What’s Going On Inside Your Sprinkler System

Monday 10, February 2020

It’s a question that rarely gets asked by sprinkler system owners. So, what are the options and why and when should we internally inspect sprinkler systems?

The American sprinkler standards advise regards internal pipe corrosion, water quality, make recommendation and advise regards why this happens. The British & European standards (BSEN) call for sprinkler systems and parts of the system to be routinely inspected externally and internally throughout the life span of the system. The overall system inspection is known throughout the UK sprinkler market a 25 Year intrusive survey. This is not a mandatory requirement in the BSEN standard, however in recent years has become a popular tool of risk insurers to evaluate the internal condition of a sprinkler system. The standard calls for the following actions to take place after 25 years of service:

  1. Remove sprinkler heads from the premises and test them against two basic functions and inspect the heads visually.
  2. Inspect sprinkler pipes internally and externally.
  3. Hydraulically pressure test the sprinkler pipes.
  4. Flush the sprinkler system and inspect the contents.

These works would typically be carried out by Sprinkler System Installers.

The number of heads and sprinkler pipes you remove are relative to the size of the site. The pressure testing of existing sprinkler pipes was revised in 2018 and now is not recommended for mainly practical reasons. The inspecting of sprinkler pipework’s has been done in different ways by the sprinkler companies / end users. Power Stations will typically scan the pipeworks using ultrasonic scanning techniques. Some sprinkler companies will take pictures down looking down the open bore of the pipes. other options include splicing the tubes lengthways (as pictured)

Figure 1 – Typical Pipe Splice



This method is favoured by A&F as it enables the internal bore to be fully inspected and also allows the pipe to dry out which can reveal more.





Certain companies in the US offer water quality testing specifically for sprinkler systems complete with bolt on water conditioning systems to treat water problems whilst the system lays idle.

The main types of steel sprinkler pipe corrosion are Galvanic, Microbial (MIC), Pitting and Crevice. Crevice corrosion is where internal or external corrosion occurs in between connecting welds, grooves and gaps. Pitting corrosion is where a localised hole or depression is formed due to a weakness in the steels structural make up. If left un-checked pitting can lead to a failure commonly known as a “Pin Hole Leak”

Galvanic is the electro chemical reaction between two different types of metals that have been connected for a length of time.

Microbial (Bacteria) induced corrosion (MIC) is probably the most commonly corrosion found inside working sprinkler pipes. This is due to the water inside a sprinkler pipe being static most of the time which encourages the MIC chemical process. The resulting structures the MIC process make on a pipes wall are very distinctive (See Figure 2) and are coincidently organic in shape. MIC can also be found in other materials such as Plastics and Concrete.

Figure 2 – Spliced Pipe Displaying Internal MIC
















Prior to inspecting pipework’s its best to keep an open mind in regards to what you will find, assuming anything can be the wrong thing to do. For instance, the age of the pipe can be irrelevant as can assuming that a heavily corroded pipe found from one part of a site means the rest of the site will be the same. This is not always the case. Variance in steel and water quality can play its part as can the configuration of the pipework’s. Some pipe layouts promote air pockets that can in time cause concentrated sections of corrosion along the inside length of a pipe. Sprinkler pipes taken from Alternate (Wet and Dry mode) sprinkler installations do usually exhibit more *corrosion than say pipes found on a wet installation. This is due to the dry and wet actions that create an atmosphere that speeds up the process of internal corrosion.

* Corrosion (Definition) is a natural process that converts a refined metal into a more chemically-stable form such as oxidehydroxide, or sulphide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. 

The removal from site and the subsequent testing of Sprinkler Heads, Multiple Jet Controllers and Dry Pendant Drops is a necessary part of the Survey works. Various head testing laboratory’s carryout the testing works to the requirements set out in BSEN12259. The number of heads removed depends upon the size of the sprinkler system being surveyed. The removed sprinkler heads are tested in the following ways.

  1. Visual Inspection.
  2. Function Test.
  3. Operating Temperature Test.
  4. K Factor Variance.
  5. Thermal Response.

