Do Pipe Leg Towers Rust from the Inside out?

Ever since the introduction of pipe leg towers the suppliers of angle only towers have been trying to convince customers that pipe leg towers cant be trusted because they will rust from the inside out and will fail without warning!

Common sense would raise a flag to the argument about pipe legs rusting from the inside out since by the very nature of a pipe the inside is shielded from  outside corrosive elements by the pipe itself.  As proof of the condition Rohn Products International installed a 90m Self supporting tower near the Red Sea port of Jeddah, Saudi Arabia downwind from a desalinization plant. Over time due to the constant attack from sand together with salt water spray the top of the tower lost its primary protection from the galvanizing.  Despite regular maintenance it was decided to replace the top sections after about 30 years of service in what could be described as an accelerated life expectancy test environment.  When the pipe leg material was brought to the ground it was decided to open the legs and answer the age old question of whether pipe legs rust from the inside out or not.  The leg flange plates were cut off and the pipes cut in half to fully expose the inside.   With the exception of natural graying in the color of the galvanizing from the original shiny finish of new galvanizing the inside was in perfect condition and the thickness of the galvanizing still compliant with the original EIA/TIA specification.

Are 4 leg towers stronger than 3  leg towers?

Like any well engineered product or project the design engineer starts with a performance specification from the customer or end user.  When the customer specifies the performance in a competitive bid environment all of the bidders will tailor their design to meet the performance specified by the client without exceeding it or they will risk their bid price disqualifying them  due to overdesign.  The answer to this question is that towers which meet the design criteria and do not exceed it are equal.

tower mountain

 

What is the best way to compare a 3 leg pipe tower to a 4 leg angle tower?

All too often customers compare costs on a material only basis not considering all the cost involved in building a tower site.    A performance comparable all angle 4 leg tower typically requires 20-25% more steel than a comparable 3 leg pipe tower. This is partially due to the greater strength of pipe steel versus angle steel in a kilogram by kilogram comparison.  Pipe also benefits from shape factor advantages of up to 33% right in the basic engineering calculations that angle does not benefit from, due to  the more aerodynamic shape of the pipe.

The cost to manufacture the angle tower is typically less on a weight comparison basis but once you factor in foundation cost, erection cost and time to get the site on the air the overall cost of a 3 leg pipe tower is typically less.

Some other reasons for this include that the 4 leg all angle tower typically has significantly more pieces including nuts and bolts and splice plates and other connection components that  are needed to assemble the tower.  The 3 leg pipe tower normally includes integrally welded connection components which actually eliminates many of the extra pieces that are needed in the all angle tower. Although the 3 leg pipe tower can be more expensive than the 4 leg all angle tower when compared on a kilogram by kilogram basis, installation is much easier, faster and less expensive.  The angle tower on the other hand can be fabricated from less costly angle rather than pipe and it can be fabricated in a computerized angle line.  The best way to compare costs is on an installed basis so the owner doesn’t have to try to calculate the pros and cons of each type of tower – simply compare the bottom line or installed cost and then look to see if there is any further benefit to being on air faster!