Stratton Mountain – Supply Line 2007

Stratton replaces steel pipe after 7 years of service, with DN600 VRS®-T DI pipe, in 10 days; through regions of high soil corrosivity and physical constraints adjacent to access road.

Project Background:

Preceding 2006 Stratton began to have leakage problems in the main steel water supply line, which had been installed in 2000.   This leakage was concentrated in a section of the pipeline which had been installed adjacent to the main access road serving the base area of the mountain.    For a short section of the entire supply line, the access road corridor was the only feasible route to follow.   Several issues with this short corridor created unusual conditions.   Because this was the only corridor available, electrical systems were installed at a deeper elevation, creating physical constraints and possible stray electric currents.   The pipe had to be installed adjacent to the access road, rather than under the road, and the shoulder area adjacent to the road was very narrow creating physical constraints.   The steel pipe being replaced had to be removed before the DI pipe could be installed.   See photos below.

The access road is salted and plowed through the entire ski season, so an extensive amount of road salt is deposited into this narrow shoulder area.   This increased soil corrosivity in this shoulder area to unusually high levels.   This is probably one reason this steel pipe had to be replaced after only seven (7) years.   Because of the proximity to the access road, regardless of the size of the repair, any pipe repairs in this area will be very costly; and, any would cause major problems tying up the access road to the base area.   In 2007 Stratton decided to replace the steel pipe in this shoulder area with high pressure Ductile iron (DI) pipe from TRM.

Project Challenges:

Find a piping system that:  would satisfy high pressures required, in this large diameter pipe; would improve the longevity of the new pipe system, to reduce future costly pipe repairs; would provide flexibility to deal with easement and infrastructure constraints through the priority area; could be installed easily and quickly because of short timelines required to minimize shutdown of the access road; and, would minimize environmental damage throughout the project region.   More specifically:

High Pressures:

Normal operating pressures in this water supply pipeline are 400 psig, with surge pressures up to 550 psig.   These pressures are not high for normal snowmaking systems, but are high for the larger diameter pipe (DN600 – 24”) being used in this supply pipeline.

Longevity:

Corrosion of any material is based on the corrosivity of the environment surrounding the material. Steel snowmaking pipe in normal alpine environments has a longevity ranging from 20 to 35 years, depending on soil corrosivity.   Soil corrosivity in this region is very high, shown by leakage occurring only 7 years after new pipe had been installed.   Other materials are available that will provide longevity that is superior to steel.   Photos below show pipe corrosion after 7 years.

NOTE: The above photos show exterior corrosion only. For information regarding interior corrosion refer to Project Follow Up section, appended below.

Short Timelines:

Any construction in this region adjacent to the access road requires partial blockage of the access road.  This made it necessary to find a pipe system that could be assembled/installed easily, safely and quickly.

Flexibilty:

This pipeline is installed in a narrow corridor, and within this corridor, it is necessary to follow the edge of the paved access road very closely.    It is a priority to have the flexibility to align pipes with the edge of the access road in this very narrow corridor.

Constraints:

In this installation primary constraints are caused by the very narrow work corridor available, and the need to follow the edge profile of the paved access road.   Perhaps less important, but still a constraint to be considered, there are electrical utility systems installed at lower elevations in this narrow work corridor.

Priority Areas:

The access road is a Priority Area to the ski resort year-round; as a major access for skiers through the winter months; and, as a major access to the base area of the resort through the summer months.

Environmental Sustainability:

A primary goal with all pipe installations in all alpine regions is to select/use materials which protect ecosystems, and maximize the integrity and sustainability of the natural resources.   DI materials from TRM have unique characteristics in these areas, not available with other pipeline materials, including:

  • DI pipe is produced using +98% recyclable materials.
  • Joint design requires no welding or open flames at any time during assembly/installation.
  • Joint design requires much less force to assemble; and, smaller/lighter construction equipment for installation.
  • Easier assembly and smaller/lighter construction equipment make it possible to: complete assembly/installation in much shorter timelines, providing much longer periods for terrain clean-up and restoration; complete the installtion using a much smaller construction footprint; deal with site constraints; and reduce the time required to complete cleanup requirements.

Project Solution:

Stratton initiated a product research study to review and evaluate other pipe systems which could improve the performance of the steel system.   As part of this research study Stratton contacted Engineers at PNP Supply, to gain more information on the VRS®-T system from TRM.  Based on this product research Stratton selected the high pressure DI pipe system from TRM for several reasons.

