bonding a short section of water supply pipe

davezawadi (David Stone):

Whilst those numbers are correct for Brinell hardness they do not really relate to the case. They are obtained by pressing a 4 sided diamond into a thick block of the material with a known load and measuring the depression. The reason I said that annealed copper was softer is that the thin sections used in pipes behave by deflection not much dependant on the hardness, but the material modulus. A BS951 clamp cannot apply enough force to deform a lead gas pipe (about 4-5mm wall) very much, whereas a 0.8mm thick copper one (particularly if soft annealed like microbore pipes or well heated and cooled larger ones). The clamp itself is designed to spread the clamping force around much of the pipe diameter, and generally prevents very much deformation of the circular shape which is inherently very strong (think of bridge arches). I think your fears are groundless, but you may care to try it one day when you find an odd bit of lead (although often a harder alloy called compo in times past) pipe. The wide ranges of the number for Brinell hardness are caused by the wide range of tempers of the material, depending on mechanical and heat treatments before you get it. Take aluminium alloys, for example, T6016 which is used for many purposes including aircraft. Its strength (or stiffness) can be varied across a wide range by heat treatment, the strongest and stiffest being T6016-T6. The same annealed correctly is very soft and easily bent, the -T6 is very stiff indeed. Neither copper or lead pipe will be punctured by mechanical deformation unless very severe, the copper being the most susceptible because it work hardens and becomes brittle.

I did read some time ago about an apprentice that tightened a B.S. 951 earthing clamp on a copper pipe so tight that he punctured the water pipe.


Z.

davezawadi (David Stone):

Whilst those numbers are correct for Brinell hardness they do not really relate to the case. They are obtained by pressing a 4 sided diamond into a thick block of the material with a known load and measuring the depression. The reason I said that annealed copper was softer is that the thin sections used in pipes behave by deflection not much dependant on the hardness, but the material modulus. A BS951 clamp cannot apply enough force to deform a lead gas pipe (about 4-5mm wall) very much, whereas a 0.8mm thick copper one (particularly if soft annealed like microbore pipes or well heated and cooled larger ones). The clamp itself is designed to spread the clamping force around much of the pipe diameter, and generally prevents very much deformation of the circular shape which is inherently very strong (think of bridge arches). I think your fears are groundless, but you may care to try it one day when you find an odd bit of lead (although often a harder alloy called compo in times past) pipe. The wide ranges of the number for Brinell hardness are caused by the wide range of tempers of the material, depending on mechanical and heat treatments before you get it. Take aluminium alloys, for example, T6016 which is used for many purposes including aircraft. Its strength (or stiffness) can be varied across a wide range by heat treatment, the strongest and stiffest being T6016-T6. The same annealed correctly is very soft and easily bent, the -T6 is very stiff indeed. Neither copper or lead pipe will be punctured by mechanical deformation unless very severe, the copper being the most susceptible because it work hardens and becomes brittle.

I did read some time ago about an apprentice that tightened a B.S. 951 earthing clamp on a copper pipe so tight that he punctured the water pipe.


Z.