Skin tags and crystalline spiders, skin tag irregularity or crystalline matrix upsets and non homogenized sections, in as-delivered material, are invisible in visual observation but may be present. The process to rule out this presence must be understood to ensure 100% zero defect in each individual part.

Fortunately, since the bicycle is the red headed step child of the aviation and aerospace industry, all necessary technical inspection procedures, techniques, tools and processes are readily available and updates to these processes are mandated to be ongoing.

Generally, advanced inspection procedure such as electron magnification in the construction of a bicycle is overkill but that overkill will be explained later and under certain circumstances might be applicable.

More common procedures such as the use of torsiometers (torsion- section meter) reactive dye check to detect spyders, crystal groups or full emerging cracks.

Measuring internal external (equal profile section) straightness checking

Specific gravity testing (for use in multiple builds in conjunction with /torsiometer tests to match tubing specifications when two or more bicycles are to be made as close to identical as possible.

Production runs vary from when the run begins and ends.  Factory production criteria allow for these variances.  A go/ no-go criteria exists in all mill runs.  Only items that grossly exceed the minimum criteria are scrapped.  Thus a supplier catalogs parts and tubes in a much more general manner than is apparent. To put that in a simple phrase, out of any given number of tubes, none will be totally identical .  Depending on the designed use, minor differences present no cause or effect to be considered in most cases, however, in tubing since each tube is in itself a single structure, at any point along that point (the skin) the tube performance can and will be different with each grain pattern.

Grain pattern- there are as many grain patterns in a mill run as the sands of time. As technology advances, much study is always invested in metal strengthening.  Currently NANO level metallurgy is being studied on all fronts.  New processes to homogenize are emerging.  More advance technologies to treat crystalline structures using methods involving cryogenics, thermo conditioning, chemical-thermo conditioning and  thermo-chemical crystal laminate bonding. (Ceramic like bonding of crystalline matrix)

In addition to inspection of products obtained through credible distribution, I must note that beginning with all mills, a process of culling removes non-conforming products from shipments. Unfortunately, this is not a completely foolproof or dependable process.  Articles culled are often pirated directly from the plant or from disposal areas relegated to surplus distribution or even offered as new products from distributors that specialize in buying them and redistributing them.

Learning inspection skills in addition to good business procedure and buying from reputable suppliers will provide the ultimate failsafe in knowing that the tube that you have just used in a construction is going to meet the needs of your design.

DEFINITIONS:
 Types of Skin tags: nearly all tubes contain skin tags of some sort

1.  Inclusion; general debris (can be small fragment of base material present from first drawing to final reeling)

2.  lubricating element

3.  First draw matrix non-homogenized portion

4.  In addition, occurs with damaged or bent mandrels allowing for improperly compressed material buildup (second most common)

Types of Spyders:

1.  Spydering automatically occurs in no-homogenized  crystalline structure along crystalline grain alignments

2.  Sypering occurs in focused over compression often caused by improper intermediate annealment during working the tube section

3.  Post draw construction spyders can occur when installing a water bottle box. ( High angle, high speed drill bits can initiate spyder, use of any type of pre drill alignment device such as a center punch in non annealed tubing will cause spyder in the crystalline matrix.

4. Machine mitering; high angle cutter, excessive feed speed, allowing cutter to chatter all automatically initiate spydering.

Types of crystalline matrix upset:

1.  These occur in all tubing and sheet metal structures.  the most simple explanation is lack of homogenized raw materials.

2.  Minor upsets will precipitate (increase) under certain heating cycles

3.  As mill delivered, tubing can change or upset at matrix level by improper heat cycles

Interesting history
In days gone by, common place technique used by Master Builders in Europe, when building for the cycling giants was to generate numerous frames based on the design criteria from which the cycling star would take out riding to select the ones he wished to race on.

Some times this production acceptance ratio could be as high as 10:1 or at least this is what I have been told over the years by the builders.