Once at the testing lab. All sampled heads are visually inspected. Typical issues found are paint contamination, deflector damage, external corrosion, external discoloration and foreign materials in the head’s waterway. K factor tests are carried out upon heads that exhibit internal corrosion.

Figure 3 – Removed Sprinkler Heads














The function test determines if the head operates correctly and involves an testing oven to break the bulb whilst a small pressure is applied behind the sprinkler heads seat. If the bulb breaks and the bulb seat remains in place this is known as “seat lodgement” the test usually continues with extra pressure applied until the seat is dislodged. The LPCB rules state a zero-fail tolerance for function testing of sprinkler heads. The most common cause of seat lodgement is where a rubber ‘O’ has been used to seal the bulb seat to the body of the head. Over time the rubber ‘O’ ring fuses the bulb seat to the body of the head causing the potential non operation of the head.

When this issue was discovered certain sprinkler head manufacturers in the United States created a replacement scheme firstly targeting the most vulnerable premises installed with ‘O’ ring sprinklers” after 13 years apparently many millions ‘O’ ring heads had been replaced. In the UK, insurers have lists of the effected sprinkler head models of which many were manufactured between the late 1980’s and mid 1990’s.

Another more unusual issue found when function testing older sprinkler heads is when the bulb breaks, and bulb seat detaches but momentarily the seat gets stuck to the sprinkler head deflector. This is known as “Deflector Lodgement” and can affect the intended water distribution spray pattern. Modern sprinkler heads have been slightly modified to make this less likely to happen.

The temperature testing of sprinkler heads is usually done in a temperature-controlled bath. Contemporary sprinkler heads are allowed to operate within an upper and lower tolerance limits which vary depending on the temperature rating of the head being tested e.g. a 68 ºC rated head is allowed to operate down to 65 degrees and up to 71 ºC  where as a head rated at 141 ºC can operate as high as 147 ºC and as low as 135 ºC. When testing older sprinkler heads the testing labs test to the current upper and lower tolerances (as set out in BSEN12259-1) and not of the allowed tolerances of the time of when they were made, of which little is know pre 1980’s.

Overall the sprinkler head testing carried out on A&F surveys since 2011 has returned a 14% failure rate. This is where an individual sprinkler has failed either the function or temperature testing. The associated sprinkler heads are normally replaced on the relevant site.

The last of the survey is the flushing works. Flushing sprinkler installations involves attaching large bore hoses to the remote ends of each installation mains pipe and pushing fresh water through the mains via the sites pumps. Its serves two main purposes. 1. To capture any foreign debris and 2. To clear the mains pipes generally of any debris.

Capturing debris through a filter can prove whether anything could clog up the installed sprinklers or nozzles on the system. The BSEN rules state if objects 5mm or more in cross section are found inside the pipework’s further investigation is required to obtain why and where the objects are originating from. The flushing of older systems can be difficult. Flushing valves were not installed until more recent years, and some buildings layouts do not lend themselves to running long large bore hoses through them so initially flushing is done to evaluate if there is an issue with foreign bodies.

Figure 4 – A&F Flushing Filters



Once the flushing hoses are fitted the upstream flushing valves are carefully throttled as to control the pumps pressure but letting enough water through to achieve the desired result. A&F use galvanised filters drilled to specified 5mm and fitted to the end of the flushing hose. After the initial waters have passed through the filter, the filter is removed and is internally inspected.

If foreign bodies are contained typically this will be a build-up of corroded steel (flakes) which has fallen away from the internal wall of the pipe. However, we have found other issues such as limescale and even stones.




The intrusive inspection of sprinkler systems is something still relatively new when you consider that fire sprinklers have been around for 100 plus years. In recent times Insurance companies have seen the benefits of the surveys and have actively promoted the need to survey to ensure sprinkler systems are 100% effective when called into action. Our experiences tell us it’s a very worthwhile exercise and when coupled with a sprinkler tank inspection can give the systems owners a good indication of the overall condition of their sprinkler system.

If you would like to enquire further or have a sprinkler system that would benefit from an intrusive survey, please contact A&F Sprinklers on 0161 470 9785 or alternatively send an email to multiworks@afsprinklers.co.uk