
4. The "white" areas are clean surfaces and are free of oxides and nitrides.
5. The "dark" areas are from inclusions in the steel and are composed of a mixture of oxides, silicates and nitrides, which appear to be stable and were not attacked in a very aggressive corrosion test.

For additional information or discussion, please contact CSI at 800.654.5635.

Responsible Testing Party: Metals and Materials Consulting Engineers LLC
Mr. John Tverberg, P.E. is the managing partner of Metals & Materials Consulting Engineers and the former Vice President of Technology for Trent Tube, E. Troy, WI. He has both a B.S. and M.S. in Metallurgical Engineering, and a minor in Physical Chemistry from the University of Arizona. He was an exchange scientist with EURATOM in Germany. His career includes nuclear power, heat transfer, alloy design and industrial systems design. He is a member of ASME, ASM International, NACE and ISPE. He served as chairman of the ASME Heat Exchanger Committee, and is past chairman of the Columbia Basin Chapter of ASM. He is a licensed professional engineer, and the author of numerous technical papers.

Study 3: Metallurgical Evaluation Report

Corrosion Evaluation of AL-6XN Stainless Steel Welds
This is a summary of a confidential report in regards to the corrosion resistance of AL-6XN alloy welded samples utilizing a combination of eight (8) different material joinings or weld procedures representing various assembly conditions in which AL-6XN stainless steel is used in service.

The report was commissioned to: 1) establish the corrosion resistance of the metal in various welded forms, 2) establish the best joining method for use in service, and 3) evaluate the effectiveness of a post weld heat treatment as compared to the use of weld insert rings. Metallurgical evaluation included:

1. X-Ray weld quality
2. Surface morphology using Scanning Electron Microscopy
3. Metallographic cross sections of each weld
4. Weld corrosion testing

Test Samples:

1. AL-6XN tube autogenously butt-welded to an AL-6XN ferrule. This assembly was then welded autogenously to a patented 316L stainless steel slip collar. The entire assembly was post weld heat treated to CSI specification 1202 Rev. 0. The annealed assembly was then seal welded both sides at the 316L spool location through a 304L stainless steel plate.
2. AL-6XN tube butt-welded to an AL-6XN ferrule utilizing an Alloy 625 weld insert ring. This assembly was then autogenously seal welded both sides through a 316L stainless steel plate.
3. AL-6XN tube butt-welded to an AL-6XN ferrule utilizing an Alloy 625 weld insert ring. This assembly was then seal welded using alloy 625 weld wire one side into a 304L stainless steel plate.
4. 316L stainless steel proximity switch autogenously welded to AL-6XN alloy tubing. The entire assembly was then post weld heat treated to CSI specification 1202 Rev.0.
5. 316L stainless steel proximity switch welded to AL-6XN alloy tubing utilizing alloy 625 weld wire.
6. 316L stainless steel proximity switch autogenously welded to AL-6XN alloy tubing.
7. AL-6XN tube autogenously seal welded both sides through AL-6XN alloy plate. The entire assembly was then post weld heat treated to CSI specification 1202 Rev.0.
8. AL-6XN tube seal welded utilizing alloy 625 weld wire both sides through AL-6XN plate.

Test Method:

A modified ASTM G-48 Practice C corrosion test was use to examine the relative pitting resistance of the samples. This test is a modified immersion test for stainless steel and related alloys using acidified ferric chloride. Conditions selected were 72 hours in 6% FeCl₃ + 1% HCl at 50° C. This corrosion test is far more severe than the normal crevice test of standard pitting test for AL-6XN stainless steel.

Results:

1. The best tube to ferrule weld (samples 1, 2, & 3) is the heat treated autogenously welded sample (sample 1). Heat treatment resulted in complete recrystallization and caused grain growth to extend from the weld nugget through the heat affected zone and into the base metal. There appears to be sufficient alloy diffusion to restore the corrosion resistance properties of the base metal.
2. Use of the collar welded to the tube (sample 1) and heat treated appears to give a metallurgically sound and corrosion resistant weld.
3. Use of weld filler on the heavy panel sections to the thin tube may be risky. Too much heat in the weld may cause chi phase formation on the tube ID and create corrosion problems.
4. Autogenous welding of proximity stem bases (samples 4, 5, & 6) appears adequate. Heat treatment or the addition of alloy 625 filler metal in this case does not give enough product improvement to justify the cost.
5. Both jacketed assemblies (Samples 7 & 8) are equivalent and show no evidence of corrosion.

For additional information or discussion, please contact CSI at 800.654.5635.

Responsible Testing Party: Metals and Materials Consulting Engineers LLC
Mr. John Tverberg, P.E. is the managing partner of Metals & Materials Consulting Engineers and the former Vice President of Technology for Trent Tube, E. Troy, WI. He has both a B.S. and M.S. in Metallurgical Engineering, and a minor in Physical Chemistry from the University of Arizona. He was an exchange scientist with EURATOM in Germany. His career includes nuclear power, heat transfer, alloy design and industrial systems design. He is a member of ASME, ASM International, NACE and ISPE. He served as chairman of the ASME Heat Exchanger Committee, and is past chairman of the Columbia Basin Chapter of ASM. He is a licensed professional engineer, and the author of numerous technical papers.

Study 4: Material / Weld Corrosion Study per ASTM G-48 Practice C

Corrosion Test 1 ASTM G-48 Practice C (modified immersion test) 6% FeCl3 + 1% HCl at 50 °C (122 °F) for 72 hours Each test run independently with fresh solution	Sample: AL-6XN Tube 316L Stainless Steel Collar 304 Stainless Steel Plate
Left: This sample represents the piece prior to testing. Right: This sample represents the test results after immersion in the test solution.

Corrosion Test 2 ASTM G-48 Practice C (modified immersion test) 6% FeCl3 + 1% HCl at 50 °C (122 °F) for 72 hours Each test run independently with fresh solution	Sample: AL-6XN Tube AL-6XN Tube Automatic fusion weld, no insert ring
Top: This sample represents the piece prior to testing. Bottom: This sample represents the test results after immersion in the test solution.

Corrosion Test 3 ASTM G-48 Practice C (modified immersion test) 6% FeCl3 + 1% HCl at 50 °C (122 °F) for 72 hours Each test run independently with fresh solution	Sample: AL-6XN Tube AL-6XN Tube Automatic fusion weld Alloy 625 washer style insert ring
Top: This sample represents the piece prior to testing. Bottom: This sample represents the test results after immersion in the test solution.

Corrosion Test 4 ASTM G-48 Practice C (modified immersion test) 6% FeCl3 + 1% HCl at 50 °C (122 °F) for 72 hours Each test run independently with fresh solution	Sample: AL-6XN Tube AL-6XN Tube Automatic fusion weld, no insert ring - full solution anneal after welding @ 2100 °F with rapid nitrogen quench
Top: This sample represents the piece prior to testing. Bottom: This sample represents the test results after immersion in the test solution.

Corrosion Test 5 ASTM G-48 Practice C (modified immersion test) 6% FeCl3 + 1% HCl at 50 °C (122 °F) for 72 hours Each test run independently with fresh solution	Sample: AL-6XN Tube 316L Tube Automatic fusion weld, no insert ring, no anneal
Top: This sample represents the piece prior to testing. Bottom: This sample represents the test results after immersion in the test solution.

	Ask a Question

For more information about the corrosion studies you've seen on this page or how AL-6XN could benefit your process, give us a call today at 800.654.5635.