Is it okay for copper water pipes to cross and rest on gas pipes so the gas pipes support the water pipes? One of the leaking water pipes rusted a gas pipe.



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No, it is not ok.

Very bad idea, separate then asap.

Copper is a more noble metal than steel generally the less noble metal will corrode first. Having 2 dissimilar metals touching is essentially a battery you get what is called a galvanic reaction, They should not touch directly. Here is a nobility chart for some interesting reading...

Galvanic Series - Scale of Nobility

Whenever two different metals are placed in contact with each other, a galvanic reaction occurs which causes corrosion in the metal(s). Sometimes this can be used to our advantage - for example galvanising is zinc and steel (iron), and the zinc will corrode to protect the steel. This mix of metals is intentional and the zinc is regarded as sacrifical.
However it is not always intuitive which metal will corrode. The table below lists various metals on the Scale of Nobility where for any combination of two dissimilar metals, the metal with the lower number will preferentially corrode (act as an anode) and protect the metal with the higher number (cathode). In the table below, zinc is No.4 and steel is No.30, so the zinc will corrode to protect the steel.
Galvanic Series in Salt Water
Scale of Nobility: least noble to most noble
Anode or base end ( + )
1. Magnesium
2. Mg alloy AZ-31B
3. Mg alloy HK-31A
4. Zinc (hot-dip, die cast, or plated)
5. Beryllium (hot pressed)
6. Aluminium 7072 clad or 7075
7. Al2014-T3
8. Al 1160-H14
9. Al 7079-T6
10. Cadmium (plated)
11. Uranium
12. Al 218 (die cast)
13. Al 5052-0
14. Al 5052-H12
15. Al 5456-0, H353
16. Al 5052-H32
17. Al 1100-0
18. Al 3003-H25
19. Al 6061 -T6
20. Al A360 (die cast)
21. Al 7075-T6
22. Al 6061-0
23. Indium
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
29. Lead
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (plated)
36. Tantalum
37. AM 350 (active)
38. Stainless steel 310 (active)
39. Stainless steel 301 (active)
40. Stainless steel 304 (active)
41. Stainless steel 430
42. Stainless steel 410
43. Stainless steel 17-7PH
44. Tungsten
45. Niobium (columbium) 1%Zr
46. Brass, yellow, 268
47. Uranium 8% Mo

48. Brass, naval (Tobin), 464
49. Yellow Brass
50. Muntz metal 280
51. Brass (plated)
52. Nickel-silver (18% Ni)
53. Stainless steel 316L (active)
54. Bronze 220
55. Copper 110
56. Brass, red
57. Stainless steel 347
58. Molybdenum, commercial pure
59. Copper-nickel 715
60. Brass, Admiralty
61. Stainless steel 202 (active)
62. Bronze, phosphor 534 (B-1)
63. Monel 400
64. Stainless steel 201
65. Carpenter 20 (active)
66. Stainless steel 321 (active)
67. Stainless steel 316 (active)
68. Stainless steel 309 (active)
69. Stainless steel 17-7PH (passive)
70. Silicone bronze 655
71. Stainless steel 304 (passive)
72. Stainless steel 301 (passive)
73. Stainless steel 321 (passive)
74. Stainless steel 201 (passive)
75. Stainless steel 286 (passive)
76. Stainless steel 316L (passive)
77. AM355 (active)
78. Stainless steel 202 (passive)
79. Carpenter 20 (passive)
80. AM355 (passive)
81. A286 (passive)
82. Titanium 5A1, 2.5 Sn
83. Titanium 13V, 11Cr. 3A1 (annealed)
84. Titanium 6A1, 4V (solution treated and aged)
85. Titanium 6A1, 4V (annealed)
86. Titanium 8Mn
87. Titanium 13V, 11 Cr3A1 (solution heat treated & aged)
88. Titanium 75A
89. AM350 (passive)
90. Silver
91. Graphite
92. Gold
93. Platinum
Cathode or noble end ( - )
Note: For any combination of dissimilar metals, the metal with the lower number will preferentially corrode (act as an anode) and protect the metal with the higher number (cathode).

PlumbCat TM 2003


Plumbermandan

I guess this explains why water heater anodes usually contain aluminum or better yet, magnesium.

Thanks for the replies all. Exactly what I thought. Does anyone know if local plumbing codes usually address this issue?



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just put some pipe insulation between the two.

Edited 1 times.

But in ALL cases, there has to be an "electrolyte", usually water, for the reaction to occur. Two metals touching without the electrolyte have NO reaction.

One pipe rubbing against the other would be the real problem in your case, and since copper is the softer metal, it could fail first.

That's what happened here. The water pipe had a very small leak, so small that it never dripped to the floor, just wet the gas pipe underneath it, which was heavily rusted.

This is in a multi-unit building. I found the problem while trying to find out how plumbing noise was telegraphing through the exposed gas pipe in my living room. The sound telegraphs and amplifies so that the sound coming from the pipe in my apartment is much louder than the noise in the basement by the pipe or at the faucet. There are gas and water pipes crisscrossing tightly in many place. The noise is annoying but the gas pipe corrosion is dangerous.

Property manager is unconcerned.

No room for standard pipe insulation. Hardly room to force a piece of cardboard between them.

can you tap a wood shingle inbetween ?

or a piece of roofing felt?