Since the release of the latest edition of IGEM/UP/1B Edition 4 - Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, NG and LPG installations the IGEM technical team have compiled a list of the most frequently asked questions for users.
Key points to remember
Permissible Limits
Permissible pressure loss is defined within the Standard and is based on:
- Installation Volume (IV), and
- Fuel Gas
These limits shall be applied where assessment of a pressure loss is required
Purging
The procedure for carrying out purging operations remains unchanged, however, the method for determining purge volume has been revised for some installations.
New Requirement
For all installations where purging is undertaken:
- Installation Volume (IV) shall be calculated, and
- Purge Volume (PV) shall be determined using PV = 1.5 × IV
Clarification – Interaction with Tightness Testing
The requirement to calculate Installation Volume for purging applies in all cases where purging is undertaken.
This includes situations where:
- Installation Volume was not required during tightness testing because the observed pressure loss was below the smallest permissible limit
In such cases the Installation Volume shall still be calculated prior to purging to determine the correct purge volume.
Table 3 states that the maximum permissible pressure loss for Natural Gas installations with an installation volume of...
Table 3 states that the maximum permissible pressure loss for Natural Gas installations with an installation volume of > 0.015 m3 ≤ 0.035 m3 is 1mbar. Does this mean that if the pressure loss is less than 1mbar no further action is required?
Answer
- Where there is perceptible movement, the engineer must investigate whether the pressure loss is on the installation pipework or the appliances, therefore the appliances shall be isolated and the pipework retested. If there is a perceptible pressure loss on pipework this is a failure and must be repaired or made safe.
- If there is no perceptible pressure loss on the pipework, the previously observed pressure loss on the whole installation including appliances shall be assessed against the permissible limits defined by:
- gas type, and
- Installation Volume (IV)
What should I do if I am unable to isolate all appliances when carrying out a tightness test?
Answer
Where it is not reasonably practicable to isolate appliances:
- The test shall be carried out with appliances connected, and
- A no perceptible movement result shall be achieved
Remember, there are no permissible leakage limits when proving installation pipework gas tightness.
Am I required to calculate the IV every time I carry out a tightness test?
Answer
Where perceptible movement is observed, which is proven not attributable to pipework, the pressure loss shall be assessed against the permissible limits. (For natural gas these are given in Table 3 of the Standard).
Where the observed pressure loss is less than the smallest permissible limit for the fuel gas under test:
- The result can be accepted as being within permissible limits, and
- Calculation of Installation Volume (IV) is not required for the purpose of comparing the observed loss to the permissible limits
Where the observed pressure loss is greater than the smallest permissible limit for the gas type under test:
- The installation volume shall be calculated to determine the maximum permissible limit
When testing the installation pipework alone does this include the meter?
Answer
Yes, (unless the test is being carried out from an AECV) as normally the meter will be fitted when undertaking a gas tightness test.
Why am I allowed to leave a pressure loss of 1 mbar on a NG installation with an IV > 0.015 m3 ≤ ......
Why am I allowed to leave a pressure loss of 1 mbar on a NG installation with an IV > 0.015 m3 ≤ 0.035 m3 but allowed to leave a pressure loss of 8 mbar on appliances on a NG installation with an IV of ≤ 0.005 m3? Surely it is not safe to leave a pressure loss of 8mbar on an appliance?
Answer
The maximum permissible pressure loss is based on a leakage rate of 19ml per minute for the Installation Volume. Therefore an 8 mbar pressure loss on a NG installation with an IV of ≤ 0.005 m3 is approximately equal to a pressure loss of 1 mbar on a NG installation with an IV > 0.015 m3 ≤ 0.035 m3 and both would be within the 19ml limit allowed.
Note a similar principle applies to other fuel gases but with different limits
Test condition |
Comment / action required |
|---|---|
| Pipework and new appliances | No permissible pressure loss is allowed |
| Pipework and existing appliances connected (not reasonably practical to isolate appliances) | No permissible pressure loss is allowed |
| Pipework and existing appliances connected | Where a pressure loss is identified, Isolate appliances and confirm that there is no pressure loss on the installation pipework and meter |
| Pipework confirmed as gas tight, existing appliances connected | Where the observed pressure loss is more than the smallest permissible limit for the fuel gas under test: Calculate the IV and confirm that the pressure loss is acceptable within Table 3 (NG) or Table 5 (LPG). If the pressure loss is within limits (within the relevant table) and there is no smell of gas, then test has passed. Where the pressure loss exceeds the limits (within the relevant table) or there is a smell of gas, the test has failed and remedial action is required. |