Seismic Resilience of Pressure Equipment

Uploaded ImageThe required seismic loads that a new building must withstand are determined from NZ Standard NZS 1170.5. There have been issues interpreting this standard when used for pressure equipment as working stress design methods are used. This year the Institution of Professional Engineers NZ issued Practice Note 19 "Seismic resistance of pressure equipment and its supports". This is a very useful 137 page technical document that should be followed for all new pressure equipment.

Requirements for existing pressure equipment are currently being debated. If existing pressure equipment is being relocated or the use is being changed, then the seismic requirements for new pressure equipment apply. If there are no modifications to equipment that is not being moved, there is no requirement to reassess the seismic capability of the equipment. The difficulty is where modifications are required to existing equipment which do not justify it being upgraded to new equipment standards.

The same issue applies to existing buildings and in August the Government announced its earthquake prone buildings policy. The aim is to have these buildings upgraded to 34% of new building seismic standards within 20 years. There are various classes of low risk buildings that do not require upgrading.

Industrial plant owners are obliged to have safe workplaces and also want the least impact on production when an earthquake occurs. But the cost of bringing every plant to 100% of new standards would result in some plants being closed rather than upgraded. As for existing buildings, an acceptable risk for existing equipment is required. Carter Holt Harvey, Fonterra, Refining NZ, Bluescope (NZ Steel) and Dobbie have prepared a submission to IPENZ and the Ministry of Building Innovation and Employment suggesting a practical method of evaluating modifications and recommending seismic levels that should apply to modified existing equipment.

We will keep clients advised of the Government's decision.