Advantages of the VRS®-T System:

  • The joint design is special for this system, to allow the large diameter pipe (DN600) to support the operating and surge (400/550 psig) pressures in this system.   In smaller diameters, normal operating pressures are 25 bar to 100 bar.
  • The corrosion rate of steel is +3 times faster than the rate for DI; making the longevity of the VRS®-T pipe +3 times greater than the longevity of steel pipe.
  • The DUPLEX coating on all pipe provides active and passive corrosion protection, and a unique sacrificial repair mechanism for any pipe damage exposing bare metal.   These characteristics extend the longevity of this pipe even more.
  • Angular deflection of this pipe provides the flexibility to deal with the constraints caused by the very narrow corridor in which the pipe has to be installed; deal with the necessity to follow the edge of the paved access road; and, deal with electrical utility systems at lower elevations.
  • The VRS®-T joint requires ±38% less force to assemble each joint; and, with the soft flexible gasket used in this joint, alignment of the pipe is not as critical.   Both issues make it easier/faster to install pipe in short timelines.  Construction could not begin until after Labor Day, and had to be completed by as quickly as possible, to minimize inconvenience caused by access road shutdown.   To minimize the length of access road shutdown, excavated areas were backfilled and fine graded at the end of each work day.   See photos below. This entire project was completed in ten (10) days.
  • Easier installation made it possible to use smaller lighter excavation equipment and hand compaction equipment to complete the entire installation.   And the smaller lighter construction equipment required a smaller construction footprint, making it possible to install this DN600 pipe in a trench ±10 ft wide.    See photos below.

Project Team Members:

CLIENT:  Stratton Resort
DESIGN:  Stratton Master Plan
DIP DESIGN/SALES/FIELD SERVICES:   PNP Supply LLC
CONTRACTOR:   In-house Personnel

Project Followup:

PNP currently is working with Stratton Resort on a project to extend the existing Ductile Iron (DI) pipe system, installed in 2007.    As part of the planning and facilities management program for this project, Stratton completed a pipe scan of the interior surface of an existing 24” steel pipe line (14 years’ service) connecting with the 24” DI pipe line (11 years’ service).    Stratton has provided PNP Supply with a copy of this long video, and PNP has created a shorter version of this video.   This shorter video can be reviewed at: www:peopleneedpipe.com/videos.

This video shows, clearly and convincingly, that interior corrosion occurs in steel pipe more rapidly and differently than DI pipe.  Some comments:

  • A subtle message from this video:  Exterior conditions of any pipe have no effect on the rate or methodology of the interior corrosion.
  • For steel pipe external and internal corrosion mechanisms are identical. There are two major corrosion mechanisms, occurring simultaneously and on-going continuously.   These mechanisms are localized pitting, and the formation of loose scale. These layers of loose scale drop off periodically; and are replaced, continuously, by new layers of loose scale, as corrosion continues.   This scaling process is shown quite clearly in the photos below
  • For DI pipe, the external corrosion mechanism is a uniform oxidation process, which forms a continuous oxide layer on the external surface of the pipe.   The DI corrosion process is a gradually diminishing process, as the thickness of the oxide layer increases.    Internally there is essentially no corrosion on the cement lining surface.   Refer to the photos below, taken from the Stratton video.
  • Below are stills, extracted from the video, showing these differences between the internal corrosion of steel pipe and the internal corrosion of DI pipe.
  • One additional point should be mentioned.   The corrosion shown in the steel pipe is in at least its second cycle.   Scale already has dropped off the surface, and the video shows areas where new scale has begun to form.
Interior surface of steel pipe. Note pinhole leak caused by pitting; loose scale has dropped off walls and collects along the bed of the pipe; and rust and scale continue to form around the walls of the pipe – after 14 years of service.
Interior surface of Ductile Iron pipe. Note loose scale from steel pipe has collected along the bed of the DI pipe, otherwise, this pipe is clean - after 11 years of service.
  • There is another subtle message throughout this video. The hydraulic characteristics for steel pipe are much different than the hydraulic characteristics for DI pipe. As scale forms on the inside surface of steel pipe, it increases friction losses in two (2) ways. Initially, as steel pipe ages interior scale builds up. This reduces the interior diameter of the pipe. Also, as scale forms it creates uneven levels of intrusion into the flow area of the pipe. This increases the friction loss coefficient of the steel pipe surface, causing higher friction losses as water moves through the pipe. These surface intrusions are shown in the photo of steel pipe above, but are shown even more clearly on the steel pipe surface in the photo below. Note how the scale on the steel pipe wall has intruded into the flow area of the pipe, increasing the coefficient of friction for the steel pipe, and reducing the useful interior diameter of the pipe.

PROJECT

Stratton Water Supply

PIPE TYPES
DN600 High Press MDR DI Water

LOCATION
Stratton Resort, Stratton, VT

PHYSICAL CHARACTERISTICS
800 ft of pipe

PROJECT TYPE
Snowmaking Pipelines

CHALLENGES

Environmental Sustainability
Priority Areas
Short Timeline
Tight Constraints