Table of Contents:

1. History of Stainless Steel
2. Chemical Resistance and Service Life
3. Stainless Steel Advantage for Spot Repair
4. Cost Benefit Analysis of GROUTING SLEEVE™/SewerSealer™sleeve Repair

1. History

Mr. James Borland, Editor of NICKEL magazine (ed. March 1995) comments on stainless steel: "Although stainless steel was first produced just 80 years ago, it quickly became known among engineers and architects for its strength, corrosion resistance, and good workability."

When the great St. Paul's Cathedral was restored between 1925 and 1930, stainless steel reinforcing bars were used to support the dome, and stainless steel tie rods were used to keep the dome together.

Recent inspections (1993) of the structure has revealed that "... no deterioration had taken place."

The art deco cap of the Chrysler Tower Building in New York, was made in 1929 of stainless steel. "Extra sheets of stainless steel, shipped from Germany during the building's construction for future maintenance needs, are still held in storage having never been required."

Why is stainless steel the best material in construction? Its "durability and resistance to corrosion, [are] important factors in modern cities where pollution can quickly cause severe damage to other materials..."

A quick glance at the chemical resistance tables shows the superiority of stainless steel when it comes to corrosion.

Water Storage Tanks

A series of articles in the September 1994 issue of NICKEL magazine, describes the benefits of Stainless Steel. At that time the Japanese City had decided to use stainless steel to ensure a steady flow of clean water for the next 60 years.

An interesting point is that large water tanks are usually made of concrete, but chlorine that is added to the water is known to penetrate the concrete walls and promote corrosion of the reinforcing bars. This is the general cause of equipment degradation. The repair costs can be numerous and expensive.

Although prestressed concrete is less expensive, the study conducted by the city of Matsuyama showed that stainless steel was less expensive to maintain. "And when a comparison was made of total construction costs plus maintenance costs, the results indicated that stainless steel was the best option, based on a useful life of at least 60 years."

2. Chemical resistance

For sewage, at 70º F or 20º C, type SST-316 stainless steel is found to erode at a rate less than 0.0025mm (0.0001in) per year in domestic sewage. (source: Climax Molybdenum Company)

What does this mean for the Sewer Rehabilitation Industry?

With the impressive track record of stainless steel in construction, little or no deterioration has been observed in even the oldest applications over the past 80 years. (see above),

It is clear that stainless steel is the best choice when it comes to sewer rehabilitation.

EXAMPLE:

Take 250mm (10”) dia. GROUTING SLEEVE™

Given Wall Thickness = 0.025-in. (0.64mm).

 Link-Pipe standard Hydraulic Load is 5-psi (33kPa)

Required wall thickness = 0.015-in (0.385mm)  (AWWA  M11 )

Allowable Erosion rate = 0.0001-ipy (0.0025 mm/yr.) 

In 100 years the material erodes = 0.01-in. (100 x 0,0025 mm=0.25mm)

 Material design Thickness is adequate at:  

                            0.015-in + 0,01-in = 0.025-in.= 0.025-in as supplied

SST-316

Exposed to 10% Sulphuric Acid

 Erosion rate (from Table…) = 0.0001 in/yr., or 0.00254 mm/yr;

In 100 years this SST will erode 0.0001 x 100 = 0.01-in.  (0.25 mm)

If Material Thickness = 0.025-in. (0.64 mm)

after 100 years 0.025 - 0.01 = 0.015-in. will remain (=0.39 mm) . 

3. Advantages in Stainless Steel  for Spot Repair

Each of the following features alone would be enough reason to specify stainless steel for no-dig spot repair. Combine all the benefits together and the case is overwhelming:

• Superior corrosion resistance
• High compression and tensile strength unrelated to how long time the loading is applied
• No creep under design loads
• Strict ISO-controlled quality control in the manufacturing process of the GROUTING SLEEVE™ - minimum dependence on field workmanship
• Standardized mill testing of materials assures consistent quality of the stainless steel
• No hazardous chemicals used
• 80 year, ref. 1995, track record in construction with no signs of deterioration assures a minimum 100 year carefree service
• Completely resistant to abrasion encountered during normal flows or high pressure sewer flushing
• High durability in enduring root cutters and other equipment.
• High flexibility in absorbing ground movements, like earth quakes, without breaking.

4. Cost benefit analysis of Spot Repair.

Why Cost Benefit Analysis is necessary?

Material durability varies from material to material. Some sewer repair materials may last only a few years, some much longer.  Some have no hard facts in evaluating service life. 

Example: If a project is assumed to cost $100,000. There is obviously a difference in the annual cost of having the repair last 15, or 100 years. 

If the repair lasts 15 years, the annual principal cost amount is $6,667 p.a.  

If the repair lasts 100 years, the equivalent cost is $1,000 p.a.

Link-Pipe chooses a stainless steel alloy that lasts 100 years in domestic, or storm sewers. For an owner it is essential to compare the cost of repair.   Service life is an important cost factor in any project.

Note this important fact: 

If the bid with the 15 year material was only, say, $25,000, it would still cost more at $1,667 per year, i.e. The annual cost of the 15-year material is still higher than the $100,000 bid that ends up costing only $1,000 a year.

Net Present Cost Analysis

A more refined comparison takes in account the annual interest earned on the money that must be invested for future contracts as well as loss of the money value due to inflation.

The following table gives the amount of money that needs to be invested for a project that must last 100 years.

Four different materials having 15, 25, 50 and 100 year service life are compared.

It becomes apparent from the following that the true cost of each tender must take into consideration the expected life of the repair.

Comparative Investment needed in the 1-st year if 100 year Service is required.

Project Cost Comparison

Front end investment required in the 1-st year  of the Service Life if interest earned is 4% and inflation is 2%.:

Investment required in the 1-st year 

One way to determine the life of the repair is to assume it is the same as the manufacturer's warranty. Another way is to run accelerated aging tests, or use historic records. Stainless steel is well researched in this respect.

Sample Specifications, structural strength analysis, and chemical resistance data for the GROUTING SLEEVE™ and SewerSealer™ Sleeve are available from LINK-PIPE Inc.

Ask Link-Pipe for detailed calculations