Burmah Castrol Strips

Burmah Castrol Strips: Temperature Indication for Surface NDT

Burmah Castrol Strips (sometimes called Castrol Tempilaq) are specialized chemical indicators used to quickly and accurately verify the surface temperature of a component, primarily in the context of Non-Destructive Testing (NDT) methods that rely on precise temperature control, such as Dye Penetrant Inspection (DPI/PT) and some stages of Magnetic Particle Inspection (MPI).

Design and Principle

These strips are composed of multiple temperature-sensitive chemical formulations, often presented in a compact, adhesive-backed sticker form:

1. Chemical Melt Points: Each small square or circle on the strip contains a chemical blend with a sharply defined, specific melting point.

2. Irreversible Change: When the component surface reaches or exceeds the rated temperature of a particular square, the chemical compound melts. Upon cooling, the indicator square undergoes a distinct and irreversible color or phase change (e.g., from opaque white to transparent black/dark green).

Application in NDT

Accurate temperature verification is vital for the integrity of NDT results:

• Dye Penetrant Inspection (DPI/PT): Penetrant materials have a specified operational temperature range (typically $40^\circ\text{F}$ to $125^\circ\text{F}$ or $5^\circ\text{C}$ to $52^\circ\text{C}$). If the surface is too hot, the penetrant can evaporate quickly or dry out before inspection, leading to false negatives. If it is too cold, the penetrant’s viscosity increases, hindering proper capillary action. Burmah Castrol strips ensure the component is within the qualified range before applying the penetrant.

• MPI (High-Temperature): In cases where MPI is performed on components pre-heated for welding, the strips are used to confirm the temperature before applying high-temperature magnetic materials.

Key Advantage

The primary advantage of these strips over standard thermometers is that they provide an instant and permanent record of the maximum temperature attained at the exact point of application, even if the temperature fluctuations occur while the inspector is away.